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A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the
coronary artery The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ o ...
of the
heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck or jaw. Often it occurs in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include
shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...
, nausea, feeling faint, a cold sweat or feeling tired. About 30% of people have atypical symptoms. Women more often present without chest pain and instead have neck pain, arm pain or feel tired. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an
irregular heartbeat Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...
, cardiogenic shock or
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...
. Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet and
excessive alcohol intake Alcohol abuse encompasses a spectrum of unhealthy alcohol drinking behaviors, ranging from binge drinking to alcohol dependence, in extreme cases resulting in health problems for individuals and large scale social problems such as alcohol-relat ...
. The complete blockage of a
coronary artery The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ o ...
caused by a rupture of an
atherosclerotic plaque An atheroma, or atheromatous plaque, is an abnormal and reversible accumulation of material in the inner layer of an arterial wall. The material consists of mostly macrophage cells, or debris, containing lipids, calcium and a variable amount ...
is usually the underlying mechanism of an MI. MIs are less commonly caused by
coronary artery spasm Coronary vasospasm refers to when a coronary artery suddenly undergoes either complete or sub-total temporary occlusion. In 1959, Prinzmetal et al. described a type of chest pain resulting from coronary vasospasm, referring to it as a variant form ...
s, which may be due to cocaine, significant emotional stress (commonly known as
Takotsubo syndrome Takotsubo cardiomyopathy or Takotsubo syndrome (TTS), also known as stress cardiomyopathy, is a type of non-ischemic cardiomyopathy in which there is a sudden temporary weakening of the muscular portion of the heart. It usually appears after a ...
or ''broken heart syndrome'') and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests and coronary angiography. An ECG, which is a recording of the heart's electrical activity, may confirm an ST elevation MI ( STEMI), if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB. Treatment of an MI is time-critical. Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen is recommended in those with low oxygen levels or shortness of breath. In a STEMI, treatments attempt to restore blood flow to the heart and include percutaneous coronary intervention (PCI), where the arteries are pushed open and may be stented, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction ( NSTEMI) are often managed with the blood thinner heparin, with the additional use of PCI in those at high risk. In people with blockages of multiple coronary arteries and diabetes, coronary artery bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long-term treatment with aspirin, beta blockers and statins, are typically recommended. Worldwide, about 15.9 million myocardial infarctions occurred in 2015. More than 3 million people had an ST elevation MI, and more than 4 million had an NSTEMI. STEMIs occur about twice as often in men as women. About one million people have an MI each year in the United States. In the developed world, the risk of death in those who have had an STEMI is about 10%. Rates of MI for a given age have decreased globally between 1990 and 2010. In 2011, an MI was one of the top five most expensive conditions during inpatient hospitalizations in the US, with a cost of about $11.5 billion for 612,000 hospital stays.


Terminology

Myocardial infarction (MI) refers to tissue death ( infarction) of the heart muscle ( myocardium) caused by ischaemia, the lack of oxygen delivery to myocardial tissue. It is a type of acute coronary syndrome, which describes a sudden or short-term change in symptoms related to blood flow to the heart. Unlike the other type of acute coronary syndrome, unstable angina, a myocardial infarction occurs when there is cell death, which can be estimated by measuring by a blood test for biomarkers (the cardiac protein troponin). When there is evidence of an MI, it may be classified as an ST elevation myocardial infarction (STEMI) or Non-ST elevation myocardial infarction (NSTEMI) based on the results of an ECG. The phrase "heart attack" is often used non-specifically to refer to myocardial infarction. An MI is different from—but can cause—
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...
, where the heart is not contracting at all or so poorly that all vital organs cease to function, thus might lead to death. It is also distinct from heart failure, in which the pumping action of the heart is impaired. However, an MI may lead to heart failure.


Signs and symptoms

Chest pain that may or may not radiate to other parts of the body is the most typical and significant symptom of myocardial infarction. It might be accompanied by other symptoms such as sweating.


Pain

Chest pain is one of the most common symptoms of acute myocardial infarction and is often described as a sensation of tightness, pressure, or squeezing. Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen. The pain most suggestive of an acute MI, with the highest likelihood ratio, is pain radiating to the right arm and shoulder. Similarly, chest pain similar to a previous heart attack is also suggestive. The pain associated with MI is usually diffuse, does not change with position, and lasts for more than 20 minutes. It might be described as pressure, tightness, knifelike, tearing, burning sensation (all these are also manifested during other diseases). It could be felt as an unexplained anxiety, and pain might be absent altogether.
Levine's sign Levine's sign is a clenched fist held over the chest to describe ischemic chest pain. It is named for Samuel A. Levine (1891–1966), an influential American cardiologist, who first observed that many patients with chest pain made this same sign ...
, in which a person localizes the chest pain by clenching one or both fists over their sternum, has classically been thought to be predictive of cardiac chest pain, although a prospective observational study showed it had a poor positive predictive value. Typically, chest pain because of ischemia, be it unstable angina or myocardial infarction, lessens with the use of nitroglycerin, but nitroglycerin may also relieve chest pain arising from non-cardiac causes.


Other

Chest pain may be accompanied by
sweating Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distri ...
, nausea or vomiting, and fainting, and these symptoms may also occur without any pain at all. In women, the most common symptoms of myocardial infarction include shortness of breath, weakness, and fatigue. Women are more likely to have unusual or unexplained tiredness and nausea or vomiting as symptoms. Women having heart attacks are more likely to have palpitations, back pain, labored breath, vomiting, and left arm pain than men, although the studies showing these differences had high variability. Women are less likely to report chest pain during a heart attack and more likely to report nausea, jaw pain, neck pain, cough, and fatigue, although these findings are inconsistent across studies. Women with heart attacks also had more indigestion, dizziness, loss of appetite, and loss of consciousness.
Shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...
is a common, and sometimes the only symptom, occurring when damage to the heart limits the output of the left ventricle, with breathlessness arising either from low oxygen in the blood, or pulmonary edema. Other less common symptoms include weakness,
light-headedness Lightheadedness is a common and typically unpleasant sensation of dizziness or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel ...
,
palpitation Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. Symptoms include a rap ...
s, and abnormalities in heart rate or blood pressure. These symptoms are likely induced by a massive surge of
catecholamines A catecholamine (; abbreviated CA) is a monoamine neurotransmitter, an organic compound that has a catechol (benzene with two hydroxyl side groups next to each other) and a side-chain amine. Catechol can be either a free molecule or a subs ...
from the sympathetic nervous system, which occurs in response to pain and, where present, low blood pressure.
Loss of consciousness Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...
due to inadequate blood flow to the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
and cardiogenic shock, and sudden death, frequently due to the development of ventricular fibrillation, can occur in myocardial infarctions. Cardiac arrest, and atypical symptoms such as palpitations, occur more frequently in women, the elderly, those with diabetes, in people who have just had surgery, and in critically ill patients.


Absence

"Silent" myocardial infarctions can happen without any symptoms at all. These cases can be discovered later on electrocardiograms, using blood enzyme tests, or at autopsy after a person has died. Such silent myocardial infarctions represent between 22 and 64% of all infarctions, and are more common in the elderly, in those with diabetes mellitus and after heart transplantation. In people with diabetes, differences in pain threshold,
autonomic neuropathy Autonomic neuropathy (AN or AAN) is a form of polyneuropathy that affects the non-voluntary, non-sensory nervous system (i.e., the autonomic nervous system), affecting mostly the internal organs such as the bladder muscles, the cardiovascular sys ...
, and psychological factors have been cited as possible explanations for the lack of symptoms. In heart transplantation, the
donor A donor in general is a person, organization or government which donates something voluntarily. The term is usually used to represent a form of pure altruism, but is sometimes used when the payment for a service is recognized by all parties as rep ...
heart is not fully innervated by the nervous system of the recipient.


Risk factors

The most prominent risk factors for myocardial infarction are older age, actively smoking, high blood pressure, diabetes mellitus, and total
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
and high-density lipoprotein levels. Many risk factors of myocardial infarction are shared with coronary artery disease, the primary cause of myocardial infarction, with other risk factors including male sex, low levels of physical activity, a past family history, obesity, and
alcohol use An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of alcohol that acts as a drug and is produced by fermentation of grains, fruits, or other sources of sugar. The cons ...
. Risk factors for myocardial disease are often included in risk factor stratification scores, such as the Framingham Risk Score. At any given age, men are more at risk than women for the development of cardiovascular disease. High levels of blood cholesterol is a known risk factor, particularly high
low-density lipoprotein Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall densi ...
, low high-density lipoprotein, and high triglycerides. Many risk factors for myocardial infarction are potentially modifiable, with the most important being tobacco smoking (including secondhand smoke). Smoking appears to be the cause of about 36% and obesity the cause of 20% of coronary artery disease. Lack of physical activity has been linked to 7–12% of cases. Less common causes include stress-related causes such as job stress, which accounts for about 3% of cases, and chronic high stress levels.


Diet

There is varying evidence about the importance of saturated fat in the development of myocardial infarctions. Eating polyunsaturated fat instead of saturated fats has been shown in studies to be associated with a decreased risk of myocardial infarction, while other studies find little evidence that reducing dietary saturated fat or increasing polyunsaturated fat intake affects heart attack risk. Dietary cholesterol does not appear to have a significant effect on blood cholesterol and thus recommendations about its consumption may not be needed.
Trans fats Trans fat, also called trans-unsaturated fatty acids, or trans fatty acids, is a type of unsaturated fat that naturally occurs in small amounts in meat and milk fat. It became widely produced as an unintentional byproduct in the industrial pro ...
do appear to increase risk. Acute and prolonged intake of high quantities of alcoholic drinks (3–4 or more daily) increases the risk of a heart attack.


Genetics

Family history of ischemic heart disease or MI, particularly if one has a male first-degree relative (father, brother) who had a myocardial infarction before age 55 years, or a female first-degree relative (mother, sister) less than age 65 increases a person's risk of MI. Genome-wide association studies have found 27 genetic variants that are associated with an increased risk of myocardial infarction. The strongest association of MI has been found with chromosome 9 on the short arm ''p'' at locus 21, which contains genes CDKN2A and 2B, although the single nucleotide polymorphisms that are implicated are within a non-coding region. The majority of these variants are in regions that have not been previously implicated in coronary artery disease. The following genes have an association with MI: PCSK9,
SORT1 Sortilin (SORT1) is a protein that in humans is encoded by the ''SORT1'' gene on chromosome 1. This protein is a type I membrane glycoprotein in the vacuolar protein sorting 10 protein (Vps10p) family of sorting receptors. While it is ubiquitous ...
,
MIA3 Melanoma inhibitory activity protein 3 (MIA3), also known as transport and Golgi organization protein 1 (TANGO1), is a protein that in humans is encoded by the ''MIA3'' gene on chromosome 1. It is ubiquitously expressed in many tissues and cell ...
,
WDR12 Ribosome biogenesis protein WDR12 is a protein that in humans is encoded by the ''WDR12'' gene on chromosome 2. It is ubiquitously expressed in many tissues and cell types. WDR12 participates in ribosome biogenesis and cell proliferation as a com ...
, MRAS,
PHACTR1 Phosphatase and actin regulator 1 (PHACTR1) is a protein that in humans is encoded by the ''PHACTR1'' gene on chromosome 6. It is most significantly expressed in the globus pallidus of the brain. PHACTR1 is an actin and protein phosphatase 1 (PP1 ...
, LPA,
TCF21 Transcription factor 21 (TCF21), also known as pod-1, capsuling, or epicardin, is a protein that in humans is encoded by the ''TCF21'' gene on chromosome 6. It is ubiquitously expressed in many tissues and cell types and highly significantly expr ...
, MTHFDSL,
ZC3HC1 Nuclear-interacting partner of ALK (NIPA), also known as zinc finger C3HC-type protein 1 (ZC3HC1), is a protein that in humans is encoded by the ''ZC3HC1'' gene on chromosome 7. It is ubiquitously expressed in many tissues and cell types though e ...
,
CDKN2A CDKN2A, also known as cyclin-dependent kinase inhibitor 2A, is a gene which in humans is located at chromosome 9, band p21.3. It is ubiquitously expressed in many tissues and cell types. The gene codes for two proteins, including the INK4 family ...
, 2B, ABO,
PDGF0 Platelet-derived growth factor (PDGF) is one among numerous growth factors that regulate cell growth and division. In particular, PDGF plays a significant role in blood vessel formation, the growth of blood vessels from already-existing blood ...
, APOA5, MNF1ASM283,
COL4A1 Collagen alpha-1(IV) chain (COL4A1) is a protein that in humans is encoded by the ''COL4A1'' gene on chromosome 13. It is ubiquitously expressed in many tissues and cell types. COL4A1 is a subunit of the type IV collagen and plays a role in angiog ...
, HHIPC1, SMAD3, ADAMTS7, RAS1,
SMG6 Telomerase-binding protein EST1A is an enzyme that in humans is encoded by the ''SMG6'' gene on chromosome 17. It is ubiquitously expressed in many tissues and cell types. The C-terminus of the EST1A protein contains a PilT N-terminus (PIN) domai ...
,
SNF8 Vacuolar-sorting protein SNF8 is a protein that in humans is encoded by the ''SNF8'' gene. Model organisms Model organisms have been used in the study of SNF8 function. A conditional knockout mouse line, called ''Snf8tm1a(EUCOMM)Wtsi'' was ...
, LDLR,
SLC5A3 Sodium/myo-inositol cotransporter is a protein that in humans is encoded by the ''SLC5A3'' gene. Expression of the myo-inositol transport protein is regulated by osmotic stress Osmotic shock or osmotic stress is physiologic dysfunction caused ...
,
MRPS6 28S ribosomal protein S6, mitochondrial is a protein that in humans is encoded by the ''MRPS6'' gene. Mammalian mitochondrial ribosomal proteins are encoded by nuclear genes and help in protein synthesis within the mitochondrion. Mitochondri ...
, KCNE2.


Other

The risk of having a myocardial infarction increases with older age, low physical activity, and low socioeconomic status. Heart attacks appear to occur more commonly in the morning hours, especially between 6AM and noon. Evidence suggests that heart attacks are at least three times more likely to occur in the morning than in the late evening. Shift work is also associated with a higher risk of MI. And one analysis has found an increase in heart attacks immediately following the start of daylight saving time. Women who use
combined oral contraceptive pill The combined oral contraceptive pill (COCP), often referred to as the birth control pill or colloquially as "the pill", is a type of birth control that is designed to be taken orally by women. The pill contains two important hormones: proges ...
s have a modestly increased risk of myocardial infarction, especially in the presence of other risk factors. The use of
non-steroidal anti inflammatory drugs Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...
(NSAIDs), even for as short as a week, increases risk. Endometriosis in women under the age of 40 is an identified risk factor.
Air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different type ...
is also an important modifiable risk. Short-term exposure to air pollution such as carbon monoxide, nitrogen dioxide, and
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
(but not
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...
) have been associated with MI and other acute cardiovascular events. For sudden cardiac deaths, every increment of 30 units in Pollutant Standards Index correlated with an 8% increased risk of out-of-hospital cardiac arrest on the day of exposure. Extremes of temperature are also associated. A number of acute and chronic infections including '' Chlamydophila pneumoniae'', influenza, '' Helicobacter pylori'', and '' Porphyromonas gingivalis'' among others have been linked to atherosclerosis and myocardial infarction. As of 2013, there is no evidence of benefit from antibiotics or
vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulat ...
, however, calling the association into question. Myocardial infarction can also occur as a late consequence of Kawasaki disease. Calcium deposits in the coronary arteries can be detected with CT scans. Calcium seen in coronary arteries can provide predictive information beyond that of classical risk factors. High blood levels of the amino acid homocysteine is associated with premature atherosclerosis; whether elevated homocysteine in the normal range is causal is controversial. In people without evident coronary artery disease, possible causes for the myocardial infarction are
coronary spasm Coronary reflex is the change of coronary diameter in response to chemical, neurological or mechanical stimulation of the coronary arteries. The coronary reflexes are stimulated differently from the rest of the vascular system. Causes of coronary c ...
or
coronary artery dissection Spontaneous coronary artery dissection (SCAD) is an uncommon but potentially lethal condition in which one of the arteries that supply the heart spontaneously develops a blood collection, or hematoma, within the artery wall. This leads to a sep ...
.


Mechanism


Atherosclerosis

The most common cause of a myocardial infarction is the rupture of an atherosclerotic plaque on an artery supplying heart muscle. Plaques can become unstable, rupture, and additionally promote the formation of a
blood clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...
that blocks the artery; this can occur in minutes. Blockage of an artery can lead to tissue death in tissue being supplied by that artery. Atherosclerotic plaques are often present for decades before they result in symptoms. The gradual buildup of
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
and fibrous tissue in plaques in the wall of the
coronary arteries The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ ...
or other arteries, typically over decades, is termed atherosclerosis. Atherosclerosis is characterized by progressive inflammation of the walls of the arteries. Inflammatory cells, particularly macrophages, move into affected arterial walls. Over time, they become laden with cholesterol products, particularly LDL, and become foam cells. A cholesterol core forms as foam cells die. In response to growth factors secreted by macrophages, smooth muscle and other cells move into the plaque and act to stabilize it. A stable plaque may have a thick fibrous cap with
calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature M ...
. If there is ongoing inflammation, the cap may be thin or ulcerate. Exposed to the pressure associated with blood flow, plaques, especially those with a thin lining, may rupture and trigger the formation of a blood clot (thrombus). The cholesterol crystals have been associated with plaque rupture through mechanical injury and inflammation.


Other causes

Atherosclerotic disease is not the only cause of myocardial infarction, but it may exacerbate or contribute to other causes. A myocardial infarction may result from a heart with a limited blood supply subject to increased oxygen demands, such as in fever, a fast heart rate,
hyperthyroidism Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidis ...
, too few red blood cells in the bloodstream, or low blood pressure. Damage or failure of procedures such as percutaneous coronary intervention or coronary artery bypass grafts may cause a myocardial infarction. Spasm of coronary arteries, such as
Prinzmetal's angina Variant angina, also known as Prinzmetal angina, vasospastic angina, angina inversa, coronary vessel spasm, or coronary artery vasospasm, is a syndrome typically consisting of angina (cardiac chest pain). Variant angina differs from stable angina ...
may cause blockage.


Tissue death

If impaired blood flow to the heart lasts long enough, it triggers a process called the ischemic cascade; the heart cells in the territory of the blocked coronary artery die ( infarction), chiefly through necrosis, and do not grow back. A collagen
scar A scar (or scar tissue) is an area of fibrous tissue that replaces normal skin after an injury. Scars result from the biological process of wound repair in the skin, as well as in other organs, and tissues of the body. Thus, scarring is a ...
forms in their place. When an artery is blocked, cells lack
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
, needed to produce ATP in mitochondria. ATP is required for the maintenance of electrolyte balance, particularly through the Na/K ATPase. This leads to an ischemic cascade of intracellular changes, necrosis and apoptosis of affected cells. Cells in the area with the worst blood supply, just below the inner surface of the heart (
endocardium The endocardium is the innermost layer of tissue that lines the chambers of the heart. Its cells are embryologically and biologically similar to the endothelial cells that line blood vessels. The endocardium also provides protection to the va ...
), are most susceptible to damage. Ischemia first affects this region, the ''subendocardial'' region, and tissue begins to die within 15–30 minutes of loss of blood supply. The dead tissue is surrounded by a zone of potentially reversible ischemia that progresses to become a full-thickness ''transmural'' infarct. The initial "wave" of infarction can take place over 3–4 hours. These changes are seen on
gross pathology Gross pathology refers to macroscopic manifestations of disease in organs, tissues, and body cavities. The term is commonly used by anatomical pathologists to refer to diagnostically useful findings made during the gross examination portion of ...
and cannot be predicted by the presence or absence of Q waves on an ECG. The position, size and extent of an infarct depends on the affected artery, totality of the blockage, duration of the blockage, the presence of collateral blood vessels, oxygen demand, and success of interventional procedures. Tissue death and
myocardial scarring Myocardial scarring is the accumulation of fibrous tissue resulting after some form of trauma to the cardiac tissue. Fibrosis is the formation of excess tissue in replacement of necrotic or extensively damaged tissue. Fibrosis in the heart is often ...
alter the normal conduction pathways of the heart, and weaken affected areas. The size and location puts a person at risk of abnormal heart rhythms (arrhythmias) or heart block, aneurysm of the heart ventricles, inflammation of the heart wall following infarction, and rupture of the heart wall that can have catastrophic consequences. Injury to the myocardium also occurs during re-perfusion. This might manifest as ventricular arrhythmia. The re-perfusion injury is a consequence of the calcium and sodium uptake from the cardiac cells and the release of oxygen radicals during reperfusion. No-reflow phenomenon—when blood is still unable to be distributed to the affected myocardium despite clearing the occlusion—also contributes to myocardial injury. Topical endothelial swelling is one of many factors contributing to this phenomenon.


Diagnosis


Criteria

A myocardial infarction, according to current consensus, is defined by elevated cardiac biomarkers with a rising or falling trend and at least one of the following: * Symptoms relating to ischemia * Changes on an electrocardiogram (ECG), such as ST segment changes, new left bundle branch block, or pathologic
Q waves In elastodynamics, Love waves, named after Augustus Edward Hough Love, are horizontally polarized surface waves. The Love wave is a result of the interference of many shear waves (S-waves) guided by an elastic layer, which is ''welded'' to a ...
* Changes in the motion of the heart wall on imaging * Demonstration of a thrombus on angiogram or at autopsy.


Types

A myocardial infarction is usually clinically classified as an ST-elevation MI (STEMI) or a non-ST elevation MI (NSTEMI). These are based on ST elevation, a portion of a heartbeat graphically recorded on an ECG. STEMIs make up about 25–40% of myocardial infarctions. A more explicit classification system, based on international consensus in 2012, also exists. This classifies myocardial infarctions into five types: # Spontaneous MI related to plaque erosion and/or rupture fissuring, or dissection # MI related to ischemia, such as from increased oxygen demand or decreased supply, e.g. coronary artery spasm, coronary embolism, anemia, arrhythmias, high blood pressure, or low blood pressure # Sudden unexpected cardiac death, including cardiac arrest, where symptoms may suggest MI, an ECG may be taken with suggestive changes, or a blood clot is found in a coronary artery by angiography and/or at autopsy, but where blood samples could not be obtained, or at a time before the appearance of cardiac biomarkers in the blood # Associated with
coronary angioplasty Percutaneous coronary intervention (PCI) is a non-surgical procedure used to treat narrowing of the coronary arteries of the heart found in coronary artery disease. The process involves combining coronary angioplasty with stenting, which is the ...
or stents #* Associated with percutaneous coronary intervention (PCI) #* Associated with stent thrombosis as documented by angiography or at autopsy # Associated with
CABG Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest pai ...
# Associated with spontaneous coronary artery dissection in young, fit women


Cardiac biomarkers

There are many different biomarkers used to determine the presence of cardiac muscle damage. Troponins, measured through a blood test, are considered to be the best, and are preferred because they have greater
sensitivity and specificity ''Sensitivity'' and ''specificity'' mathematically describe the accuracy of a test which reports the presence or absence of a condition. Individuals for which the condition is satisfied are considered "positive" and those for which it is not are ...
for measuring injury to the heart muscle than other tests. A rise in troponin occurs within 2–3 hours of injury to the heart muscle, and peaks within 1–2 days. The level of the troponin, as well as a change over time, are useful in measuring and diagnosing or excluding myocardial infarctions, and the diagnostic accuracy of troponin testing is improving over time. One high-sensitivity cardiac troponin can rule out a heart attack as long as the ECG is normal. Other tests, such as CK-MB or myoglobin, are discouraged. CK-MB is not as specific as troponins for acute myocardial injury, and may be elevated with past cardiac surgery, inflammation or electrical cardioversion; it rises within 4–8 hours and returns to normal within 2–3 days. Copeptin may be useful to rule out MI rapidly when used along with troponin.


Electrocardiogram

Electrocardiograms (ECGs) are a series of leads placed on a person's chest that measure electrical activity associated with contraction of the heart muscle. The taking of an ECG is an important part of the workup of an AMI, and ECGs are often not just taken once but may be repeated over minutes to hours, or in response to changes in signs or symptoms. ECG readouts product a waveform with different labelled features. In addition to a rise in biomarkers, a rise in the ST segment, changes in the shape or flipping of
T wave In electrocardiography, the T wave represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the ''absolute refractory period''. The last half of the T wave ...
s, new
Q waves In elastodynamics, Love waves, named after Augustus Edward Hough Love, are horizontally polarized surface waves. The Love wave is a result of the interference of many shear waves (S-waves) guided by an elastic layer, which is ''welded'' to a ...
, or a new left bundle branch block can be used to diagnose an AMI. In addition, ST elevation can be used to diagnose an ST segment myocardial infarction (STEMI). A rise must be new in V2 and V3 ≥2 mm (0,2 mV) for males or ≥1.5 mm (0.15 mV) for females or ≥1 mm (0.1 mV) in two other adjacent chest or limb leads. ST elevation is associated with infarction, and may be preceded by changes indicating ischemia, such as ST depression or inversion of the T waves. Abnormalities can help differentiate the location of an infarct, based on the leads that are affected by changes. Early STEMIs may be preceded by peaked T waves. Other ECG abnormalities relating to complications of acute myocardial infarctions may also be evident, such as atrial or ventricular fibrillation.


Imaging

Noninvasive imaging plays an important role in the diagnosis and characterisation of myocardial infarction. Tests such as chest X-rays can be used to explore and exclude alternate causes of a person's symptoms. Echocardiography may assist in modifying clinical suspicion of ongoing myocardial infarction in patients that can't be ruled out or ruled in following initial ECG and Troponin testing. Myocardial perfusion imaging has no role in the acute diagnostic algorithm, however it can confirm a clinical suspicion of Chronic Coronary Syndrome when the patient's history, physical examination (including
cardiac examination In medicine, the cardiac examination, also precordial exam, is performed as part of a physical examination, or when a patient presents with chest pain suggestive of a cardiovascular pathology. It would typically be modified depending on the indi ...
) ECG, and cardiac biomarkers suggest coronary artery disease. Echocardiography, an ultrasound scan of the heart, is able to visualize the heart, its size, shape, and any abnormal motion of the heart walls as they beat that may indicate a myocardial infarction. The flow of blood can be imaged, and contrast dyes may be given to improve image. Other scans using radioactive contrast include
SPECT Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is ...
CT-scans using thallium,
sestamibi Technetium (99mTc) sestamibi (INN) (commonly sestamibi; USP: technetium Tc 99m sestamibi; trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex consisting of the radioisotope techn ...
(
MIBI scan Technetium (99mTc) sestamibi (INN) (commonly sestamibi; USP: technetium Tc 99m sestamibi; trade name Cardiolite) is a pharmaceutical agent used in nuclear medicine imaging. The drug is a coordination complex consisting of the radioisotope techn ...
s) or
tetrofosmin Technetium (99mTc) tetrofosmin is a drug used in nuclear medicine cardiac imaging. It is sold under the brand name Myoview (GE Healthcare). The radioisotope, technetium-99m, is chelated by two 1,2-''bis'' i-(2-ethoxyethyl)phosphinothane ligands wh ...
; or a
PET scan Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flo ...
using Fludeoxyglucose or rubidium-82. These
nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
scans can visualize the perfusion of heart muscle. SPECT may also be used to determine viability of tissue, and whether areas of ischemia are inducible. Medical societies and professional guidelines recommend that the physician confirm a person is at high risk for Chronic Coronary Syndrome before conducting diagnostic non-invasive imaging tests to make a diagnosis, as such tests are unlikely to change management and result in increased costs. Patients who have a normal ECG and who are able to exercise, for example, most likely do not merit routine imaging. File:UOTW 36 - Ultrasound of the Week 1.webm, Poor movement of the heart due to an MI as seen on ultrasound File:UOTW 36 - Ultrasound of the Week 2.webm, Pulmonary edema due to an MI as seen on ultrasound


Differential diagnosis

There are many causes of chest pain, which can originate from the heart, lungs, gastrointestinal tract, aorta, and other muscles, bones and nerves surrounding the chest. In addition to myocardial infarction, other causes include angina, insufficient blood supply ( ischemia) to the heart muscles without evidence of cell death, gastroesophageal reflux disease; pulmonary embolism, tumors of the lungs,
pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severit ...
, rib fracture, costochondritis, heart failure and other musculoskeletal injuries. Rarer severe differential diagnoses include aortic dissection, esophageal rupture, tension pneumothorax, and
pericardial effusion A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous connective membrane and an inner two-layered serous membrane. The two layers of t ...
causing cardiac tamponade. The chest pain in an MI may mimic heartburn. Causes of sudden-onset breathlessness generally involve the lungs or heart – including pulmonary edema, pneumonia, allergic reactions and
asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
, and pulmonary embolus, acute respiratory distress syndrome and
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
. There are many different causes of fatigue, and myocardial infarction is not a common cause.


Prevention

There is a large crossover between the lifestyle and activity recommendations to prevent a myocardial infarction, and those that may be adopted as
secondary prevention Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
after an initial myocardial infarction, because of shared risk factors and an aim to reduce atherosclerosis affecting heart vessels. The influenza vaccine also appear to protect against myocardial infarction with a benefit of 15 to 45%.


Primary prevention


Lifestyle

Physical activity can reduce the risk of cardiovascular disease, and people at risk are advised to engage in 150 minutes of moderate or 75 minutes of vigorous-intensity aerobic exercise a week. Keeping a healthy weight, drinking alcohol within the recommended limits, and quitting smoking reduce the risk of cardiovascular disease. Substituting
unsaturated fat An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond ...
s such as olive oil and rapeseed oil instead of saturated fats may reduce the risk of myocardial infarction, although there is not universal agreement. Dietary modifications are recommended by some national authorities, with recommendations including increasing the intake of wholegrain starch, reducing sugar intake (particularly of refined sugar), consuming five portions of fruit and vegetables daily, consuming two or more portions of fish per week, and consuming 4–5 portions of unsalted nuts,
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
s, or legumes per week. The dietary pattern with the greatest support is the Mediterranean diet. Vitamins and mineral supplements are of no proven benefit, and neither are plant stanols or
sterols Sterol is an organic compound with formula , whose molecule is derived from that of gonane by replacement of a hydrogen atom in position 3 by a hydroxyl group. It is therefore an alcohol of gonane. More generally, any compounds that contain the gon ...
.
Public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
measures may also act at a population level to reduce the risk of myocardial infarction, for example by reducing unhealthy diets (excessive salt, saturated fat, and trans fat) including food labeling and marketing requirements as well as requirements for catering and restaurants, and stimulating physical activity. This may be part of regional cardiovascular disease prevention programs or through the health impact assessment of regional and local plans and policies. Most guidelines recommend combining different preventive strategies. A 2015 Cochrane Review found some evidence that such an approach might help with  blood pressurebody mass index and  waist circumference. However, there was insufficient evidence to show an effect on mortality or actual cardio-vascular events.


Medication

Statins, drugs that act to lower blood cholesterol, decrease the incidence and mortality rates of myocardial infarctions. They are often recommended in those at an elevated risk of cardiovascular diseases. Aspirin has been studied extensively in people considered at increased risk of myocardial infarction. Based on numerous studies in different groups (e.g. people with or without diabetes), there does not appear to be a benefit strong enough to outweigh the risk of excessive bleeding. Nevertheless, many clinical practice guidelines continue to recommend aspirin for primary prevention, and some researchers feel that those with very high cardiovascular risk but low risk of bleeding should continue to receive aspirin.


Secondary prevention

There is a large crossover between the lifestyle and activity recommendations to prevent a myocardial infarction, and those that may be adopted as
secondary prevention Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
after an initial myocardial infarct. Recommendations include stopping smoking, a gradual return to exercise, eating a healthy diet, low in saturated fat and low in
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...
, drinking alcohol within recommended limits, exercising, and trying to achieve a healthy weight. Exercise is both safe and effective even if people have had stents or heart failure, and is recommended to start gradually after 1–2 weeks. Counselling should be provided relating to medications used, and for warning signs of depression. Previous studies suggested a benefit from omega-3 fatty acid supplementation but this has not been confirmed.


Medications

Following a heart attack, nitrates, when taken for two days, and ACE-inhibitors decrease the risk of death. Other medications include: Aspirin is continued indefinitely, as well as another antiplatelet agent such as clopidogrel or ticagrelor ("dual antiplatelet therapy" or DAPT) for up to twelve months. If someone has another medical condition that requires anticoagulation (e.g. with warfarin) this may need to be adjusted based on risk of further cardiac events as well as bleeding risk. In those who have had a stent, more than 12 months of clopidogrel plus aspirin does not affect the risk of death. Beta blocker therapy such as metoprolol or carvedilol is recommended to be started within 24 hours, provided there is no acute heart failure or heart block. The dose should be increased to the highest tolerated. Contrary to what was long believed, the use of beta blockers does not appear to affect the risk of death, possibly because other treatments for MI have improved. When beta blocker medication is given within the first 24–72 hours of a STEMI no lives are saved. However, 1 in 200 people were prevented from a repeat heart attack, and another 1 in 200 from having an abnormal heart rhythm. Additionally, for 1 in 91 the medication causes a temporary decrease in the heart's ability to pump blood. ACE inhibitor therapy should be started within 24 hours, and continued indefinitely at the highest tolerated dose. This is provided there is no evidence of worsening kidney failure, high potassium, low blood pressure, or known narrowing of the renal arteries. Those who cannot tolerate ACE inhibitors may be treated with an angiotensin II receptor antagonist. Statin therapy has been shown to reduce mortality and subsequent cardiac events and should be commenced to lower LDL cholesterol. Other medications, such as
ezetimibe Ezetimibe is a medication used to treat high blood cholesterol and certain other lipid abnormalities. Generally it is used together with dietary changes and a statin. Alone, it is less preferred than a statin. It is taken by mouth. It is also ...
, may also be added with this goal in mind. Aldosterone antagonists ( spironolactone or eplerenone) may be used if there is evidence of left ventricular dysfunction after an MI, ideally after beginning treatment with an ACE inhibitor.


Other

A
defibrillator Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current (often called a ''coun ...
, an electric device connected to the heart and surgically inserted under the skin, may be recommended. This is particularly if there are any ongoing signs of heart failure, with a low left ventricular ejection fraction and a New York Heart Association grade II or III after 40 days of the infarction. Defibrillators detect potentially fatal arrhythmia and deliver an electrical shock to the person to depolarize a critical mass of the heart muscle.


Management

A myocardial infarction requires immediate medical attention. Treatment aims to preserve as much heart muscle as possible, and to prevent further complications. Treatment depends on whether the myocardial infarction is a STEMI or NSTEMI. Treatment in general aims to unblock blood vessels, reduce blood clot enlargement, reduce ischemia, and modify risk factors with the aim of preventing future MIs. In addition, the main treatment for myocardial infarctions with ECG evidence of ST elevation (STEMI) include thrombolysis or percutaneous coronary intervention, although PCI is also ideally conducted within 1–3 days for NSTEMI. In addition to clinical judgement, risk stratification may be used to guide treatment, such as with the
TIMI The Thrombolysis In Myocardial Infarction, or TIMI Study Group, is an Academic Research Organization (ARO) affiliated with Brigham and Women's Hospital and Harvard Medical School dedicated to advancing the knowledge and care of patients with ca ...
and
GRACE Grace may refer to: Places United States * Grace, Idaho, a city * Grace (CTA station), Chicago Transit Authority's Howard Line, Illinois * Little Goose Creek (Kentucky), location of Grace post office * Grace, Carroll County, Missouri, an uninc ...
scoring systems.


Pain

The pain associated with myocardial infarction is often treated with nitroglycerin, a vasodilator, or opioid medications such as
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies ('' Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
. Nitroglycerin (given under the tongue or injected into a vein) may improve blood supply to the heart. It is an important part of therapy for its pain relief effects, though there is no proven benefit to mortality. Morphine or other opioid medications may also be used, and are effective for the pain associated with STEMI. There is poor evidence that morphine shows any benefit to overall outcomes, and there is some evidence of potential harm.


Antithrombotics

Aspirin, an antiplatelet drug, is given as a loading dose to reduce the clot size and reduce further clotting in the affected artery. It is known to decrease mortality associated with acute myocardial infarction by at least 50%.
P2Y12 inhibitors P2Y12 is a chemoreceptor for adenosine diphosphate (ADP) that belongs to the Gi class of a group of G protein-coupled (GPCR) purinergic receptors. This P2Y receptor family has several receptor subtypes with different pharmacological selectiv ...
such as
clopidogrel Clopidogrel — sold under the brand name Plavix, among others — is an antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following ...
, prasugrel and ticagrelor are given concurrently, also as a loading dose, with the dose depending on whether further surgical management or fibrinolysis is planned. Prasugrel and ticagrelor are recommended in European and American guidelines, as they are active more quickly and consistently than clopidogrel. P2Y12 inhibitors are recommended in both NSTEMI and STEMI, including in PCI, with evidence also to suggest improved mortality. Heparins, particularly in the unfractionated form, act at several points in the
clotting cascade Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism ...
, help to prevent the enlargement of a clot, and are also given in myocardial infarction, owing to evidence suggesting improved mortality rates. In very high-risk scenarios, inhibitors of the platelet glycoprotein αIIbβ3a receptor such as eptifibatide or
tirofiban Tirofiban, sold under the brand name Aggrastat, is an antiplatelet medication. It belongs to a class of antiplatelets named glycoprotein IIb/IIIa inhibitors. Tirofiban is a small molecule inhibitor of the protein-protein interaction between fibri ...
may be used. There is varying evidence on the mortality benefits in NSTEMI. A 2014 review of P2Y12 inhibitors such as
clopidogrel Clopidogrel — sold under the brand name Plavix, among others — is an antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following ...
found they do not change the risk of death when given to people with a suspected NSTEMI prior to PCI, nor do heparins change the risk of death. They do decrease the risk of having a further myocardial infarction.


Angiogram

Primary percutaneous coronary intervention (PCI) is the treatment of choice for STEMI if it can be performed in a timely manner, ideally within 90–120 minutes of contact with a medical provider. Some recommend it is also done in NSTEMI within 1–3 days, particularly when considered high-risk. A 2017 review, however, did not find a difference between early versus later PCI in NSTEMI. PCI involves small probes, inserted through peripheral blood vessels such as the femoral artery or
radial artery In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm. Structure The radial artery arises from the bifurcation of the brachial artery in the antecubital fossa. It runs distally on the anterior part of the f ...
into the blood vessels of the heart. The probes are then used to identify and clear blockages using small balloons, which are dragged through the blocked segment, dragging away the clot, or the insertion of stents.
Coronary artery bypass grafting Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest pa ...
is only considered when the affected area of heart muscle is large, and PCI is unsuitable, for example with difficult cardiac anatomy. After PCI, people are generally placed on aspirin indefinitely and on dual antiplatelet therapy (generally aspirin and
clopidogrel Clopidogrel — sold under the brand name Plavix, among others — is an antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk. It is also used together with aspirin in heart attacks and following ...
) for at least a year.


Fibrinolysis

If PCI cannot be performed within 90 to 120 minutes in STEMI then fibrinolysis, preferably within 30 minutes of arrival to hospital, is recommended. If a person has had symptoms for 12 to 24 hours evidence for effectiveness of thrombolysis is less and if they have had symptoms for more than 24 hours it is not recommended. Thrombolysis involves the administration of medication that activates the enzymes that normally dissolve blood clots. These medications include tissue plasminogen activator, reteplase, streptokinase, and tenecteplase. Thrombolysis is not recommended in a number of situations, particularly when associated with a high risk of bleeding or the potential for problematic bleeding, such as active bleeding, past
stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
s or bleeds into the brain, or severe hypertension. Situations in which thrombolysis may be considered, but with caution, include recent surgery, use of anticoagulants, pregnancy, and proclivity to bleeding. Major risks of thrombolysis are major bleeding and
intracranial bleed Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds ( intraventricular bleeds and intraparenchymal bleeds), subarachnoid bleeds, epidural bleeds, and subdural bleed ...
ing. Pre-hospital thrombolysis reduces time to thrombolytic treatment, based on studies conducted in higher income countries, however it is unclear whether this has an impact on mortality rates.


Other

In the past, high flow oxygen was recommended for everyone with a possible myocardial infarction. More recently, no evidence was found for routine use in those with normal oxygen levels and there is potential harm from the intervention. Therefore, oxygen is currently only recommended if oxygen levels are found to be low or if someone is in respiratory distress. If despite thrombolysis there is significant cardiogenic shock, continued severe chest pain, or less than a 50% improvement in ST elevation on the ECG recording after 90 minutes, then rescue PCI is indicated emergently. Those who have had
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...
may benefit from targeted temperature management with evaluation for implementation of hypothermia protocols. Furthermore, those with cardiac arrest, and ST elevation at any time, should usually have angiography.
Aldosterone antagonists An antimineralocorticoid, also known as a mineralocorticoid receptor antagonist (MRA or MCRA) or aldosterone antagonist, is a diuretic drug which antagonizes the action of aldosterone at mineralocorticoid receptors. This group of drugs is often u ...
appear to be useful in people who have had an STEMI and do not have heart failure.


Rehabilitation and exercise

Cardiac rehabilitation Cardiac rehabilitation (CR) is defined by the World Health Organization (WHO) as "''The sum of activity and interventions required to ensure the best possible physical, mental, and social conditions so that patients with chronic or post-acute card ...
benefits many who have experienced myocardial infarction, even if there has been substantial heart damage and resultant left ventricular failure. It should start soon after discharge from the hospital. The program may include lifestyle advice, exercise, social support, as well as recommendations about driving, flying, sports participation, stress management, and sexual intercourse. Returning to sexual activity after myocardial infarction is a major concern for most patients, and is an important area to be discussed in the provision of holistic care. In the short-term, exercise-based cardiovascular rehabilitation programs may reduce the risk of a myocardial infarction, reduces a large number of hospitalizations from all causes, reduces hospital costs, improves
health-related quality of life In general, quality of life (QoL or QOL) is the perceived quality of an individual's daily life, that is, an assessment of their well-being or lack thereof. This includes all emotional, social and physical aspects of the individual's life. In h ...
, and has a small effect on all-cause mortality. Longer-term studies indicate that exercise-based cardiovascular rehabilitation programs may reduce cardiovascular mortality and myocardial infarction.


Prognosis

The prognosis after myocardial infarction varies greatly depending on the extent and location of the affected heart muscle, and the development and management of complications. Prognosis is worse with older age and social isolation. Anterior infarcts, persistent ventricular tachycardia or fibrillation, development of heart blocks, and left ventricular impairment are all associated with poorer prognosis. Without treatment, about a quarter of those affected by MI die within minutes and about forty percent within the first month. Morbidity and mortality from myocardial infarction has however improved over the years due to earlier and better treatment: in those who have a STEMI in the United States, between 5 and 6 percent die before leaving the hospital and 7 to 18 percent die within a year. It is unusual for babies to experience a myocardial infarction, but when they do, about half die. In the short-term, neonatal survivors seem to have a normal quality of life.


Complications

Complications may occur immediately following the myocardial infarction or may take time to develop. Disturbances of heart rhythms, including atrial fibrillation, ventricular tachycardia and fibrillation and heart block can arise as a result of ischemia, cardiac scarring, and infarct location.
Stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...
is also a risk, either as a result of clots transmitted from the heart during PCI, as a result of bleeding following anticoagulation, or as a result of disturbances in the heart's ability to pump effectively as a result of the infarction. Regurgitation of blood through the mitral valve is possible, particularly if the infarction causes dysfunction of the papillary muscle. Cardiogenic shock as a result of the heart being unable to adequately pump blood may develop, dependent on infarct size, and is most likely to occur within the days following an acute myocardial infarction. Cardiogenic shock is the largest cause of in-hospital mortality. Rupture of the ventricular dividing wall or left ventricular wall may occur within the initial weeks. Dressler's syndrome, a reaction following larger infarcts and a cause of pericarditis is also possible. Heart failure may develop as a long-term consequence, with an impaired ability of heart muscle to pump, scarring, and an increase in the size of the existing muscle. Aneurysm of the left ventricle myocardium develops in about 10% of MI and is itself a risk factor for heart failure, ventricular arrhythmia, and the development of clots. Risk factors for complications and death include age,
hemodynamic Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously mo ...
parameters (such as heart failure,
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...
on admission, systolic blood pressure, or
Killip class The Killip classification is a system used in individuals with an acute myocardial infarction (heart attack), taking into account physical examination and the development of heart failure in order to predict and stratify their risk of mortality. Ind ...
of two or greater), ST-segment deviation, diabetes, serum creatinine, peripheral vascular disease, and elevation of cardiac markers.


Epidemiology

Myocardial infarction is a common presentation of coronary artery disease. The
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
estimated in 2004, that 12.2% of worldwide deaths were from ischemic heart disease; with it being the leading cause of death in high- or middle-income countries and second only to lower respiratory infections in lower-income countries. Worldwide, more than 3 million people have STEMIs and 4 million have NSTEMIs a year. STEMIs occur about twice as often in men as women. Rates of death from ischemic heart disease (IHD) have slowed or declined in most high-income countries, although cardiovascular disease still accounted for one in three of all deaths in the US in 2008. For example, rates of death from cardiovascular disease have decreased almost a third between 2001 and 2011 in the United States. In contrast, IHD is becoming a more common cause of death in the developing world. For example, in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, IHD had become the leading cause of death by 2004, accounting for 1.46 million deaths (14% of total deaths) and deaths due to IHD were expected to double during 1985–2015. Globally,
disability adjusted life year The disability-adjusted life year (DALY) is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. It was developed in the 1990s as a way of comparing the overall health and life ex ...
s (DALYs) lost to ischemic heart disease are predicted to account for 5.5% of total DALYs in 2030, making it the second-most-important cause of disability (after unipolar depressive disorder), as well as the leading cause of death by this date.


Social determinants of health

Social determinants such as neighborhood disadvantage, immigration status, lack of social support, social isolation, access to health services play an important role in myocardial infarction risk and survival. Studies have shown that low socioeconomic status is associated with an increased risk of poorer survival. There are well-documented disparities in myocardial infarction survival by socioeconomic status, race,
education Education is a purposeful activity directed at achieving certain aims, such as transmitting knowledge or fostering skills and character traits. These aims may include the development of understanding, rationality, kindness, and honesty ...
, and census-tract-level poverty. Race: In the U.S. African Americans have a greater burden of myocardial infarction and other cardiovascular events. On a population level, there is a higher overall prevalence of risk factors that are unrecognized and therefore not treated, which places these individuals at a greater likelihood of experiencing adverse outcomes and therefore potentially higher morbidity and mortality. Socioeconomic status: Among individuals who live in the low- socioeconomic (SES) areas, which is close to 25% of the US population, myocardial infarctions (MIs) occurred twice as often compared with people who lived in higher SES areas. Immigration status: In 2018 many lawfully present immigrants who are eligible for coverage remain uninsured because immigrant families face a range of enrollment barriers, including fear, confusion about eligibility policies, difficulty navigating the enrollment process, and
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of ...
and
literacy Literacy in its broadest sense describes "particular ways of thinking about and doing reading and writing" with the purpose of understanding or expressing thoughts or ideas in Writing, written form in some specific context of use. In other wo ...
challenges. Uninsured undocumented immigrants are ineligible for coverage options due to their immigration status. Health care access: Lack of health insurance and financial concerns about accessing care were associated with delays in seeking emergency care for acute myocardial infarction which can have significant, adverse consequences on patient outcomes. Education: Researchers found that compared to people with graduate degrees, those with lower educational attainment appeared to have a higher
risk In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environm ...
of heart attack, dying from a cardiovascular event, and overall death.


Society and culture

Depictions of heart attacks in popular media often include collapsing or loss of consciousness which are not common symptoms; these depictions contribute to widespread misunderstanding about the symptoms of myocardial infarctions, which in turn contributes to people not getting care when they should.


Legal implications

At
common law In law, common law (also known as judicial precedent, judge-made law, or case law) is the body of law created by judges and similar quasi-judicial tribunals by virtue of being stated in written opinions."The common law is not a brooding omniprese ...
, in general, a myocardial infarction is a disease, but may sometimes be an injury. This can create coverage issues in the administration of no-fault insurance schemes such as workers' compensation. In general, a heart attack is not covered;Workers' Compensation FAQ
. Prairie View A&M University. Retrieved November 22, 2006.
however, it may be a work-related injury if it results, for example, from unusual emotional stress or unusual exertion.SIGNIFICANT DECISIONS Subject Index
. Board of Industrial Insurance Appeals. Retrieved November 22, 2006.
In addition, in some jurisdictions, heart attacks had by persons in particular occupations such as police officers may be classified as line-of-duty injuries by statute or policy. In some countries or states, a person having had an MI may be prevented from participating in activity that puts other people's lives at risk, for example driving a car or flying an airplane.


References


Sources

* * * * * * *


Further reading

* *


External links

*
American Heart Association's Heart Attack web site
— Information and resources for preventing, recognizing, and treating a heart attack. * TIMI Score fo
UA/NSTEMI
an
STEMI

HEART Score for Major Cardiac Events
* {{Authority control Aging-associated diseases Causes of death Ischemic heart diseases Medical emergencies Articles containing video clips Wikipedia medicine articles ready to translate Acute pain Wikipedia emergency medicine articles ready to translate