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[Regularization of ventricular intervals in atrial fibrillation--electrophysiologic findings on the underlying
Insights
Gallopamil, a calcium antagonist, regularized ventricular response in patients with chronic atrial fibrillation by causing atrioventricular nodal depression, suggesting a junctional escape pacemaker.
Area of Science:
- Cardiology
- Electrophysiology
- Pharmacology
Context:
- Chronic atrial fibrillation presents challenges in managing ventricular response.
- Programmed right ventricular pacing is a tool to study cardiac electrophysiology.
- Calcium antagonists have known effects on cardiac conduction.
Purpose:
- To investigate the effect of gallopamil on ventricular response in chronic atrial fibrillation.
- To explore the electrophysiological mechanisms underlying gallopamil's effects.
- To assess the impact of gallopamil on atrioventricular nodal function.
Summary:
- Intravenous gallopamil (4 mg) was administered to 13 patients with chronic atrial fibrillation undergoing right ventricular pacing.
- Gallopamil significantly decreased and, in 7 patients, regularized ventricular response, despite persistent atrial fibrillation.
- Electrophysiological studies during regularization indicated atrioventricular nodal depression and a potential junctional escape pacemaker, evidenced by consistent postextrasystolic intervals and prolonged pacing recovery cycles.
Impact:
- Demonstrates gallopamil's efficacy in controlling ventricular rate during atrial fibrillation.
- Provides insights into the role of the atrioventricular node and potential junctional pacemakers in rhythm regularization.
- Suggests a therapeutic strategy for managing irregular ventricular responses in atrial fibrillation.
Abstract:
In 13 patients with chronic atrial fibrillation, programmed right ventricular pacing was performed before and after intravenous administration of 4 mg gallopamil. Application of the Ca-antagonist resulted in a marked decrease in the ventricular response in all and in a regularization of the ventricular response (variation coefficient of the ventricular cycle length: less than 10%) in 7 of 13 cases, while atrial fibrillation persisted. During regularization right ventricular extrastimulus testing showed a constancy of the postextrasystolic interval irrespective of the changes in the coupling interval of the extrasystole. The postextrasystolic cycle was slightly longer than the basic cycle; the difference amounts to a mean value of 107 +/- 22 ms. During the control period the postextrasystolic cycle showed the same irregularity as the basic cycle. The same random distribution was observed if the first 10 cycles of the spontaneous rhythm were analyzed after a short period of ventricular overdrive pacing. After regularization the first 2-3 postpacing cycles were markedly prolonged, and during the following cycles a gradual adjustment to the length of the basic cycles before overdrive pacing was seen, resembling the warming up of a pacemaker. It is concluded that regularization is most probably due to atrioventricular nodal depression and the occurrence of a junctional escape pacemaker.