Arrhythmias are caused by a disruption of the normal electrical conduction system of the heart. Normally, the four chambers of the heart (two atria and two ventricles) contract in a very specific, coordinated manner. The signal for the heart to contract in a synchronized manner is an electrical impulse that begins in the sinoatrial node (also called the SA node), which is the body's natural pacemaker. The signal leaves the sinoatrial node and travels through the two atria, stimulating them to contract. Then the signal passes through another node (the AV node), and finally travels through the ventricles and stimulates them to contract in synchrony.
Problems can occur anywhere along the conduction system, causing various arrhythmias. There can 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.
Arrhythmias include tachycardias (the heartbeat is too fast), bradycardias (the heartbeat is too slow), and "true" arrhythmias (a disturbed rhythm). Arrhythmias can be life-threatening if they cause a severe decrease in the pumping function of the heart. When the pumping function is severely decreased for more than a few seconds, blood circulation is essentially stopped, and organ damage (such as brain damage) may occur within a few minutes. Life-threateaning arrhythmias include the following: - Ventricular fibrillation
- Ventricular tachycardia that is rapid and sustained or pulseless
- Sustained episodes of other arrhythmias
Other arrhythmias include the following: People at higher risk for arrhythmias and complications from arrhythmias include the following: Arrhythmias can 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.
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