Multiple Shocks Affect Thoracic Electrical Impedance During External Cardioversion of Atrial Fibrillation

Abstract

Background: Thoracic impedance (TI) influences the success of external cardioversion (ECV) or defibrillation because current intensity traversing (PACE 2009; 32:371-377)

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.…”

“…However, there remains a paucity of studies examining the correlation of the intracardiac impedance (DC impedance, dynamic impedance and waveform spectral content) during internal atrial defibrillation to clinical outcomes. In addition, recent publications have indicated that multiple low energy intracardiac shocks may give rise to lower cardioversion thresholds [ 18 , 19 , 20 , 21 , 22 , 23 ] thereby significantly minimising patient discomfort. Yet again, a paucity of studies comparing the efficaciousness of such protocols exists.…”

Atrial fibrillation and flutter – the state of the art. Part 2

“…The phenomenon is linear in character, which means that the larger the number of shocks, the greater the reduction of transthoracic impedance, which indicates that decreased thoracic impedance is reversible in this case. Thoracic impedance is also dependent on size, position, and distance between defibrillator electrodes, type of defibrillator electrodes, contact pressure on the chest, chemical properties of electrode gels used during cardioversion/defibrillation, and skin reaction [56,[59][60][61]. In AF the effectiveness of DCC ranges from 75% to 94% in restoring sinus rhythm and is inversely related to AF duration and transthoracic impedance [38,46,57,59,[62][63][64][65][66][67].…”

Impedance compensated passive implantable atrial defibrillator

“…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.…”

“…Discussion: In the context of laboratory test results, transcutaneous coupling of up to 5 W continuous and up to 2.2 J of impulse energy was reliably and repeatedly demonstrated. In the context of the in vivo experimental results observed, initial analysis of the data suggests that the changes in inter-catheter impedance can be attributed to (i) physical variation in the mechanical interface between the catheter and cardiac substrate (systematic) and (ii) modulation of the electrical impedance of the cardiac substrate due to electro-physiological effects (physiological) [8]. Consequently, capture, analysis and full understanding of intercatheter impedance spectra before and after atrial cardioversion will be critical to the future development of new low-energy cardioversion protocols.…”