Prolonged QRS duration increases QT dispersion but does not relate to arrhythmias in survivors of acute myocardial infarction

QT dispersion has been suggested and disputed as a risk marker for ventricu lar arrhythmias after myocardial infarction. Delayed ventricular activation after myocardial infarction may affect arrhythmic risk and QT intervals. T his study determined if delayed activation as assessed by (1) QRS duration in the 12-lead ECG and by (2) late potentials in the signal-averaged ECG af fects QT dispersion and its ability to assess arrhythmic risk after myocard ial infarction. QT duration, JT duration, QT dispersion, and JT dispersion were compared to QRS duration in the 12-lead ECG and to late potentials in the signal-averaged ECG recorded in 724 patients 2-3 weeks after myocardial infarction. Prolonged QRS duration (> 110 ms) and high QRS dispersion incr eased QT and JT dispersion by 12%-15% (P < 0.05). Presence of late potentia ls, in contrast, did not change QT dispersion. Only the presence of late po tentials (n = 113) was related to arrhythmic events during 6-month follow-u p. QT dispersion, JT dispersion, QRS duration, and QRS dispersion were equa l in patients with (n = 29) and without arrhythmic events (QT disp 80 +/- 7 vs 78 +/- 1 ms, JT disp 80 +/- 6 vs 79 +/- 2 ms, mean +/- SEM P > 0.2). In conclusion, prolonged QRS duration increases QT dispersion irrespective of arrhythmic events in survivors of myocardial infarction. Presence of late potentials, in contrast, relates to arrhythmic events but does not affect Q T dispersion. Therefore, QT dispersion may not be an adequate parameter to assess arrhythmic risk in survivors of myocardial infarction.