title: Towards Low Energy Atrial Defibrillation.
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 intracardiac impedance (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.
authors.affiliation: Centre for Advanced Cardiovascular Research, Ulster University, BT37 0QB, UK. Walsh-P3@email.ulster.ac.uk.
authors.forename: Philip
authors.initials: P
authors.lastname: Walsh
authors.affiliation: The Heart Centre, Royal Victoria Hospital, Belfast, BT12 6BA, UK. Vivek.kodoth@rbch.nhs.uk.
authors.forename: Vivek
authors.initials: V
authors.lastname: Kodoth
authors.affiliation: Craigavon Area Hospital, Craigavon, BT63 5QQ, UK. David.McEneaney@southerntrust.hscni.net.
authors.forename: David
authors.initials: D
authors.lastname: McEneaney
authors.affiliation: Centre for Advanced Cardiovascular Research, Ulster University, BT37 0QB, UK. Rodrigues-P@email.ulster.ac.uk.
authors.forename: Paola
authors.initials: P
authors.lastname: Rodrigues
authors.affiliation: Centre for Advanced Cardiovascular Research, Ulster University, BT37 0QB, UK. Velasquez-J@email.ulster.ac.uk.
authors.forename: Jose
authors.initials: J
authors.lastname: Velasquez
authors.affiliation: Centre for Advanced Cardiovascular Research, Ulster University, BT37 0QB, UK. n.waterman@ulster.ac.uk.
authors.forename: Niall
authors.initials: N
authors.lastname: Waterman
authors.affiliation: Centre for Advanced Cardiovascular Research, Ulster University, BT37 0QB, UK. oj.escalona@ulster.ac.uk.
authors.forename: Omar
authors.initials: O
authors.lastname: Escalona
mesh_terms: D003198:Computer Simulation; D054326:Coronary Sinus / Q000473:pathology; D017147:Defibrillators, Implantable; D011211:Electric Power Supplies; D005583:Fourier Analysis; D006325:Heart Atria / Q000473:pathology*; D006801:Humans; D011846:Radio Waves; D013997:Time Factors; D058067:Wavelet Analysis
keywords: RF; battery-free; defibrillator; impedance; implantable; wireless