Defibrillation Energy Requirements with Single Endocardial (Endotak™) Lead

The need for thoracotomy in usually high risk patients has limited the use of the implantable cardioverter defibrillator. Initial clinical results with endocardial and subcutanous patch electrodes (SQPs) are en couraging. Using a single endocardial lead in the absence of a SQP for chronic implantation of the cardioverter defibrillator, the goal of the study was to obtain defibrillation thresholds (DFTs) of 15 Joules (J) or less and to investigate changes in DFT over time. We tested 19 consecutive patients (15 men, 4 women] age 62 ± 8.5 years with malignant ventricular arrhythmias (14 VT/5 VF). The underlying heart disease was coronary artery disease in 15 pafients, dilative cardiomyopathy in two patients, and primary electricaJ disease in two patients. Four patients had undergone previous cardiac surgery. Left ventricular ejection fraction ranged between 14% and 66% (39%± 12.6%). Pacing thresholds (0.54 ± 0.17 Vat 0.5 msec), R wave amplitude for pacemaker sensing (14.2 ± 7.0 mV), slew rate (2.12 ± 1.4 V/sec), and resistance (500.3 ± 73.9 W) were sufficient in all patients. Eighteen patients met our endocardial impiant criteria with a DFT ≤ 15 J (10.05 ± 4.03 J) using monophasic (14 patients) or biphasic (four patients) pulse wave forms. In the one remaining patient, with a DFT of 20 J, we implanted a SQP but there was no reduction of the DFT. All patients tested showed successful defibrillation prior to discharge. During follow-up of 88 patient-months (1–9 months), 114 spontaneous VT/VF episodes occurred in five patients and were all successfully terminated. Eleven patients with a minimum follow-up of 2 months were reassessed. In seven out of 11 patients, termination of VF was achieved with the same minimal energy requirements obtained intraoperatively. In three patients, DFT increased by 5 J (one patient) and 10 J (two patients). In a further patient, X ray revealed dislocation of the endocardial lead. Our data suggest that effective defibrillation is feasible with a single endocardial lead for implantation of cardioverter defibrillator. In addition, we strongly recommend repetitive x-ray control to detect asymptomatic lead dislocation. Despite stable DFTs in most of our patients, an energy difference of ≤ 15 J between acute DFT and cardioverter defibrillator energy rating seems to be currently desirable to ensure successful postoperative defibrillation.