Diagnosis of high-voltage conductor fractures in Sprint Fidelis leads.

Background: Fractures of pace/sense conductors in implantable cardioverter-defibrillator (ICD) leads have been studied extensively, but little is known about fractures of high-voltage (HV) conductors.

Objective: To characterize the presentation of isolated HV conductor fractures, define the optimal impedance threshold for identifying them, and compare it to the existing nominal impedance threshold (200 Ω) for patient and remote-monitoring alerts.

Methods: This retrospective study analyzed HV fractures in explanted, dual-coil, model 6949 Sprint Fidelis leads (Medtronic, Minneapolis, MN). The study group consisted of 25 leads with structurally and electrically confirmed HV conductor fractures; 41 leads that were structurally and electrically intact served as controls. We analyzed long-term HV impedance trends from stored ICD data files of both groups to determine the optimal impedance threshold that would discriminate fractures from normal leads.

Results: In the study group, 14 leads (56%) had fractures of the cable to the right ventricular coil, 9 (36 %) leads had fractures of the cable to the superior vena cava (SVC) coil, and 2 (8%) had both. We found that an impedance threshold of >100 Ω and/or an abrupt 75% increase in chronic HV impedance were diagnostic of HV conductor fractures with 100% sensitivity and specificity. HV fractures proximal to the SVC coil were more likely to be associated with concomitant pace/sense fractures. Large (200 Ω to infinity), abrupt increases in impedance were more common when fractures occurred proximal to the right ventricular coil but distal to the SVC coil.

Conclusions: HV conductor fractures can be diagnosed when HV impedance exceeds 100 Ω or abruptly increases by 75% from baseline.