Arrhythmia

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Irregular heartbeat
)
Arrhythmia
Other namesCardiac arrhythmia, cardiac dysrhythmia, irregular heartbeat, heart arrhythmia
pacemaker), surgery[6]
FrequencyMillions[4]

Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the

decreased level of consciousness.[1] While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure.[2][3] Others may result in sudden death.[3]

Arrhythmias are often categorized into four groups:

Many arrhythmias can be effectively treated.

Arrhythmia affects millions of people.

Sudden cardiac death is the cause of about half of deaths due to cardiovascular disease and about 15% of all deaths globally.[12] About 80% of sudden cardiac death is the result of ventricular arrhythmias.[12] Arrhythmias may occur at any age but are more common among older people.[4] Arrhythmias may also occur in children; however, the normal range for the heart rate varies with age.[3]

Classification

Broad classification of arrhythmias according to region of heart required to sustain the rhythm

Arrhythmia may be classified by rate (tachycardia, bradycardia), mechanism (automaticity, re-entry, triggered) or duration (isolated premature beats; couplets; runs, that is 3 or more beats; non-sustained = less than 30 seconds or sustained= over 30 seconds).[citation needed]

Arrhythmias are also classified by site of origin:[citation needed]

Atrial arrhythmia

Junctional arrhythmia

Ventricular arrhythmia

Heart blocks

These are also known as AV blocks, because the vast majority of them arise from pathology at the atrioventricular node. They are the most common causes of bradycardia:[citation needed]

  • First-degree heart block
    , which manifests as PR prolongation
  • Second-degree heart block
    • Wenckebach
    • Mobitz II
  • complete heart block

First, second, and third-degree blocks also can occur at the level of the sinoatrial junction. This is referred to as sinoatrial block typically manifesting with various degrees and patterns of sinus bradycardia.[citation needed]

Sudden arrhythmic death syndrome

myocardial ischemia or a heart attack[15] Approximately 180,000 to 250,000 people die suddenly of this cause every year in the US. SADS may occur from other causes. There are many inherited conditions and heart diseases that can affect young people which can subsequently cause sudden death without advance symptoms.[16]

Causes of SADS in young people include

Fetal arrhythmia

Arrhythmias may also occur in the fetus.[19] The normal heart rate of the fetus is between 110 and 160 beats per minute. Any rhythm beyond these limits is abnormal and classed as a fetal arrhythmia. These are mainly the result of premature atrial contractions, usually give no symptoms, and have little consequence. However, around one percent of these will be the result of significant structural damage to the heart.[19]

Signs and symptoms

The term cardiac arrhythmia covers a very large number of very different conditions.[citation needed]

The most common symptom of arrhythmia is an awareness of an abnormal heartbeat, called

distracting for patients) but some of them predispose to adverse outcomes. Arrhythmias also cause chest pain and shortness of breath.[citation needed
]

Some arrhythmias do not cause symptoms and are not associated with increased mortality. However, some asymptomatic arrhythmias are associated with adverse events. Examples include a higher risk of blood clotting within the heart and a higher risk of insufficient blood being transported to the heart because of a weak heartbeat. Other increased risks are of embolization and stroke, heart failure, and sudden cardiac death.[citation needed]

If an arrhythmia results in a heartbeat that is too fast, too slow, or too weak to supply the body's needs, this manifests as lower blood pressure and may cause lightheadedness, dizziness, syncope, loss of consciousness,

persistent vegetative state, or brain death due to insufficient supply of blood and oxygen to the brain.[20]

Some types of arrhythmia result in cardiac arrest, or sudden death.[citation needed]

Medical assessment of the abnormality using an

electrocardiogram is one way to diagnose and assess the risk of any given arrhythmia.[citation needed
]

Mechanism

Cardiac arrhythmia are caused by one of two major mechanism. The first of arrhythmia is a result of enhanced or abnormal impulse formation originating at the pacemaker or the His-Purkinje network. The second is due to re-entry conduction disturbances.[21]

Diagnostic

Cardiac arrhythmia is often first detected by simple but nonspecific means: auscultation of the heartbeat with a stethoscope, or feeling for peripheral pulses. These cannot usually diagnose specific arrhythmia but can give a general indication of the heart rate and whether it is regular or irregular. Not all the electrical impulses of the heart produce audible or palpable beats; in many cardiac arrhythmias, the premature or abnormal beats do not produce an effective pumping action and are experienced as "skipped" beats.[citation needed]

The simplest specific diagnostic test for assessment of heart rhythm is the

electrocardiogram (abbreviated ECG or EKG).[22][23] A Holter monitor is an EKG recorded over a 24-hour period, to detect arrhythmias that may happen briefly and unpredictably throughout the day.[citation needed
]

A more advanced study of the heart's electrical activity can be performed to assess the source of the

Differential diagnosis

Normal electrical activity

Each heartbeat originates as an electrical impulse from a small area of tissue in the right atrium of the heart called the sinus node or sinoatrial node (SA node). The impulse initially causes both atria to contract, then activates the atrioventricular node (AV node), which is normally the only electrical connection between the atria and the ventricles (main pumping chambers). The impulse then spreads through both ventricles via the bundle of His and the Purkinje fibers causing a synchronized contraction of the heart muscle and, thus, the pulse.[citation needed]

In adults, the normal resting heart rate ranges from 60 to 90 beats per minute. The resting heart rate in children is much faster. In athletes, however, the resting heart rate can be as slow as 40 beats per minute, and be considered normal.[citation needed]

The term

sinus arrhythmia[26] refers to a normal phenomenon of alternating mild acceleration and slowing of the heart rate that occurs with breathing in and out respectively. It is usually quite pronounced in children and steadily decreases with age. This can also be present during meditation breathing exercises that involve deep inhaling and breath holding patterns.[27]

Bradycardias

Normal sinus rhythm, with solid black arrows pointing to normal P waves representative of normal sinus node function, followed by a pause in sinus node activity (resulting in a transient loss of heartbeats). Note that the P wave that disrupts the pause (indicated by the dashed arrow) does not look like the previous (normal) P waves – this last P wave is arising from a different part of the atrium, representing an escape rhythm.

A slow rhythm (less than 60 beats/min) is labelled bradycardia. This may be caused by a slowed signal from the sinus node (sinus bradycardia), by a pause in the normal activity of the sinus node (sinus arrest), or by blocking of the electrical impulse on its way from the atria to the ventricles (AV block or heart block). Heart block comes in varying degrees and severity. It may be caused by reversible poisoning of the AV node (with drugs that impair conduction) or by irreversible damage to the node. Bradycardias may also be present in the normally functioning heart of endurance athletes or other well-conditioned persons. Bradycardia may also occur in some types of seizures.[citation needed]

Tachycardias

In adults and children over 15, resting heart rate faster than 100 beats per minute is labeled

amphetamines, and an overactive thyroid gland (hyperthyroidism) or anemia.[citation needed
]

Tachycardia that is not sinus tachycardia usually results from the addition of abnormal impulses to the normal cardiac cycle. Abnormal impulses can begin by one of three mechanisms: automaticity, re-entry, or triggered activity. A specialized form of re-entry which is both common and problematic is termed fibrillation.[citation needed]

Although the term "tachycardia" has been known for over 160 years, bases for the classification of arrhythmias are still being discussed.[citation needed]

Heart defects

Congenital heart defects are structural or electrical pathway problems in the heart that are present at birth. Anyone can be affected by this because overall health does not play a role in the problem. Problems with the electrical pathway of the heart can cause very fast or even deadly arrhythmias. Wolff–Parkinson–White syndrome is due to an extra pathway in the heart that is made up of electrical muscle tissue. This tissue allows the electrical impulse, which stimulates the heartbeat, to happen very rapidly. Right ventricular outflow tract tachycardia is the most common type of ventricular tachycardia in otherwise healthy individuals. This defect is due to an electrical node in the right ventricle just before the pulmonary artery. When the node is stimulated, the patient will go into ventricular tachycardia, which does not allow the heart to fill with blood before beating again. Long QT syndrome is another complex problem in the heart and has been labeled as an independent factor in mortality. There are multiple methods of treatment for these including cardiac ablations, medication treatment, or lifestyle changes to have less stress and exercise.[citation needed]

Automaticity

Automaticity refers to a cardiac muscle cell firing off an impulse on its own. All of the cells in the heart have the ability to initiate an action potential; however, only some of these cells are designed to routinely trigger heartbeats. These cells are found in the conduction system of the heart and include the SA node, AV node, Bundle of His, and Purkinje fibers. The sinoatrial node is a single specialized location in the atrium that has a higher automaticity (a faster pacemaker) than the rest of the heart and, therefore, is usually responsible for setting the heart rate and initiating each heartbeat.[citation needed]

Any part of the heart that initiates an impulse without waiting for the sinoatrial node is called an

ectopic focus fires more often than the sinoatrial node, it can produce a sustained abnormal rhythm. Rhythms produced by an ectopic focus in the atria, or by the atrioventricular node, are the least dangerous dysrhythmias; but they can still produce a decrease in the heart's pumping efficiency because the signal reaches the various parts of the heart muscle with different timing than usual and can be responsible for poorly coordinated contraction.[citation needed
]

Conditions that increase automaticity include

hypoxia
. The resulting heart rhythm depends on where the first signal begins: If it is the sinoatrial node, the rhythm remains normal but rapid; if it is an ectopic focus, many types of dysrhythmia may ensue.

Re-entry

Re-entrant arrhythmias occur when an electrical impulse recurrently travels in a tight circle within the heart, rather than moving from one end of the heart to the other and then stopping.[28][29]

Every cardiac cell can transmit impulses of excitation in every direction but will do so only once within a short time. Normally, the action potential impulse will spread through the heart quickly enough that each cell will respond only once. However, if there is some essential heterogeneity of refractory period or if conduction is abnormally slow in some areas (for example in heart damage) so the myocardial cells are unable to activate the fast sodium channel, part of the impulse will arrive late and potentially be treated as a new impulse. Depending on the timing, this can produce a sustained abnormal circuit rhythm.

As a sort of re-entry, vortices of excitation in the myocardium (

WPW
syndromes, which utilize abnormal conduction pathways.

Although omega-3 fatty acids from fish oil can be protective against arrhythmias, they can facilitate re-entrant arrhythmias.[31]

Fibrillation

When an entire chamber of the heart is involved in multiple micro-re-entry circuits and is, therefore, quivering with chaotic electrical impulses, it is said to be in fibrillation.

Fibrillation can affect the atrium (atrial fibrillation) or the ventricle (ventricular fibrillation): ventricular fibrillation is imminently life-threatening.

  • Atrial fibrillation affects the upper chambers of the heart, known as the atria. Atrial fibrillation may be due to serious underlying medical conditions and should be evaluated by a physician. It is not typically a medical emergency.
  • Ventricular fibrillation occurs in the ventricles (lower chambers) of the heart; it is always a medical emergency. If left untreated, ventricular fibrillation (VF, or V-fib) can lead to death within minutes. When a heart goes into V-fib, effective pumping of the blood stops. V-fib is considered a form of cardiac arrest. An affected individual will not survive unless cardiopulmonary resuscitation (CPR) and defibrillation are provided immediately.

CPR can prolong the survival of the brain in the lack of a normal pulse, but defibrillation is the only intervention that can restore a healthy heart rhythm. Defibrillation is performed by applying an electric shock to the heart, which resets the cells, permitting a normal beat to re-establish itself.

Triggered beats

Triggered beats occur when problems at the level of the ion channels in individual heart cells result in abnormal propagation of electrical activity and can lead to a sustained abnormal rhythm. They are relatively rare and can result from the action of anti-arrhythmic drugs, or after depolarizations.[citation needed]

Management

The method of cardiac rhythm management depends firstly on whether the affected person is stable or unstable. Treatments may include physical maneuvers, medications, electricity conversion, or electro- or cryo-cautery.[citation needed]

In the United States, people admitted to the hospital with cardiac arrhythmia and conduction disorders with and without complications were admitted to the intensive care unit more than half the time in 2011.[32]

Physical maneuvers

Several physical acts can increase parasympathetic nervous supply to the heart, resulting in blocking of electrical conduction through the AV node. This can slow down or stop several arrhythmias that originate above or at the AV node (see main article: supraventricular tachycardias). Parasympathetic nervous supply to the heart is via the vagus nerve, and these maneuvers are collectively known as vagal maneuvers.

Antiarrhythmic drugs

There are many classes of antiarrhythmic medications, with different mechanisms of action and many different individual drugs within these classes. Although the goal of drug therapy is to prevent arrhythmia, nearly every antiarrhythmic drug has the potential to act as a

pro-arrhythmic
, and so must be carefully selected and used under medical supervision.

Other drugs

Several groups of drugs slow conduction through the heart, without actually preventing an arrhythmia. These drugs can be used to "rate control" a fast rhythm and make it physically tolerable for the patient.[citation needed]

Some arrhythmias promote blood clotting within the heart and increase the risk of embolus and stroke. Anticoagulant medications such as warfarin and heparins, and anti-platelet drugs such as aspirin can reduce the risk of clotting.

Electricity

Arrhythmias may also be treated electrically, by applying a shock across the heart – either externally to the chest wall, or internally to the heart via implanted electrodes.[33]

Cardioversion is either achieved pharmacologically or via the application of a shock synchronized to the underlying heartbeat. It is used for the treatment of supraventricular tachycardias. In elective cardioversion, the recipient is usually sedated or lightly anesthetized for the procedure.

Defibrillation differs in that the shock is not synchronized. It is needed for the chaotic rhythm of ventricular fibrillation and is also used for pulseless ventricular tachycardia. Often, more electricity is required for defibrillation than for cardioversion. In most defibrillation, the recipient has lost consciousness so there is no need for sedation.

Defibrillation or cardioversion may be accomplished by an implantable cardioverter-defibrillator (ICD).

Electrical treatment of arrhythmias also includes

pacemaker
may be placed in situations where the bradycardia is not expected to recover.

Electrical cautery

Some cardiologists further sub-specialize into electrophysiology. In specialized catheter laboratories, they use fine probes inserted through the blood vessels to map electrical activity from within the heart. This allows abnormal areas of conduction to be located very accurately and subsequently destroyed by heat, cold, electrical, or laser probes in a process called catheter ablation.

This procedure may be completely curative for some forms of arrhythmia, but for others, the success rate remains disappointing. AV nodal reentrant tachycardia is often curable by ablating one of the pathways in the AV node (usually the slow pathway). Atrial fibrillation can also be treated, by performing a pulmonary vein isolation, but the results are less reliable.

Research

Arrhythmias due to medications have been reported since the 1920s with the use of

ventricular arrhythmia, and may be considered a benign physiological phenomenon, associated with lower mortality in univariable analyses.[35]

See also

References

  1. ^ a b c d "What Are the Signs and Symptoms of an Arrhythmia?". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 19 February 2015. Retrieved 7 March 2015.
  2. ^ a b c d e f g "What Is Arrhythmia?". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 2 March 2015. Retrieved 7 March 2015.
  3. ^ a b c d e f g h i "Types of Arrhythmia". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 7 June 2015. Retrieved 7 March 2015.
  4. ^ a b c d "Who Is at Risk for an Arrhythmia?". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 3 March 2015. Retrieved 7 March 2015.
  5. ^ a b "How Are Arrhythmias Diagnosed?". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 18 February 2015. Retrieved 7 March 2015.
  6. ^ a b c d e f g "How Are Arrhythmias Treated?". National Heart, Lung, and Blood Institute. July 1, 2011. Archived from the original on 17 February 2015. Retrieved 7 March 2015.
  7. PMID 22422742
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  20. ^ "Passing Out (Syncope) Caused by Arrhythmias". Retrieved 13 April 2020.
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  32. from the original on 2015-04-02.
  33. ^ "AED Buyer's Guide | AED Prices & Comparison". AED Brands. Retrieved 2021-08-13.
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External links