Abstract 240: AMSA Predicts Shock Success in Cardiac Arrest Patients with Different Transthoracic Impedance
Introduction: Amplitude spectrum area (AMSA), which is calculated from the Fourier transformation of ventricular fibrillation (VF) waveforms, has shown its ability in predicting the likelihood of successful defibrillation and monitoring the effectiveness of chest compression [1-3]. In the present study, we retrospectively evaluated the reliability of AMSA in predicting shock success over entire transthoracic impedance (TTI) range in pre-hospital cardiac arrest victims.
Methods ECG recordings, along with TTI measurements between two shocking pads, were collected from multiple emergency medical services (EMS) in the USA through a regular field case submission program sponsored by ZOLL Medical Corporation. All the EMSs in this study use ZOLL AED which employs current-based impedance compensation technique. AMSA was calculated based on a 1024 point ECG window ending at 0.5 sec before each shock attempt. Shock success was defined as an organized rhythm that was present for a minimum of 30 seconds, started within 60 seconds after the shock, and had a rate of 40 beats per minute or greater.
Results: A total of 599 patients with witnessed rhythm of VF were included in the analyses. Only the first shock (120J) was analyzed. As shown in Figure 1, AMSA was significantly higher for successful shocks as compared with failed shocks in different TTI ranges. With an AMSA threshold of 8 mVHz, a large amount of unnecessary shocks (79.3%, 92.4% and 98.1%) were avoided with accuracy of 61.5%, 65.4% and 62.2% when TTI was low, normal and high, respectively. Logistic regression indicated that both AMSA (O.R. 1.19) and TTI (O.R. 0.99) were independent predictors for shock success, though, AMSA was a positive predictor and TTI was a negative predictor for shock success.
Conclusion: In this patient population, AMSA was confirmed to be significantly higher in the presence of successful defibrillation over the entire TTI range. AMSA therefore can reliably predict shock outcome at different TTI ranges. References 1. Marn-Pernat A, Weil MH, Tang W, et al. Crit Care Med 2001,29(12): 2360-2365. 2. Povoas HP, Weil MH, Tang W, et al. Resuscitation 2002;53(1):77-82. 3. Li Y, Ristagno G, Bisera J, et al. Crit Care Med. 2008 Jan;36(1):211-5.
- © 2011 by American Heart Association, Inc.