QT Interval Prolongation in Acute Myocardial Infarction

Abstract

The relationship between corrected QT (QTc) interval and clinical factors in acute myocardial infarction (AMI) was studied, as well as long-term prognostic implications of QTc after AMI. QTc was measured on admission to the coronary care unit (CCU). Patients with AMI who showed ventricular fibrillation or severe ventricular tachycardia (n = 27) had prolonged QTc in comparison to AMI patients without ventricular arrhythmias (VA) and noninfarction patients. QTc was measured at discharge from hospital in 463 survivors of AMI. Patients with anterior infarcts had longer QTc than those with inferior infarcts. Patients with VA in the CCU had longer QTc. Patients who died (3-6 years) had shorter QTc; explained by digitalis therapy. Among patients (less than 66 years) without bundle branch block digitalis and quinidine, those who died within six months tended to have longer QTc than the survivors. QTc intervals were measured on the first two days in the CCU, the first post-CCU day, at discharge, and at 1-3, 6 and 12 months after discharge, in 160 AMI patients (less than 66 years). The highest QTc values were registered in the CCU, the lowest at the 1-year control. During the acute phase, patients with anterior infarcts had longer QTc than those with inferior infarcts. Those with subendocardial infarcts had longer QTc intervals. Patients who reinfarcted or died (particularly when sudden) after discharge had longer QTc during the post-CCU period; QTc at discharge was of significant independent value for predicting major cardiac events. QTc intervals were measured as in study III. Metoprolol (n = 59) or placebo (n = 52) were given prior to discharge to AMI patients (less than 70 years). QTc decreased in both groups between discharge and the 3-month control; most marked in those on beta-receptor blockade with prolonged QTc. Patients on metoprolol had shorter QTc during the follow-up. Patients who died suddenly had longer QTc prior to discharge than those without major cardiac events. In a prospective collaborative study, QTc intervals were measured at discharge from hospital in 865 patients. All patients who died after discharge within 30 days after admission were on medication or pacemaker therapy which would influence QTc. When this was taken into consideration, QTc was significantly longer in patients who died within 180 days and 1 year.(ABSTRACT TRUNCATED AT 400 WORDS)