Evaluation of arrhythmia scoring systems and exercise-induced cardioprotection

INTRODUCTION: Exercise is protective against ventricular arrhythmias induced by ischemia (I), the condition of inadequate blood flow, and reperfusion (R), the reestablishment of blood flow. This protection is observed clinically and scientifically by decreased incidence in ECG abnormalities. Numerous scoring systems exist for the quantification of ventricular arrhythmia severity. On the basis of preventricular contractions, ventricular tachycardia, and ventricular fibrillation frequency, these scoring systems are intended to provide more robust ECG outcome indicators than individual arrhythmia variables. Scoring systems vary primarily on continuous versus discontinuous treatment of the data, which should be considered when matching these arrhythmia metrics to scientific applications. PURPOSE: The aim of this investigation was to evaluate seven ECG scoring systems in the assessment of ventricular arrhythmia severity after IR in male Sprague-Dawley rats. METHODS: Animals remained sedentary or exercised (3 d of treadmill exercise for 60 min) before surgically induced IR. A subset of sedentary animals served as sham, undergoing surgical procedure without IR. ECGs were evaluated under blinded conditions by three trained individuals. Single arrhythmia data and the parametric score were analyzed by one-way ANOVA, whereas the Kruskal-Wallis was used to compare group means for all nonparametric scoring systems between groups. RESULTS: IR produced a significant arrhythmic response in exercised and sedentary rats as determined by all arrhythmia scoring systems. Four arrhythmia metrics resulted in significant differences between exercised and sedentary treatments (P < 0.001), whereas three metrics did not. CONCLUSIONS: Continuous versus discontinuous treatment of the data may account for variation in scoring system outcomes. These data confirm that exercise protects against IR-induced arrhythmias, and care must be taken when selecting an arrhythmia scoring system for ECG evaluation.