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Refractory Period Extension During Ventricular Pacing at Fibrillatory Pacing Rates
Author(s) -
GILL ROBERT M.,
SWEENEY ROBERT J.,
REID PHILIP R.
Publication year - 1997
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.1997.tb03883.x
Subject(s) - refractory period , medicine , cardiology , defibrillation , effective refractory period , ventricular fibrillation , refractory (planetary science) , ventricular pacing , fibrillation , heart rate , anesthesia , atrial fibrillation , heart failure , materials science , blood pressure , composite material
Refractory period extension (RPE) bas been proposed as a basic mechanism for defibrillation but it remains unclear if RPE exists at the fast rates associated with ventricular fibrillation. In 7 pentobarbital anesthetized dogs, we measured refractory periods with and without 8 ms rectangular transcardiac shocks at left ventricular pacing rates of 200–600 beats/min. To achieve these high rates, an incremental rate pacing method was used to produce pacing train timing sequences requiring 4.5–27 seconds. A variably timed premature stimulus followed the last stimulus in each pacing train. To determine refractoriness, a 128 electrode arrav (4 × 4 cm) was used to detect the presence, or absence of an activation sequence sweeping away from the pacing site. At each rate, a control refractory period (RPc) was measured and refractory periods were also measured for 8 and 12 V/cm shocks with coupling intervals of 60% to 90% of RPc. RPc decreased as the rate increased with a minimum RPc of 94 ms at a rate of 600 beats/min (100 ms cycle length). RPE/RPc versus shock coupling interval was similar at all pacing rates. RPE/RPc increased with increased coupling interval or higher shock intensity. We conclude that during ventricular pacing at fibrillatory rates tissue is nearly always in a refractory state: that RPE exists at fibrillatory activation rates; and that RPE/RPc versus shock coupling interval does not vary strongly with pacing rate. These findings support the hypothesis that RPE contributes to defibrillation.