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Parasystole and its variants
The Medical Clinics of North America
|January 1, 1976
Summary
This study reviews mechanisms causing parasystolic rhythm variations, including fixed coupling and exit block. Abnormal diastolic depolarization in subsidiary pacemakers underlies these complex cardiac arrhythmias.
Area of Science:
- Cardiology
- Cardiac Electrophysiology
Background:
- Parasystole is a cardiac arrhythmia where an ectopic pacemaker competes with the sinus node.
- Classical parasystole has predictable patterns, but variations can complicate diagnosis.
Purpose of the Study:
- To review and illustrate mechanisms causing deviations from classical parasystolic rhythm.
- To explain the electrophysiologic basis of these arrhythmias.
Main Methods:
- Review of clinical electrocardiograms illustrating parasystolic rhythm variations.
- Discussion of electrophysiologic principles underlying observed phenomena.
Main Results:
- Identified mechanisms include fixed coupling (due to synchronization, reversed coupling, supernormal excitability, or intermittent parasystole) and irregular responses to regular parasystolic discharge (due to exit block).
- Abnormal spontaneous diastolic (Phase 4) depolarization in subsidiary pacemakers is proposed as the electrophysiologic basis.
Conclusions:
- Deviations in parasystolic rhythm arise from specific electrophysiologic interactions between basic and ectopic rhythms.
- Understanding these mechanisms is crucial for accurate electrocardiographic interpretation of complex arrhythmias.
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