Arrhythmias

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Heart, section through the middle

Heart, front view

Atrioventricular block, EKG tracing

Normal heart rhythm

Bradycardia

Ventricular tachycardia

Conduction system of the heart

Arrhythmias

Definition:

An arrhythmia is any disorder of heart rate or rhythm.

Alternative Names:
Dysrhythmias; Abnormal heart rhythms
Causes, incidence, and risk factors:

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Arrhythmias are caused by a disruption of the normal electrical conduction system of the heart. Normally, the 4 chambers of the heart (2 atria and 2 ventricles) contract in a very specific, coordinated manner. When the heart beats faster than normal, it is called tachycardia. Bradycardia is a slower-than-normal rhythm.

The electrical impulse that signals the heart to contract in a synchronized manner begins in the sinoatrial node (SA node), which is the body's natural pacemaker.

The signal leaves the SA node and travels through the 2 upper chambers (atria), stimulating them to contract. Then the signal passes through another node (the AV node), and finally, through the lower chambers (ventricles), stimulating them to contract in synchrony.

Problems can occur anywhere along this conduction system, causing various arrhythmias. There may be a problem in the heart muscle itself, causing it to respond differently to the signal, or causing the ventricles to contract independently of the normal conduction system.

Tachycardia that originates in the atria is called supraventricular tachycardia, and ventricular tachycardia when it originates in the ventricles. The most common supraventricular tachycardias are atrial fibrillation, atrial flutter, and atrioventricular nodal reentry tachycardia.

Bradycardia is due either to altered pacemaker function of the SA node or an interrupted impulse conduction through the natural electrical pathways of the heart.

The incidence of tachycardia and bradycardia varies greatly, depending on the condition of the heart itself, the history of prior heart attack, blood chemistry imbalance, or endocrine abnormalities.

Arrhythmias may also be caused by some substances or drugs. These include beta blockers, psychotropics, sympathomimetics, caffeine, amphetamines, and cocaine. Sometimes antiarrhythmic medications -- prescribed to treat one type of arrhythmia -- can actually cause another type of arrhythmia.

Some types of arrythmias may be life-threatening if not promptly and adequately treated.