Abstract 16837: Increased Heart Rate Aggravates Diastolic Dysfunction in Left Bundle Branch Block

Introduction: In left bundle branch block (LBBB) left ventricular (LV) pressure decay is slowed due to dyssynchronous relaxation. At low heart rates (HR) this may not substantially affect diastolic pressure as there is still sufficient time for complete relaxation and filling. Hypothesis: The slowed pressure decay and abbreviated diastole in LBBB will increase LV filling pressure and increase diastolic stiffness due to incomplete relaxation at high HR. Methods: In 7 canines we performed atrial pacing at high (166± 17 (SD)) and low (120± 1 bpm) HR before and after induction of LBBB. LV volume and pressure and pericardial pressure were measured. Mean diastolic pressure was calculated as average LV pressure between mitral valve opening and closure. The time constant of LV pressure decay ( tau ), and minimum dP/dt were calculated. LV diastolic stiffness was assessed using end diastolic transmural LV pressure-volume (PV) relations. Results: Tau was increased, minimum dP/dt lower, and duration of diastole shorter at both HRs in LBBB compared to baseline (p Conclusions: Increased HR in LBBB increased diastolic stiffness and increased LV diastolic pressure. This mechanism may lead to dyspnoea and exercise intolerance in LBBB patients.