Acute hemodynamic improvement but worsening myocardial mechanics with RV pacing in a patient with intrinsic left bundle branch block: a case report

Abstract Background Right ventricular (RV) pacing may impair left ventricular (LV) function through electromechanical dyssynchrony. Although physiologic pacing is recommended when high ventricular pacing burden is anticipated, many elderly patients with legacy dual-chamber pacemakers may not be good candidates for pacemaker upgrades and undergo programming optimization instead. The acute effects of transitioning from intrinsic left bundle branch block (LBBB) to RV-paced activation remain incompletely understood. Case summary An 85-year-old man with dilated cardiomyopathy, intrinsic LBBB, progressive renal dysfunction, and dual-chamber pacemaker with long programmed AV delay and <1% RV pacing presented with reduced LVEF and pedal edema. ECG showed left bundle branch block with QRS width of 166 ms. Baseline echocardiography showed marked AV dyssynchrony with shortened mitral filling time (30% of R–R interval) and impaired global longitudinal strain (GLS −11.0%) and LVEF of 37% by biplane Simpson’s. AV delay (120 ms) optimization induced RV capture and improved filling time (50% of R–R interval), ventricular velocity–time integrals, and interventricular delay. Despite favorable hemodynamic changes, GLS worsened (−8.3% with increased apical rocking, indicating deteriorated myocardial mechanics. Discussion Improved diastolic filling, stroke volume and interventricular delay during RV pacing may occur at the expense of myocardial efficiency. Strain imaging provided incremental insight beyond conventional Doppler indices and may assist pacing optimization in patients with intrinsic conduction disease. Key words: left bundle branch block, right ventricular pacing, atrioventricular delay optimization, global longitudinal strain, ventricular dyssynchrony, echo Doppler, case report