Submitted on July 9, 2007
Accepted on August 10, 2007
The Role of Maximum Rate of Depolarization in Predicting Activation Potential Duration during Ventricular Fibrillation
Jian Huang1*, Kang-An Cheng2, Derek J Dosdall3, William M. Smith4, and Raymond E. Ideker5
1 Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
2 Medicine, Peking Union Medical College Hospital, Beijing, China
3 Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States
4 Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States
5 Medicine, Physiol and Biomed Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States
* To whom correspondence should be addressed. E-mail: jh{at}crml.uab.edu.
Background: 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 (Vdotmax ), also helps account for its APD.
Methods: 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 6 pigs. Vdotmax, APD60 and DI were calculated throughout all episodes. Stepwise linear regression was used to determine how well each APD60(APD60n) was predicted by Vdotmax 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).
Results: Vdotmax 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 3 variables entered 1st or 2nd, their coefficients were almost always positive, consistent with a longer APD associated with a (1) larger Vdotmax , (2) longer APD(n-1) and (3) longer DI(n-1). R2 of the regression for all entered variables was 0.51±0.01 (mean±SD) .
Conclusion: During the first 20 s of VF in swine, Vdotmax is a more important determinant of APD than is the previous DI (restitution) or the previous APD (memory). All variables together account for only one-half of APD variation during VF.
