Validation of left bundle branch pacing criteria: are we really doing it well?

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Left bundle branch (LBB) area pacing (LBBAP) has been widely adopted for an increasing number of antibradycardia and CRT procedures worldwide. Two different types of capture have been described during LBBAP: left ventricular septal myocardial capture (LVSP) or direct LBB capture (LBBP). Nevertheless, electrocardiographic diagnosis of LBBAP remains one of the challenges of modern conduction system pacing because there is a big overlap between both electrocardiographic morphologies. Among the new ECG-based criteria, the R wave peak time in lead V6 (V6-RWPT) and V6-V1 interpeak interval seem to be the most practical ones and have been widely adopted. However, their performance have never been validated in an external population. PURPOSE: We aim to validate the reported criteria V6-RWTP and the V6-V1 interpeak interval in an our population. METHODS: Single-center study involving all consecutive patients who received LBBAP. LBBP was defined according to the presence of QRS morphology transition criteria during decremental pacing. The performance of binary decision rules was described using sensitivity (SN) and specificity (SP). The performance of V6-RWPT and V6-V1 interpeak interval in discriminating between LBBP and LVSP was assessed using the receiver operating characteristic (ROC) curve. RESULTS: A total of 188 patients with intended LBBAP were screened. Successful LBBAP was achieved in 174 (92.5%). Only 71 patients with confirmed LBBP by the QRS morphology transition criteria were included to analyse the performance of V6-RWPT and V6-V1 interpeak interval. The V6-RWPT was 75.7±9.6 ms for LBBP tracings and 94.4±10.1 ms for LVS tracings (p<0.001), and V6-V1 interpeak interval was 41.9±12.1 ms for LBB capture and 25.6±8.7 ms for LVS capture (p<0.001). The average difference in V6-RWPT for the transition from LBBP to LVSP was 16.5±5.2 ms. The ROC curves for the differential diagnosis of LBBP and LVS capture (Figure 1, which compares them with those from the original articles) showed a diagnostically optimal V6-RWPT value for the differentiation of LBBP and LVS capture of 83 ms (SN of 80.3% and SP of 91.1%). A SP of 100% for the diagnosis of LBBP was achieved with a cut-off value of 79.5 ms (SN 69.0%). For the V6-V1 interpeak interval, the diagnostically optimal value for the differentiation of LBBP was 33.5 ms (SN of 77.1% and SP of 84.6%). A SP of 100% for the diagnosis of LBBP was obtained with a cut-off value >44 ms (SN 37.1%) (Figure 2). CONCLUSIONS: Our study comprises an external validation of the proposed ECG-based criteria for LBB capture. We found a nearly absolute concordance with the originally reported V6-RWPT and V6-V1 interpeak interval cut-off values. Only the V6-RWPT cut-off value with 100% specificity differed from the initially reported in the general cohort. Thus, the V6-RWPT and V6-V1 interpeak interval criteria seem to be consistent and emerge as practical and easily reproducible surrogates of the QRS transition criteria. [Figure: see text] [Figure: see text]