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2015 ; 15
(9
): 22378-400
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Towards Low Energy Atrial Defibrillation
#MMPMID26404298
Walsh P
; Kodoth V
; McEneaney D
; Rodrigues P
; Velasquez J
; Waterman N
; Escalona O
Sensors (Basel)
2015[Sep]; 15
(9
): 22378-400
PMID26404298
show ga
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
? (SD(?) = 1.62 ?), 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 ?-Hz
(SD(?) = 10.77 ?-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.
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