ectopic pacemaker

An ectopic pacemaker is a beat that comes from the wrong place. Normally the sinoatrial node is in sole charge of starting each heartbeat; an ectopic pacemaker is some other patch of heart tissue that takes the initiative and fires off its own impulse, out of turn. The word ectopic simply means out of the usual place.

This can happen for two broad reasons. Sometimes it is a rescue: if the sinoatrial node slows or fails, a latent pacemaker lower down — in the atria, the atrioventricular junction, or the ventricles — steps in with an escape rhythm to keep the heart going. Other times it is an intrusion: tissue that is injured, stretched, ischemic, or chemically irritated develops enhanced automaticity or becomes triggered, and fires when it should not, interrupting the normal rhythm.

The consequences range from trivial to serious depending on where the focus sits and how often it fires. A single early beat from an ectopic atrial or ventricular focus (a premature beat) is extremely common and usually harmless. But a persistently firing ectopic focus can drive a sustained arrhythmia — and a rapidly firing ventricular focus can be life-threatening. Identifying and, where appropriate, ablating such a focus is a core part of electrophysiology practice.