QT interval in relation to ventricular arrhythmias and sudden cardiac death in postmyocardial infarction patients.

Ninety-one consecutive patients below the age of 70 years were subjected to a 60-second resting ECG and 24-hour ambulatory ECG monitoring two weeks and one, three and six months after an acute myocardial infarction. The corrected QT (QTc) interval decreased from the late hospital phase to the investigations three and six months after the infarction (p less than 0.01, less than 0.05). ECG monitorings showing complicated ventricular ectopic beats (multiform, repetitive, R-on-T) were associated with an insignificantly longer QTc than other recordings. Eleven patients suffered a sudden cardiac death during a median follow-up period of 24 months (range 22-27). The QTc intervals in patients who died suddenly were insignificantly longer than in the survivors. Only four patients, who all survived, had a constantly prolonged QTc. After exclusion of tracings during quinidine therapy, a QTc longer than 440 msec was found in 7 (23%) of 31 recordings from patients who suffered a sudden cardiac death compared to 29 (10%) of 287 recordings from the survivors (p less than 0.05). A combination of complicated ventricular ectopic beats and a QT longer than 440 msec was demonstrated in 5 (16%) of 31 and 14 (5%) of 287 recordings from the two groups of patients (p less than 0.05). A trend towards longer QTc intervals was observed in patients with complicated ventricular arrhythmias and in those who died suddenly, but no well defined high-risk groups could be identified.