EARLY POSTOPERATIVE INCREASE IN DEFIBRILLATION THRESHOLD WITH NONTHORACOTOMY SYSTEM IN HUMANS

The stability of the defibrillation threshold (DFT) early after implantation of an implantable cardioverter defibrillator was evaluated in 15 patients. All but one patient had a three lead nonthoracotomy system using a subcutaneous patch, a right ventricular endocardial lead, and a lead in coronary sinus (n = 5) or superior vena cava (n = 9). Shocks were delivered using simultaneous in nine, sequential in three, and single pathway (coronary sinus not used) in one patient. DFTs were measured at implant (n = 15), 2-8 days postoperation (postop, n = 15), and 4-6 weeks later (n = 8). The DFT was defined as the lowest energy shock that resulted in successful defibrillation. The DFT was assessed with output beginning at 18 joules or 2-4 joules above the implant DFT. All shocks were delivered in 2- to 4-joule increments or decrements. DFTs were significantly higher postoperatively than DFTs at implant (22.7 +/- 7.0 J vs 16.9 +/- 3.9 J; P < 0.05). Eight of 15 patients had DFT determined at all three study periods. In these patients, DFT increased at postop (22.8 +/- 8.3 J vs 16.4 +/- 3.9 J at implant; P < 0.05) and returned to baseline at 4-6 weeks (16 +/- 7.1 J vs 16.4 +/- 3.9 J at implant; P = N.S.). Thus, in patients with a multilead nonthoracotomy system, a DFT rise was observed early after implant. The DFT appears to return to baseline in 4-6 weeks. These results have important implications for programming energy output after implantable cardioverter defibrillator implantation.