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.
Therefore, on ECG, the coupling intervals of the manifest ectopic beats will wander through the basic cycle of the sinus rhythm.
Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are: 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.
In this case, the timing of the arrival of the electronic stimulus will serve to delay or advance the subsequent pacemaker activation.
In this case, the coupling intervals between the manifest ectopic and sinus discharges will be either fixed or variable, depending on the cycle length relations between the two pacemakers.