Left ventricular lead placement in cardiac resynchronization therapy: current data and potential explanations for lack of benefit

This paper reviews the literature on image-guided cardiac resynchronization therapy (CRT) studies. Improved outcome to CRT has been associated with the placement of an LV lead in the latest activated segment free from scar. The majority of randomized clinical trials investigating a guided LV lead implantation did not show superiority over conventional implantation approaches. Several factors may contribute to this paradoxical observation, including inclusion criteria favoring left bundle branch block patients who already respond well to conventional anatomical implantation, differences in activation wavefronts during simultaneous right ventricular and LV pacing, incorrect definition of target regions, and limitations in coronary venous anatomy that prevent access to target regions that are detected by imaging. It is imperative that exclusion of patients lacking access to target regions from these studies would lead to larger benefit of image guided CRT.