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Rate-dependent accessory pathway conduction due to phase 3 and phase 4 block. Antegrade and retrograde conduction
1Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Japan.
Insights
This study examined accessory pathway block, finding a conduction "window" during premature atrial stimulation. The findings suggest spontaneous diastolic depolarization may cause antegrade block in accessory pathways.
Area of Science:
- Electrophysiology
- Cardiology
- Cardiac Electrophysiology
Background:
- Accessory pathways are crucial in understanding supraventricular tachycardias.
- Antegrade block in accessory pathways can manifest as distinct electrophysiological phenomena.
- Understanding these blocks is key to managing cardiac arrhythmias.
Purpose of the Study:
- To investigate the characteristics of antegrade phase 3 and phase 4 block in accessory pathways.
- To identify the electrophysiological mechanisms underlying these block patterns.
- To correlate accessory pathway conduction properties with clinical presentation.
Main Methods:
- Electrophysiological study in six patients with antegrade accessory pathway block.
- Assessment of antegrade and retrograde accessory pathway conduction during programmed atrial and ventricular stimulation.
- Analysis of the "window" of accessory pathway conduction during premature atrial stimulation.
Main Results:
- Antegrade accessory pathway conduction was absent at sinus and slower rates but present during a specific premature atrial stimulation window (20-160 ms duration).
- Retrograde accessory pathway conduction was preserved in three patients and impaired in three others with orthodromic atrioventricular reentrant tachycardia.
- Retrograde concealed conduction prolonged the antegrade conduction window in two patients.
Conclusions:
- Antegrade phase 3 and phase 4 block in accessory pathways may involve spontaneous diastolic depolarization.
- Conduction disturbances at the atrial and/or ventricular insertion sites likely contribute to the observed block patterns.
- These findings provide insights into the complex electrophysiology of accessory pathways in patients with arrhythmias.
Abstract:
Six patients who had antegrade phase 3 and phase 4 block in the accessory pathway were examined. In each patient, antegrade conduction over the accessory pathway was absent both at the sinus rate and at slower heart rates. During premature atrial stimulation a "window" of accessory pathway conduction was identified in all patients. The outer limits of the window ranged from 480 ms to 670 ms. The inner limits ranged from 410 ms to 620 ms. The durations of the window ranged from 20 ms to 160 ms. Three patients with orthodromic atrioventricular reentrant tachycardia showed preserved retrograde accessory pathway conduction. The remaining three patients had impaired retrograde accessory pathway conduction. One of the patients showed retrograde phase 4 block in the accessory pathway. In two patients, retrograde concealed conduction in the accessory pathway induced by ventricular stimulation prolonged the outer limit of the window in the antegrade accessory pathway conduction. These findings suggest that the mechanism of antegrade phase 3 and phase 4 block in the accessory pathway may be spontaneous diastolic depolarization in the accessory pathway and conduction disturbance at the ventricular and/or atrial insertion of the accessory pathway.