parasystole

Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are:

PVCs are not the only aberrant beat that makes use of these adjectives; others are premature atrial contractions, parasystole, and escape complexes.

Two forms of ventricular parasystole have been described in the literature, fixed parasystole and modulated parasystole.

Fixed ventricular parasystole occurs when an ectopic pacemaker is protected by entrance block, and thus its activity is completely independent from the sinus pacemaker activity.

Therefore, appropriate diagnosis of modulated parasystole relies upon the construction of a "phase response curve" as theoretical evidence of modulation of the ectopic pacemaker cycle length by the electrotonic activity generated by the sinus discharges across the area of protection.

According to the modulated parasystole hypothesis, rigid constancy of a pacemaker might be expected if the entrance block were complete, but if there is an escape route available for the emergence of ectopic activity, then clearly there must be an effective ionic communication, not complete insulation, between the two tissues.