Matthew Jolley

A computer modeling tool for comparing novel ICD electrode orientations in children and adults

BACKGROUNDnUse of implantable cardiac defibrillators (ICDs) in children and patients with congenital heart disease is complicated by body size and anatomy. A variety of creative implantation techniques has been used empirically in these groups on an ad hoc basis.nnnOBJECTIVEnTo rationalize ICD placement in special populations, we used subject-specific, image-based finite element models (FEMs) to compare electric fields and expected defibrillation thresholds (DFTs) using standard and novel electrode configurations.nnnMETHODSnFEMs were created by segmenting normal torso computed tomography scans of subjects ages 2, 10, and 29 years and 1 adult with congenital heart disease into tissue compartments, meshing, and assigning tissue conductivities. The FEMs were modified by interactive placement of ICD electrode models in clinically relevant electrode configurations, and metrics of relative defibrillation safety and efficacy were calculated.nnnRESULTSnPredicted DFTs for standard transvenous configurations were comparable with published results. Although transvenous systems generally predicted lower DFTs, a variety of extracardiac orientations were also predicted to be comparably effective in children and adults. Significant trend effects on DFTs were associated with body size and electrode length. In many situations, small alterations in electrode placement and patient anatomy resulted in significant variation of predicted DFT. We also show patient-specific use of this technique for optimization of electrode placement.nnnCONCLUSIONnImage-based FEMs allow predictive modeling of defibrillation scenarios and predict large changes in DFTs with clinically relevant variations of electrode placement. Extracardiac ICDs are predicted to be effective in both children and adults. This approach may aid both ICD development and patient-specific optimization of electrode placement. Further development and validation are needed for clinical or industrial utilization.

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

BACKGROUNDnTotal subcutaneous implantable subcutaneous defibrillators are in development, but optimal electrode configurations are not known.nnnOBJECTIVEnWe 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 implantable cardioverter-defibrillators (S-ICD).nnnMETHODSnAn image-based FEM of an adult man 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.nnnRESULTSnA total of 122 single-electrode/array configurations and 28 dual-electrode configurations were simulated. Pseudo-DFTs for single-electrode orientations ranged from 0.60 to 16.0 (mean 2.65 +/- 2.48) times that predicted for the base case, an anterior-posterior configuration recently tested clinically. A total of 32 of 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 (R(2) = 0.70, each factor P < .05) in a combined general linear model in which parameter estimates were calculated for each factor.nnnCONCLUSIONnFurther 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 that maximize shock vector alignment with the center of myocardial mass and use of longer leads is more likely to result in lower DFT.

Extracorporeal membrane oxygenation in patients undergoing superior cavopulmonary anastomosis

OBJECTIVEnPatients who have undergone the superior cavopulmonary anastomosis (Glenn procedure) have unique cardiopulmonary-cerebral physiology that may limit the success of cardiopulmonary resuscitation and extracorporeal membrane oxygenation (ECMO). Limited data published to date suggest grim morbidity and mortality when ECMO is used. We utilized the Extracorporeal Life Support Organization registry database to more thoroughly assess outcomes in these patients.nnnMETHODSnData from the Extracorporeal Life Support Organization registry from 1999 to 2012 for children with Glenn physiology aged 3 months to 1 year were retrospectively analyzed. Demographics and ECMO characteristics were compared between survivors and nonsurvivors. Factors associated with mortality were evaluated using multivariate logistic regression.nnnRESULTSnOf 103 infants, 42 (41%) survived to hospital discharge. Neurologic complications (eg, seizure, hemorrhage, or embolic stroke) were documented in 23% of patients (24 of 103) and 14% of survivors (6 of 42). In univariate analysis, inotropic requirement before ECMO, duration of ECMO, mechanical complications with the ECMO circuit, renal failure, and pulmonary hemorrhage or pneumothorax were predictors of mortality. In multivariate logistic regression, inotrope requirement (odds ratio [OR], 3.6; 95% confidence interval [CI], 1.3-9.8), longer duration of ECMO support (OR, 7.2; 95% CI, 1.8-28), combined cardiopulmonary indication for ECMO (OR, 3.7; 95% CI, 1.4-9.7), and renal failure (OR, 4.2; 95% CI, 1.5-12) were associated with mortality.nnnCONCLUSIONSnMortality in infants with Glenn physiology supported with ECMO is lower than that previously reported, but the incidence of neurologic injury is high. These data support use of ECMO in patients with Glenn physiology with refractory cardiopulmonary failure.

Extracorporeal membrane oxygenation-supported cardiopulmonary resuscitation following stage 1 palliation for hypoplastic left heart syndrome.

Objectives: To report on survival from a large multicenter cohort of neonates with hypoplastic left heart syndrome requiring extracorporeal membrane oxygenation–assisted cardiopulmonary resuscitation after stage 1 palliation operation. Design: Retrospective analysis of data from the Extracorporeal Life Support Organization data registry (1998 through 2013). We computed the survival to hospital discharge for neonates (age < 30 d) who required extracorporeal membrane oxygenation after stage 1 palliation and evaluated factors associated with mortality using multivariate logistic regression analysis. Setting: Multicenter data reported to Extracorporeal Life Support Organization registry. Patients: Infants with hypoplastic left heart syndrome after stage 1 palliation who received extracorporeal membrane oxygenation–assisted cardiopulmonary resuscitation. Interventions: None. Measurements and Main Results: There were 307 extracorporeal membrane oxygenation runs in the setting of extracorporeal membrane oxygenation–assisted cardiopulmonary resuscitation in 293 neonates with hypoplastic left heart syndrome following stage 1 palliation operation. The median age at cannulation was 9 days (interquartile range, 5–14 d). Survival to hospital discharge was 36%. In univariate analysis, gestational age, weight, extracorporeal membrane oxygenation duration, presence of air embolism, hemorrhagic complications, renal failure, and pulmonary complications (pulmonary hemorrhage and pneumothorax) were all associated with nonsurvival. In multivariate analysis, lower body weight at cannulation (odds ratio, 3.9; 95% CI, 1.9–8.3), duration of the extracorporeal membrane oxygenation (odds ratio, 3.4; 95% CI, 1.9–7.3), and renal failure while on extracorporeal membrane oxygenation (odds ratio, 2; 95% CI, 1.2–3.5) increased odds of mortality. Conclusions: Mortality for neonates with hypoplastic left heart syndrome supported with extracorporeal membrane oxygenation–assisted cardiopulmonary resuscitation after stage 1 palliation is high. Lower body weight, increased duration of extracorporeal membrane oxygenation support, and renal failure increased mortality.

Predictive modeling of defibrillation using hexahedral and tetrahedral finite element models: recent advances

Implanted cardioverter/defribillator (ICD) implants may be complicated by body size and anatomy. One approach to this problem has been the adoption of creative, extracardiac implant strategies using standard ICD components. Because data on safety or efficacy of such ad hoc implant strategies are lacking, we have developed image-based finite element models to compare electric fields and expected defibrillation thresholds (DFTs) using standard and novel electrode locations. In this article, we review recently published studies by our group using such models and progress in meshing strategies to improve efficiency and visualization. Our preliminary observations predict that they may be large changes in defibrillation thresholds with clinically relevant variations of electrode placement. Extracardiac ICDs of various lead configurations are predicted to be effective in both children and adults. This approach may aid both ICD development and patient-specific optimization of electrode placement, but the simplified nature of current models dictates further development and validation before clinical or industrial use.

Evaluation of different meshing algorithms in the computation of defibrillation thresholds in children

In this paper we evaluate different meshing schemes to solve for the bioelectric fields that arise in the human body due to the defibrillation shock generated by an Implantable Cardiac Defibrillator, with particular emphasis on implantation in children. For children, the question of relative performance of different electrode locations remains open. Computational simulation is a critical tool to address this question, and mesh design is a critical component of such simulations. We use the SCIRun software package to address this simulation problem because it combines the powerful numeric tools required with interactive flexibility allowing easy comparison of both algorithms and electrode orientation. We describe a pipeline that starts with segmented CT-images and produces clinically useful parameters. Using this framework we report below that a meshing scheme using regularly spaced hexahedral elements which are locally refined around the electrodes constitute a quick and relatively accurate way of solving this problem.

The role of volume conductivities in simulation of implantable defibrillators

In the quest for patient specific models for predicting defibrillation efficacy, one of the questions is which tissue types to include into a volume conductor model of the torso. We present a comparison between a model consisting of 11 different tissue types to models with only a subset of of tissue types across a database of electrode orientations including transvenous, epicardial, and subcutaneous electrodes. The simulations show that the volume conductor models should at least include segmentations for the heart, lungs, blood, and bones, and possibly the fat layers and the amount of gaseous space in the stomach and intestines. The latter ones may be necessary for modeling subcutaneous electrode configurations and ICD ldquocansrdquo in the abdomen.

Open-source environment for interactive finite element modeling of optimal ICD electrode placement

Placement of Implantable Cardiac Defibrillator (ICD) leads in children and some adults is challenging due to anatomical factors. As a result, novel ad hoc non-transvenous implant techniques have been employed clinically. We describe an open-source subject-specific, image-based finite element modeling software environment whose long term goal is determining optimal electrode placement in special populations of adults and children Segmented image-based finite element models of two children and one adult were created from CT scans and appropriate tissue conductivities were assigned. The environment incorporates an interactive electrode placement system with a library of clinically-based, user-configurable electrodes. Finite element models are created from the electrode poses within the torsos and the resulting electric fields, current, and voltages computed and visualized.

Image based modeling of defibrillation in children.

Volume imaging, defibrillation electrode models, and finite element modeling are employed in patient-specific procedural modeling in pediatric patients with cardiac arrhythmias. Due to variable size and anatomy, these patients may not be well-served by devices designed for adult defibrillation. A pipeline for rapid creation of image based models that can be interactively interrogated to determine optimal defibrillation scenarios and preliminary proof-of-concept work are presented. This approach has potential clinical applications for therapy planning and broad applications for finite element modeling in anatomical models. Clinical studies investigating the effects of body size, habitus, and anatomical variation on myocardial voltage gradients are planned

Resting heart rate influences right ventricular volume in repaired tetralogy of Fallot.

Abstractn The aim of this study is to examine the impact of heart rate (HR) on right ventricular end-diastolic volume indexed to body surface area (RVEDVi) in patients with repaired tetralogy of Fallot (TOF). In this cross-sectional study, an institutional database search identified all patients with repaired TOF who underwent cardiac magnetic resonance (CMR) and had a Holter study within 3xa0months. The association of HR on Holter, HR at the time of CMR, and other clinical and CMR parameters on RVEDVi was explored with univariate and then multivariable models. In the study group (nxa0=xa0161, median age 23xa0years), a lower mean Holter HR was associated with a larger RVEDVi (pxa0=xa00.004). In a model that also included pulmonary regurgitation fraction, tricuspid regurgitation grade, RV ejection fraction, age at CMR, and gender, mean Holter HR remained associated with RVEDVi (pxa0<xa00.0001); for a decrease of 1xa0bpm, mean RVEDVi increased by 1.09xa0ml/m2. When limiting to those with a Holter within 5xa0days of CMR (nxa0=xa070), the impact of mean Holter HR on RVEDVi was stronger (−1.9xa0ml/m2/bpm). HR at time of CMR had a significant but less pronounced relationship to RVEDVi (−0.58xa0ml/m2/bpm, pxa0=xa00.002). In conclusion, in repaired TOF patients, a lower HR was significantly associated with a larger RVEDVi. This relationship was stronger with a shorter time interval between the Holter and CMR, and stronger for the mean HR on Holter than for the HR at CMR. Accounting for HR in the interpretation of RVEDVi may impact decisions regarding pulmonary valve replacement and the interpretation of serial CMR data.