Effects of transient myocardial ischemia on the QT interval in man

Prolongation of the QT interval may be associated with ventricular arrhythmias. Prolongation of the QT interval has been found during the evolution of acute myocardial infarction. To investigate the effect of transient myocardial ischemia on the QT interval, 80 patients admitted to the coronary care unit with unstable angina were studied, 60 retrospectively and 20 prospectively. The corrected QT intervals (QTc) in multiple leads were compared during ischemic pain to those recorded within 24 h in the absence of pain. During pain, the mean +/- SD QTc was 0.44 +/- 0.04 s which was identical to the mean QTc recorded without pain. The mean QTc during pain was not different between patients with and without ischemic electrocardiographic abnormalities, between patients with and without previous myocardial infarction or between patients with single and multiple vessel disease on angiography (P greater than 0.5). In conclusion, the QTc interval does not change during transient myocardial ischemia, regardless of previous infarction, extent of coronary artery disease or therapy with type 1 antiarrhythmic drugs.