The surface electrocardiogram: a simple and reliable method for detecting overt and latent heart disease in rats.

1. The following changes may be observed in the resting ECG of Wistar rats having different forms of heart disease: pathological Q wave, QRS deviations, lengthening of both P wave and QRS complex, increased PR interval and J point alterations. 2. The ajmaline test, when applied to rats with myocardial disease but with normal resting ECG, presented the following ECG alterations which were not observed in normal rats: indeterminate axis (QRS axis in the 3rd space), increased PR interval and lengthening of both P wave and QRS complex. 3. When compared with histopathological studies, the ECG changes have a high positive predictive value for detecting underlying myocardial disease. 4. The surface ECG can be a useful tool for detecting myocardial disease in different experimental models of rat heart disease. It can also be used to characterize rat models of heart disease and to evaluate treatment of experimental rat heart disease.