Transvenous placement of the subcutaneous coil electrode to reduce elevated defibrillation thresholds: an alternative to an azygous or subcutaneous coil

Abstract

Purpose: Despite waveform optimization, high output devices, dual coil electrodes (DCE) or the addition of a standard (Medtronic Transvene) proximal coil (TVCE) high defibrillation thresholds (DFT) continue to be a problem in patients with implantable cardioverter defibrillator (ICD). Placement of a coil electrode (Medtronic 6996) posterior in the subcutaneous (SQ) tissue (SQCE) reduces DFTs but requires a second procedure in many centers and is not readily applicable to a right-sided implant. Placement of a TVCE in the azygous vein or coronary sinus can be challenging and may be extremely difficult/dangerous to extract. We present an alternative approach to high DFT's by transvenous rather than SQ placement of the SQCE. Methods: Between Sept 2009 and May 2012, eight patients with high DFT's (mean ≥ 35.3 SD ± 2.7) despite a DCE (proximal coil surface area {SA} 860 mm2) or addition of a TVCE (SA 125 mm2) who had a SQCE (SA 500 mm2) placed in the left innominate/SVC (7 left-sided implants) or azygos vein (1 right-sided implant). After connecting the SQCE to the proximal port, the generator was implanted in the subcutaneous space and DFT's repeated. Results: The mean age was 63±16 years (range 30-79) with 3 females and 1 right-sided implant. The initial ICD lead was dual coiled in seven with the addition of a TVCE in one. After removal of the plastic tip, the subcutaneous coil electrode was positioned in the left innominate/SVC (n=7) and the azygos vein (n=1) for the right-sided implant. The mean DFT was reduced from > 35.3 J ± 2.7 to ≤ 20.3 J ± 4.9 (p=0.003) and the high voltage lead impedance reduced from 41.5±16.7 to 31.1±6.8 Ω (p = 0.2) There were no perioperative complications such as lead dislodgements, fractures, infections or sensing problems noted till last follow up. One patient expired from progressive congestive heart failure one year after the implant. None of the patients have had a spontaneous arrhythmic episode and there were no inappropriate therapies recorded since implant till last follow up. Conclusion: Despite a lower SA than the proximal coil of a DCE, transvenous placement of the SQCE in the left innominate/SVC reduces high DFT's below that seen with a dual coil system and does not require a second procedure. For right-sided implants, azygos placement of the subcutaneous coil may be preferred than the conventional transvenous coil for reducing DFT's.