Amplitude Spectrum Area to Guide Defibrillation

Abstract

Background-This study sought to validate the ability of amplitude spectrum area (AMSA) to predict defibrillation success and long-term survival in a large population of out-of-hospital cardiac arrests. Methods and Results-ECGs recorded by automated external defibrillators from different manufacturers were obtained from patients with cardiac arrests occurring in 8 city areas. A database, including 2447 defibrillations from 1050 patients, was used as the derivation group, and an additional database, including 1381 defibrillations from 567 patients, served as validation. A 2-second ECG window before defibrillation was analyzed, and AMSA was calculated. Univariable and multivariable regression analyses and area under the receiver operating characteristic curve were used for associations between AMSA and study end points: defibrillation success, sustained return of spontaneous circulation, and long-term survival. Among the 2447 defibrillations of the derivation database, 26.2% were successful. AMSA was significantly higher before a successful defibrillation than a failing one (13±5 versus 6.8±3.5 mV-Hz) and was an independent predictor of defibrillation success (odds ratio, 1.33; 95% confidence interval, 1.20-1.37) and sustained return of spontaneous circulation (odds ratio, 1.22; 95% confidence interval, 1.17-1.26). Area under the receiver operating characteristic curve for defibrillation success prediction was 0.86 (95% confidence interval, 0.85-0.88). AMSA was also significantly associated with long-term survival. The following AMSA thresholds were identified: 15.5 mV-Hz for defibrillation success and 6.5 mV-Hz for defibrillation failure. In the validation database, AMSA ≥15.5 mV-Hz had a positive predictive value of 84%, whereas AMSA ≤6.5 mV-Hz had a negative predictive value of 98%. Conclusions-In this large derivation-validation study, AMSA was validated as an accurate predictor of defibrillation success. AMSA also appeared as a predictor of long-term survival. (Circulation. 2015;131:478-487.

Application of Entropy-Based Features to Predict Defibrillation Outcome in Cardiac Arrest

“…All classical predictors showed significantly different statistical distributions (p < 10 −10 ), and the boxplots visually show little overlap between the classes. Moreover, the values obtained for the features in both classes are in line with the values reported on other studies on shock outcome prediction [12,20,21,25,30]. The entropy measures of regularity also showed good class separation and significantly different distributions (p < 10 −10 ).…”

“…Shocks were labeled valid for analysis if they contained an artifact-free VF during the pre-shock segment and at least one minute of post-shock ECG for shock outcome annotation. A shock was considered successful when sustained and narrow QRS complexes (rate ≥ 40 min −1 ) appeared within one minute of the shock [12]. Figure 1 shows three representative examples of shocks in which the pre-shock segment (analysis) and the post-shock segment (annotation) are shown.…”

“…AMSA is a frequency weighted mean of the spectral amplitudes of the VF waveform [27], and it is the most extensively studied of all predictors [12]. To compute AMSA, the signal was Hamming windowed, and its fast Fourier transform (FFT), X(k), was computed using a N FFT = 2048 point FFT.…”

“…To compute AMSA, the signal was Hamming windowed, and its fast Fourier transform (FFT), X(k), was computed using a N FFT = 2048 point FFT. The amplitude for frequency index k is then A k = |X(k)|, and AMSA was computed as [12]:…”

“…During the analysis pause, the defibrillator's shock advisory algorithm analyzes the ECG waveform [10], then if VF is detected, the defibrillator is charged, and a shock is delivered to the patient. However, many defibrillation attempts are futile [11,12]. The consequences are longer CPR interruptions to charge the defibrillator and potential damage to the myocardium caused by the shock; both of these factors compromise the survival of the patient [13,14].…”