V8 assessment may refine lead positioning and patient selection without the need for invasive tools. Cardiac resynchronization therapy (CRT) improves outcomes in heart failure patients with electrical dyssynchrony, but optimal LV lead placement remains a challenge. A study published in EP Europace evaluated whether the negative derivative activation time (NDAT) in surface ECG lead V8 reflects delayed posterolateral LV activation.

In 43 patients with wide QRS (non-RBBB) undergoing CRT or generator replacement, NDAT in V8 was compared with the invasively measured QLV interval. V8 showed a strong correlation with QLV (r = 0.895; mean difference 1 ± 11 ms), while V6 correlated less strongly (r = 0.592; mean difference 21 ± 24 ms). During LV-only pacing, QS morphology in V8 consistently identified posterolateral lead placement, whereas more anterior or apical positions produced larger QLV–NDAT differences and non-QS morphologies.

The findings suggest that V8 ECG, combined with LV-paced QRS morphology, provides a simple and non-invasive way to guide CRT lead positioning. It may also help refine patient selection without the need for additional tools.