Optimized pacing mode for hypertrophic cardiomyopathy: Impact of ECG fusion during pacing

Background Electrocardiographic (ECG) fusion with intrinsic QRS could reduce the benefit of atrial synchronous biventricular pacing (AS-BiVP) in patients with hypertrophic obstructive cardiomyopathy (HOCM). Objectives The purpose of this study was to assess the benefit of AS-BiVP and the influence of ECG fusion for reduction of left ventricular outflow tract gradient (LVOTG) in these patients. Methods Twenty-one symptomatic HOCM patients with severe LVOTG were included. Twelve patients were evaluated retrospectively for the prevalence of fusion and its influence on outcomes after AS-BiVP. Eleven patients (2 of the first population were also evaluated retrospectively) were prospectively included to evaluate the benefit of performing atrioventricular node ablation (AVNA) to achieve full ventricular capture if fusion was present during AS-BiVP. Results Seven of the first 12 patients (58%) had ECG fusion. After 54 ± 24 months of AS-BiVP, the presence of fusion was associated with lower values for reduction of resting, dynamic LVOTG and New York Heart Association (NYHA) class. In the prospectively evaluated patients, after 12 months of follow-up, resting LVOTG decreased from 98 ± 39 to 39 ± 24 mm Hg ( P = .008); dynamic LVOTG decreased from 112 ± 38 to 60 ± 24 mm Hg ( P = .013); NYHA class decreased from 2.8 ± 0.4 to 1.7 ± 0.6 ( P = .014); endurance time during constant work rate cycling exercise (80% of peak oxygen consumption) increased from 399 ± 148 to 691 ± 249 seconds ( P = .046); quality of life improved from 46 ± 22 to 22 ± 20 points ( P = .02); and brain natriuretic peptide levels decreased from 318 ± 238 to 152 ± 118 pg/mL ( P = .09). Eight of the 11 prospectively evaluated patients (73%) needed AVNA, which further decreased LVOTG from 108 ± 40 mm Hg at baseline to 89 ± 29 mm Hg after BiVP to 54 ± 22 mm Hg after AVNA ( P = .003). Conclusion As-BiVP that ensures no ECG fusion, by means of AVNA when needed, appears to be the optimal pacing mode in HOCM patients.