Lead V8 as a simple non-invasive tool for assessing lv activation delay across different conduction abnormalities

Background Cardiac resynchronization therapy (CRT) improves outcomes in heart failure (HF) patients with electrical dyssynchrony, typically characterized by a wide QRS complex of left bundle branch block (LBBB) or atypical right bundle branch block (RBBB) morphology. Delayed activation of the LV posterolateral wall, identified by the QLV measurement, has been shown to predict CRT response but necessitates the presence of a lead within the coronary sinus. Purpose To evaluate whether the surface electrode in the V8 position can non-invasively identify delayed activation of the LV posterolateral wall in patients undergoing CRT implantation, thereby hypothetically identifying patients most likely to benefit from CRT. Methods Consecutive patients with wide QRS undergoing CRT-implantation or -replacement at two tertiary hospitals were included. Standard 12-lead ECGs were obtained with the V5 electrode placed at the V8 position at the inferior aspect of the left scapula. The local electrical activation time at V8 was defined as the interval from QRS onset to the steepest negative downslope of the QRS complex, a marker of local tissue activation: negative derivative activation time, (NDAT-V8) (Figure 1). The NDAT-V8 and NDAT-V6 were compared with the invasively measured QLV interval recorded from the LV lead. Correlation and agreement were assessed using linear regression and Bland-Altman analysis. Results Sixty-nine patients were included (35 Strauss-criteria LBBB, 8 intraventricular conduction delay (IVCD) and 26 RBBB). NDAT-V8 showed a strong correlation with the QLV interval (r=0.927), whereas the NDAT-V6 correlation was weaker (r=0.614). The correlation between NDAT-V8 and QLV interval was consistent across all conduction abnormalities (LBBB, IVCD and RBBB). Bland-Altman analyses demonstrated good agreement between NDAT-V8 and QLV interval with a small mean bias (3±11ms), whereas NDAT-V6 showed a larger mean bias (21±24ms). Moreover, NDAT-V8 distinguished IVCD patients with marked posterolateral wall delay, identified Strauss-criteria LBBB patients lacking significant delay, and demonstrated superior discrimination of posterolateral wall delay compared with both atypical and typical RBBB cohorts. Conclusion NDAT-V8 provides a non-invasive measure of LV posterolateral electrical delay and strongly correlates with the invasively measured QLV interval across different conduction abnormalities, outperforming lead V6. The NDAT-V8 may be easily implemented in clinical practice and guide decision-making for CRT in HF patients with wide QRS.