Right ventricular papillary muscle electrography. Analysis of the site of surgically induced right bundle branch...

It is believed that the prognosis of patients with surgically induced right bundle branch block (RBBB) related to correction of congenital heart diseases varies according to the site of block. Thus, it is necessary to differentiate the proximal type from the distal type of RBBB. The main purpose of this study was to develop a practical and precise method for the determination of the site of block. The right ventricular papillary muscle activation time (V-PM) was measured 1 or 2 weeks after surgery by means of a temporary pacing electrode placed on the epicardial surface of the right ventricular anterior papillary muscle. This technique is referred to as "right ventricular papillary muscle electrography (PME)". The presence of a proximal RBBB is diagnosed by the finding of a prolongation of V-PM. The unique characteristics of this newly developed PME are as follows: 1) the appropriate site of electrode placement is selected anatomically during surgery by observations of local systolic concavity, and 2) with a unipolar lead, the local activation time can be measured with sufficient accuracy. The average V-PM was 21.0 +/- 6.3 msec (+/- S.D.) in 64 patients without RBBB and 51.1 +/- 7.5 msec in 13 patients with confirmed proximal RBBB in whom distal RBBB had been excluded in view of the surgical procedures that had been performed. As a result, the criterion for the diagnosis of proximal RBBB was established as a V-PM of longer than or equal to 35 msec. According to this criterion, the incidence of proximal RBBB found in surgically repaired tetralogy of Fallot (TF), membranous ventricular septal defect (VSD (2] and supracristal ventricular septal defect (VSD (1] were 46% (11/24), 33% (15/45) and 11% (2/18), respectively. Distal RBBB was observed only in TF, where the incidence was 17% (4/24).