Right bundle branch block. Echocardiographic study with special reference to the site of block within the right bundle.

One hundred and fifty-seven patients with complete right bundle branch block (CRBBB) were studied with echocardiography (UCG). In 87 of them, both ECG and UCG of good quality were obtained and analyzed to differentiate the site of the block within the right bundle. Their mean age was 53.2 +/- 17.6 (SD) years, and they consisted of 62 males (50.2 +/- 16.8 years) and 25 females (60.8 +/- 17.3 years), suggesting that males were more susceptible to CRBBB than females, with a male to female ratio of 2.48 among our study group. In a normal control group, the time interval from the initial deflection of the QRS complex of the ECG to mitral valve closure (QMC) was 52.3 +/- 11.6 msec, to tricuspid valve closure (QTC) 87.7 +/- 11.5 msec, to the point of full opening of the pulmonary valve (QPO) 124.5 +/- 13.7 msec, from mitral to tricuspid valve closure (MCTC) 35.5 +/- 11.2 msec, and from tricuspid valve closure to the maximum opening of the pulmonary valve (TCPO) 38.0 +/- 13.8 msec, and in patients with CRBBB, QMC 58.7 +/- 13.2 msec, QTC 95.4 +/- 24.2 msec, QPO 169.1 +/- 24.6 msec, MCTC 36.7 +/- 18.2 msec, and TCPO 73.7 +/- 23.7 msec. Although prolonged QMC and QTC are characteristic features in CRBBB as a whole, CRBBB was divided into 4 groups in this study depending on the difference in MCTC and TCPO: Proximal block with prolonged MCTC, peripheral block with prolonged TCPO, diffuse block with both MCTC and TCPO prolonged, and non-specific block without prolongation of either of the two. The incidences were 11.5% (10 patients) for proximal block, 64.4% (56 patients) for peripheral block, 16.1% (14 patients) for diffuse block, and 8.0% (7 patients) for non-specific block. Thus, conduction disturbance in the peripheral portion of the right bundle branch was observed in 80.5% of our cases, suggesting that peripheral block is much more common than proximal block in adults.