Finite element modeling of subcutaneous implantable defibrillator electrodes in an adult torso

Abstract

Background Total subcutaneous implantable subcutaneous defibrillators are in development, but optimal electrode configurations are not known. Objective We used image-based finite element models (FEM) to predict the myocardial electric field generated during defibrillation shocks (pseudo-DFT) in a wide variety of reported and innovative subcutaneous electrode positions, to determine factors affecting optimal lead positions for subcutaneous ICDs (S-ICD). Methods An image-based FEM of an adult male was used to predict pseudo-DFTs across a wide range of technically feasible S-ICD electrode placements. Generator location, lead location, length, geometry and orientation, and spatial relation of electrodes to ventricular mass were systematically varied. Best electrode configurations were determined, and spatial factors contributing to low pseudo-DFTs were identified using regression and general linear models. Results 122 single-electrode/array configurations and 28 dual-electrode configurations were simulated. Pseudo-DFTs for single-electrode orientations ranged from 0.60 – 16.0 (mean 2.65 ± 2.48) times that predicted for the base case, an anterior posterior configuration recently tested clinically. 32/150 tested configurations (21%) had pseudo-DFT ratios ≤ 1, indicating the possibility of multiple novel, efficient, and clinically relevant orientations. Favorable alignment of lead-generator vector with ventricular myocardium and increased lead length were the most important factors correlated with pseudo-DFT, accounting for 70% of the predicted variation (R2=0.70, each factor p <0.05) in a combined general linear model in which parameter estimates were calculated for each factor. Conclusions Further exploration of novel and efficient electrode configurations may be of value in the development of the S-ICD technologies and implant procedure. FEM modeling suggests that the choice of configurations which maximizes shock vector alignment with the center of myocardial mass and use of longer leads is more likely to result in lower DFT.

Rise in defibrillation threshold after postoperative cardiac remodeling in a patient with severe Ebstein’s anomaly

“…Using a transverse cut of a chest MRI and CT with the largest proportion of myocardium visible, the center of a circle around the myocardium was chosen as the center of the myocardial mass (Figure 1). Efficacy is improved by aligning the inter-electrode shock vector as closely as possible to the center of the mass of the ventricular myocardium, and by use of longer electrode coil lengths 8 . In our patient, the initial 2-epicardial-coil configuration did not cover the myocardial mass on the left chest and failed to depolarize a sufficient amount of fibrillating myocardium to terminate fibrillation.…”

Efficacy and Myocardial Injury With Subcutaneous Implantable Cardioverter Defibrillators – Computer Simulation of Defibrillation Shock Conduction –

“…Consequently, the myocardial injury in the right ventricle was more mass hypothesis, the DFT in the simulation was the minimum energy output of the ICD generator with a voltage gradient >5 V/cm for >90% of myocardium. 18, 19 Furthermore, we also calculated the percentage of myocardium with a voltage gradient >30 V/cm as an index to predict any possible myocardial injury. 18,19 DFT was calculated using E=J=1/2 • C • V 2 , where C=130 μF and V is the defibrillation voltage, given that the defibrillation critical mass criterion was reached.…”

Subcutaneous Implantable Cardioverter Defibrillator

“…The efficiency of subcutaneous defibrillation has been shown by finite element modeling to be improved by longer electrode coil length as well as using configurations that place the shock vector close to the center of ventricular myocardial mass. 15 As such, other shock vectors have been assessed for defibrillation using various combinations of electrode lead length, lead placement, and pulse generator location. Grace et al 16 evaluated an anterolateral shock vector using an 8 cm left parasternal electrode and a left lateral thoracic can, and reported a defibrillation threshold (DFT) of 36.6 J, with patient not defibrillated up to 83 J. Burke et al 17 evaluated an anterior-anterior vector by placing an anterior can in a clavicular pocket and an anterior cutaneous defibrillation patch electrode.…”