QT DISPERSION AND COMPONENTS OF THE QT INTERVAL IN ISCHEMIA AND INFARCTION

Objective-To evaluate changes in QT dispersion and components of the Q T interval in patients admitted with unstable angina and acute myocard ial infarction and to study the dynamics of these changes in patients with infarction. Methods-Prospective study recording electrocardiogram s at 50 mm/s in patients admitted with typical cardiac chest pain. Sub sequent confirmation of acute myocardial infarction according to stand ard criteria. Single blind analysis for QT dispersion and QT component s using a digitiser and simple computer program. Results are expressed as native QT dispersion, QTc dispersion, and the QT dispersion ratio defined as QT dispersion divided by cycle length and expressed as a pe rcentage. Results-QT dispersion, QTc dispersion, and QT dispersion rat io were all higher in patients with acute myocardial infarction than i n those with unstable angina (mean (SD) 66 (18) ms, 75 (26) ms(1/2), a nd 8.1 (24.) % compared with 38 (13) ms, 39 (13) ms', and 4.5 (1.7) % respectively). Dynamic changes in QTc dispersion were seen after acute infarction with significant differences in the QT components occurrin g between the different patient groups. Levels of QT dispersion (87 (1 5) ms), QTc dispersion (105 (17) ms(1/2)), and QT dispersion ratio (11 .7 (0.8) %) in the four patients with ventricular fibrillation were si gnificantly higher. Use of QT dispersion ratio gave a narrower confide nce interval. Conclusion-QT dispersion is increased after myocardial i nfarction and levels are higher in patients with ventricular fibrillat ion. The changes in QT dispersion are dynamic and may reflect the chan ging pattern of underlying ventricular recovery of ventricular excitab ility, which is profoundly disturbed in the earliest phase of acute in farction. Expressing QT dispersion as a percentage of cycle length (QT dispersion ratio) rather than using standard rate correction may be s uperior in identifying patients who develop ventricular fibrillation.