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Role of maximum rate of depolarization in predicting action potential duration during ventricular fibrillation

¹Cardiac Rhythm Management Laboratory, Division of Cardiovascular Disease, Department of Medicine, ⁴Department of Physiology, and ³Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama; and ²Peking Union Medical College Hospital, Beijing, China

Submitted 9 July 2007 ; accepted in final form 10 August 2007

During ventricular fibrillation (VF) only 39% of the variation in action potential duration (APD) is accounted for by the previous diastolic interval [DI_(n–1)], i.e., restitution, and the previous APD [APD_(n–1)], i.e., memory. We tested the hypothesis that a characteristic of the AP upstroke, the maximum rate of depolarization (_max), also helps account for its APD. A floating microelectrode was used to make transmembrane recordings at 16,000 samples/s from the anterior left ventricular wall during four 20-s episodes of VF in each of six pigs. _max, time from _max to 60% repolarization (APD₆₀), and DI were calculated throughout all episodes. Stepwise linear regression was used to determine how well each APD₆₀ (APD_60n) was predicted by _max of that AP, the four previous DIs (n–1, n – 2, n – 3, n – 4), and the three previous APD₆₀s (n–1, n – 2, n – 3). _max entered in the regression equation significantly more often (86% of VF episodes) than either APD_(n–1) (47% of episodes) or DI_(n–1) (58% of episodes). When these three variables entered first or second, their coefficients were almost always positive, consistent with a longer APD associated with 1) a larger _max, 2) a longer APD_(n–1), and 3) a longer DI_(n–1). R² of the regression for all entered variables was 0.51 ± 0.01 (mean ± SD). During the first 20 s of VF in swine, _max is a more important determinant of APD than the previous DI (restitution) or the previous APD (memory). All variables together account for only one-half of APD variation during VF.

electrophysiology

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