Prognostic significance of the electrocardiogram after Q wave myocardial infarction. The Framingham Study.

Abstract

The prognostic value of abnormalities on the electrocardiogram (ECG) present 1 year after initial myocardial infarction (MI) is examined in relation to reinfarction and coronary death throughout 32 years (mean, 10.1 years) of follow-up in the Framingham Heart Study. Resting 12-lead ECGs were available in 251 survivors (190 men and 61 women) of clinically recognized Q wave MI. The ECG reverted to normal in 31 (12.4%) cases and was abnormal but without Q waves in 37 (14.7%). Q waves persisted without other significant abnormalities in 108 (43.0%) and with other abnormalities in 75 (29.9%) cases. Electrocardiographic abnormalities at follow-up were more common in women and in those persons whose initial MI was anterior as compared with inferior. Nonspecific T wave, ST segment changes, and electrocardiographic left ventricular hypertrophy on the ECG before or after MI were powerful predictors (p less than 0.01) of coronary death. The relation of these residual post-MI electrocardiographic findings to reinfarction and coronary death was assessed by Cox regression analysis. The follow-up electrocardiographic status was unrelated to the risk of subsequent reinfarction. Subjects who lost Q wave evidence of MI but whose ECG continued to show evidence of repolarization abnormalities, left ventricular hypertrophy, or blocked intraventricular conduction were at a 3.5-fold increased risk (p less than 0.01) of coronary death as compared with those reverting to a normal ECG. Persons with a persistent Q wave MI accompanied by these abnormalities were at a 2.7-fold excess risk (p = 0.01) of coronary death as compared with those with a normalized ECG. These findings remained significant when considering age and standard coronary risk factors. The presence of other electrocardiographic abnormalities without persistent Q waves yields a worse prognosis than a Q wave persisting alone. The prognostic value of a follow-up ECG with abnormalities other than a persistent Q wave MI also remained after considering the effects of left ventricular hypertrophy and cardiac enlargement on x-ray, functional classification, and diuretic usage. Specific electrocardiographic abnormalities present before infarction, however, were potent indicators of long-term prognosis prognosis and diminished the importance of the follow-up ECG. Although survival after initial MI is improved only if the ECG reverts to normal, information on electrocardiographic abnormalities before MI can be especially useful in evaluating long-term risk.