Clinical significance of QT dispersion after exercise in patients with previous myocardial infarction

To evaluate the clinical significance of QT dispersion after exercise in patients with previous myocardial infarction, QT dispersion (QTd) and corrected QTd (QTcd) were assessed with standard 12 leads electrocardiogram in 90 patients with previous myocardial infarction and 30 healthy persons before and 3 min after a treadmill exercise test. In addition, 24 h ambulatory electrocardiogram and echo-cardiography were examined in all the subjects studied. Patients were followed up for 37.25±10.71 months. The results showed that there were no significant differences in the QTd and QTcd between the patients and the controls before exercise (36.11±13.42 ms versus 34.81±12.32 ms, P>0.05, 41.22±13.49 as versus 39.91±13.56 ms, P>0.05). Compared with those before exercise, QTd and QTcd were significantly increased in the patients 3 min after the exercise test (36.11±13.42 ms versus 47.20±14.41 ms, P<0.01, 41.22±13.49 ms versus 59.57±18.90 ms, P<0.01), but not in the controls (34.81±12.32 ms versus 38.76±12.09 ms, P>0.05, 39.91±13.56 ms versus 43.27±17.77 ms, P>0.05). The incidences of abnormal contraction of the left ventricular wall, aneurysms, NYHA III class, >III class of Lownʹs ventricular arrhythmia classification and cardiac sudden death were significantly higher in group A with QTcd >50 ms than that of group B with QTcd <50 ms (P<0.01). These findings indicate that the increased QT dispersion after exercise in 12 standard leads electrocardiogram might be associated with high incidences of sudden cardiac death and ventricular arrhythmia in the patients with previous myocardial infarction.