Diagnosis of high-voltage conductor fractures in Sprint Fide Lis 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 Omega) 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 Omega and/or an abrupt 75% increase in chronic HV impedance were diagnostic of HV conductor fractures with 1000% sensitivity and specificity. HV fractures proximal to the SVC coil were more likely to be associated with concomitant pace/sense fractures. Large (200 Omega 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 Omega or abruptly increases by 75% from baseline.