Abstract 260: Automatic Shock Advisory Without Interrupting Chest Compression by Filtering Compression Artifact
Background: Both AHA and ERC Guidelines 2010 focus on minimizing “hands-off time” - the time interval a patient in cardiac arrest is not receiving chest compressions (CC). The primary device-related cause of CC interruption is automated ECG rhythm analysis for accurate shock advisory. The mechanical activity of CC produces artifact on the ECG waveform that most automated ECG analysis programs cannot fully differentiate from the patient’s inherent ECG morphology. Furthermore, clinicians observing an ECG waveform on the defibrillator’s display cannot see the patient’s underlying rhythm through the electrical noise created by CC, forcing an interruption to CC for rhythm assessment.
Objective: Improving the performance of ECG analysis programs by filtering artifacts due to CC in out of hospital cardiac arrest (OHCA) patients.
Methods: Recordings from 175 OHCA patients collected for a separate study using Laerdal HeartStart 4000 defibrillators in 6 ambulances in 3 European regions between March 2002 and October 2003. The transition times from CC to hands-off were marked. Assuming no rhythm change within a few seconds around the transition time, experts selected 1378 4.5-second ECG segments with CC artifact, and the same number without the artifact. Each category included 340 shockable ventricular fibrillation, 342 asystole, 646 pulseless electrical activity, and 50 pulsatile rhythms. A two-step process was designed to filter the CC artifact prior to the analysis by the shock advisory algorithm. By analyzing both ECG and thoracic impedance waveforms the fundamental frequency of CC was found, to then be filtered along with all its harmonics using a comb filter.
Results: Defining a positive event as shock advice for shockable rhythm, the shock advisory algorithm achieved sensitivity of 97% and specificity of 99% when no CC was being performed. However during CC both sensitivity and specificity dropped to 63% and 91% respectively. Filtering the CC artifact increased the sensitivity back up to 89% at the expense of slightly reducing the specificity to 90%.
Conclusion: It is possible to improve the performance of shock advisory algorithms during CC by filtering the CC artifact. However additional techniques may be needed to achieve accuracy high enough for practical use.
- © 2013 by American Heart Association, Inc.