Continuous QT Interval Measurements from 24‐Hour Electrocardiography and Risk after Myocardial Infarction

Objectives: The aim of this study was to examine the clinical value of QT analysis from Holter recordings in patients after myocardial infarction (Ml). Background: Prolongation and dispersion of QT intervals in the 12‐lead standard ECG have been proposed as indicators of risk for arrhythmic events. However, the value of QT and T wave measurements from Holter recordings has yet to be established. Methods: Intervals from Q to the peak and to the end of T were determined every 30 seconds from 24‐hour Holter recordings and corrected for cycle length (QTc). The duration of late repolarization was calculated as QT end minus QT peak. 24‐hour QT variability was determined as the standard error of estimate from the linear regression analysis of QT and RR intervals. In a case control design, 51 post‐MI patients suffering from subsequent cardiac death within 1 year were compared to 51 post‐MI patients with an uncomplicated follow‐up. Results: QTc intervals as well as 24‐hour QT variability did not differ between post‐MI patients with favorable and unfavorable clinical outcome. However, there was a prolonged interval from the peak to the end of the T wave in cardiac death victims (mean ± SE: 110 ± 4 ms) as compared to controls (95 ± 3ms, P < 0.001). Conclusions: Prolongation of the late repolarization phase seems to be associated with an increased risk of cardiac death after Ml. Standard QT measurements from ambulatory ECG recordings have no predictive value in post‐MI patients.