901-9 QT Dispersion and Prognosis After Myocardial Infarction

Abstract

QT dispersion (QT max minus QT min) is an important measure of arrhythmia risk, providing information about heterogeneity of ventricular repolarisation. We studied QT dispersion for all cause mortality in patients from the placebo arm of a large therapeutic intervention trial in acute myocardial infarction. Standard 12 lead electrocardiograms (ECGs) were analysed from day 2 or 3 of the acute infarction; and if available, from a later period of life (more than 1 month post infarct). The only exclusions were patients with chronic atrial fibrillation or paced rhythm, or those with ECGs of too poor quality to be analysed. The ECGs were scanned, and the image divided into12 files corresponding to the 12 leads of the standard ECG. Specially designed software then skeletonised and joined each file, which is then available for either user-interactive or automatic measurement of QT dispersion, again using specially designed software. The following results are all user interactive, and are rate and lead corrected (rate corrected QT max minus QT min divided by the square root of the number of leads with a measureable QT interval). For the group known to have deceased 163 patients had ECGs analysed during the early stage of acute myocardial infarction, and 53 had ECGs recorded later in life. 163 age and sex matched survivors in the same study have been analysed, of these 82 have had ECGs recorded later in life. Mean adjusted QT dispersion for the death group is 36.6 ms (SD 14.7), andfor survivors 35.2 ms (SD 13.9), p-NS; for ECGs recorded on day 2 or 3 of acute myocardial infarction. ECGs recorded later in life have an adjusted OT dispersion of 31.2 ms (SD 13.9) for the deceased group, and for survivors of 24.5 ms (SD 9.5), p < 0.01. QT dispersion is prolonged in the early stages of acute myocardial infarction, and for long term survivors then falls towards more normal values. The failure of QT dispersion to normalise in patients who subsequently decease is an important observation, and may provide insight into the causes of mortality in this group.