Influence of Body Position on Defibrillation Thresholds of Nonthoracotomy Implantable Defibrillators:

Abstract

(1) DFTs for biphasic shocks delivered by nonthoracotomy defibrillators are higher in the upright compared to the supine body position. (2) Differences remain significant 3 months after implantation. For both body positions, DFT decreases significantly from 1 week to 3 months after implantation. These findings have important implications for programming first shock energy to lower than maximal values or for development of devices with lower maximal stored energy.

Orthostatic increase in defibrillation threshold leading to defibrillation failure and prolonged cardiac arrest in a sitting position: Lessons from a patient’s near-fatal experience

“…However, the mean magnitude of this increase is relatively small, about 1.9–2.0 J, which would not be expected to cause complete failure to defibrillate in the patient presented here, since a 10 J safety margin was observed during the initial implant 1, 3. Our patient’s relatively increased DFT at baseline and subsequent treatment with amiodarone in the hospital may have contributed to the failure to defibrillate.…”

“…The mechanism underlying the increased DFT in the upright position remains speculative 1 . The inferior and anterior displacement of the ICD can relative to the intravenous lead system after the patient assumes an upright position, especially in patients who have severe obesity such as the one presented here, may have contributed to the increased DFT.…”

“…Influence of body position on DFT has long been studied by Schauerte et al, 1 who found a significant increase in DFT in an upright position compared to the supine position. However, the mean magnitude of this increase is relatively small, about 1.9–2.0 J, which would not be expected to cause complete failure to defibrillate in the patient presented here, since a 10 J safety margin was observed during the initial implant 1, 3.…”

“…It has previously been reported that patients with an implantable cardioverter-defibrillator (ICD) may have a slightly higher defibrillation threshold (DFT) in an upright position compared to a supine position 1 . However, the significance of this and the potential impact on clinical practice remains unclear.…”

Seventh Try's a Charm

“…1 Interestingly, the body position presents another influential factor: DFTs are higher in the upright than the supine position. 4 One might speculate the syncope after the first ICD shocks could have contributed to the finally successful conversion. Taken together, the present case report emphasizes all the factors potentially altering defibrillation outcome, suggesting that annual chest radiographs and/or regular DFT testing may be reasonable in patients with SQ arrays.…”