Redefining Left Bundle Branch Block from High-density Electroanatomical Mapping

Background The current ECG criteria for diagnosing left bundle branch block (LBBB) still cannot fully differentiate between true and false blocks. The absence or presence of an LBBB is key in improving the response rate of clinical cardiac resynchronization therapy (CRT). Methods We hypothesized that the notch width of the QRS complex in the lateral leads (I, avL, V5, V6) on the LBBB-like ECG could further confirm the diagnosis of true complete left bundle branch block (t-LBBB). We performed high-density, three-dimensional electroanatomical mapping in the cardiac chambers of 37 patients scheduled to undergo CRT and whose preoperative electrocardiograms met the ACC/AHA/HRS guidelines for the diagnosis of complete LBBB. If the left bundle branch potential could be mapped from the bottom of the heart to the apex on the left ventricular septum, it was defined as a false complete left bundle branch block (f-LBBB). Otherwise, it was categorized as a t-LBBB. We compared the clinical characteristics, the real-time correspondence between the spread of ventricular electrical excitation and the QRS wave, the QRS notch width of the lateral leads (I, avL, V5, V6), and the notch width/left ventricular end-diastolic diameter (Nw/LVd) ratio between the two groups. Through ROC correlation analysis of Nw/LVd and t-LBBB, the sensitivity, specificity, and cut-off value of Nw/LVd diagnostic authenticity were obtained. Results Twenty-five patients were recruited to the t-LBBB group, and 12 to the f-LBBB group. In the t-LBBB group, the first peak of the QRS notch corresponded to the depolarization of the right ventricle and septum, the trough corresponded to the depolarization of the left ventricle across the left ventricle, and the second peak corresponded to the depolarization of the left ventricular free wall. In the f-LBBB group, the first peak corresponded to the depolarization of the right ventricle and most of the left ventricle, the second peak corresponded to the depolarization of the latest, locally-activated myocardium of the left ventricle, and the trough was caused by the off-peak delayed activation of the left ventricle. The QRS notch width (45.2 ± 12.3 ms vs. 52.5 ± 9.2 ms, P <0.05) and the Nw/LVd (0.65 ± 0.19 ms/mm vs. 0.81 ± 0.17 ms/mm, P <0.05) were compared between the two groups. Through ROC correlation analysis, the sensitivity (88%), specificity (58%), and cut-off value (0.56) for Nw/LVd diagnosis of t-LBBB was obtained. Conculuion Using the current diagnostic criteria of LBBB, increasing the Nw/LVd value can diagnose LBBB more effectively.