Safety margins: lessons from the Low Energy Endotak Trial (LEET)

The Low Energy Endotak Trial (LEET) was designed as a prospective, randomized, multicenter study to evaluate the efficacy and safety in nonthoracotomy cardioverter-defibrillator therapy with lower defibrillation energies compared to the conventional programming with devices set at maximum output. Between December 1993 and January 1996, 172 consecutive patients, undergoing implantation of a biphasic cardioverter-defibrillator with a single endocardial defibrillation lead system, were screened for study enrollment in 4 European study centers. Study inclusion criteria were defined as documented ventricular fibrillation, polymorphic ventricular tachycardia, or fast, hemodynamically unstable ventricular tachycardia, unresponsive to antitachycardia pacing and an augmented defibrillation threshold (DFT+) < or = 15 Joules (J). Patients presenting slow, pace-terminable ventricular tachycardias were excluded. Patients were randomized into 2 study arms: (1) test group patients: the first-shock energy of the implanted devices was programmed at 2 X DFT+, the second to fifth shocks at maximum output (34 J); (2) control group patients: all shocks were programmed at 34 J. Ventricular fibrillation (VF) conversion tests (first shock energy DFT+; second shock 2 X DFT+) were performed in test group patients intraoperatively, during predischarge test, and after 12 months follow-up. In the control group patients, the arrhythmia conversion tests were performed with maximum device output (34 J). Spontaneous tachyarrhythmia episodes were classified by stored intracardiac electrogram analysis, and conversion rates were compared between the 2 study groups. Of the 172 screened patients, 162 (94%) met the inclusion criteria and were enrolled in the study. The mean DFT+ was 9.6 +/- 3.2 J in the test group and 10.0 +/- 3.5 J in the control group. The success rate for the test group for a repeated arrhythmia conversion test at DFT + was 84.4% (157 of 186 induced VF episodes); the cumulative success rate for the first and the second shocks was 99.5% (185 of 186 induced episodes). In the control group, the first-shock conversion rate at 34 J was 98.8% (158 of 160 induced episodes). During a mean follow-up of 10 +/- 7 months, the first-shock conversion rate for spontaneous arrhythmia episodes was 98.5% (65 of 66 episodes) in the test group patients and 92% (69 of 75 episodes) in control group patients (p>0.05). Analyzing the pooled data of spontaneous and induced arrhythmia episodes, there were no differences regarding the first shock conversion rate between the 2 groups (test group: 98.4%; control group: 96.6%, p>0.05). The overall mortality was 3%, equally distributed in both groups. The preliminary results of this study suggest that over a 1-year period, the "2 X DFT+" safety margin was equally effective as the margin provided by a 34-J device for conversion of induced and spontaneous tachyarrhythmia episodes.