Further Electrocardiographic Observations on Direct Epicardial Potentials in Congenital Heart Lesions

Epicardial electromotive potentials have been recorded at the time of open thoracotomy on 130 patients, 124 having congenital heart disease. These data confirm characteristic epicardial potentials with right ventricular preponderance, incomplete right bundle-branch block, and complete right bundle-branch block, as well as with normal rS and rSr′ complexes, as identified in the right precordial leads of unipolar electrocardiograms. The major differential feature between right ventricular preponderance and incomplete right bundle-branch block is a critical difference in onset of depolarization of the free wall of the right ventricle. This measurement, AB of figure 1, is 0.02 second with right ventricular preponderance and 0.03 second or greater with incomplete right bundle-branch block. Although rR′ or rsR′ right precordial QRS complexes are identified with both right ventricular preponderance and incomplete right bundle-branch block, the broad left ventricular S wave of the incomplete right bundle-branch block aids in differentiating them on the conventional electrocardiogram. A tall predominant late R wave in aVR, arising from the R′ component of the rR′ potential of the hypertrophied right ventricular outflow tract, serves to denote an advanced degree of right ventricular hypertrophy, whether the classic pattern of right ventricular preponderance or an incomplete right bundle-branch block associated with right ventricular preponderance presents on the routine electrocardiogram. The apparent slurred or pure R waves, the Rs and qR right precordial QRS complexes, seen with instances of right ventricular preponderance or incomplete right bundle-branch block, are actually rR′ or rsR′ complexes. Additional exploratory right anterior chest leads will invariably bring out the initial septal r wave component. The rR′ or rsR′ potentials of right ventricular preponderance or right bundle-branch block arise from a relatively selective site of the high medial outflow tract of the right ventricle.