Ability of the electrocardiogram to detect myocardial lesions in isoproterenol induced rat cardiomyopathy.

Resting electrocardiograms were recorded in 18 male adult rats injected subcutaneously with two doses of isoproterenol (200 mg.kg-1 body weight) 10 days before the animals were submitted to the ajmaline test (1 mg.kg-1 body weight iv). After the ajmaline test all rats were killed and the hearts examined histologically. Electrocardiographic changes were detected at rest in 72% of the isoproterenol injected rats: pathological Q waves, lengthening of the QRS complex, and QRS abnormality were found in 50%, 44%, and 44% of these animals respectively. Ajmaline induced similar changes in both control and isoproterenol treated rats (P wave enlargement (p less than 0.01 and p less than 0.001 respectively), increased PR interval (p less than 0.003 and p less than 0.001 respectively), and increased QaT interval (p less than 0.001 in both groups]. However, ajmaline caused an increase in heart rate only in isoproterenol treated rats (p less than 0.05). A pronounced increase in PR interval, not observed in control rats, was detected in one of five isoproterenol injected rats with a normal resting ECG but showing microscopical cardiac lesions. Apical aneurysm of the left ventricle was found in 16% of isoproterenol injected rats. A mononuclear inflammatory reaction was observed in 13 (72%) of the isoproterenol injected rats and was multifocal in at least three regions of the myocardium in six (46%) and disseminated throughout the myocardium in seven (53%) of these animals. When the electrocardiographic and pathological findings were compared, the ECG changes were found to have a 91% sensitivity, 83% specificity, and 91% positive predictive value.(ABSTRACT TRUNCATED AT 250 WORDS)