OPTIMAL ELECTRODE CONFIGURATION FOR PECTORAL TRANSVENOUS IMPLANTABLE DEFIBRILLATOR WITHOUT AN ACTIVE CAN

A new 83 cm(3) implantable cardioverter-defibrillator (ICD) designed f or pectoral implantation has been implanted most frequently using righ t ventricular and superior vena cava (RV-->SVC) electrodes; a patch el ectrode (RV-->patch + SVC) has been added when necessary to decrease t he 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-->patch + 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 i nnominate vein. In the first 15 patients, all 3 electrode configuratio ns were tested in random order; in the last 10 patients, only the RV-- >patch and RV-->patch + SVC configurations were tested. In the first 1 5 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 conf iguration (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-->patc h + SVC configuration (9.7 +/- 5.1 J) than for the RV-->patch configur ation (12.4 +/- 6.6 J, p = 0.005). The pathway resistance was highest for the RV-->patch configuration (72 +/- 9 Omega), lower for the RV--> SVC configuration (63 +/- 6 Omega, p < 0.01), and lowest for the RV--> patch + SVC configuration (46 + 3 Omega, p <0.001). The addition of an SVC electrode to the RV-->patch configuration reduced the DFT substan tially for high-resistance RV-->patch pathways (>73 Omega: 13.0 +/- 8. 4 vs 8.3 +/- 5.6 J, p <0.005), but not for low-resistance RV-->patch p athways (>73 Omega: 11.7 +/- 4.9 vs 11.0 + 4.5 J, p = NS). Overall, th e DFT was greater than or equal to 20 J in 6 of 15 patients (40%) with the RV-->SVC configuration, in 4 of 25 patients (16%) with the RV-->p atch configuration, and in none of 25 patients (0%) with the RV-->patc h + SVC configuration. All 25 RV-->patch and RV-->patch + SVC configur ations met the implant criterion, but 3 of the 15 RV-->SVC configurati ons (20%) did not. For this ICD, electrode configurations that include a patch provide the lowest DFTs. An additional SVC electrode lowers t he DFT only if the resistance of the RV-->patch pathway is high.