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The role of the va interval in the atrioventricular nodal wenckebach phenomenon


, : The role of the va interval in the atrioventricular nodal wenckebach phenomenon. Journal of Cardiovascular Electrophysiology 1(4): 354-363

We induced atrioventricular (AV) nodal Wenckebach periodicity by rapidly pacing the atria in open-chest, anesthetized dogs. The minimum cardiac cycle lengths (AAmin) that permit 1:1 AV conduction were always greater than the basic cardiac cycle length that induced Wenckebach periodicity. Nevertheless, we found that the effective refractory periods (ERP) of the AV node during atrial pacing at AAmin were not significantly different from the ERPs that prevail during the second cycles of 5:4 Wenckebach periods. While we were pacing the atria at a constant frequency that induced Wenckebach periodicity, we could suddenly switch to a pacing mode (VA mode), in which we could regulate the VA interval. When we switched to the VA mode during an early cycle (i.e., cycle 2 of a 4:3 Wenckebach period), we found that the AV conduction time decreased by 17.5 .+-. 4.3 msec (P < 0.02) as we gradually increased the VA interval by 21.3 .+-. 5.5 msec; cycle length did not change significantly. Similarly, the AV conduction time increased by 34.2 .+-. 4.9 msec (P < 0.001) as we gradually decreased the VA interval by 25.0 .+-. 4.3 msec, despite a concomitant increase in the cycle length of 9.2 .+-. 3.5 msec (P < 0.03). These findings support the hypothesis that the VA interval constitutes a critical link in a positive feedback mechanism that is involved in the genesis of the AV nodal Wenckebach phenomenon.

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