Arrhythmias or dysrhythmias describe an absent or abnormal heart rhythm with a concomitant abnormal or irregular heartbeat. They result from abnormalities of impulse generation, impulse conduction, or both. Main causes are delayed after-depolarization, re-entry, ectopic pacemaker activity, or heart block such as AV block.

Arrhythmias can be classified according to their site of origin into supraventricular (with origin in the atria or AV node) or ventricular; and according to heart rate into tachycardia (increased HR) or bradycardia(decreased HR). Supraventricular arrhythmias include AV block, atrial tachycardia, and atrial flutter or fibrillation. Ventricular arrhythmias include ventricular tachycardia, torsades de pointes, and ventricular fibrillation. There are diverse underlying causes: arteriosclerosis, coronary artery spasm, myocardial ischemia, reperfusion, and heart block mostly starting in the AV-node.

Arrhythmias are defined according to their ECG. Characteristics of the most common arrhythmias are:

  • Atrial fibrillation gives rapid, asynchronous atrial beats and usually an AV-block, so that not every atrial beat is conducted to the ventricles. The P waves are usually irregular or absent on the ECG.
  • Ventricular fibrillation is defined by peaks that vary in size and frequency.
  • Ventricular tachycardia is defined as a series of four or more consecutive premature ventricular contractions.
  • Torsades de pointes is a form of polymorphic ventricular tachycardia associated with a long QT interval on the ECG. It is characterized by irregular QRS complexes that appear to be twisting around the baseline and may degenerate into ventricular fibrillation.


In which arrhythmia is the cardiac output insufficient to support life?