Gabriel A. Mouchawar

Does an SVC electrode further reduce DFT in a hot-can ICD system?

Pectorally implanted ICDs that defibrillate with the RV electrode and the ICD housing have gained clinical acceptance. However, it is still debatable whether adding an SVC electrode connected to the housing will further reduce the threshold of defibrillation (DFT). This study utilized eight pigs. DFTs were measured with a 50 V step‐down protocol starting at 650 V (20 J). Shock strength for 50% success (E50) was estimated with the average of three reversals. In addition to a dummy device, Lead I (Pacesetter Models 1558 and 1538) or Lead II (Endotak 72) were used. Leads I are active fixation, true bipolar sensing with 5‐cm shocking coils. Lead II has an integrated bipolar sensing with a 4.7‐cm RV and 6.9‐cm SVC shocking coils. A 95 μF defibrillation system was used to deliver a 44% tilt tuned biphasic 1.6/2.5 ms waveform, and to measure lead impedance. The RV electrode was the anode during phase I. With Lead I RV → CAN the DFT was 531 ± 75 V (13.6 ± 3.8 J) and the E50 was 496 ± 89 (12 ± 4.3 J). These were not significantly (NS) different than the DFT for RV → CAN and SVC which was 518 ± 84 V (13 ± 4.2 J) or the E50 which was 476 ± 84 V (11 ± 3.9 J). Similar results were obtained with Lead II. Despite a decrease in lead impedance there was no apparent benefit from the addition of the SVC electrode. Lead I provided equivalent DFT performance to Lead II.

Effect of Implantable Nonthoracotomy Defibrillation System on Permanent Pacemakers: An In Vitro Analysis with Clinical Implications

Implantable cardioverter defibrillation systems are capable of delivering over 700 volts, and upwards of 40 joules (J) directly to the heart. Nonthoracotomy lead (NTL) systems allow the delivery of this energy to the inside of the heart, and potentially in close proximity to the leads of an endocardial pacing system. The effect of repeated maximal energy discharges (stored energy 40 J, delivered energy 38 J), utilizing both monophasic as well as biphasic shock pulses delivered via two different configuration NTL systems on a series of Pacesetter polarity programmable present generation single, and dual chamber pacemakers was evaluated in vitro using a saline test tank. All pulse generators studied demonstrated normal function and were not reprogrammed nor adversely affected by repeated defibrillation shocks. The current induced in the leads was assessed, and shown to be as high as 1.5 amps in the proximal conductor and 1.2 amps in the distal conductor of the ventricular lead, which may cause damage at the electrode‐myocardial interface, and explain some of the postshock rise in capture and sensing thresholds that have been reported with implanted pacing systems postdefibrillation.

Plateau waveform shape allows a much higher patient shock energy tolerance in AF patients.

Objectives: To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients.

Modeling of MRI-induced heating in pacemaker patients during 1.5T MRI scans

Some MRI scans, including many cardiac and spinal scans, exceed 2 W/kg whole body SAR. We utilized the ISO/IEC JWG 10974 Tier 3 (ED2) approach to evaluate heating of pacemaker systems under normal (2 W/kg) and 1st level controlled mode (4 W/kg). Electric fields were simulated using five virtual human models with various transvenous pathways in MRI RF body coils. Clinically relevant lead states of various levels of fluid ingress were studied, and the validated lead transfer function (TF) with the highest heating was selected. It was then integrated with the extracted electric fields along lead pathways inside human models to estimate the temperature rises without blood flow (in vitro). A validated thermal model scaled the in vitro temperature estimates to in-vivo results. Uncertainties from measurements, TF, thermal model and in vivo simulations were incorporated with the Monte Carlo (MC) method. Safety was assessed based upon the accepted 43°C standard for cardiac tissue interfacing with the lead helix electrode and lead MRI filter inductor.

Comparison of measurement and calculation of the electric field transfer function for an active implant lead in different media

Patients with an active implantable medical device (AIMD) may be at risk of harm from RF-induced heating during an MRI scan. The electric field transfer function (TFE) is a measure of the sensitivity of the heating at the electrode of the AIMD to the incident tangential electric field (Etan) along its length. It is demonstrated that the TFE depends on boundaries of the phantom, phantom media and the trajectory of the AIMD.