Available online 13 November 2025, 154155

Author links open overlay panel, AbstractBackground

Early detection of interstitial septal fibrosis remains challenging. We describe a novel ECG pattern that may represent an early marker of fibrotic conduction changes.

Case findings

We evaluated a case demonstrating a triphasic QRS sequence evolving from narrow QRS (88 ms) to complete LBBB-like pattern (160 ms) within three beats. Notable features included: (i) a subtle notch within the initial 20 ms of QRS in leads II, V5 and V6; (ii) disappearance of physiological septal q waves in V5–V6; (iii) multiple notches in leads II, V4-V6; and (iv) late-QRS notching in leads III, aVL, aVF. These findings differed significantly from true LBBB criteria.

Interpretation

This ECG pattern may represent functional conduction alternans within fibrotic myocardium rather than anatomical His-Purkinje block. The presence of preserved rapid early forces, absence of mandatory mid-QRS notching in lateral leads, and reduced lateral voltage suggests myocardial conduction slowing rather than true complete LBBB.

Limitations

This is a single-case observation without confirmatory cardiac MRI or histopathology. Computer modeling referenced was not performed by our group. The proposed mechanism remains hypothetical and requires validation in prospective cohorts.

Introduction

The early detection of interstitial septal fibrosis represents a significant challenge in clinical cardiology. While subtle electrocardiographic changes may precede obvious conduction abnormalities, identifying specific patterns that reliably indicate early fibrotic changes remains an area of active investigation. The case presented by Helseth & Frick [1] provides a unique opportunity to explore potential early markers of septal fibrosis through careful analysis of evolving QRS morphologies.

We herein present a detailed analysis of this intriguing case, proposing that specific subtle ECG changes, a septal notch within the first 20 ms of QRS accompanied by disappearance of physiological septal q waves in leads V5–V6, while QRS duration remains below 120 ms, may represent an early ECG sign of interstitial septal fibrosis. Importantly, this pattern can be observed before QRS duration reaches 120 ms, distinguishing it from true His-Purkinje block [[2], [3], [4], [5], [6]].

Section snippetsCase analysis and quantitative measurements

Patient and ECG Characteristics (Fig. 1).

The 58-year-old woman with hypertension and pulmonary vascular congestion presented with a triphasic QRS sequence showing beat-to-beat variation. Quantitative measurements were obtained from the ECG tracings using standard calibration (25 mm/s, 10 mm/mV):

QRS A (narrow complex):

QRS duration: 88 ms.

Septal notch timing: 12–16 ms from QRS onset.

R-wave amplitude in V5: 0.95 mV.

R-wave amplitude in V6: 1.42 mV.

S-wave amplitude in V1: 1.72 mV.

QRS B

Morphological clues against “true” complete LBBBThe QRS-C complex fulfills duration criteria for complete LBBB but exhibits five key features that argue against an anatomical left-bundle lesion and favor a “myocardial-slowed” mechanism:1.

Relatively stable initial activation vector

The initial 20 ms of QRS B and QRS C are virtually superimposable in all leads except aVL, where the septal q-wave shrinks step-wise from QRS A to B and vanishes in QRS C (Fig. 1). This relatively stable initial activation vector from QRS B to QRS C suggests that the

Conclusion

This case illustrates a novel ECG pattern that may represent an early marker of interstitial septal fibrosis rather than anatomical His-Purkinje disruption. The combination of septal notching, q-wave loss, and cycle-to-cycle widening with attenuated lateral voltage constitutes a potential marker of myocardial conduction slowing. However, this remains a single observation requiring validation in larger cohorts with imaging correlation before clinical application.

CRediT authorship contribution statement

Zhong-Qun Zhan: Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Funding acquisition, Formal analysis, Data curation, Conceptualization. Xin-Yi Yu: Writing – review & editing, Writing – original draft, Software, Formal analysis, Data curation.

Uncited reference

[11]

Declaration of competing interest

None.

Acknowledgment

This work was supported by the Shenzhen Guangming District Program for Introducing High-Level Medical Teams (Grant No. szgmtd2025004).

References (11)

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