Disorders of the heart rhythm are known as cardiac arrhythmia. Cardiac arrhythmia can be very mild insignificant disorders like an occasional skipped beat or premature beat to life threatening rhythm disorders which could stop the functioning of the heart known as cardiac arrest. Most common cardiac arrhythmia would be premature contractions originating from the lower chambers of the heart known as ventricular premature contraction (VPC). They are also known as ventricular premature beats or VPBs. If isolated, they are of very little significance, though large number of them occurring on a daily basis can cause worsening of the pump function of the heart. This is due to dyssynchronous contraction of the heart caused by the abnormal sequence of activation of the lower chambers of the heart.
Most common sustained cardiac arrhythmia is an irregularity originating from fast electrical activity in the upper chambers of the heart known as atrial fibrillation. In atrial fibrillation, there is no mechanical activity of the upper chambers of the heart so that blood clots can form inside them. These clots can move to the brain, blocking the blood vessels there, causing sudden weakness of a part of the body known as stroke.
Most important life threatening cardiac arrhythmia is ventricular fibrillation, in which the heart is at standstill. Unless immediate treatment in the form of cardiopulmonary resuscitation (CPR) – compression of the chest and providing artificial mouth to mouth breaths, is initiated, death is almost certain. Ventricular fibrillation is abolished by an electrical countershock delivered from a medical device known as defibrillator. Automated external defibrillators (AED) which prompts the lay user on how to use it are increasingly being deployed in public places and can be useful in saving precious lives.
In addition to these heart rhythm disorders, there are various others and the study of heart rhythm disorders is known as cardiac electrophysiology. A fast regular rhythm originating from the lower chambers of the heart is known as ventricular tachycardia. A fast regular rhythm originating in the upper chambers of the heart is known as atrial tachycardia or supraventricular tachycardia (meaning originating above the ventricles or the lower chambers of the heart). Another form of regular fast rhythm originating in the upper chambers of the heart is known as atrial flutter.