Usefulness of the Current of Injury Function in a Pacing System Analyzers for Left Bundle Branch Area Pacing Implantation : A Case Report

During left bundle branch area pacing (LBBAP), the current of injury (COI) follows a characteristic depth-dependent course: it rises as the lead advances through the interventricular septum, then falls as the tip approaches the left ventricular endocardium. This transition has been proposed as a practical procedural endpoint. Such monitoring has conventionally required an electrophysiology (EP) laboratory system, as pacing system analyzers (PSAs) were thought to lack real-time capability. This report describes a 76-year-old man with complete atrioventricular block and preserved ejection fraction (70%) who underwent LBBAP because a high pacing burden was anticipated. An INGEVITY lead and SSPC NXT guiding catheter were used, with simultaneous recording by an EP system and a Boston Scientific PSA equipped with beat-by-beat COI monitoring and a reference-waveform storage function. After the initial screw-in, the COI waveform was stored as a reference at the right ventricular septal position. During subsequent body turns, the COI rose sharply relative to this reference and then declined within tens of seconds. Lead V1 showed a right bundle branch block-like morphology with stable threshold and impedance, and this position was accepted as final. Waveforms from the PSA and the EP system showed comparable temporal patterns. Because absolute COI amplitude varies widely between patients, within-patient comparison against a stored reference allows assessment not only of whether the COI has begun to fall, but how far it has fallen - relevant to the risk of endocardial penetration. Limitations include the single-case design and absence of quantitative analysis.