Defibrillation thresholds with right pectoral implantable cardioverter defibrillators and impact of waveform tuning (the Tilt and Tune trial)

Aims Assess defibrillation thresholds (DFTs) with right active pectoral implantable cardioverter defibrillator (RICDs). Defibrillation thresholds in patients receiving RICDs are regarded as 'high' and potentially improved by waveform optimization (tuning). However, this has not been systematically tested. Methods and results Patients receiving RICDs [Single chamber (VVI) =16, DDD = 32, cardiac resynchronization therapy (CRT) = 43] were randomized to either 50/50% fixed tilt (FT) or tuned waveform(3.5 ms time constant based). Defibrillation threshold was tested with a binary search protocol in single coil anodal configuration. Then RICDs were compared with left-sided placements. Baseline patient characteristics in FT (n = 54) and tuned (n = 37) were similar (65 +/- 14 years, 71% male, Left ventricular ejection fraction 31 +/- 13%; and proportions VVI/DDD/Cardiac resynchronization therapy defibrillator). Tuning reduced Phase 1 by 15% and Phase 2 by 45%. For FT vs. tuned: high voltage impedancewas 61.9 +/- 13.2 vs. 64.5 +/- 12.7 Omega (P = 0.33) and mean DFT 14.2 +/- 8.8 vs. 14.9 +/- 9.2 J (P = 0.8). When high voltage impedance was >62 Omega (mean 73.6 +/- 8.6 Omega), DFT was identical [FT 13.0 +/- 7.9 J vs. tuned 12.0 +/- 5.9 J (P = 0.7)]. Defibrillation thresholds exceeded 20 J (600 Omega) in >20% of patients [FT 11/54 (20.4%) vs. tuned 12/37 (32%) patients]. Defibrillation threshold with RICD was greater and exhibited wider dispersion compared with left ICDs (n =54) under similar conditions. Conclusion This first randomized trial investigating DFTs with right ICDs confirms relatively higher DFTs with RICDs than reported for left pectoral ICDs. However, DFTs were generally unaffected by 3.5 ms time constant-based waveform tuning compared with a 50% tilt waveform. Implant testing may be preferred with RICDs.