title: Reduced Ventricular Arrhythmogeneity and Increased Electrical Complexity in Normal Exercised Rats.
abstract: The mechanisms whereby aerobic training reduces the occurrence of sudden cardiac death in humans are not clear. We test the hypothesis that exercise-induced increased resistance to ventricular tachycardia and fibrillation (VT/VF) involve an intrinsic remodeling in healthy hearts.
  
  
  
  Thirty rats were divided into a sedentary (CTRL, n = 16) and two exercise groups: short- (4 weeks, ST, n = 7) and long-term (8 weeks, LT, n = 7) trained groups. Following the exercise program hearts were isolated and studied in a Langendorff perfusion system. An S1-S2 pacing protocol was applied at the right ventricle to determine inducibility of VT/VF. Fast Fourier transforms were applied on ECG time-series. In-vivo measurements showed training-induced increase in aerobic capacity, heart-to-body weight ratio and a 50% low-to-high frequency ratio reduction in the heart rate variability (p<0.05). In isolated hearts the probability for VF decreased from 26.1±14.4 in CTRL to 13.9±14.1 and 6.7±8.5% in the ST and LT, respectively (p<0.05). Duration of VF also decreased from 19.0±5.7 in CTRL to 8.8±7.1 and 6.0±5.8 sec in ST and LT respectively (p<0.05). Moreover, the pacing current required for VF induction increased following exercise (2.9±1.7 vs. 5.4±2.1 and 8.5±0.9 mA, respectively; p<0.05). Frequency analysis of ECG revealed an exercise-induced VF transition from a narrow single peak spectrum at 17 Hz in CTRL to a broader range of peaks ranging between 8.8 and 22.5 Hz in the LT group (p<0.05).
  
  
  
  Exercise in rats leads to reduced VF propensity associated with an intrinsic cardiac remodeling related to a broader spectral range and faster frequency components in the ECG.
authors.affiliation: Heart Institute, Hadassah-Hebrew University Medical Center, Jerusalem, Israel.
authors.forename: Horesh
authors.initials: H
authors.lastname: Dor-Haim
authors.forename: Omer
authors.initials: O
authors.lastname: Berenfeld
authors.forename: Michal
authors.initials: M
authors.lastname: Horowitz
authors.forename: Chaim
authors.initials: C
authors.lastname: Lotan
authors.forename: Moshe
authors.initials: M
authors.lastname: Swissa
mesh_terms: D000818:Animals; D004562:Electrocardiography; D006321:Heart / Q000033:anatomy & histology; D006339:Heart Rate; D008297:Male; D010805:Physical Conditioning, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D017180:Tachycardia, Ventricular / Q000503:physiopathology*; D014693:Ventricular Fibrillation / Q000503:physiopathology*