Parasystole

Parasystole is a kind of arrhythmia caused by the presence and function of a secondary pacemaker in the heart, which works in parallel with the SA node. Parasystolic pacemakers are protected from depolarization by the SA node by some kind of entrance block. This block can be complete or incomplete.

Parasystolic pacemakers can exist in both the atrium or the ventriculus. Atrial parasystolia are characterized by narrow QRS complexes

ECG signals
On an ECG, parasystole may be recognized by: Another feature is the varying coupling interval between sinus and ectopic beats.
 * spotting ectopic P or QRS waves which either:
 * occur at regular intervals
 * the time between them is always exact multiple of the smallest time between such two occurrences
 * spotting "fusioned" P or QRS complexes (sometimes rare)