title: Restitution properties during ventricular fibrillation in the in situ swine heart.
abstract: BACKGROUND
  Although restitution has been hypothesized to determine action potential duration (APD) during ventricular fibrillation (VF), cardiac memory may also be important.
  
  
  RESULTS
  Transmembrane recordings were made with a floating microelectrode from the anterior right ventricular wall in 6 pigs during up to 60 seconds of VF. The recordings were divided into 5-second intervals, and APD60 and the diastolic interval (DI) were calculated for each activation cycle throughout each interval. Stepwise linear regression was used to determine how well each APD60 [APD60(n)] was predicted by the 4 previous DIs (n-1, n-2, n-3, n-4) and the 3 previous APD60s (n-1, n-2, n-3). A mean+/-SD of 3+/-1.5 of the variables entered the regression equation. DI(n-1) (70% of intervals) and APD60(n-1) (71% of intervals) appeared most frequently in the regression equations and were the first or second variables entered during the stepwise regression in 87% and 76% of the intervals in which they were present, respectively. The coefficients of DI(n-1) and APD60(n-1) were positive 89% and 98% of the time, respectively. R2 of the regression for all entered variables during all intervals was 0.39+/-0.05.
  
  
  CONCLUSIONS
  The high incidence and positive coefficient of DI(n-1) indicate that restitution is important in determining APD during VF, whereas the similarly high incidence and positive coefficient of APD(n-1) indicate that cardiac memory is equally important. The finding that the regression equation accounts for only 39% of the variability of APD indicates that factors other than restitution and memory are also important in determining APD during VF.
authors.affiliation: Cardiac Rhythm Management Laboratory, Division of Cardiovascular Disease, Department of Medicine, University of Alabama at Birmingham, Volker Hall B140, 1530 3rd Ave S, Birmingham, AL 35294-0019, USA. jh@crml.uab.edu
authors.forename: Jian
authors.initials: J
authors.lastname: Huang
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhou
authors.forename: William M
authors.initials: WM
authors.lastname: Smith
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Ideker
mesh_terms: D000200:Action Potentials; D000818:Animals; D002304:Cardiac Pacing, Artificial; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D016014:Linear Models; D008839:Microelectrodes; D032383:Myocytes, Cardiac / Q000502:physiology; D034421:Sus scrofa; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000503:physiopathology*