Influence of “high” defibrillation thresholds on patient survival and impact of system modification

Abstract

Objective: To test whether a high defibrillation threshold (DFT) marks patients with poor outcomes which are improved when DFT is decreased by system modification (subcutaneous coil implant; SM). Background:The electrical substrate generating fast ventricular arrhythmias may generate poor outcomes among patients treated with implantable cardioverterdefibrillators (ICDs), even when arrhythmias are treated successfully. Since patients with high DFTs have increased mortality, we contrasted survival among patients with high DFT treated with and without SM. Methods:We studied consecutive patients undergoing ICD implantation and DFT testing at Cleveland Clinic over a 14-year period. High DFT was defined as successful defibrillation by shock strength >25 J or ≤10 J of maximal device output.Mortality was recorded using the Social Security Death Index. Survival was compared among those high DFT patients receiving SM versus the remainder.Results: Out of 6353 patients tested, 191 (3%) had high DFT (32.1 ± 3.7 J) versus 13.9 ± 4.9 J in the remainder ("acceptable DFT," p < .001). One hundred twenty-one high DFT patients (63%; 33.3 ± 3.4 J) underwent SM, which significantly decreased DFT (24.8 ± 5.9 J; p < .001). Seventy patients (37%; 30.3 ± 3.3 J) did not undergo SM.During follow-up, 38% (2363/6162; 7.8 yrs) patients with acceptable DFT died versus 48% high DFT patients (91/191; 5.6 yrs.; p < .001). Concomitantly, 48% patients with SM (58/121) died, as compared to 47% patients (33/70) without SM (p = .91); median follow-up 4.9 yrs). Conclusion:Patients with high DFT have a higher mortality than those with acceptable DFT. The additional subcutaneous coil implant decreases DFT to an acceptable range but does not appear to improve survival. The electrical substrate underlying high DFT appears to determine survival.

Successful defibrillation by modifying from fixed-tilt to tuned-duration defibrillation waveform: When less is more?

“…1 Furthermore, Siddiqi N et al reported that patients with high DFTs have a higher mortality than those with acceptable DFT. 2 Identifying patients with potentially high DFTs or system failure is difficult with the tools of ICD interrogation and programming. Reducing this defibrillation failure risk, with a low DFT, is an important goal.…”

“…However, when DFT testing is done in specific populations, elevated DFTs have been reported in 2.2%–12% of subjects. 1 Furthermore, Siddiqi and colleagues 2 reported that patients with high DFTs have a higher mortality than those with acceptable DFT. Identifying patients with potentially high DFTs or system failure is difficult with the tools of ICD interrogation and programming.…”