Electrocardiographic findings in rats with cardiomyopathy

The purpose of this study was to evaluate changes in the ECG in a strain of rats, SHHF/Mcc-cp that developed cardiomyopathy and congestive heart failure naturally. Lead-I, -aVF, and -V5 ECG were obtained from male rats at approximately 6, 10, and 19 months of age, corresponding to early, mild, and severe heart failure, respectively. Electrocardiograms also were obtained from male Wistar-Furth rats matched for age with SHHF/Mcc-cp rats. Heart rate, amplitude and duration of component deflections, degree of notching of P waves and QRS complexes, and orientation of means QRS vectors in the frontal plane were analyzed from the ECG. Durations of P waves, PQ intervals, QRS complexes, and QT intervals were prolonged and amplitude of R waves in lead aVF was decreased only in SHHF/Mcc-cp rats at the 19-month recording. Increased notching in QRS complexes, but not in P waves, was observed more frequently at all ages, in SHHF/Mcc-cp rats than in Wistar rats, and notching was greatest at 19 months. Arrhythmias were not observed in Wistar rats, but infrequent supraventricular premature depolarizations were observed in 2 of 10 SHHF/Mcc-cp rats at 19 months. In leads aVF and V5, T waves increased in amplitude as Wistar rats aged; however, in SHHF/Mcc-cp rats, T-wave amplitude peaked in all leads at 10 months, but returned to the 6-month value at month 19. We conclude that cardiomyopathy, heart failure, or both, resulted in changes in the ECG, but that these changes could be used to detect heart failure only when rats reached 19 months of age and were severely affected.