Effect of Isometric Exercise on QTc Interval

INTRODUCTION: The QTc interval is affected by heart rate, autonomic nervous system and diseases like diabetes. However, the affect of exercise which alters autonomic nervous system activity, on QTc is not clear. On the other hand, the incidence of sudden cardiac death increases many fold post exercise. These events may be better explained by studying the effect of exercise on QTc. AIM: This study was designed with an aim to record the QTc interval changes in response to isometric exercise in a group of normal individuals with or without parental history of diabetes mellitus. Also the QTc duration was correlated with the LF-HF ratio. MATERIALS AND METHODS: Twenty nine, healthy medical students were subjected to isometric hand grip test for 5min. ECG was recorded pre-exercise and at various time intervals post-exercise. STATISTICAL ANALYSIS: All data are expressed in mean ± SD. Intra group comparison was done using paired t-test and unpaired t-test was used for comparison among group I and group II subjects, and among males and females. RESULT: The difference in the pre and post exercise QTc values both within and between groups was statistically significant with group I subjects recording lower values. The post exercise LF: HF values were significantly increased when compared to pre exercise values in both the groups. There was no correlation between LF: HF and QTc. CONCLUSION: A longer than normal QTc interval predisposes to arrhythmia. Exercise brings about detectable changes in the QTc interval after a period of isometric exercise in normal individuals which in high risk individuals may predispose to sudden cardiac death. In addition women may be more susceptible to post-exercise arrhythmia owing to a longer QTc even at rest.