Association of Electrocardiographic Parameters with Left Ventricular Ejection Fraction in Patients with Left Bundle Branch Block and Permanent Cardiac Pacemakers

Background: Patients with right ventricular (RV) pacing from permanent cardiac pacemakers have electrocardiographic (ECG) patterns similar to those with left bundle branch block (LBBB). Although ECG criteria for LBBB in patients with reduced left ventricular ejection fraction (LVEF) are well established, these criteria have not been clarified for patients with RV pacing. Methods: In this retrospective observational study, between January 2016 and August 2025, 193 patients were diagnosed with LBBB, of whom 118 were included. During the same period, 475 patients with permanent cardiac pacemakers were identified, of whom 178 were eligible for the study. Results: In the LBBB group (male/female, 55/63; mean [SD] age, 67 [12] years), 57% of patients had LV systolic dysfunction (LVEF <50%), whereas in the pacemaker group (male/female, 93/85; mean [SD] age, 72 [11] years), only 26% had an LVEF less than 50%. Mean QRS duration was longer in patients with reduced LVEF than in those with normal LV systolic function (155 [13] vs 147 [12] milliseconds, respectively; P=.034). Conclusion: Although the ECG pattern associated with RV pacing from a permanent cardiac pacemaker resembles that of LBBB, its association with LV dysfunction differs. In patients with LBBB, longer QRS duration and the presence of q waves in leads I, aVL, V5, and V6 were associated with reduced LVEF, whereas in patients with RV pacing, a broad, notched, or slurred R wave in leads I, aVL, V5, and V6 was associated with reduced LVEF