APCU25CR14 Stable pacing despite lead migration into the left bundle branch: a unique case report

Introduction We report an unusual case of conduction system pacing (CSP) lead migration associated with an atypical paced QRS morphology.Case Presentation A 57-year-old male with ischemic heart disease, hypertension, and hyperlipidemia presented with symptomatic Mobitz type II second-degree atrioventricular block. He underwent Conduction system pacing pacemaker with the pacing lead positioned at the posterior fascicle. Initial pacing parameters and electrocardiogram (ECG) morphology were satisfactory. Subsequently, the patient developed palpitations, Electrocardiogram demonstrated a left bundle branch block (LBBB) pattern, raising concern for lead displacement. Despite this finding, pacing thresholds remained stable, sensing was intact, and the patient remained asymptomatic with effective device function.Discussion This case highlights a rare scenario in which lead migration altered paced QRS morphology without compromising hemodynamic performance or device efficacy. Awareness of such atypical presentations is important, as they may mimic lead malfunction or ineffective pacing. Careful ECG analysis in combination with device interrogation is essential to distinguish clinically benign changes from those requiring intervention. Lead migration is a recognized complication in traditional right ventricular pacing, but it is less well described in CSP, particularly with selective engagement of conduction fascicles. Migration into the left bundle region is rare and may present with atypical paced QRS morphology. In most cases, such migration could lead to loss of capture, high thresholds, or ineffective pacing. However, our patient remained clinically stable, with preserved sensing and capture, underscoring that not all migration results in adverse hemodynamic consequences.Conclusion The main clinical challenge was differentiating whether the new LBBB morphology represented ischemia versus pacing-related changes. This highlights the importance of systematic evaluation: device interrogation, imaging, and, when indicated, coronary angiography. In our case, excluding ischemia was essential before attributing the findings to lead migration. This case appears to be the first reported instance of CSP lead migration from the posterior fascicle into the left bundle branch—manifesting as a paced LBBB morphology—without intervention and with preserved pacing function