Defibrillation waveform and post-shock rhythm in out-of-hospital ventricular fibrillation cardiac arrest
Introduction
Out-of-hospital ventricular fibrillation cardiac arrest (OHCA) is one of the most common causes of cardiovascular death in the United States. Prompt defibrillation is the most effective means to resuscitate victims of OHCA [1], [2], [3]. Several different electrical waveforms may be used to achieve defibrillation. Monophasic waveforms deliver current in only one direction between anode and cathode, while biphasic waveforms deliver current of one polarity during the initial phase and then reverse the current's polarity in the second phase. Monophasic or biphasic waveforms may also vary in their individual configuration, having either a truncated exponential or damped sinusoidal shape. Defibrillation waveforms have been well studied in the electrophysiology laboratory in electrically induced ventricular fibrillation (VF), but our understanding of the relative performance of different waveforms in the setting of OHCA is incomplete [4], [5], [6], [7], [8]. In a randomized study of defibrillation in OHCA, an impedance compensating biphasic truncated exponential (BTE) waveform terminated VF more frequently than monophasic waveforms consisting primarily of monophasic truncated exponential (MTE) [9]. However, the defibrillation efficacy of the MTE waveform may be inferior to the monophasic damped sinusoidal (MDS) waveform [10], [11]. Such variability in waveform configuration complicates making comparisons solely on the basis of whether a shock was “biphasic” or “monophasic”. The importance of defibrillation waveform with respect to its effect on the evolving cardiac rhythm after shock, return of spontaneous circulation (ROSC), and eventual patient survival in OHCA is also uncertain.
The primary objective of this study was to evaluate cardiac rhythms following the first defibrillation shock, comparing MDS, MTE, and BTE waveforms in patients experiencing OHCA.
Section snippets
Study design and setting
The investigation was a retrospective cohort study of cardiac arrest patients presenting with an initial rhythm of VF, who were treated with at least one automated external defibrillator (AED) shock by emergency medical services (EMS) first-tier responders prior to arrival or treatment by second-tier EMS responders in King County (excluding Seattle) from 1 January 1999 through 31 August 2002. This area is served by a two-tiered EMS response system with providers who are all trained to identical
Results
A total of 467 patients suffered out-of hospital VF arrest due to heart disease and received at least one shock from an EMS first-tier responder during the study period. Of these cases, 79 were missing electronic or written records and 22 were incomplete due to malfunctions in the recording equipment, leaving 366 cases (78%) for analysis. There were no significant differences between missing and reviewed cases with regard to the distribution of waveforms, patient, or event characteristics (age,
Discussion
In cardiac arrest, VF is the most frequent initial rhythm [17]. The first step in successful resuscitation is defibrillation, whereby the VF rhythm is terminated. Subsequent steps for successful resuscitation require the restoration of an organized rhythm and ROSC. In this retrospective cohort study of VF cardiac arrest patients treated with first-tier EMS defibrillation, the MDS and BTE waveforms were associated with a higher frequency of defibrillation with the first shock or following the
Conclusion
In this retrospective cohort investigation, the MDS and BTE waveforms were associated with significantly greater defibrillation than the MTE waveform. By 60 s following the initial shock, an organized rhythm was present in a greater proportion of BTE patients. No clear differences were observed across the waveforms with regard to the subsequent steps of resuscitation: ROSC and hospital admission. However, a greater proportion of patients receiving initial treatment with MTE defibrillation
Acknowledgements
The authors thank the EMTs, paramedics, and emergency dispatchers of King County, Washington, for their ongoing excellence in the care of cardiac arrest, as well as Linda Becker, Terry Sinclair, Dan Anderson, and James Scappini of King County EMS for their technical assistance, preliminary review, and organization of the AED recordings.
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