Sir,—We read with interest O’Sullivanet al’s article “Abnormal ventricular activation and repolarisation during dobutamine stress echocardiography in coronary artery disease”.1 In that study patients with coronary artery disease (CAD) had an increased QTc interval but not QT dispersion during positive dobutamine exercise stress testing. QT interval is a measure of the duration of ventricular repolarisation,2 and is sensitive to myocardial ischaemia. Therefore, the authors suggest that there are repolarisation abnormalities in patients with CAD during positive dobutamine stress testing. The interlead variation of QT interval in the 12 lead ECG referred to as QT dispersion reflects heterogeneity in the duration of myocardial repolarisation.2 O’Sullivanet al showed that QT dispersion was not heart rate dependent and did not change with increasing heart rate in control subjects. They found that QT dispersion decreased, …