Towards Low Energy Atrial Defibrillation.

Philip Walsh,Vivek Kodoth,Jose Velasquez,David Mceneaney,Omar Escalona,Paola Rodrigues,Niall Waterman

doi:10.3390/s150922378

Abstract

A wireless powered implantable atrial defibrillator consisting of a battery driven hand-held radio frequency (RF) power transmitter (ex vivo) and a passive (battery free) implantable power receiver (in vivo) that enables measurement of the intracardiacimpedance (ICI) during internal atrial defibrillation is reported. The architecture is designed to operate in two modes: Cardiac sense mode (power-up, measure the impedance of the cardiac substrate and communicate data to the ex vivo power transmitter) and cardiac shock mode (delivery of a synchronised very low tilt rectilinear electrical shock waveform). An initial prototype was implemented and tested. In low-power (sense) mode, >5 W was delivered across a 2.5 cm air-skin gap to facilitate measurement of the impedance of the cardiac substrate. In high-power (shock) mode, >180 W (delivered as a 12 ms monophasic very-low-tilt-rectilinear (M-VLTR) or as a 12 ms biphasic very-low-tilt-rectilinear (B-VLTR) chronosymmetric (6ms/6ms) amplitude asymmetric (negative phase at 50% magnitude) shock was reliably and repeatedly delivered across the same interface; with >47% DC-to-DC (direct current to direct current) power transfer efficiency at a switching frequency of 185 kHz achieved. In an initial trial of the RF architecture developed, 30 patients with AF were randomised to therapy with an RF generated M-VLTR or B-VLTR shock using a step-up voltage protocol (50–300 V). Mean energy for successful cardioversion was 8.51 J ± 3.16 J. Subsequent analysis revealed that all patients who cardioverted exhibited a significant decrease in ICI between the first and third shocks (5.00 Ω (SD(σ) = 1.62 Ω), p < 0.01) while spectral analysis across frequency also revealed a significant variation in the impedance-amplitude-spectrum-area (IAMSA) within the same patient group (|∆(IAMSAS1-IAMSAS3)[1 Hz − 20 kHz] = 20.82 Ω-Hz (SD(σ) = 10.77 Ω-Hz), p < 0.01); both trends being absent in all patients that failed to cardiovert. Efficient transcutaneous power transfer and sensing of ICI during cardioversion are evidenced as key to the advancement of low-energy atrial defibrillation.

Highlights

Atrial fibrillation (AF) is one of the most common cardiac arrhythmias observed in medicine
In this paper we propose and demonstrate a wireless powered implantable atrial defibrillator architecture that enables capture of the intracardiac impedance between successive shocks during the internal cardioversion procedure; thereby enabling implementation of impedance compensated internal atrial defibrillation therapies that are optimized to each individual patient and that could potentially be delivered in a non-acute care setting
Wireless powered in vivo sensing and measurement of intracardiac impedance during cardioversion are evidenced as key to the advancement of low-energy defibrillation therapies

Summary

Introduction

Atrial fibrillation (AF) is one of the most common cardiac arrhythmias observed in medicine. It is caused by rapid unsynchronised contractions that give rise to “quivering” of the upper atria. This results in a partial loss of cardiac output. Atrial fibrillation is associated with deterioration in cardiac function and increased risk of stroke resulting in significant morbidity and mortality. The most recently published data from the Rotterdam study reports a 5.5% prevalence of AF in individuals over the age of 55 years while AF is currently estimated to account for 30%–40% of all hospitalizations due to cardiac arrhythmias. The need for improved and more efficacious therapies remains self evident [2,3,4,5]

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