Arrhythmias

Alternative names:

abnormal heart rhythms; dysrhythmias

Definition:

Any disorder of heart rate or rhythm.

Causes, incidence, and risk factors:

Arrhythmias are caused by a disruption of the normal functioning of the electrical conduction system of the heart. Normally, the chambers of the heart (atria and ventricles) contract in a coordinated manner. The signal to contract is an electrical impulse that begins in the sinoatrial node (sinus node, SA node). It is conducted through the atria and stimulates them to contract. The impulse passes through the atrioventricular node (AV node), then travels through the ventricles and stimulates them to contract. Problems can occur anywhere along the conduction system, causing various arrhythmias. Problems can also occur in the heart muscle itself, causing it to respond differently to the signal to contract, also causing arrhythmias, or causing the ventricles to contract independently of the normal conduction system.

Arrhythmias include tachycardias (heartbeat too fast), bradycardias (heartbeat too slow) and "true" arrhythmias (disturbed rhythm). Arrhythmias are classified as lethal 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. Lethal arrhythmias include ventricular fibrillation, also ventricular tachycardia that is rapid and sustained, or pulseless, and may include sustained episodes of other arrhythmias.

Some other arrhythmias include atrial fibrillation/flutter, multifocal atrial tachycardia, paroxysmal supraventricular tachycardia, Wolff-Parkinson-White syndrome, sinus tachycardia, sinus bradycardia, bradycardia associated with heart block, sick sinus syndrome, and ectopic heartbeat.

People who have a history of coronary artery disease, heart valve disorders, or other cardiac disorders, and people with imbalances of blood chemistries, are at higher risk for arrhythmias and complications from arrhythmias.

Arrhythmias are also caused by some drugs. These include antiarrhythmics, Beta blockers, caffeine, cocaine, psychotropics, and sympathomimetics.