Conduction system pacing restores interpretability and diagnostic performance of exercise stress ECG in patients with prior left bundle branch block: a single-centre pilot study

Background/Introduction

In patients with left bundle branch block (LBBB), abnormal septal activation produces baseline ST-segment abnormalities and perfusion artefacts, rendering exercise ECG uninterpretable for ischaemia detection. Current guidelines therefore recommend vasodilator stress imaging or dobutamine stress echocardiography. Conduction system pacing (CSP), using His-bundle or left bundle branch area capture, restores near-physiological ventricular activation. Whether CSP enables interpretable and diagnostically reliable exercise ECG has not been systematically assessed.

Purpose

To evaluate whether CSP restores interpretability of exercise ECG in patients with prior LBBB and whether this translates into improved diagnostic performance compared with reference imaging.

Methods

This prospective, single-centre pilot enrolled adults with LBBB undergoing CSP with stable capture. At ≥6 weeks post-implant, patients underwent protocolised symptom-limited treadmill testing, independent of acute clinical symptoms. Myocardial perfusion positron emission tomography (PET) was the preferred reference, with dobutamine stress echocardiography (DSE) performed if PET was unavailable, within 14 days of exercise testing. Device programming was optimised to ensure CSP capture during exercise, confirmed with 12-lead ECG and post-test interrogation.

Primary endpoint: Feasibility of interpreting exercise ECG (pre-specified ST-segment criteria), adjudicated by two blinded readers with kappa agreement.

Secondary endpoints: Diagnostic accuracy versus imaging, exercise capacity in metabolic equivalents (METs), and safety outcomes.

Results

Eighteen patients were included; 17 (94%) completed treadmill testing. Interpretable ST-segment analysis was achieved in 14/18 (78%) post-CSP compared with 0/18 pre-CSP. Reference imaging was available in 15/18 (PET 9, DSE 6). Against imaging, post-CSP exercise ECG demonstrated sensitivity 77% and specificity 86% for ischaemia detection, with wide confidence intervals due to small sample size. Median exercise capacity was 7.1 METs (IQR 6.0–8.4). No malignant arrhythmias, loss of capture, or device complications occurred. Inter-reader agreement for interpretability was strong (κ=0.82).

Conclusion(s)

In this single-centre pilot, CSP restored the feasibility of interpreting exercise ECG in patients with prior LBBB. Preliminary findings suggest improved diagnostic performance compared with the pre-CSP standard of uninterpretable ECGs. Larger multicentre studies are required to confirm diagnostic value and clinical impact.