When Pacing Fails After Generator Replacement: A Stepwise Diagnostic Approach to a Reversible Lead–Header Interface Problem

Background and Clinical Significance: Early loss of pacing capture after pacemaker generator replacement is an uncommon but potentially life-threatening event, especially in pacemaker-dependent patients. In this setting, device malfunction is often initially attributed to intrinsic lead damage, prompting consideration of invasive lead revision or extraction. However, not all early failures reflect true structural lead dysfunction. Careful interpretation of device interrogation findings, particularly in relation to pacing configuration, may uncover reversible causes and support a more targeted diagnostic and management approach; Case Presentation: A 61-year-old man with complete atrioventricular block presented with recurrent syncope six days after elective pacemaker generator replacement. The electrocardiogram showed absence of effective ventricular pacing with a slow escape rhythm. Device interrogation revealed loss of ventricular capture in bipolar configuration associated with markedly elevated impedance, initially raising concern for lead malfunction. However, switching to unipolar pacing restored effective capture with normal electrical parameters, suggesting preserved lead integrity and prompting reconsideration of the underlying mechanism. Further diagnostic evaluation, including imaging and intraoperative assessment, was therefore undertaken to clarify the cause and guide management; Conclusions: Early pacing failure should not automatically be equated with lead damage. Beyond documenting a reversible lead–header interface problem, this case highlights the diagnostic value of a stepwise approach integrating pacing configuration behavior, targeted imaging, and intraoperative header-independent testing. Such an approach may facilitate rapid localization of reversible defects and help avoid unnecessary lead revision.