Comparison of Ventricular Refractory Periods Determined by Incremental and Decremental Scanning of an Extrastimulus

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Abstract
This study compared the ventricular effective refractory periods measured by scanning diastole with an extrastimulus in incremental and decremental steps of 5 msec. The subjects of the study were 80 patients undergoing a clinically indicated electrophysiological test. Eight beat basic drive trains at a cycle length of 600 msec and an intertrain pause of 4 seconds were used to measure the ventricular effective refractory period (VERP). In the incremental method, the extrastimulus initially was positioned at a coupling interval shorter than the VERP and the coupling interval then was progressively increased until ventricular capture occurred. In the decremental method, the initial extrastimulus coupling interval was longer than the VERP and the coupling interval was progressively shortened until ventricular capture was lost. In 50 subjects, the mean VERP determined by the incremental method, 252 +/- 18 (+/- standard deviation), was significantly longer than the mean VERP determined in the same patients by the decremental method, 248 +/- 18 msec (P less than 0.0001). In ten subjects, a subthreshold stimulus (S') positioned 10 msec earlier than the VERP had an inhibitory effect that lengthened the VERP by an average of 7 msec; however, when S' was positioned after the seventh beat of an eight beat drive train, no inhibitory effect could be demonstrated. In 20 subjects, VERP's were determined by the incremental and decremental methods using intertrain pauses of 1, 4, 8, 12, and 20 seconds.(ABSTRACT TRUNCATED AT 250 WORDS)