Cardiac output response to changes of the atrioventricular delay in different body positions and during exercise in patients receiving cardiac resynchronization therapy

The aim of this study was to study the haemodynamic effect of atrioventricular delay (AVD) modifications within a narrow range in different body positions and during exercise in patients receiving cardiac resynchronization therapy (CRT). The previously optimized AVD was shortened and prolonged by 40 ms in 27 CRT patients and 9 controls without heart failure. Cardiac output (CO) was measured by inert gas rebreathing (Innocor) as the average over different body positions (left-lateral, supine, sitting, standing, and exercise). In eight CRT patients with an implantable haemodynamic monitor, the estimated pulmonary artery diastolic pressure (ePAD) was analysed. The magnitude of CO response to AVD changes was greater in CRT patients than in controls (0.25 vs. 0.20 L/min, P < 0.05), varied substantially between individuals (range: 0.12-0.56 L/min), and correlated with left atrial size (r = 0.61, P < 0.001). On average, AVD shortening decreased CO slightly (0.07 +/- 0.17 L/min) and increased ePAD (1.1 +/- 0.8 mmHg, both P < 0.05), whereas prolongation had no significant effect. The haemodynamic response to AVD modifications within a narrow range is larger in CRT patients than in normal controls and varies substantially between individuals. These findings suggest that optimal AVD tuning is clinically important in selected patients.