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A cardiac stress test (also referred to as a cardiac diagnostic test, cardiopulmonary exercise test, or abbreviated CPX test) is a cardiological test that measures the
heart The heart is a muscular 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 carbon dioxide t ...
's ability to respond to external
stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
in a controlled clinical environment. The stress response is induced by exercise or by intravenous pharmacological stimulation. Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation during maximum cardiac exertion, showing any abnormal
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
flow to the myocardium (heart muscle tissue). The results can be interpreted as a reflection on the general physical condition of the test patient. This test can be used to diagnose coronary artery disease (also known as ischemic heart disease) and assess patient prognosis after a
myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...
(heart attack). Exercise-induced stressors are most commonly either exercise on a treadmill or pedalling a stationary exercise bicycle ergometer. The level of stress is progressively increased by raising the difficulty (steepness of the slope on a treadmill or resistance on an ergometer) and speed. People who cannot use their legs may exercise with a bicycle-like crank that they turn with their arms, or may be given a medication to induce cardiac stress. Once the stress test is completed, the patient generally is advised to not suddenly stop activity but to slowly decrease the intensity of the exercise over the course of several minutes. The test administrator or
attending physician In the United States and Canada, an attending physician (also known as a staff physician or supervising physician) is a physician (usually an M.D. or D.O.) who has completed residency and practices medicine in a clinic or hospital, in the spec ...
examines the symptoms and blood pressure response. To measure the heart's response to the stress the patient may be connected to an electrocardiogram (ECG); in this case the test is most commonly called a cardiac stress test but is known by other names, such as exercise testing, stress testing treadmills, exercise tolerance test, stress test or stress test ECG. Alternatively a stress test may use an
echocardiogram An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler ultrasound. Echocardiography has become routinely used in th ...
for ultrasonic imaging of the heart (in which case the test is called an echocardiography stress test or stress echo), or a
gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...
to image
radioisotopes A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
injected into the bloodstream (called a nuclear stress test).


Stress echocardiography

A stress test may be accompanied by echocardiography. The echocardiography is performed both before and after the exercise so that structural differences can be compared. A resting echocardiogram is obtained prior to stress. The images obtained are similar to the ones obtained during a full surface echocardiogram, commonly referred to as transthoracic echocardiogram. The patient is subjected to stress in the form of exercise or chemically (usually
dobutamine Dobutamine is a medication used in the treatment of cardiogenic shock (as a result of inadequate tissue perfusion) and severe heart failure. It may also be used in certain types of cardiac stress tests. It is given by IV only, as an injection in ...
). After the target heart rate is achieved, 'stress' echocardiogram images are obtained. The two echocardiogram images are then compared to assess for any abnormalities in wall motion of the heart. This is used to detect obstructive coronary artery disease.


Cardiopulmonary exercise test

While also measuring breathing gases (e.g. O2, VO2), the test is often referred to as a cardiopulmonary exercise test (CPET). Common indications for a cardiopulmonary exercise test is: Evaluation of dyspnea. Work up before
heart transplantation A heart transplant, or a cardiac transplant, is a surgical transplant procedure performed on patients with end-stage heart failure or severe coronary artery disease when other medical or surgical treatments have failed. , the most common procedu ...
. Prognosis and risk assessment of heart failure patients. The test is also common in sport science for measuring athlete's
VO2 max VO2 max (also maximal oxygen consumption, maximal oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption attainable during physical exertion. The name is derived from three abbreviations: "V̇" for volume (the dot ap ...
.


Nuclear stress test

A nuclear stress test uses a
gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...
to image radioisotopes injected into the bloodstream. The best known example is
myocardial perfusion imaging Myocardial perfusion imaging or scanning (also referred to as MPI or MPS) is a nuclear medicine procedure that illustrates the function of the heart muscle ( myocardium). It evaluates many heart conditions, such as coronary artery disease (CAD), ...
. Typically, a
radiotracer A radioactive tracer, radiotracer, or radioactive label is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tr ...
( Tc-99 sestamibi,
Myoview 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 thallous chloride 201) may be injected during the test. After a suitable waiting period to ensure proper distribution of the radiotracer, scans are acquired with a gamma camera to capture images of the blood flow. Scans acquired before and after exercise are examined to assess the state of the coronary arteries of the patient. Showing the relative amounts of radioisotope within the heart muscle, the nuclear stress tests more accurately identify regional areas of reduced blood flow. Stress and potential cardiac damage from exercise during the test is a problem in patients with ECG abnormalities at rest or in patients with severe motor disability. Pharmacological stimulation from vasodilators such as dipyridamole or adenosine, or positive chronotropic agents such as dobutamine can be used. Testing personnel can include a cardiac radiologist, a nuclear medicine physician, a nuclear medicine technologist, a cardiology technologist, a cardiologist, and/or a nurse. The typical dose of radiation received during this procedure can range from 9.4 to 40.7 millisieverts.


Function

The American Heart Association recommends ECG treadmill testing as the first choice for patients with medium risk of coronary heart disease according to risk factors of smoking, family history of coronary artery stenosis, hypertension, diabetes and high cholesterol. In 2013, in its "Exercise Standards for Testing and Training", the AHA indicated that high frequency QRS analysis during ECG treadmill test have useful test performance for detection of coronary heart disease. * Perfusion stress test (with 99mTc labelled sestamibi) is appropriate for select patients, especially those with an abnormal resting electrocardiogram. * Intracoronary ultrasound or angiogram can provide more information at the risk of complications associated with cardiac catheterization.


Diagnostic value

The common approach for stress testing by American College of Cardiology and American Heart Association indicates the following: * Treadmill test: sensitivity 73-90%, specificity 50-74% (modified Bruce protocol) * Nuclear test: sensitivity 81%, specificity 85-95% ( Sensitivity is the percentage of people with the condition who are correctly identified by the test as having the condition; specificity is the percentage of people without the condition are correctly identified by the test as not having the condition). To arrive at the patient's posttest likelihood of disease, interpretation of the stress test result requires integration of the patient's pretest likelihood with the test's sensitivity and specificity. This approach, first described by Diamond and Forrester in the 1970s, results in an estimate of the patient's post-test likelihood of disease. The value of stress tests has always been recognized as limited in assessing heart disease such as
atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...
, a condition which mainly produces wall thickening and enlargement of the arteries. This is because the stress test compares the patient's coronary flow status before and after exercise and is suitable to detecting specific areas of ischemia and lumen narrowing, not a generalized arterial thickening. According to American Heart Association data, about 65% of men and 47% of women present with a heart attack or sudden
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 possib ...
as their first symptom of cardiovascular disease. Stress tests, carried out shortly before these events, are not relevant to the prediction of infarction in the majority of individuals tested. Over the past two decades, better methods have been developed to identify atherosclerotic disease before it becomes symptomatic. These detection methods include ''anatomical'' and ''physiological'' methods. ; Examples of anatomical methods * CT coronary calcium score *
Coronary CT angiography Coronary CT angiography (CTA or CCTA) is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The patient receives an intravenous injection of radiocontrast and then the heart is scanned using a high spe ...
* Intima-media thickness (IMT) *
Intravascular ultrasound Intravascular ultrasound (IVUS) or intravascular echocardiography is a medical imaging methodology using a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter. The proximal end of the cath ...
(IVUS) ; Examples of physiological methods *
Lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, su ...
analysis *
HbA1c Glycated hemoglobin, also known as HbA1c, glycohemoglobin, hemoglobin A1c, A1C, is a form of hemoglobin (Hb) that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously (i.e. non-enzymati ...
* Hs-CRP *
Homocysteine Homocysteine is a non-proteinogenic α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH2-). It is biosynthesized from methionine by the removal of its terminal Cε methyl group. In th ...
The anatomic methods directly measure some aspects of the actual process of atherosclerosis itself and therefore offer the possibility of early diagnosis but are often more expensive and may be invasive (in the case of IVUS, for example). The physiological methods are often less expensive and safer but are not able to quantify the current status of the disease or directly track progression.


Contraindications and termination conditions

Stress cardiac imaging is not recommended for asymptomatic, low-risk patients as part of their routine care. Some estimates show that such screening accounts for 45% of cardiac stress imaging, and evidence does not show that this results in better outcomes for patients. Unless high-risk markers are present, such as diabetes in patients aged over 40,
peripheral arterial disease Peripheral artery disease (PAD) is an abnormal narrowing of arteries other than those that supply the heart or brain. When narrowing occurs in the heart, it is called coronary artery disease, and in the brain, it is called cerebrovascular disea ...
; or a risk of
coronary heart disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...
greater than 2 percent yearly, most health societies do not recommend the test as a routine procedure. Absolute contraindications to cardiac stress test include: *
Acute myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may t ...
within 48 hours * Unstable angina not yet stabilized with medical therapy * Uncontrolled cardiac arrhythmia, which may have significant hemodynamic responses (e.g. ventricular tachycardia) * Severe symptomatic
aortic stenosis Aortic stenosis (AS or AoS) is the narrowing of the exit of the left ventricle of the heart (where the aorta begins), such that problems result. It may occur at the aortic valve as well as above and below this level. It typically gets worse ov ...
,
aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or ...
,
pulmonary embolism Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream ( embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathin ...
, and pericarditis * Multivessel coronary artery diseases that have a high risk of producing an acute myocardial infarction * Decompensated or inadequately controlled
congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
* Uncontrolled hypertension (blood pressure>200/110mm Hg) * Severe pulmonary hypertension * Acute aortic dissection * Acutely ill for any reason Indications for termination: A cardiac stress test should be terminated before completion under the following circumstances: Absolute indications for termination include: *
Systolic blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
decreases by more than 10 mmHg with increase in work rate, or drops below baseline in the same position, with other evidence of ischemia. * Increase in nervous system symptoms: Dizziness,
ataxia Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...
or near syncope * Moderate to severe anginal pain (above 3 on standard 4-point scale) * Signs of poor perfusion, e.g.
cyanosis Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...
or pallor * Request of the test subject * Technical difficulties (e.g. difficulties in measuring blood pressure or EGC) * ST Segment elevation of more than 1 mm in aVR, V1 or non-Q wave leads * Sustained
ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period ...
Relative indications for termination include: * Systolic blood pressure decreases by more than 10 mmHg with increase in work rate, or drops below baseline in the same position, without other evidence of ischemia. * ST or QRS segment changes, e.g. more than 2 mm horizontal or downsloping ST segment depression in non-Q wave leads, or marked axis shift * Arrhythmias other than sustained ventricular tachycardia e.g. Premature ventricular contractions, both multifocal or triplet; heart block; supraventricular tachycardia or
bradyarrhythmias Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...
* Intraventricular conduction delay or
bundle branch block A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart. Anatomy and physiology The heart's electrical activity begins in the sinoatrial node (the heart's natural pacemaker), which is situat ...
or that cannot be distinguished from ventricular tachycardia * Increasing chest pain * Fatigue, shortness of breath, wheezing,
claudication Claudication is a medical term usually referring to impairment in walking, or pain, discomfort, numbness, or tiredness in the legs that occurs during walking or standing and is relieved by rest. The perceived level of pain from claudication can be ...
or leg cramps * Hypertensive response (systolic blood pressure > 250 mmHg or diastolic blood pressure > 115 mmHg)


Adverse effects

Side effects from cardiac stress testing may include * Palpitations, chest pain, myocardial infarction, shortness of breath, headache, nausea or fatigue. * Adenosine and dipyridamole can cause mild hypotension. * As the tracers used for this test are carcinogenic, frequent use of these tests carries a small risk of cancer.


Pharmacological agents

Pharmacologic stress testing relies on
coronary steal Coronary steal (with its symptoms termed coronary steal syndrome or cardiac steal syndrome) is a phenomenon where an alteration of circulation patterns leads to a reduction in the blood flow directed to the coronary circulation. It is caused when ...
. Vasodilators are used to dilate coronary vessels, which causes increased blood velocity and flow rate in normal vessels and less of a response in stenotic vessels. This difference in response leads to a steal of flow and perfusion defects appear in cardiac nuclear scans or as ST-segment changes. The choice of pharmacologic stress agents used in the test depends on factors such as potential drug interactions with other treatments and concomitant diseases. Pharmacologic agents such as adenosine, Lexiscan (regadenoson), or dipyridamole is generally used when a patient cannot achieve adequate work level with treadmill exercise, or has poorly controlled hypertension or left
bundle branch block A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart. Anatomy and physiology The heart's electrical activity begins in the sinoatrial node (the heart's natural pacemaker), which is situat ...
. However, an exercise stress test may provide more information about exercise tolerance than a pharmacologic stress test. Commonly used agents include: *
Vasodilators Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction ...
acting as
adenosine receptor The adenosine receptors (or P1 receptors) are a class of purinergic G protein-coupled receptors with adenosine as the endogenous ligand. There are four known types of adenosine receptors in humans: A1, A2A, A2B and A3; each is encoded by a di ...
agonists, such as adenosine itself, and
dipyridamole Dipyridamole (trademarked as Persantine and others) is a nucleoside transport inhibitor and a PDE3 inhibitor medication that inhibits blood clot formation when given chronically and causes blood vessel dilation when given at high doses over a ...
(brand name "Persantine"), which acts indirectly at the receptor. *
Regadenoson Regadenoson, sold under the brand name Lexiscan among others, is an A2A adenosine receptor agonist that is a coronary vasodilator that is commonly used in pharmacologic stress testing. It produces hyperemia quickly and maintains it for a durati ...
(brand name "Lexiscan"), which acts specifically at the
adenosine A2A receptor The adenosine A2A receptor, also known as ADORA2A, is an adenosine receptor, and also denotes the human gene encoding it. Structure This protein is a member of the G protein-coupled receptor (GPCR) family which possess seven transmembrane alph ...
, thus affecting the heart more than the lung. *
Dobutamine Dobutamine is a medication used in the treatment of cardiogenic shock (as a result of inadequate tissue perfusion) and severe heart failure. It may also be used in certain types of cardiac stress tests. It is given by IV only, as an injection in ...
. The effects of beta-agonists such as dobutamine can be reversed by administering
beta-blocker Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack (secondary prevention). They are al ...
s such as
propranolol Propranolol, sold under the brand name Inderal among others, is a medication of the beta blocker class. It is used to treat high blood pressure, a number of types of irregular heart rate, thyrotoxicosis, capillary hemangiomas, performance an ...
. Lexiscan (Regadenoson) or Dobutamine is often used in patients with severe
reactive airway disease Reactive airway disease (RAD) is an informal label that physicians apply to patients with symptoms similar to those of asthma. An exact definition of the condition does not exist. Individuals who are typically labeled as having RAD generally have ...
(
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, cou ...
or
COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
) as adenosine and dipyridamole can cause acute exacerbation of these conditions. If the patient's Asthma is treated with an inhaler then it should be used as a pre-treatment prior to the injection of the pharmacologic stress agent. In addition, if the patient is actively wheezing then the physician should determine the benefits versus the risk to the patient of performing a stress test especially outside of a hospital setting.
Caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
is usually held 24 hours prior to an adenosine stress test, as it is a competitive antagonist of the A2A adenosine receptor and can attenuate the vasodilatory effects of adenosine. Aminophylline may be used to attenuate severe and/or persistent adverse reactions to Adenosine and Lexiscan.


Limitations

The stress test does not detect: *
Atheroma 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 o ...
* Vulnerable plaques The test has relatively high rates of false positives and false negatives compared with other clinical tests. Females in particular have a higher rate of false positives, which is theorized to be because on average they have smaller hearts.


Results

* Increased spatial resolution allows a more sensitive detection of ischemia. * Stress testing, even if made in time, is not able to guarantee the prevention of symptoms, fainting, or death. Stress testing, although more effective than a resting ECG at detecting heart function, is only able to detect certain cardiac properties. * The detection of high-grade coronary artery stenosis by a cardiac stress test has been the key to recognizing people who have heart attacks since 1980. From 1960 to 1990, despite the success of stress testing to identify many who were at high risk of heart attack, the inability of this test to correctly identify many others is discussed in medical circles but unexplained. * High degrees of coronary artery stenosis, which are detected by stress testing methods are often, though not always, responsible for recurrent symptoms of angina. * Unstable atheroma produces "vulnerable plaques" hidden within the walls of coronary arteries which go undetected by this test. * Limitation in blood flow to the left ventricle can lead to recurrent angina pectoris.


See also

* Cardiac steal syndrome * Duke Treadmill Score *
Harvard step test The Harvard step test, in scientific literature sometimes referred to as the Brouha Test, is a type of cardiac stress test for detecting and diagnosing cardiovascular disease. It is also a good measurement of fitness and a person's ability to re ...
*
Metabolic equivalent The metabolic equivalent of task (MET) is the objective measure of the ratio of the rate at which a person expends energy, relative to the mass of that person, while performing some specific physical activity compared to a reference, set by convent ...
*
Robert A. Bruce Robert Arthur Bruce (November 20, 1916 – February 12, 2004) was an American Cardiology, cardiologist and a professor at the University of Washington. He was known as the "father of exercise cardiology" for his research and development of the Bru ...
*
Wasserman 9-Panel Plot The Wasserman 9-Panel Plot, often called a Nine-Panel Plot, is a standard layout for the graphical representation of data produced by a Cardiac stress test, cardiopulmonary exercise test. The layout was updated in 2012. The graphs give an overview ...


References


External links


Preparing for the exercise stress test

"A Simple Exercise Tolerance Test for Circulatory Efficiency with Standard Tables for Normal Individuals," ''American Journal of the Medical Sciences''

"Optimal Medical Therapy with or without PCI for Stable Coronary Disease," ''New England Journal of Medicine''

Stress test information from the American Heart Association


at NIH MedLine {{DEFAULTSORT:Cardiac Stress Test Diagnostic cardiology Nuclear medicine