P1504Impact of myocardial ischemia induced by exercise stress echocardiography on the QT dispersion in patients with the left bundle branch block

Abstract Background/Introduction ECG has always provided very useful information that can be used to diagnosis, treatment and prevention of cardiovascular events, but ECG changes is not useful to the detection of myocardial ischemia in patients with left bundle branch block (LBBB). 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 impact of myocardial ischemia induced by exercise stress echocardiography on the QT dispersion in patients with the left bundle branch block. Methods The study involved 123 patients with LBBB, average age 52.7 years. In all subjects clinical examination, standard ECG and exercise stress echocardiography, were performed. The criterion for myocardial ischemia was the appearance of transient segmental wall motion abnormality. The first ECG was done before the exercise stress echocardiography and the second one was done immediately after exercise, with calculation of corrected QT dispersion (QTdc). Results During exercise stress echocardiography, in 45 (36.6%) subjects wall motion abnormality occurred (group with myocardial ischemia: MI), and 78 (63.4%) subjects were without ischemia (group without myocardial ischemia: NMI). Before starting the exercise stress echocardiography, MI group patients had significantly higher values of QTdc (61.2±17.6 vs 43.6±15.4 ms; p<0.001) in comparison to NMI group patients. During the exercise stress echocardiography, the QTdc significantly increased in MI group from 61.2±17.6 to 87.4±20.3 ms (p<0.001). In the NMI group there were no significant changes in the values QTdc during exercise stress echocardiography (from 43.6±15.4 to 46.5±19.8 ms (p - NS). Conclusions Significant increase of QT dispersion is associated with the occurrence of myocardial ischemia during exercise stress echocardiography in patients with LBBB. This new diagnostic approach, of using QT dispersion, significantly improves the clinical usefulness of exercise stress echocardiography in detecting myocardial ischemia in patients with LBBB.