Bradycardia (also sinus bradycardia) is a slow resting
heart rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and e ...
, commonly under 60
beats per minute
Beat, beats or beating may refer to:
Common uses
* Patrol, or beat, a group of personnel assigned to monitor a specific area
** Beat (police), the territory that a police officer patrols
** Gay beat, an area frequented by gay men
* Battery ( ...
(BPM) as determined by an
electrocardiogram.
It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, and in
athletes
An athlete (also sportsman or sportswoman) is a person who competes in one or more sports that involve physical strength, speed, or endurance.
Athletes may be professionals or amateurs. Most professional athletes have particularly well-dev ...
.
[
In some people, bradycardia below 60 BPM may be associated with ]fatigue
Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
, weakness
Weakness is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, i ...
, dizziness
Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness.
Dizziness is a common medical ...
, 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 ...
, and fainting
Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...
.[ The term "relative bradycardia" is used to refer to a heart rate slower than an individual's typical resting heart rate. Athletes may have athletic heart syndrome, which includes bradycardia as part of the cardiovascular adaptations to training and participation.
The word "bradycardia" is from the ]Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
βραδύς ''bradys'' "slow", and καρδία ''kardia'' "heart".
Classification
Sinus
Atrial bradycardias are divided into three types. The first, respiratory sinus arrhythmia Vagal tone is activity of the vagus nerve, the 10th cranial nerve and a fundamental component of the parasympathetic branch of the autonomic nervous system. This branch of the nervous system is not under conscious control and is largely responsible ...
, is usually found in young and healthy adults. Heart rate increases during inhalation and decreases during exhalation. This is thought to be caused by changes in the vagal tone during respiration.
Sinus bradycardia
Sinus bradycardia is a sinus node dysfunction giving a heart rate that is lower than the normal 60–100 beats per minute (bpm) in humans. Bradycardia is generally defined to be a heart rate of under 60 bpm.
Signs and symptoms
The decreased hea ...
is a sinus rhythm
A sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node. It is characterised by the presence of correctly oriented P waves on the electrocardiogram (ECG). Sinus rhythm is necessary, but not ...
of less than 60 BPM.[ It is a common condition found in both healthy individuals and those considered well-conditioned athletes.][ Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has a higher ]stroke volume
In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood ...
, so requires fewer contractions to circulate the same volume of blood.[
The third, sick sinus syndrome, covers conditions that include severe sinus bradycardia, ]sinoatrial block
A sinoatrial block (also spelled sinuatrial block) is a disorder in the normal rhythm of the heart, known as a heart block, that is initiated in the sinoatrial node. The initial action impulse in a heart is usually formed in the sinoatrial node ...
, sinus arrest
Sinoatrial arrest is a medical condition wherein the sinoatrial node of the heart transiently ceases to generate the electrical impulses that normally stimulate the myocardial tissues to contract and thus the heart to beat. It is defined as lasti ...
, and bradycardia-tachycardia syndrome ( atrial fibrillation, atrial flutter
Atrial flutter (AFL) is a common abnormal heart rhythm that starts in the atrial chambers of the heart. When it first occurs, it is usually associated with a fast heart rate and is classified as a type of supraventricular tachycardia. Atrial ...
, and paroxysmal supraventricular tachycardia
Paroxysmal supraventricular tachycardia (PSVT) is a type of supraventricular tachycardia, named for its intermittent episodes of abrupt onset and termination. Often people have no symptoms. Otherwise symptoms may include palpitations, increased h ...
).[
]
Atrioventricular junction
An AV-junctional rhythm, or atrioventricular nodal bradycardia, is usually caused by the absence of the electrical impulse from the sinus node. This usually appears on an electrocardiogram (ECG) with a normal QRS complex
The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the r ...
accompanied with an inverted P wave either before, during, or after the QRS complex.[
An AV-junctional escape beat is a delayed heartbeat originating from an ectopic focus somewhere in the AV junction. It occurs when the rate of ]depolarization
In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...
of the SA node falls below the rate of the AV node.[ This dysrhythmia also may occur when the electrical impulses from the SA node fail to reach the AV node because of SA or AV block.] This is a protective mechanism for the heart, to compensate for an SA node that is no longer handling the pacemaking activity and is one of a series of backup sites that can take over pacemaker function when the SA node fails to do so. This would present with a longer PR interval
In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarizatio ...
. An AV-junctional escape complex is a normal response that may result from excessive vagal tone on the SA node. Pathological causes include sinus bradycardia, sinus arrest, sinus exit block, or AV block.[
]
Ventricular
Idioventricular rhythm
An idioventricular rhythm is a cardiac rhythm characterized by a rate of <50 beats per minute (bpm), absence of P waves and widening of the QRS complex. In cases where the heart rate is between 50 and 110 bpm, it is known as ...
, also known as atrioventricular bradycardia or ventricular escape rhythm, is a heart rate of less than 50 BPM. This is a safety mechanism when a lack of electrical impulse or stimuli from the atrium occurs.[ Impulses originating within or below the ]bundle of His
The bundle of His (BH) or His bundle (HB) ( "hiss"Medical Terminology for Health Professions, Spiral bound Version'. Cengage Learning; 2016. . pp. 129–.) is a collection of heart muscle cells specialized for electrical conduction. As part of ...
in the AV node will produce a wide QRS complex with heart rates between 20 and 40 BPM. Those above the bundle of His, also known as junctional, will typically range between 40 and 60 BPM with a narrow QRS complex.[ In a third-degree heart block, about 61% take place at the bundle branch-Purkinje system, 21% at the AV node, and 15% at the bundle of His.] AV block may be ruled out with an ECG indicating "a 1:1 relationship between P waves and QRS complexes." Ventricular bradycardias occurs with sinus bradycardia, sinus arrest, and AV block. Treatment often consists of the administration of atropine
Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically giv ...
and cardiac pacing.[
]
Infantile
For infants, bradycardia is defined as a heart rate less than 100 BPM (normal is around 120–160 BPM). Premature babies are more likely than full-term babies to have apnea and bradycardia spells; their cause is not clearly understood. The spells may be related to centers inside the brain that regulate breathing which may not be fully developed. Touching the baby gently or rocking the incubator slightly will almost always get the baby to start breathing again, which increases the heart rate. Medications (theophylline
Theophylline, also known as 1,3-dimethylxanthine, is a phosphodiesterase inhibiting drug used in therapy for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma under a variety of brand names. As a member of the ...
or 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 t ...
) can be used to treat these spells in babies if necessary. Neonatal intensive-care unit (NICU) standard practice is to electronically monitor the heart and lungs for this reason.
Causes
Bradycardia arrhythmia
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 ...
may have many causes, both cardiac and non-cardiac.
Non-cardiac causes are usually secondary, and can involve recreational drug use
Recreational drug use indicates the use of one or more psychoactive drugs to induce an altered state of consciousness either for pleasure or for some other casual purpose or pastime by modifying the perceptions and emotions of the user. When a ...
or abuse
Abuse is the improper usage or treatment of a thing, often to unfairly or improperly gain benefit. Abuse can come in many forms, such as: physical or verbal maltreatment, injury, assault, violation, rape, unjust practices, crimes, or other t ...
, metabolic or endocrine issues, especially hypothyroidism
Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as ...
, an electrolyte imbalance
Electrolyte imbalance, or water-electrolyte imbalance, is an abnormality in the concentration of electrolytes in the body. Electrolytes play a vital role in maintaining homeostasis in the body. They help to regulate heart and neurological function ...
, neurological factors, autonomic reflexes, situational factors, such as prolonged bed rest
Bed rest, also referred to as the rest-cure, is a medical treatment in which a person lies in bed for most of the time to try to cure an illness. Bed rest refers to voluntarily lying in bed as a treatment and not being confined to bed because of ...
, and autoimmunity
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an " autoimmune disease ...
.
Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease
Valvular heart disease is any cardiovascular disease process involving one or more of the four valves of the heart (the aortic and mitral valves on the left side of heart and the pulmonic and tricuspid valves on the right side of heart). These ...
, or degenerative primary electrical disease. Ultimately, the causes act by three mechanisms: depressed automaticity of the heart, conduction block, or escape pacemakers and rhythms.
In general, two types of problems result in bradycardias: disorders of the SA node, and disorders of the AV node.
With SA node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the SA node into the surrounding atrial tissue (an "exit block"). Second-degree sinoatrial blocks can be detected only by use of a 12-lead ECG. It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia, but the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker
An artificial cardiac pacemaker (or artificial pacemaker, so as not to be confused with the natural cardiac pacemaker) or pacemaker is a medical device that generates electrical impulses delivered by electrodes to the chambers of the heart ei ...
.
AV conduction disturbances (AV block; primary AV block, secondary type I AV block, secondary type II AV block, tertiary AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the bundle of His. The clinical relevance pertaining to AV blocks is greater than that of SA blocks.
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 ...
medicines also can slow the heart rate and decrease how forcefully the heart contracts. Beta-blockers may slow the heart rate to a dangerous level if prescribed with calcium channel blocker-type medications. Bradycardia is also part of the mammalian diving reflex
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It op ...
.
Diagnosis
A diagnosis of bradycardia in adults is based on a heart rate less than 60 BPM,[ although some studies use a heart rate of less than 50 BPM.] This is determined usually either by palpation or ECG.[ If symptoms occur, a determination of electrolytes may be helpful in determining the underlying cause.]
Management
The treatment of bradycardia is dependent on whether or not the person is stable or unstable.[
]
Stable
Emergency treatment is not needed if the person is asymptomatic or minimally symptomatic.
Unstable
If a person is unstable, the initial recommended treatment is intravenous atropine
Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically giv ...
.[ Doses less than 0.5 mg should not be used, as this may further decrease the rate.][ If this is not effective, intravenous ]inotrope
An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction.
The term ''inot ...
infusion (dopamine
Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 8 ...
, epinephrine
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
) or transcutaneous pacing should be used.[ ]Transvenous pacing
Transvenous cardiac pacing (TVP), also called endocardial pacing, is a potentially life-saving intervention used primarily to correct profound bradycardia. It can be used to treat symptomatic bradycardias that do not respond to transcutaneous paci ...
may be required if the cause of the bradycardia is not rapidly reversible.[
In children, giving oxygen, supporting their breathing, and ]chest compressions
Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore sponta ...
are recommended.
Epidemiology
In clinical practice, elderly people over age 65 and young athletes of both sexes may have sinus bradycardia.[ The US ]Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
reported in 2011 that 15.2% of adult males and 6.9% of adult females had clinically-defined bradycardia (a resting pulse rate
Heart rate (or pulse rate) is the frequency of the cardiac cycle, heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's Human body, physical needs, including the need ...
below 60 BPM).
Society and culture
Records
* Daniel Green holds the world record for the slowest heartbeat in a healthy human, with a heart rate measured in 2014 of 26 BPM.
* Martin Brady holds the Guinness world record for the slowest heart rate with a certified rate over a minute duration of 27 BPM.
* Professional cyclist Miguel Indurain
-->
Miguel is a given name and surname, the Portuguese and Spanish form of the Hebrew name Michael. It may refer to:
Places
* Pedro Miguel, a parish in the municipality of Horta and the island of Faial in the Azores Islands
* São Miguel (disa ...
had, during his career, a resting heart rate of 28 BPM.
See also
*
References
External links
{{Cardiovascular system symptoms and signs
Cardiac arrhythmia
Symptoms and signs: Cardiac