Introduction A significant minority of patients do not experience clinical benefit following cardiac resynchronisation therapy (CRT). Haemodynamically-guided adjustment of the intervals between chambers paced (“optimisation” of atrio-ventricular (AV) and left-right ventricular (VV) delays) may be undertaken to improve the chance of response to CRT. However, data to support this approach as standard management are lacking and many institutions programme CRT devices to deliver “out-of-the-box” intervals, only undertaking optimisation when clinical response is lacking. We sought to determine how often the “out-of-the-box” settings are optimal or acceptable and how often CRT optimisation results in significant alteration of the pre-programmed pacing intervals.

Methods Data were collected from 180 consecutive patients who underwent CRT followed by optimisation within 24 h. Optimisation was performed with serial adjustment of AV and VV intervals. Haemodynamic assessment was undertaken using either echocardiography or Non-Invasive Cardiac Output Measurement. The optimal pacing intervals were considered to be those which resulted in greatest acute augmentation of cardiac output and the device was programmed accordingly. The final settings were compared with the pre-programmed settings for that device and the difference (AV or VV Adjustment) derived, taking into account the preset paced or sensed AV delay. An AV or VV Adjustment of more than 40 ms was considered to be clinically significant. Data are presented as mean (SD).

Results Optimal AV delay ranged from 60 to 200 ms (mean 124 ms (30)), VV delay ranged from 0 to 100 ms (mean 23 ms (19)). With the pre-set pacing parameters, cardiac output was acutely augmented by 13.1 (34)%. Optimised CRT produced further improvement of cardiac output, to 24.9 (32)% augmentation. “Out-of-the-box” settings were found to be optimal in 11 (6.1%), or requiring only minor alteration in 120 (66.7%). A clinically significant alteration in AV delay was made in 40 (22.2%), in VV delay in 12 (6.7%) or in either parameter in 49 (27.2%).

Conclusions Significant adjustment of AV or VV delay is required in over a quarter of patients receiving CRT. Optimisation of pacing intervals provides augmentation of cardiac output over and above the “out-of-the-box” settings. The findings suggest that optimisation is an important component of resynchronisation therapy.