Acute haemodynamic improvement but worsening myocardial mechanics with right ventricular pacing in a patient with intrinsic left bundle branch block: a case report

Right ventricular (RV) pacing may impair left ventricular 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.

An 85-year-old man with dilated cardiomyopathy, intrinsic LBBB, progressive renal dysfunction, and dual-chamber pacemaker with long programmed atrioventricular delay and <1% RV pacing presented with reduced left ventricular ejection fraction (LVEF) and pedal oedema. Electrocardiogram (ECG) showed left bundle branch block (LBBB) with a 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 an LVEF of 37% by biplane Simpson’s. Atrioventricular delay (120 ms) optimization induced RV capture and improved filling time (50% of R–R interval), ventricular velocity–time integrals, and interventricular delay. Despite favourable haemodynamic changes, GLS worsened (−8.3% with increased apical rocking, indicating deteriorated myocardial mechanics).

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.