Left bundle branch block disturbs left anterior descending coronary artery flow: study using transthoracic Doppler echocardiography.

BACKGROUND: This study was performed to evaluate the influence of left bundle branch block (LBBB) on left anterior descending coronary artery (LAD) flow.

METHODS: We divided 89 subjects (34 males and 55 females, mean age 64 +/- 14 years) into an LBBB group (n = 40), a right ventricular (RV) pacing group (n = 26), and a control group (n = 23). All of the patients were examined with surface electrocardiography (ECG) and underwent transthoracic Doppler echocardiography (TTE) to measure QRS duration on the ECG, left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV), and left ventricular end-systolic volume (LVESV). Coronary flow velocity was measured in the distal LAD with TTE, and the percentage of diastolic flow duration (%DD) was expressed as the percentage of diastolic duration of coronary artery flow divided by the R-R interval.

RESULTS: The %DD of the LAD was significantly shorter in the LBBB group (40.4% +/- 12.4%) with LVEF < 50% than in the RV pacing group (60.3% +/- 7.3%) and the control group (59.3% +/- 7.6%) (P < .01 vs the control and RV pacing groups), and it was also significantly shorter in the LBBB group (49.3% +/- 10.5%) with LVEF > or = 50% than in the control and RV pacing groups (P < .01 vs the control and RV pacing groups). In the LBBB group, the %DD of the LAD had a positive correlation with LVEF (P < .05; r = .50), a negative correlation with LVEDV (P < .05; r = -.57), and a negative correlation with QRS duration (P < .05; r = -.41).

CONCLUSIONS: Unlike RV pacing, LBBB itself can disturb the coronary perfusion of the LAD through shortening of the diastolic flow duration. Furthermore, systolic dysfunction potentiates the shortening effect of diastolic flow duration by LBBB. Whether left ventricular systolic dysfunction is the result of the coronary flow disturbance by LBBB or vice versa merits further investigation.