Intensive exercise training improves cardiac electrical stability in myocardial-infarcted rats

Background-moderate exercise training has been shown to decrease sudden cardiac death post myocardial infarction. however,the effects of intensive exercise are still controversial. methods and results-fourteen myocardial-infarcted rats were divided into sedentary (n=8) and intensive training groups (n=6) and 18 sham control rats to sedentary (n=10) and intensive training groups (n=8). heart rate variability was obtained at weeks 1 and 8. the inducibility of ventricular tachycardia/fibrillation was assessed in a langendorff system. fast fourier transforms were applied on the recorded ventricular tachycardia/fibrillations. training reduces low to high frequency ratio of heart rate variability at week 8 compared with that at week 1 (p < 0.05). in isolated hearts,the probability for ventricular tachycardia/fibrillation was decreased from 4.5 ±0.8% in sedentary controls to 1.56±0.2% in intensive training controls (p < 0.05) and from 13.5±2.1% in the sedentary group to 5.4±1.2% in the intensive training group (p < 0.01). moreover,the pacing current required for ventricular fibrillation induction in the trained groups was increased following exercise (p < 0.05). fast fourier transform analysis of ecg findings revealed an exercise-induced ventricular fibrillation transition from a narrow,single-peak spectrum at 17 hz in sedentary controls to a broader range of peaks ranging from 13 to 22 hz in the intensive training controls. conclusions-intensive exercise in infarcted rats leads to reduced ventricular fibrillation propensity and is associated with normalization of refractoriness and intrinsic spatiotemporal electrical variations. © 2017 the authors.