Association between transthoracic impedance and electrical cardioversion success with biphasic defibrillators: An analysis of 1055 shocks for atrial fibrillation and flutter.

Received: 25 November 2017 Revised: 22 February 2018 Accepted: 8 March 2018 DOI: 10.1002/clc.22947 CLINICAL INVESTIGATIONS Association between transthoracic impedance and electrical cardioversion success with biphasic defibrillators: An analysis of 1055 shocks for atrial fibrillation and flutter Mouhannad M. Sadek1 | Varsha Chaugai2 | Mark J. Cleland2 | Timothy J. Zakutney2 | David H. Birnie1 | F. Daniel Ramirez1,3 1 Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada Background: The relevance of transthoracic impedance (TTI) to electrical cardioversion (ECV) 2 success for atrial tachyarrhythmias when using biphasic waveform defibrillators is unknown. Biomedical Engineering, University of Ottawa Heart Institute, Ottawa, Ontario, Canada 3 School of Epidemiology and Public Health, University of Ottawa, Ottawa, Ontario, Canada Correspondence Mouhannad M. Sadek, MD, University of Ottawa Heart Institute, 40 Ruskin Street, H-1285A, Ottawa, ON, Canada K1Y 4W7 Email: Hypothesis: TTI is predictive of ECV success with contemporary defibrillators. Methods: De-identified data stored in biphasic defibrillator memory cards from ECV attempts for atrial fibrillation (AF) or atrial flutter (AFL) over a 2-year period at our center were evaluated. ECV success, defined as arrhythmia termination and ≥ 1 sinus beat, was adjudicated by 2 blinded cardiac electrophysiologists. The association between TTI and ECV success was assessed via Cochrane-Armitage trend and Spearman rank correlation tests, as well as simple and multivariable logistic regression. The influence of TTI on the number of shocks and on cumulative energy delivered per patient was also examined. Results: 703 patients (593 with AF, 110 with AFL) receiving 1055 shocks were included. Last shock success was achieved in 88.0% and 98.2% of patients with AF and AFL, respectively. In patients with AF, TTI was positively associated with last shock failure (Ptrend =0.019), the need for multiple shocks (Ptrend <0.001), and cumulative energy delivered (ρ = 0.348; P < 0.001). After adjusting for first shock energy, 10-Ω increments in TTI were associated with odds ratios of 1.36 (95% CI: 1.24–1.49) and 1.22 (95% CI: 1.09–1.37) for first and last shock failure, respectively (P < 0.001 for both). Conclusions: Although contemporary defibrillators are designed to compensate for TTI, this variable continues to be associated with ECV failure in patients with AF. Strategies to lower TTI during ECV for AF may improve procedural success. KEYWORDS Atrial Fibrillation, Cardioversion, Defibrillation, General Clinical Cardiology/Adult waveform based on the patient's transthoracic impedance (TTI).5,6 1 | I N T RO D UC T I O N This technology has superseded previous generations of monophaSynchronized electrical cardioversion (ECV) is considered a safe and sic waveform devices, as it has demonstrated comparable ECV effective method to restore sinus rhythm in patients with atrial success rates at lower energies and therefore with a lower risk of fibrillation (AF) or atrial flutter (AFL), thanks in part to advances tissue injury.1,2,7 in defibrillator technology. 1–4 Contemporary defibrillators deliver TTI has long been considered an important predictor of ECV suc- impedance-compensated biphasic waveforms that adjust the shock cess by influencing the current fraction that reaches the myocardium.7–9 However, though strategies to modify TTI during ECV Mouhannad M. Sadek, MD, and Varsha Chaugai, MEng, contributed equally to this work. 666 © 2018 Wiley Periodicals, Inc. attempts continue to be endorsed in current guidelines,3 its importance in the era of impedance-compensated biphasic defibrillators is wileyonlinelibrary.com/journal/clc Clinical Cardiology. 2018;41:666–670. 667 SADEK ET AL. unclear, with some data suggesting that its influence may be negligible.5,10 We therefore sought to explore the relevance of TTI on AF and AFL ECV success using contemporary defibrillators. We hypothesized that TTI continues to be associated with ECV failure in patients with atrial tachyarrhythmias. 2 | METHODS 2.1 | Patient selection, data collection, and study outcomes All patients undergoing ECV for AF or AFL over a 2-year period at the University of Ottawa Heart Institute were included. De-identified data stored in Philips HeartStart XL and HeartStart MRx defibrillators were downloaded using HeartStart Event Review Pro (Philips Healthcare, FIGURE 1 ECV case selection. Abbreviations: AF, atrial fibrillation; AFL, atrial flutter; ECV, electrical cardioversion; VF, ventricular fibrillation; VT, ventricular tachycardia Andover, MA), including electrocardiograms, number of shocks delivered, energy per shock, and TTI. All rhythm strips were reviewed by 3 | RE SU LT S 2 cardiac electrophysiologists blinded to the patient's TTI to confirm the baseline rhythm and to determine whether shocks were success- 3.1 | Electrical cardioversion outcomes ful. A shock was considered successful if it terminated the arrhythmia In total, 703 patients undergoing ECV for AF or AFL were included and resulted in ≥1 sinus beat. Otherwise, the shock was considered to (593 with AF and 110 with AFL; Figure 1). In the AFL cohort, first- have failed. shock failure occurred in 5 patients (4.5%) and last-shock failure in The primary outcome measure was last-shock success. Secondary 2 (1.8%), precluding detailed analyses of predictors of ECV failure. In outcomes included first-shock success, the number of shocks deliv- the AF cohort, first-shock and last-shock failure were observed in ered, and the cumulative energy delivered. The study was approved 183 and 71 patients (30.9% and 12.0%), respectively (Table 1). The by the Ottawa Health Science Network Research Ethics Board as an TTI associated with the first shock ranged from 26 Ω to 146 Ω in institutional quality-improvement initiative and was in accordance patients with AF. with the Declaration of Helsinki. 2.2 | Statistical analysis 3.2 | Association between TTI and procedural success Categorical data are reported as frequency and percentage, and con- Among patients with AF, patients with last-shock failure had a higher tinuous variables as mean SD. Analyses of AFL ECV failures were mean first-shock TTI compared with those with successful last shocks limited due to the small number of events. In patients with AF, associ- (81.2 25.3 vs 72.5 19.7 Ω; P = 0.007). Dividing the AF cohort into ations of first-shock TTI with last-shock success and with the need for quartiles based on first-shock TTI indicated a graded relationship multiple shocks were assessed via t tests and Cochran-Armitage trend whereby higher TTI was associated lower last-shock success, higher tests. The association between TTI and the cumulative shock energy delivered was assessed using the Spearman rank correlation coefficient. Individual shock success stratified by shock-specific (...truncated)