Intraventricular Conduction in Man Studied with an Endocardial Electrode Catheter Mapping Technique Patients with Normal QRS and Right Bundle Branch Block

The sequence of intraventricular conduction has been studied in a total of 60 patients, 38 of whom had normal QRS morphology and 37 of whom had right bundle branch block (RBBB) either present con-tinuously or produced as functional aberrant RBBB by the introduction of atrial premature depolarizations or by rapid atrial pacing. Activation times were measured with intracardiac electrode catheters positioned at the right ventricular inflow tract (RVIT), right ventricular apex (RVA), right ventricular outflow tract (RVOT), left ventricular apex (LVA) and left ventricular outflow tract (LVOT). The activation after begin-ning of QRS in milliseconds ± 1 SD and the number of patients studied at each location were: RVIT nor-mal 23 ± 13 (15 patients); RVIT-RBBB 49 ± 16 (15 patients); RVA normal 18 ± 9 (28 patients); RVA-RBBB 54 ± 16 (30 patients); RVOT- normal 40 ± 10 (28 patients); RVOT-RBBB 78 ± 21 (30 patients); LVA normal 9 ± 9 (18 patients); LVA-RBBB 6 ± 10 (10 patients); LVOT- normal 45 ± 13 (10 patients); LVOT-RBBB 32 + 9 (7 patients). Significant differences observed were: RVA-normal versus RVA-RBBB P < 0.001; RVOT-normal versus RVOT-RBBB P < 0.001; RVA-normal versus LVA-normal P < 0.005; LVA-normal versus LVA-RBBB NS, LVOT-normal versus LVOT-RBBB P < 0.05. The LVOT change was unexpected and suggests changes in left ventricular depolarization may occur when right bun-dle branch block develops. In patients with RBBB the activation of the RVA (r = 0.82) and of the RVO