Hemodynamic effects of right and biventricular pacing during exercise in hypertrophic obstructive cardiomyopathy

Abstract Background One third of patients with hypertrophic cardiomyopathy present with dynamic left ventricular outflow tract obstruction (LVOTO), referred to as hypertrophic obstructive cardiomyopathy (HOCM). Symptomatic treatment aims at reducing LVOTO with either medications, invasive septal reduction, or pacing. The importance of pacing site is unclear, and effects of pacing during physical activity have not been investigated. Purpose To determine the effect of right ventricular (RV) and biventricular (BiV) pacing, respectively, on LVOTO and cardiac output (CO) during exercise in patients with HOCM. Methods Patients with symptomatic HOCM, sinus rhythm, and no bundle branch block, scheduled for alcohol septal ablation (ASA), were eligible for inclusion. The day before ASA, we placed temporary pacing leads in the right atrium, the RV apex, and on the left ventricle’s lateral wall via the coronary sinus. LVOTO was assessed by echocardiography, and CO was measured by thermodilution with a pulmonary artery catheter. Patients performed supine cycling for 2 minutes until heart rate (HR) increased ≥20 bpm. We measured LVOTO and CO in sinus rhythm, and during cycling with atrial sensed RV pacing, and atrial sensed BiV pacing. The order of pacing sites was randomized, and the personnel performing echocardiography and CO measurements were blinded to the order of pacing. Results We included six patients (54±15 years) with a mean maximal left ventricular wall thickness of 16.7±1.8 mm. Resting LVOTO was 55.7±30.9 mmHg. The figures show LVOTO and CO in sinus rhythm (HR 85±10 bpm), RV pacing (HR 90±10 bpm), and BiV pacing (HR 91±9 bpm) during supine cycling. The LVOTO declined from 56±34 mmHg in sinus rhythm to 27±12 mmHg and 25±5 mmHg respectively for atrial sensed RV and BiV pacing. CO remained unchanged during sinus rhythm (9.0±1.2 L/min), atrial sensed RV pacing (9.0±1.7 L/min), and BiV pacing (8.9±1.5 L/min). Conclusion In this ongoing study evaluating cardiac pacing in HOCM, preliminary data indicate that both RV and BiV pacing are effective in reducing LVOTO during exercise, without compromising CO.