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Cardiac arrhythmia
Classification and external resources
Ventricular Fibrillation or V-Fib, an example of cardiac arrhythmia.
ICD-10 I47. - I49.
ICD-9 427
DiseasesDB 15206
MedlinePlus 001101
MeSH D001145

Cardiac arrhythmia (also dysrhythmia) is a term for any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The International Statistical Classification of Diseases and Related Health Problems 10th Revision ( ICD -10) is a coding of diseases and signs symptoms abnormal findings I00-I99 - Diseases of the Circulatory system (I00-I02 Acute rheumatic fever ( Rheumatic fever without mention of Heart I00-I99 - Diseases of the Circulatory system (I00-I02 Acute rheumatic fever ( Rheumatic fever without mention of Heart The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. The Diseases Database is a free Website that provides information about the relationships between medical conditions Symptoms, and Medications. MedlinePlus, with the MedlinePlus Medical Encyclopedia, is a website network containing Health information from the world's largest medical Library Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books The normal electrical conduction in the heart allows the impulse that is generated by the Sinoatrial node (SA node of the Heart to be propagated to (and stimulate the The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic The heart beat may be too fast or too slow, and may be regular or irregular.

Some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest and sudden death. A medical emergency is an Injury or Illness that is acute and poses an immediate risk to a person's life or long term health A cardiac arrest, also known as cardiorespiratory arrest, cardiopulmonary arrest or circulatory arrest, is the abrupt cessation of normal circulation of Others cause aggravating symptoms such as an abnormal awareness of heart beat, and may be merely annoying. Others may not be associated with any symptoms at all, but pre-dispose toward potentially life threatening stroke or embolus. A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain In Medicine, an embolism occurs when an object (the embolus, plural emboli) migrates from one part of the Body (through circulation

Some arrhythmias are very minor and can be regarded as variants of normal. In fact, most people will sometimes feel their heart skip a beat, or give an occasional extra strong beat - neither of which are usually a cause for alarm[1].

The term sinus arrhythmia refers to a normal phenomenon of mild acceleration and slowing of the heart rate that occurs with breathing in and out. It is usually quite pronounced in children, and steadily lessens with age.

Contents

Manifestations

The term cardiac arrhythmia covers a very large number of very different conditions, many of which receive separate articles in depth elsewhere in Wikipedia.

The most common symptom of arrhythmia is an abnormal awareness of heartbeat, termed palpitations. A palpitation (medical term ectopic heart beat) is an abnormal awareness of the beating of the Heart, whether it is too slow too fast irregular These may be infrequent, frequent, or continuous. Some of these arrhythmias are harmless (though annoying) but many of them predispose to adverse outcomes.

Some arrhythmias do not cause symptoms, and are not associated with increased mortality. However, some asymptomatic arrhythmias are associated with adverse events. Examples include increase in risk of blood clotting within the heart, and also an insufficient amount of blood is transported to the heart beacause of weak heart beat, and thus increase the risk of embolisation and stroke, or increase in the risk of heart failure, or increase in the risk of sudden cardiac death.

If an arrhythmia results in a heart beat that is too fast, too slow or too weak to supply the body's needs, this manifests as a lower blood pressure and may cause lightheadedness or dizziness, or fainting.

Some types of arrhythmia result in cardiac arrest, or sudden death. A cardiac arrest, also known as cardiorespiratory arrest, cardiopulmonary arrest or circulatory arrest, is the abrupt cessation of normal circulation of

Medical assessment of the abnormality using an electrocardiogram is the best way to diagnose and assess the risk of any given arrhythmia.

Mechanisms and aetiology

Normal electrical activity in the heart

Main article: Electrical conduction system of the heart

Each heart beat originates as an electrical impulse from a small area of tissue in the right atrium of the heart called the sinus node. The normal electrical conduction in the heart allows the impulse that is generated by the Sinoatrial node (SA node of the Heart to be propagated to (and stimulate the In Anatomy, the atrium (plural atria) refers to a chamber or space The Sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker tissue located in the Right atrium The impulse initially causes both of the atria to contract, then activates the atrioventricular (or AV) node which is normally the only electrical connection between the atria and the ventricles or main pumping chambers. The normal electrical conduction in the heart allows the impulse that is generated by the Sinoatrial node (SA node of the Heart to be propagated to (and stimulate the In the Heart, a ventricle is a heart chamber which collects Blood from an atrium (another heart chamber that is smaller than a ventricle and The impulse then spreads through both ventricles via the His Purkinje fibres causing a synchronised contraction of the heart muscle, and thus, the pulse. The bundle of His, also known as the AV bundle or atrioventricular bundle is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical

In adults the normal resting heart rate ranges from 60 to 100 beats per minute. The resting heart rate in children is much faster.

Bradycardias

A slow rhythm, (less than 60 beats/min), is labelled bradycardia. Bradycardia, as applied to adult medicine is defined as a resting Heart rate of under 60 beats per minute though it is seldom symptomatic until the rate drops below 50 beat/min This may be caused by a slowed signal from the sinus node (termed sinus bradycardia), a pause in the normal activity of the sinus node (termed sinus arrest), or by blocking of the electrical impulse on its way from the atria to the ventricles (termed 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.

Tachycardias

Any heart rate faster than 100 beats/minute is labelled tachycardia. Tachycardia may result in palpitation, however, tachycardia is not necessarily an arrhythmia. Increased heart rate is a normal response to physical exercise or emotional stress. This is mediated by the sympathetic nervous system on the sinus node, and is called sinus tachycardia. The Sympathetic Nervous System ( SNS) is a branch of the Autonomic nervous system along with the Enteric nervous system and Parasympathetic nervous Other things that increase sympathetic nervous system activity in the heart include ingested or injected substances such as caffeine or amphetamines, and an overactive thyroid gland (hyperthyroidism). Caffeine is a bitter white crystalline Xanthine Alkaloid that acts as a Psychoactive Stimulant Drug and a mild Diuretic Amphetamine, and related drugs such as Methamphetamine are a group of drugs that act by increasing levels of Norepinephrine, Serotonin, and Dopamine Hyperthyroidism is the term for overactive tissue within the Thyroid gland resulting in overproduction and thus an excess of circulating free thyroid hormones Thyroxine

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, reentry or triggered activity. A specialised form of re-entry problem is termed fibrillation.

Automaticity

Automaticity refers to a cardiac muscle cell firing off an impulse on its own. The cardiac muscle is a type of involuntary striated Muscle found in the walls of the Heart. 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 heart beats. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal 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 which 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 heart beat. The Sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker tissue located in the Right atrium

Any part of the heart that initiates an impulse without waiting for the sinoatrial node is called an ectopic focus, and is by definition a pathological phenomenon. Cardiac ectopy or "ventricular extra beats" is a disturbance of the Electrical conduction system of the heart in which beats arise from the wrong part of the heart This may cause a single premature beat now and then, or, if the ectopic focus fires more often than the sinoatrial node, it can produce a sustained abnormal rhythm. An ectopic pacemaker or ectopic focus is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the human 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 to usual and can be responsible for poorly coordinated contraction. The atrioventricular node (abbreviated AV node) is an area of specialized tissue between the atria and the ventricles of the Heart, specifically

Conditions that increase automaticity include sympathetic nervous system stimulation and hypoxia. The Sympathetic Nervous System ( SNS) is a branch of the Autonomic nervous system along with the Enteric nervous system and Parasympathetic nervous Chronic Hypoxia is a pathological condition in which the body as a whole ( generalized hypoxia) or region of the body ( tissue hypoxia) is deprived of adequate 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 can result.

Re-entry

Re-entry dysrhythmias 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. Every cardiac cell is able to transmit impulses in every direction, but will only do so once within a short period of time. Normally an action potential impulse will spread through the heart quickly enough that each cell will only respond once. However, if conduction is abnormally slow in some areas, 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. Re-entry circuits are responsible for atrial flutter, most paroxysmal supraventricular tachycardia, and dangerous ventricular tachycardia. Atrial flutter is an abnormal heart rhythm that occurs in the atria of the Heart. A supraventricular tachycardia ( SVT) is a rapid rhythm of the Heart in which the origin of the electrical signal is either the atria or Ventricular tachycardia ( V-tach or VT) is a Tachycardia, or fast heart rhythm that originates in one of the ventricles of the Heart

By analogy, imagine a room full of people all given these instructions: "If you see anyone starting to stand up, then stand up for three seconds and sit back down. " If the people are quick enough to respond, the first person to stand will trigger a single wave which will then die out; but if there are stragglers on one side of the room, people who have already sat down will see them and start a second wave, and so on.

Fibrillation

When an entire chamber of the heart is involved in a multiple micro-reentry circuits, and 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 ( AF or afib) is a Cardiac arrhythmia (abnormal heart rhythm that involves the two upper chambers ( atria) of the Heart Ventricular fibrillation ( V-fib or VF) is a condition in which there is uncoordinated contraction of the Cardiac muscle of the ventricles in the

Atrial fibrillation affects the upper chambers of the heart, known as the atria. In Anatomy, the atrium (plural atria) refers to a chamber or space Atrial fibrillation may be due to serious underlying medical conditions, and should be evaluated by a physician. A physician, medical practitioner or medical doctor who practices Medicine, and is concerned with maintaining or restoring human Health It is not typically a medical emergency.

Ventricular fibrillation occurs in the ventricles (lower chambers) of the heart; it is always a medical emergency. In the Heart, a ventricle is a heart chamber which collects Blood from an atrium (another heart chamber that is smaller than a ventricle and If left untreated, ventricular fibrillation (VF, or V-fib) can lead to death within minutes. Ventricular fibrillation ( V-fib or VF) is a condition in which there is uncoordinated contraction of the Cardiac muscle of the ventricles in the When a heart goes into V-fib, effective pumping of the blood stops. V-fib is considered a form of cardiac arrest, and an individual suffering from it will not survive unless cardiopulmonary resuscitation (CPR) and defibrillation are provided immediately. A cardiac arrest, also known as cardiorespiratory arrest, cardiopulmonary arrest or circulatory arrest, is the abrupt cessation of normal circulation of Defibrillation is the definitive treatment for the life-threatening Cardiac arrhythmias Ventricular fibrillation and Ventricular tachycardia.

CPR can prolong the survival of the brain in the lack of a normal pulse, but defibrillation is the only intervention which can restore a healthy heart rhythm. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain 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 sustained abnormal rhythm. They are relatively rare, but can result from the action of anti-arrhythmic drugs.

Classification of common cardiac arrhythmias

Arrhythmia may be classified by rate (normal, tachycardia, bradycardia), or mechanism (automaticity, reentry, fibrillation).

It is also appropriate to classify by site of origin:

Atrial

Junctional arrhythmias

Atrio-ventricular

Ventricular

Heart blocks

These are also known as AV blocks, because the vast majority of them arise from pathology at the atrioventricular node. Premature atrial contractions (PACs are a type of premature Heart beat irregular heart beat or benign Arrhythmia which start in the upper two chambers of the heart In Cardiology, a wandering pacemaker is an Atrial Arrhythmia that occurs when the natural cardiac Pacemaker site shifts between the SA node Multifocal atrial tachycardia is a Cardiac arrhythmia, specifically a type of Supraventricular tachycardia. Atrial flutter is an abnormal heart rhythm that occurs in the atria of the Heart. Atrial fibrillation ( AF or afib) is a Cardiac arrhythmia (abnormal heart rhythm that involves the two upper chambers ( atria) of the Heart A supraventricular tachycardia ( SVT) is a rapid rhythm of the Heart in which the origin of the electrical signal is either the atria or AV nodal reentrant tachycardia ( AVNRT) is a type of Tachycardia (fast rhythm of the Heart. Junctional rhythm is an abnormal heart rhythm where the AV node initiates electrical activity in the heart. Lown- Ganong -Levine syndrome ( LGL) is a syndrome of pre-excitation of the ventricles due to an accessory pathway providing an abnormal electrical communication Premature ventricular contraction (PVC, also known as ventricular premature beat (VPB or extrasystole, is a form of irregular heartbeat in which the The rate of cardiac contraction is determined by the intrinsic rate of depolarisation of the cardiac cells Ventricular tachycardia ( V-tach or VT) is a Tachycardia, or fast heart rhythm that originates in one of the ventricles of the Heart Ventricular tachycardia ( V-tach or VT) is a Tachycardia, or fast heart rhythm that originates in one of the ventricles of the Heart Ventricular fibrillation ( V-fib or VF) is a condition in which there is uncoordinated contraction of the Cardiac muscle of the ventricles in the The atrioventricular node (abbreviated AV node) is an area of specialized tissue between the atria and the ventricles of the Heart, specifically They are the commonest cause of bradycardia:

Diagnosis

Cardiac dysrhythmias are often first detected by simple but nonspecific means: auscultation of the heartbeat with a stethoscope, or feeling for peripheral pulses. First degree AV block or PR prolongation is a disease of the electrical conduction system of the Heart in which the PR interval is lengthened Second degree AV block is a disease of the electrical conduction system of the Heart. Second degree AV block is a disease of the electrical conduction system of the Heart. Second degree AV block is a disease of the electrical conduction system of the Heart. Second degree AV block is a disease of the electrical conduction system of the Heart. Second degree AV block is a disease of the electrical conduction system of the Heart. Second degree AV block is a disease of the electrical conduction system of the Heart. Third degree AV block, also known as complete heart block, is a defect of the electrical system of the Heart, in which the impulse generated in the atria (typically Third degree AV block, also known as complete heart block, is a defect of the electrical system of the Heart, in which the impulse generated in the atria (typically For the ancient monasterial worker see Auscultare Auscultation is the technical term for listening to the internal sounds of the body usually The stethoscope (from Greek στηθοσκόπιο, of στήθος stéthos - chest and σκοπή skopé - examination) is an acoustic In Medicine, a person's pulse is the throbbing of their arteries. These cannot usually diagnose specific dysrhythmias, 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.

The simplest specific diagnostic test for assessment of heart rhythm is the electrocardiogram (abbreviated ECG or EKG). A Holter monitor is an EKG recorded over a 24-hour period, to detect dysrhythmias that may happen briefly and unpredictably throughout the day. In Medicine, a Holter monitor (also called an ambulatory electrocardiography device) named after its inventor Dr

SADS

SADS, or sudden arrhythmia death syndrome, is a term used to describe sudden death due to cardiac arrest brought on by an arrhythmia. Death is the termination of the biological functions that define living Organisms It refers both to a specific A cardiac arrest, also known as cardiorespiratory arrest, cardiopulmonary arrest or circulatory arrest, is the abrupt cessation of normal circulation of The most common cause of sudden death in the US is coronary artery disease. Approximately 300,000 people die suddenly of this cause every year in the US. SADS can also occur from other causes. Also, there are many inherited conditions and heart diseases that can affect young people that can cause sudden death. Many of these victims have no symptoms before dying suddenly.

Causes of SADS in young people include viral myocarditis, long QT syndrome, Brugada syndrome, Catecholaminergic polymorphic ventricular tachycardia and hypertrophic cardiomyopathy and arrhythmogenic right ventricular dysplasia. In Medicine ( Cardiology) myocarditis is Inflammation of the Myocardium, the muscular part of the Heart. The long QT syndrome ( LQTS) is a Heart condition associated with prolongation of repolarization (recovery following depolarization (excitation of the cardiac The Brugada syndrome is a Genetic disease that is characterised by abnormal Electrocardiogram (ECG findings and an increased risk of Sudden cardiac death Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT is an inherited heart rhythm disorder caused by a mutation in Voltage gated ion channels and resulting in Arrhythmias Hypertrophic cardiomyopathy, or HCM, is a disease of the Myocardium (the Muscle of the Heart) in which a portion of the myocardium is Arrhythmogenic right ventricular dysplasia ( ARVD, also known as arrhythmogenic right ventricular cardiomyopathy or ARVC) is a type of nonischemic Cardiomyopathy

Treatment

Because arrhythmias are such a heterogeneous group of conditions, treatment needs to be carefully selected by a patient with their physician. Some arrhythmias require no treatment at all. Others require immediate emergency treatment if death is to be avoided.

Treatments include physical maneuvers, antiarrhythmic drugs, other drugs, electricity, and electro or cryo cautery.

Physical maneuvers

A number of 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 a number of arrhytmias that originate above or at the AV node (see main article: supraventricular tachycardias). A supraventricular tachycardia ( SVT) is a rapid rhythm of the Heart in which the origin of the electrical signal is either the atria or Parasympathetic nervous supply to the heart is via the vagus nerve, and these maneuvers are collectively known as vagal maneuvers. The vagus nerve (ˈveɪˌgəs (VĀ-gəs (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired Cranial nerves, and is the

Antiarrhythmic drugs

See main article on antiarrhythmic agents. Antiarrhythmic agents are a group of Pharmaceuticals that are used to suppress fast rhythms of the Heart ( Cardiac arrhythmias) such as Atrial fibrillation

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

A number of other drugs can be useful in cardiac arrhythmias.

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 a patient.

Some arrhythmias promote blood clotting within the heart, and increase 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. An anticoagulant is a substance that prevents coagulation; that is it stops Blood from clotting

Electricity

Dysrhythmias 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.

Cardioversion is the application of a shock synchronised to the underlying heartbeat. Synchronized electrical cardioversion is the process by which an abnormally fast Heart rate or Cardiac arrhythmia is terminated by the delivery of a therapeutic dose It is used for treatment of supraventricular tachycardias. In elective cardioversion, the recipient is usually sedated or lightly anesthetized for the procedure. Anesthesia, or anaesthesia (see spelling differences; from Greek grc αν- an-, "without" and grc αἲσθησις

Defibrillation differs in that the shock is not synchronised. Defibrillation is the definitive treatment for the life-threatening Cardiac arrhythmias Ventricular fibrillation and Ventricular tachycardia. 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). An implantable cardioverter-defibrillator ( ICD) is a small battery -powered electrical impulse generator which is implanted in patients who are at risk of Sudden

Electrical treatment of dysrhythmia also includes cardiac pacing. For other uses see Pacemaker (disambiguation A pacemaker (or artificial pacemaker, so as not to be confused with the heart's natural pacemaker Temporary pacing may be necessary for reversible causes of very slow heartbeats, or bradycardia, (for example, from drug overdose or myocardial infarction). Bradycardia, as applied to adult medicine is defined as a resting Heart rate of under 60 beats per minute though it is seldom symptomatic until the rate drops below 50 beat/min The term drug overdose (or simply overdose or OD) describes the Ingestion or application of a Drug or other substance in quantities Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply A permanent pacemaker may be placed in situations where the bradycardia is not expected to recover. For other uses see Pacemaker (disambiguation A pacemaker (or artificial pacemaker, so as not to be confused with the heart's natural pacemaker

Electrical cautery

Some cardiologists further sub-specialise into electrophysiology. In specialised 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 with heat, cold, electrical or laser probes.

This may be completely curative for some forms of arrhythmia, but for others, the success rate remains disappointing. AV nodal reentrant tachycardia is often curable. AV nodal reentrant tachycardia ( AVNRT) is a type of Tachycardia (fast rhythm of the Heart. Atrial fibrillation can also be treated with this technique (e. g. pulmonary vein isolation), but the results are less reliable.

See also

References

  1. ^ http://familydoctor.org/online/famdocen/home/articles/286.html familydoctor. org]

External links

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