Epicardial excitation studies in dogs with congenital right ventricular hypertrophy.

The time and sequence of epicardial activation was determined by measuring the onset of activation at 26 to 47 representative epicardial sites on each ventricle. Normal dogs and dogs with right ventricular hypertrophy resulting from various congenital heart lesions were studied. The total right ventricular epicardial activation time was slightly prolonged (10 msec) in some dogs with right ventricular hypertrophy, but it was not directly related to the severity of the lesion. In the dogs with right ventricular hypertrophy and right ventriclepulmonary artery systolic pressure differences greater than 40 mm Hg, the activation of the right ventricular epicardium was consistently completed after that of the left ventricular epicardium. The delay in right ventricular epicardial activation was best shown by plotting the epicardial data on a simultaneously recorded QRS complex. In the dogs with right ventricular hypertrophy, right ventricular epicardial activation was shifted in time within the QRS complex so that 39% of the sites were activated during the last one-third of the QRS interval; only 1% of the right ventricular epicardial sites were activated during this time in the normal group. The QRS electrocardiographic changes in right ventricular hypertrophy were associated not only with a slight prolongation in epicardial activation time, but also with a shift in timing of this activation within the QRS complex. ADDITIONAL