Normally, the 4 chambers of the heart (2 atria and 2 ventricles) contract in a very specific, coordinated manner. The electrical impulse that signals your heart to contract in a synchronized manner begins in the sinoatrial node (SA node), which is your heart's natural pacemaker. The signal leaves the SA node and travels through the 2 upper chambers (atria). Then the signal passes through another node (the AV node), and finally, through the lower chambers (ventricles). The result is that the chambers contract in a coordinated fashion. Problems can occur anywhere along this conduction system, causing various arrhythmias. Examples include: - Supraventricular tachycardia - a fast heart rate that originates in the upper chambers (atria). The most common are atrial fibrillation or flutter, and atrioventricular nodal reentry tachycardia.
- Ventricular tachycardia - a fast heart rate that originates in the lower chambers (ventricles).
- Bradycardia - a slow heart rate due to problems with the SA node's pacemaker ability, or some interruption in conduction through the natural electrical pathways of the heart.
The risks of getting a tachycardia or bradycardia varies greatly, depending on the condition of your heart, any history of a prior heart attack, blood chemistry imbalances, 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 arrhythmias may be life-threatening if not promptly and adequately treated.
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