Energy Dissipation in Resynchronization Therapy: Impact of Atrioventricular Delay

Optimal atrioventricular delay (AVD) achieves maximum cardiac output in patients undergoing cardiac resynchronization therapy (CRT). Nonoptimal AVD decreases left ventricular (LV) end-diastolic volume and causes loss of flow momentum prior to LV ejection. We investigated the potential role of energy dissipation (ED) in these changes in cardiac output through the study of intraventricular flow. We hypothesized that short and long AVD increases ED when compared with optimal AVD by altering the physiologic flow mechanics that preserve kinetic energy in the LV. Forty-four patients under CRT underwent echocardiographic LV flow analysis under optimal, short, and long AVD. LV ED and vortical flow in the inflow-outflow tract were studied during the end-diastolic and early systolic period, and paired comparisons were obtained between optimal and nonoptimal values. ED in the left ventricle was minimal in optimal AVD and significantly increased with nonoptimal values (79.1 ± 27.5 J/m·sec in optimal AVD vs 96.5 ± 34.7 J/m·sec in short AVD; n = 18, P = .006; 123.3 ± 67.6 J/m·sec in optimal AVD vs 292.4 ± 202.5 J/m·sec in long AVD; P