Implementation of lead V8 as a simple non-invasive tool to improve patient selection in cardiac resynchronization therapy and guide left ventricular lead placement

Aims Cardiac resynchronization therapy (CRT) improves outcomes in heart failure patients with electrical dyssynchrony. The QLV interval, a marker of delayed left ventricular (LV) activation, independently predicts CRT response. This study aimed to determine whether activation time measured in surface ECG lead V8 reflects posterolateral LV delay by correlating with the QLV interval during biventricular (BiV) CRT implantation. Methods and results Consecutive patients with wide QRS (non-RBBB) undergoing BiV-CRT or generator change were prospectively enrolled. Surface ECGs were recorded with the V5 electrode repositioned to the V8 location. Local wavefront activation was determined using the steepest negative downslope of the precordial leads, referred to as the negative derivative activation time (NDAT). The LV lead was connected to the EP recording system, and NDAT and QLV measurements were obtained. Forty-three patients were included. The NDAT in V8 strongly correlated with the QLV interval (r = 0.895; mean difference 1 ± 11 ms) across both LBBB and IVCD patterns. In contrast, NDAT in V6 showed weaker correlation (r = 0.592; mean difference 21 ± 24 ms). During LV-only pacing, a QS morphology in V8 consistently indicated posterolateral lead placement. More anterior/apical lead positions showed larger QLV–negative derivative activation time (NDAT) V8 differences and non-QS morphologies, indicating suboptimal positioning. Conclusion NDAT in lead V8 is a non-invasive marker of delayed activation in the posterolateral LV, outperforming V6 in identifying late activation. When combined with LV-paced QRS morphology, V8 facilitates accurate lead localization without additional tools. These findings may support the use of lead V8 to refine patient selection and optimize CRT delivery.