Purpose: Chest compressions (CCs) delivered by a Load Distributing Band (LDB, AutoPulse) compressor induce artefacts in the ECG that may make the shock advice algorithms (SAA) of defibrillators inaccurate during CCs. The aim of this study was to design an adaptive filter to remove the LDB-artefact preserving ECG quality and thus allowing a reliable rhythm analysis
during CCs.
Materials and methods: Data from 362 out-of-hospital cardiac arrest patients treated with the LDB from one Circulation Improving Resuscitation Care trial site. A total of 1686 ECG segments were extracted during LDB CCs, whereof 235 were shockable rhythms and 1451 non-shockable (677 asystole, 774 organized). Filtering was performed using a Recursive-Least-Squares filter adjusted to the LDB frequency (80 min-1) with a variable number of harmonics (N). Data was partitioned randomly and patient-wise into training (60%) and test (40%). Training set was used to optimize the filter parameters (0.98<λ<1 and 25<N<36). Filtered test segments were diagnosed as shock/no-shock using the SAA of the Reanibex 800 (BexenCardio) defibrillator. The procedure was repeated 500 times to estimate the statistical distributions of sensitivity (Se) and specificity (Sp).
Results: The mean(SD) signal to noise level of unfiltered rhythms was -9.96(8.48) dB. The median (95% confidence interval) peak-peak amplitude of the artefact during asystole was 4.78 (0.58-23.58) mV, and was reduced to 0.25 (0.04-1.76) mV after filtering. Before filtering Se was 31.9%, and Sp were 89.4% and 95.6% for organized rhythms and asystole, respectively. Filtering increased the mean(SD) Se to 91.5 (2.0), but lowered the Sp to 82.4 (2.0) and 95.3 (1.3), respectively. The optimal filter used 31 harmonics and λ=0.988.
Conclusions: Adaptive filtering considerably reduced the LDB-artefact. The filter followed by a SAA provided an accurate rhythm diagnosis for shockable rhythms and asystole. Further studies are needed to increase the Sp for organized rhythms.

3 - Removing Mechanical Chest Compression Artefacts induced by a Load Distributing Band Device from the ECG