Impedance compensated passive implantable atrial defibrillator

Abstract

An impedance compensated passive implantable atrial defibrillator is reported. The two-part system consists of a handheld lithium-ion powered base unit (external power transmitter) and a passive (battery free) implantable coil (power receiver), with integrated rectifilter and power control unit, electrocardiogram (ECG) and bioimpedance measurement circuits, data communications circuitry and atrial connection leads. The system is designed to operate in two distinct modes: cardiac sense mode (wake-up, measure the impedance of the cardiac substrate and communicate data to the external base unit) and shock mode (delivery of an ECG synchronised impedance compensated monophasic very low tilt rectilinear shock waveform). A prototype was implemented and tested. In the sense mode, up to 5 W of sustained DC power was delivered across a 2.5 cm air-skin barrier with approximately 40% DC-to-DC power transfer efficiency at a transmission frequency of 185 kHz achieved, thereby providing 15.9 VDC (320 mA) to the implant side for measurement and communication at 433 MHz with the base unit. In the shock delivery mode, >186.9 W (rectilinear monophasic shock pulse: 100 V, 1.9 A, 12 ms duration) was repeatedly and reliably delivered transcutaneously to a 50 Ω cardiac load. Further testing in ten porcine models verified the in vivo operation, with intercatheter impedance variations of ±20.1% measured between successive defibrillation attempts.Introduction: Atrial fibrillation (AF) accounts for 30-40% of all cardiac arrhythmia-related hospital admissions and is associated with increased morbidity and mortality [1,2]. Consequently, the need for continued improvements in AF therapies remains self-evident. Recent publications indicate that the advancement of treatment for chronic AF sufferers (patients where pharmacological interventions have failed) may result from two specific lines of enquiry: (i) optimisation of the electrical defibrillation shock waveform for the lowest possible energy to achieve successful internal cardioversion (<1 J would potentially avoid the need for patient sedation) and (ii) the development of battery-free semi-passive implantable atrial defibrillators (facilitating AF arrhythmia detection and synchronised self-cardioversion, under controlled circumstances, in a minimal critical care setting) [3][4][5][6][7][8]. Controlled transcutaneous delivery of moderate amounts of electrical energy to the cardiac substrate is therefore of key importance in developing strategies for lowenergy treatment of AF [4,5,8]. Here we report a passive (battery-free) implantable atrial defibrillator architecture that facilitates measurement of the impedance spectrum of the cardiac substrate as a means of precisely controlling the energy delivered to the heart during ECG synchronised internal defibrillation.

Towards Low Energy Atrial Defibrillation

“…However, the use of IAD’s for the treatment of AF has not yet achieved critical acceptance; predominately due to the impact of unit automaticity on the patients quality of life and the lack of patient tolerance to the discomfort produced by high energy shocks [ 11 , 12 ]. Recent publications indicate that the further advancement of internal cardioversion for AF may therefore result from two specific lines of enquiry: (i) optimisation of the defibrillation shock impulse to achieve the lowest energy necessary to successfully cardiovert a patient (less than 1 J could potentially negate the need for patient sedation) and (ii) investigation of passive (battery free) implantable atrial defibrillators that can facilitate AF arrhythmia detection and cardioversion under controlled circumstance in a non-acute care (out-of-hospital) setting [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. In respect of the optimisation of electrical shock waveforms to achieve a defibrillation threshold of <1 J, transthoracic impedance (TTI) is a key determinant in the success of both atrial and ventricular defibrillation; due to the fact that cardioversion outcome highly correlates to the current vector delivered to the cardiac substrate.…”

“…In respect of the potential for passive (battery free) implantable defibrillator technologies to enable treatment in a non-acute care setting, the concept has several obvious merits; the issue of implant automaticity and inappropriate shocks is resolved (thereby addressing the potential quality of life associated issues previously identified) while the need for repeat surgery to replace batteries over the lifetime of the patient is entirely eliminated. Consequently, low-energy cardioversion using passive implantable defibrillator technology offers the potential for the development of AF treatment modalities and protocols that could be safely delivered in a non-acute (out-of-hospital) care setting; thereby eliminating the need for repeated hospitalisation and significantly reducing the long term cost burden associated with treatment [ 20 , 25 ].…”

Напрямки Застосування Біоімпедансометрії В Медицині

“…Вимірювання біоімпедансу дозволяють охарактеризувати біологічні середовища та органічні тканини, включаючи людське тіло, а також неорганічні середовища. Методи біоімпедансометрії було використано для моніторингу стану шкіри (діагностика захворювань та оцінка прогресу лікування) [27], характеристики та виявлення ракових Biomedical Engineering and Technology Issue 13(1), 2024 ISSN (Online) 2707-8434 тканин [20], для виявлення апное уві сні [28], як засіб точного контролю енергії, що надходить до серця під час дефібриляції [29], для точного фрезерування кісткового цементу під час ревізії тотального ендопротезування кульшового суглоба [30], для моніторингу ішемії та життєздатності трансплантованих органів [31], для визначення набряку [32], для моніторингу функцій мозку та легенів [33], та як метод неінвазивного вимірювання рівня глюкози [34].…”

Fundamentals, Recent Advances, and Future Challenges in Bioimpedance Devices for Healthcare Applications

“…Given their characteristics, bioimpedance measurements allow the characterization of biological media and organic tissues, including the human body, but also inorganic media [38]. In this sense, bioimpedance methods have been employed in skin monitoring (diagnosis of diseases and evaluation of a treatment progress) [38], cancerous tissue characterization and detection [31], sleep apnea detection through bioimpedance measurements [39], as a means of precisely controlling the energy delivered to the heart during defibrillation [40], as a predictor of intradialytic hypotension [41], for precise bone cement milling during revision of total hip replacement [42], for longitudinal knee joint health assessment [43,44], for the evaluation of high-resolution temporal information corresponding to pharyngeal swallowing [45], to monitor the ischemia and viability of transplanted organs [46,47], edema determination [48], brain and pulmonary function monitoring [49,50], and even as a method for the noninvasive measurement of glucose level [51].…”