QT Interval Prolongation in Acute Myocardial Infarction

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Abstract
The relationship between corrected QT (QTc) interval and clinical factors in acute myocardial infarction (AMI) was studied, as well as the long-term prognostic implications of QTc after AMI. (I) 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. (II) 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 (c than the survivors. (III) 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 (c 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. (IV) QTc intervals were measured as in study III. Metoprolol (n=59) or placebo (n=52) were given prior to discharge to AMI patients (c 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. (V) 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. In patients followed 1 year, not on therapy, those who died (n=13) tended to resemble survivors (n=201), except for a somewhat older age, having pulmonary rales during hospitalization and longer QTc intervals at discharge. If a QTc of 0·44 s was used as a discriminant value, QTc yielded a sensitivity of 77% and specifity of 84%.

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