756-5 Hypertrophic Cardiomyopathy and Dual Chamber Pacing: Impact of Atrio-Ventricular Delay on Obstruction Assessed by Doppler Echocardiography

Obstruction in hypertrophic cardiomyopathy (HCM) benefits from atrioventricular (AV) pacing with apical preexcitation To assess the impact of the duration of AV delay on left ventricular outflow tract gradient (LVOTG), we studied 8 patients with HCM and resting LVOTGs, implanted by permanent AV pacemakers. LVOTG was measured by continuous Doppler echocardiography before implantation (B) and after, with the AV delay set at 120, 100, and 80 ms: AV delay was randomly changed every day and LVOTG was measured after 24 hours. LVOTG decreased significantly with shorter AV delays (Figure). All patients had significant LVOTGs (i.e >30mmHg) at B, 6 at AV delay of 120ms, 3 at AV delay of 100ms, and 4 at AV delay of 80ms (p<005 at X2for the group); moreover, the incidence of significant LVOTG was significantly less with AV delays of 100 (p<0.01) and 80 ms (p<0.05) than in B. Furthermore, minimum LVOTG was obtained with AV delay of 100 and 80 ms in 4 patients each.Conclusions1) AV pacing reduces LVOTG in HCM; 2) the decrease in LVOTG is greater with shorter AV delays; 3) significant LVOTGs are abolished by short AV delays; 4) optimal AV delay seems to be between 80 and 100ms