Towards Low Energy Atrial Defibrillation

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

Linear variation analysis of intracardiac atrial impedance during internal cardioversion using rectilinear waveforms and energy step up protocol

Abstract The major determinants of success during internal cardioversion of atrial fibrillation (AF

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Waveform optimisation for internal cardioversion of atrial fibrillation

Direct current transthoracic cardioversion is a well-established treatment for atrial fibrillation (AF). Significant changes in the device technology have taken place since the procedure was first described. Since then there has been a constant quest to improve the efficacy of the device by optimising various parameters that affect the success of cardioversion. Particular waveforms used in different models of defibrillators determine the energy used and efficacy of defibrillators. The technique of internal cardioversion was developed to treat patients in whom transthoracic cardioversion was unsuccessful. The aims of this thesis was to address issues surrounding optimisation of internal cardioversion. Data from this thesis will help. in developing a novel atrial defibrillator. Commercially available internal and external cardioversion devices use a capacitor based exponential energy. A unique radiofrequency energy powered defibrillator was developed at the Royal Victoria Hospital in collaboration with the Centre for Advanced Cardiovascular Research (University of Ulster). This device was extensively studied both in animal models and clinical studies at the Royal Victoria Hospital, Belfast. In this study, I compared the safety and efficacy of a novel radiofrequency low tilt monophasic waveform with a low tilt biphasic waveform for internal cardioversion of persistent AF. All the persistent AF patients had a previous history of failed external cardioversion. I also compared the waveforms in patients who inadvertently go into AF during electrophysiological studies. In both the studies, significant proportion of patients were successfully cardioverted to sinus rhythm with low energy. The radiofrequency powered defibrillator was safely used for transvenous cardioversion of atrial fibrillation. In this thesis, I have discussed about cardioversion, internal cardioversion, atrial defibrillators, various waveforms used for cardioversion, development of radiofrequency defibrillator and the concept of novel atrial defibrillator. Data from my work will add to the development of a novel radiofrequency atrial defibrillator. This device will eventually contain a passive implantable atrial defibrillator that is powered by an externally transmitted pulse of RF energy.EThOS - Electronic Theses Online ServiceGBUnited Kingdo