Left ventricle lead placement in areas with a higher CART score, indicating late mechanical activation, is associated with greater response in cardiac resynchronisation therapy patients

Left ventricular (LV) lead position is an important determinant for response to cardiac resynchronisation therapy (CRT). However, optimising LV lead position remains challenging due to variations in myocardial activation patterns and scar tissue between patients. Therefore, an image guidance platform was developed that can detect scar tissue and determine mechanical activation of the LV based on MRI images for the individual patient. This led to the formulation of a novel index, the CART score, which quantifies mechanical activation by combining time-to-peak strain and peak strain amplitude in individual myocardial segments.

This study tested the hypothesis that higher CART scores, indicating later mechanical activation, are associated with greater reductions in left ventricular end-systolic volume (LVESV) following CRT.

This sub-analysis utilised data from the ADVISE-CRT III randomised trial, where patients received CRT implantation using either on-screen image guidance to mechanically late-activated segments or conventional implantation. On a specially developed cloud-based platform, MRI feature tracking was used to determine mechanical activation in a 36-segment model of the LV. Septal segments were excluded from the analysis. The CART score (0–100) for the LV lead-implanted segment was calculated by summing the relative time to peak strain (0–50) and peak strain amplitude (0–50) for each individual patient. Scar burden, the percentage of the area of the lead-implanted segment affected by scar tissue, and scar transmurality, the depth of the scar tissue across the LV wall of the lead-implanted segment, were also measured. LVESV was measured at baseline and after six months using echocardiography.

A significant positive correlation was observed between the CART score of the LV lead-implanted segment and LVESV reduction after six months of CRT (B=0.310, 95% confidence interval=0.088–0.533, p = 0.007), indicating that each unit increase in CART score was associated with a 0.31% mean reduction in LVESV. Scarred segments exhibited significantly lower peak strain amplitude compared to non-scarred segments (20.5±18.4% vs. 33.05±24.1%, p<0.001). Additionally, both scar burden (B=-0.114, p<0.001) and scar transmurality (B=-0.202, p<0.001) were associated with reduced strain amplitude, reflecting impaired contractile function in scarred tissue.

Selecting myocardial segments with higher CART scores for LV lead implantation may enhance LVESV reduction. The lower strain amplitude observed in scarred segments underscores the importance of avoiding scar tissue.