Vulnerability to unidirectional conduction block and reentry in rabbit left ventricular wedge preparation: effects of...

Many factors influence the initiation of unidirectional conduction block and reentry. To explore the influential factors on the temporal vulnerable window of the unidirectional conduction block, we investigated the effect of stimulation sequence and location on the temporal vulnerability in epicardial and endocardial sites in an arterially perfused rabbit left ventricular wedge preparation at three basic cycle lengths (BCL) of 2,000, 1,000 and 500 ms. An extrastimulus (S2) was introduced at coupling intervals incremented by 1 ms to scan the entire diastolic interval. The results showed that the vulnerable window increased with the lengthening of BCL, which ranged from 48.55 +/- 18.04 ms at BCL of 500 ms to 92.50 +/- 25.59 ms at BCL of 2,000 ms for endocardial, and is a similar style for epicardial from 21.00 +/- 14.02 ms at BCL of 500 ms to 75.71 +/- 16.34 ms at BCL of 2,000 ms (P < 0.05). The vulnerable window of endocardial was wider than that of epicardial (P < 0.05). Furthermore, the window size for reentry was about 39% smaller than that for unidirectional conduction block. Meanwhile, we found that increasing the number of premature beats enlarged the vulnerable window markedly due to enhanced transmural dispersion of repolarization (TDR) of ventricle. The vulnerable window is an effective index to evaluate the increased risk for unidirectional conduction block. Therefore, the factors that increase the vulnerable window are associated with the higher incidence of ventricular arrhythmias.