Spread of the epicardial excitation in right bundle branch block pattern.

Electrophysiologic mapping was performed on 29 dogs and 35 patients to investigate the ventricular excitation sequence of normal hearts and various cardiac lesions exhibiting the electrocardiographic pattern of right bundle branch block (RBBB). The activation times of epicardial surface were referenced to the onset of left ventricular cavity potential or QRS wave of lead II ECG. Epicardial activation sequence was represented by isochrones. 1. In normal hearts, the earliest epicardial breakthrough occurred at the mid-anterior paraseptal area in the right ventricle and the activation spread in a circular fashion. In the left ventricle, the epicardial activation occurred at three areas and then spread to the posterobasal area. The epicardial activation sequence was a good representation of the ventricular excitation. 2. In RBBB due to trauma to the main right bundle branch, the right ventricular activation showed marked delay and the characteristic V-shaped pattern. 3. Following vertical ventriculotomy, the right ventricular epicardial activation showed marked delay at sites distal to the incision but no significant delay proximal to it. Regarding postoperative RBBB, central right bundle branch injury was able to be differentiated from distal Purkinje injury due to right ventriculotomy by means of epicardial mapping. 4. In left ventricular pacing, the activation spread in a circular fashion with the prolonged right ventricular activation. 5. In ostium secundum defect, the right ventricular epicardial activation sequence showed various patterns of activation delay resulting from right ventricular hypertrophy. In ostium primum defect, the earliest epicardial activation was found in the left posterior paraseptal area, and the right ventricular activation showed a normal pattern with some delay. Epicardial mapping has been the precise representation of ventricular excitation by direct measurement of cardiac potentials. Cardiac lesions exhibiting the electrocardiographic RBBB pattern provided various patterns of the right ventricular activation delay according to the geneses of RBBB.