Injury potential as a diagnostic tool for implantable cardioverter-defibrillator lead perforation

An implantable cardioverter-defibrillator (ICD) was placed in a 64-year-old man with hypertrophic cardiomyopathy who had inducible ventricular arrhythmias during electrophysiology study. At routine 6-week follow-up, the patient had fatigue but no complaints of chest pain. Clinical examination was unremarkable. Ventricular lead functions were normal (impedance 728 Ω, threshold 0.5 V at 0.3 ms and R-wave sensed at 5.5 mV). However, the sinus rhythm electrogram (EGM), recorded between the lead tip to adjacent ring electrode, showed an injury current (Figure 1B) compared with day 1 postimplant (Figure 1A). This finding raised the suspicion of lead perforation. Two-dimensional echocardiography showed trivial pericardial effusion with the possibility of lead perforation. Cardiac computed tomography (CT) confirmed the perforation (Figure 2, volume-rendered CT image; arrow indicates protruding screw of perforating ICD lead from the epicardial surface). The ventricular lead was repositioned, and the injury potential disappeared (Figure 1C). The genesis of the injury potential by the perforating ventricular lead can be explained on the basis of voltage drop between coupled injured and uninjured myocardial cells. These potentials usually are transient (minutes to hours) as a result of electrical uncoupling between injured and uninjured cells. Hence, the lead should have perforated acutely for an injury current to be recorded on the defibrillator EGM. However, it is possible to record a chronic current of injury if the perforating active fixation lead is sufficiently stable to cause continuous minimal cellular alterations that lead to depolarization but not electrical uncoupling. The normal pacing and sensing parameters of the lead support this. A very localized myopericardial inflammation by the perforating lead also could explain the chronic injury current. The sinus rhythm EGM helped in diagnosing the perforation, which otherwise could have been overlooked, thus emphasizing the importance of careful device follow-up.