Ultra-high-frequency ECG outperforms strauss criteria for diagnosing true left bundle branch block in candidates of cardiac resynchronization therapy

Abstract Background We still lack clinically suitable methods to distinguish between the complete block within fibers of the left bundle branch (trueLBBB) and the more peripheral conduction disorder (intraventricular conduction delay, IVCD). Ultra-high-frequency ECG (UHF-ECG) displays ventricular activation from standard V1-V8 leads in less than 5 minutes. Objective To compare the performance of UHF-ECG and Strauss criteria in differentiating trueLBBB from IVCD during the spontaneous rhythm in patients with heart failure and a wide QRS complex. Methods Patients indicated for cardiac resynchronization therapy (CRT) and treated by biventricular pacing (BVP) or left bundle branch area pacing (LBBAP), having QRS complex of non-RBBB morphology lasting ≥ 130 ms, were recruited. Invasive mapping of the left septal activation using a multipolar catheter was considered a gold-standard method for diagnosing trueLBBB or IVCD. UHF-ECG recording was obtained during spontaneous rhythm, and the UHF-ECG-based dyssynchrony index (e-DYS) was defined as the interval between the first and last ventricular activation assessed from the V1-V8 chest leads. An experienced electrophysiologist blindly evaluated the presence of LBBB by Strauss criteria. Left ventricular ejection fraction (LVEF) was assessed by echocardiography before and 6 months after the CRT. Results Invasive left septal mapping in 58 patients (41 males; 24 ischemic cardiomyopathies; LVEF: 28 ± 8%; QRS duration: 169 ± 17 ms) identified trueLBBB in 38 patients and IVCD in 20. Patients with trueLBBB compared to IVCD had longer QRS duration (177 ± 15 vs. 153 ± 10 ms; P = 0.01) and spontaneous e-DYS (91 ± 20 vs. 40 ± 18 ms; P 0.001). Based on ROC analysis, the area under the curve for e-DYS and Strauss-based LBBB to discriminate trueLBBB from IVCD was 0.97 and 0.70 (P 0.001). The optimal cut-off value of e-DYS 60 ms identified trueLBBB with a sensitivity of 100% and specificity of 95%. Strauss criteria had sensitivity and specificity of 84% and 55%. Patients with trueLBBB experienced an improvement in LVEF of 15 ± 8% at six months after CRT compared to 6 ± 15% in patients with IVCD (P = 0.06). Conclusion UHF-ECG effectively distinguishes trueLBBB from IVCD, demonstrating greater accuracy than the Strauss criteria, which may have practical implications for CRT. Patients with trueLBBB tend to respond more favourably to CRT than patients with IVCD.