Nineteen patients with symptomatic nHCM and normal LV systolic function were prospectively enrolled. Inclusion criteria included an E/e’ ≥15 and an indication for ICD implantation. A Doppler echocardiographic study was performed during sinus rhythm and atrial synchronous ventricular pacing at various atrioventricular(AV) intervals. Pacing was performed at three right ventricular sites : RV apex(RVA), RV mid-septum(RVS), and RV outflow tract(RVO). The site and sensed AV delay(SAD) at which optimal diastolic filling occurred was chosen based on diastolic filling period and E/e’. During ICD implantation, the RV lead was implanted at the site selected by the pacing study. Devices were programmed in DDD mode at the optimal SAD. During follow up, diastolic function and functional capacity (NYHA Class, 6 Minute Walk Distance(6MWD)) were assessed.
Among the 19 patients (age 47.6±7.8 yrs, males 73.9%, ESC SCD Risk 3.9±0.4%), the baseline PR interval, E/A and E/e’ were 178.2±19.5ms, 2.4±0.5, and 17.2±2.3, respectively. There was an improvement in diastolic function (E/A, E/e’) in 16 patients (responders) when pacing from the RVA(1.5±0.3,p<0.001;12.9±3.1,p<0.001) compared to the RVS (2.2±0.5,16.5±2.4)and RVO (2.2±0.4,16.8±2.1). There was no improvement in diastolic function in the three other patients (non-responders). In responders, optimal diastolic filling occurred at an AV delay of 130-160ms during RVA. At shorter and longer SAD, there was a worsening of E/e’(Fig). Baseline RBBB(25% vs. 0%, p=0.212) and lower LGE (12.4% vs. 23.2%, p=0.004) were more common among responders. During follow up (9.8±1.8 months), ventricular pacing was 98.3±1.4%. Compared to baseline, there was an improvement (Δ) in diastolic function (E/A -1.0±0.3, E/e’ -4.1±0.5), NT proBNP (-51.4±13.2pg/ml), and functional capacity (NYHA -1.4±0.3, 6MWD -51.2±6.7 m). There was no change in LVEF during follow up.