P649Impact of short-term exercise training and residual ischemia on QT dispersion and double product in patients after bypass graft surgery

Abstract

Background/Introduction: Patients after coronary artery bypass graft surgery (CABG) are at high risk of cardiovascular and arrhythmic events. QT dispersion (QTd) is a measure of inhomogeneous repolarization of myocardium. Abnormally high QTd has been correlated with risk of cardiac death in coronary patients. Purpose: The aim of this study was to establish the influence of short‐term exercise training and residual ischemia (RI) on QT dispersion and double product (DP) as well, in patients after CABG. Methods: The study involved 172 patients after CABG, in the sinus rhythm without AV blocks or branch blocks. Average age of patients was 57.3 years. Patients were randomly divided into the physical training group (TG: 133 patients) and non‐training group (39 patients). Patients were of similar age and baseline stress test duration. In all subjects clinical examination, standard ECG and exercise test on treadmill according to Bruce protocol, were performed and after that TG patients were included in rehabilitation treatment for three weeks. TG of patients were instructed to follow a training program using the bicycle ergometer (10 min, 2 times a day). The patients continued to take the same medicaments in same doses. From standard ECG corrected QT dispersion (QTdc) was calculated. Results: RI was present in 29 (21.8%) patients in the TG and in 9 (23.1%) patients in the control group. In the TG, before starting with the program of physical training, patients with RI had significantly higher values of QTdc (55.6±13.4 vs 47.2±16.8 ms; p<0.005), while the values of DP did not significantly vary (11752.6±653.8 vs 11505.3±724.4 beat/min x mmHg; p‐NS) in comparison to those without RI. After three weeks, in the TG, significant reduction of QTdc was found (from 55.6±13.4 to 48.8±12.5 ms; p<0.05 in patients with RI and from 47.2±16.8 to 39.6±15.9 ms; p<0.001 in patients without RI). In the TG, significant reduction of DP was found (from 11752.6±653.8 to 11390.5±492.7 beat/min x mmHg; p<0.02 in patients with RI and from 11505.3±724.4 to 10124.5±529.6 beat/min x mmHg; p<0.001 in patients without RI). In contrast, the non‐training group showed no significant changes. Conclusions: The study showed that short‐term exercise training has favourable effects on QT dispersion and double product in patients after CABG. In patients without RI physical training had more favourable effects on the followed parameters. Physical training led to the significant decrease of myocardial oxygen uptake at rest and probably decreased the possibility of arrhythmia events, especially in patients without RI.