What does this research mean for the field?

Ultra-high-frequency ECG identifies true left bundle branch block with 100% sensitivity and 95% specificity, outperforming Strauss criteria in heart failure patients. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.CHALLENGES_CONSENSUS.

What question did this study set out to answer?

The study aims to compare the effectiveness of UHF-ECG against Strauss criteria in diagnosing true left bundle branch block (trueLBBB) in patients indicated for cardiac resynchronization therapy.

February 8, 2026

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

Key Result

UHF-ECG e-DYS >60 ms identified trueLBBB with 100% sensitivity and 95% specificity, outperforming Strauss criteria (84% sensitivity, 55% specificity) in CRT candidates.

Key Points

The study aims to compare the effectiveness of UHF-ECG against Strauss criteria in diagnosing true left bundle branch block (trueLBBB) in patients indicated for cardiac resynchronization therapy.
Conducted with heart failure patients needing cardiac resynchronization therapy.
UHF-ECG recordings were made during spontaneous rhythm and analyzed for ventricular activation.
Invasive mapping assessed left septal activation to establish a gold standard diagnosis.
QRS duration and left ventricular ejection fraction were monitored before and after CRT.
Invasive mapping identified trueLBBB in 38 out of 58 patients, while 20 had IVCD.
UHF-ECG metrics, such as e-DYS, outperformed Strauss criteria in distinguishing trueLBBB from IVCD with an area under the curve of 0.97 vs. 0.70.
The optimal e-DYS cutoff value of > 60 ms achieved 100% sensitivity and 95% specificity for trueLBBB diagnosis.
Patients with trueLBBB demonstrated a statistically favorable increase in LVEF post-CRT compared to those with IVCD.

Structured PICO

Does Ultra-high-frequency ECG (UHF-ECG) improve the diagnosis of true left bundle branch block compared to Strauss criteria in patients indicated for CRT?

Population

58 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. 41 males, 24 ischemic cardiomyopathies, mean LVEF 28 ± 8%, mean QRS duration 169 ± 17 ms.

Intervention

Ultra-high-frequency ECG (UHF-ECG) based dyssynchrony index (e-DYS)

Comparator

Strauss criteria for LBBB (evaluated blindly by an experienced electrophysiologist)

Outcome

Diagnostic accuracy (AUC, sensitivity, specificity) for differentiating true LBBB from intraventricular conduction delay (IVCD) using invasive left septal mapping as the gold standardsurrogate

UHF-ECG significantly outperforms Strauss criteria in diagnosing true LBBB, offering a highly accurate, non-invasive tool to potentially optimize patient selection for CRT.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

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.

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