Intraoperative Comparison of a Subthreshold Test Pulse with the Standard High‐Energy Shock Approach for the Measurement of Defibrillation Lead Impedance

UNLABELLED: There are two methods to measure shocking lead impedance: delivery of high-energy shocks that require patient sedation, and the painless measurement of impedance from subthreshold test pulses. The aim of this study was to compare the two methods. METHODS: The study included 131 patients implanted with a standard DR (n = 71) or VR (n = 60) ICD connected to either single-coil (n = 39) or dual-coil (n = 92) defibrillation leads. The noninvasive high-energy impedance test was done using a 17 J shock after induction of ventricular tachyarrhythmias and compared to a 0.4 microJ test pulse used by the ICD for the subthreshold measurements. RESULTS: Defibrillation lead impedance measurements were not significantly different between patients with the same shocking vector configuration. In patients with a single-coil defibrillation lead the impedance was 62 +/- 9 Omega with the high-energy shock and 62 +/- 8 Omega with the subthreshold test pulses (P = 0.13). Patients with a dual-coil configuration recorded average impedances of 40 +/- 5 Omega from both tests (P = 0.44). While there was no difference in values recorded within each lead configuration, there was a significant difference in impedance between the single-coil and the dual-coil patient groups (P = 0.001). CONCLUSIONS: There was no significant difference between shocking lead impedances measured with the high-energy shock or the subthreshold test pulses. This offers the possibility of noninvasive, low-energy serial measurements of shocking lead impedance at follow-up visits and removing the need for sedation.