Optimal electrode configuration for pectoral transvenous intplantable defibrillator without an active can

A new 83 cm3 implantable cardioverter-defibrillator (ICD) designed for pectoral implantation has been implanted most frequently usina right ventricular and superior vena cava (RV → SVC) electrodes; a patch electrode (RV → patch + SVC) has been added when necessary to decrease the defibrillation threshold (DFT). The goal of this prospective study was to compare biphasic waveform DFTs for 3 electrode configurations: RV → patch, RV → SVC, and RV → pafch + SVC in 25 consecutive patients. The patch was positioned in a left retropectoral pocket, and the SVC electrode was positioned with the tip at the junction of the SVC and innominate vein. In the first 15 patients, all 3 electrode configurations were tested in random order; in the last 10 patients, only the RV → patch and RV → patch + SVC configurations were tested. In the first 15 patients, the stored-energy DFT for the RV → SVC configuration (15.2 ± 7.7 J) was higher (p < 0.001) than the DFT for the RV → patch configuration (11.3 ± 6.2 J) and the RV → patch + SVC configuration (10.0 ± 5.8 J). For all 25 patients, the DFT was lower for the RV → patch + SVC configuration (9.7 ± 5.1 J) than for the RV → patch configuration (12.4 ± 6.6 J, p = 0.005). The pathway resistance was highest for the RV → patch configuration (72 ± 9 Ω), lower for the RV → SVC configuration (63 ± 6 Ω, p < 0.01), and lowest for the RV → patch + SVC configuration (46 ± 3 Ω, p < 0.001). The addition of an SVC electrode to the RV → patch configuration reduced the DFT substantially for high-resistance RV → patch pathways (>73 Ω: 13.0 ± 8.4 vs 8.3 ± 5.6 J, p < 0.005), but not for low-resistance RV → patch pathways (>73 Ω: 11.7 ± 4.9 vs 11.0 ± 4.5 J, p = NS). Overall, the DFT was ≥ 20 J in 6 of 15 patients (40%) with the RV → SVC configuration, in 4 of 25 patients (16%) with the RV → patch configuration, and in none of 25 patients (0%) with the RV → patch + SVC configuration. All 25 RV → patch and RV → patch + SVC configurations met the implant criterion, but 3 of the 15 RV → SVC configurations (20%) did not. For this ICD, electrode configurations that include a patch provide the lowest DFTs. An additional SVC electrode lowers the DFT only if the resistance of the RV → patch pathway is high.