Impact of short-term exercise training on QT dispersion and double product in diabetic patients after surgical aortic valve replacement

Abstract

Abstract Background QT dispersion (QTd) represents the heterogeneity in the repolarization of the ventricular myocardium and electrical instability of the myocardium, reflecting the increased tendency towards ventricular arrhythmias. Abnormally high QTd has been correlated with risk of cardiac death. Purpose The aim of this study was to establish the influence of short-term exercise training on QT dispersion and double product (DP), in diabetic patients after surgical aortic valve replacement (SAVR). Methods The study involved 147 patients after SAVR, in the sinus rhythm without AV blocks or branch blocks. Average age of patients was 59.3 years. 45 patients were with diabetes mellitus, and 102 were without diabetes. Patients were similar as to 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 patients were included in program of physical training for three weeks. Patients were instructed to follow a training program using the bicycle ergometer (10 min, 2 times a day), gymnastic exercises and walking. The patients continued to take the same medicaments in same doses. From standard ECG corrected QT dispersion (QTdc) was calculated. Results Before starting with the program of physical training, patients with diabetes had significantly higher values of QTdc (83.4 ± 15.3 vs 74.6 ± 16.9 ms; p<0.005) in comparison to those without diabetes. After three weeks, significant reduction of QTdc was found (from 83.4 ± 15.3 to 77.3 ± 15.4 ms; p<0.02 in patients with diabetes and from 74.6 ± 16.8 to 68.7 ± 17.1 ms; p<0.005 in patients without diabetes). After three weeks, significant reduction of DP was found (from 11763.8 ± 779.9 to 11314.8 ± 635.8 beat/min x mmHg; p<0.005 in patients with diabetes and from 114376.4 ± 792.3 to 10034.2 ± 521.3 beat/min x mmHg; p<0.001 in patients without diabetes). In diabetic patients, after program of physical training, significant reduction of glycemia was found (from 7.0 ± 2.3 to 5.9 ± 1.5 mmol/L; p<0.005), of total cholesterol from 5.2 ± 1.3 to 4.6 ± 1.1 mmol/L (p<0.025), of LDL cholesterol from 3.2 ± 0.8 to 2.8 ± 0.6 mmol/L (p<0.05). After three weeks, both groups of patients in the exercise test reached a significantly longer time (p<0.001). Conclusions The study showed that patients with diabetes have a higher value QTdc, probably due to diffuse interstitial fibrosis. Short-term exercise training has favourable effects on QT dispersion and double product in patients after SAVR. In patients without diabetes 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.