Reduction of CPR artifacts in the ventricular fibrillation ECG by coherent line removal

Abstract

BackgroundInterruption of cardiopulmonary resuscitation (CPR) impairs the perfusion of the fibrillating heart, worsening the chance for successful defibrillation. Therefore ECG-analysis during ongoing chest compression could provide a considerable progress in comparison with standard analysis techniques working only during "hands-off" intervals.MethodsFor the reduction of CPR-related artifacts in ventricular fibrillation ECG we use a localized version of the coherent line removal algorithm developed by Sintes and Schutz. This method can be used for removal of periodic signals with sufficiently coupled harmonics, and can be adapted to specific situations by optimal choice of its parameters (e.g., the number of harmonics considered for analysis and reconstruction). Our testing was done with 14 different human ventricular fibrillation (VF) ECGs, whose fibrillation band lies in a frequency range of [1 Hz, 5 Hz]. The VF-ECGs were mixed with 12 different ECG-CPR-artifacts recorded in an animal experiment during asystole. The length of each of the ECG-data was chosen to be 20 sec, and testing was done for all 168 = 14 × 12 pairs of data. VF-to-CPR ratio was chosen as -20 dB, -15 dB, -10 dB, -5 dB, 0 dB, 5 dB and 10 dB. Here -20 dB corresponds to the highest level of CPR-artifacts.ResultsFor non-optimized coherent line removal based on signals with a VF-to-CPR ratio of -20 dB, -15 dB, -10 dB, -5 dB and 0 dB, the signal-to-noise gains (SNR-gains) were 9.3 ± 2.4 dB, 9.4 ± 2.4 dB, 9.5 ± 2.5 dB, 9.3 ± 2.5 dB and 8.0 ± 2.7 (mean ± std, n = 168), respectively. Characteristically, an original VF-to-CPR ratio of -10 dB, corresponds to a variance ratio var(VF):var(CPR) = 1:10. An improvement by 9.5 dB results in a restored VF-to-CPR ratio of -0.5 dB, corresponding to a variance ratio var(VF):var(CPR) = 1:1.1, the variance of the CPR in the signal being reduced by a factor of 8.9.DiscussionThe localized coherent line removal algorithm uses the information of a single ECG channel. In contrast to multi-channel algorithms, no additional information such as thorax impedance, blood pressure, or pressure exerted on the sternum during CPR is required. Predictors of defibrillation success such as mean and median frequency of VF-ECGs containing CPR-artifacts are prone to being governed by the harmonics of the artifacts. Reduction of CPR-artifacts is therefore necessary for determining reliable values for estimators of defibrillation success.ConclusionsThe localized coherent line removal algorithm reduces CPR-artifacts in VF-ECG, but does not eliminate them. Our SNR-improvements are in the same range as offered by multichannel methods of Rheinberger et al., Husoy et al. and Aase et al. The latter two authors dealt with different ventricular rhythms (VF and VT), whereas here we dealt with VF, only. Additional developments are necessary before the algorithm can be tested in real CPR situations.

A Review of the Performance of Artifact Filtering Algorithms for Cardiopulmonary Resuscitation

“…Among these publications, 56 engineering and medical papers were used as references according to the criteria. Finally, 8 papers from ScienceDirect, Web of Science and IEEEXplore about Kalman filter [28,29], independent component analysis (ICA) [30], coherent line removal [31] and adaptive filter [25,[32][33][34] were described, compared and discussed according to different artifact removal strategies.…”

“…Coherent line removal algorithm removes the periodic signals with sufficiently coupled harmonics [43]. For the reduction of CPR-related artifacts in VF, Amann et al [31] s…”

“…For coherent line removal, Amann et al [31] generated the corrupted ECG signals by mixing 14 human VF signals with 12 CPR artifacts recorded in an animal during asystole with different SNR levels. The performance of the algorithm was tested through 168 episode pairs.…”

A new method to detect ventricular fibrillation from CPR artifact-corrupted ECG based on the ECG alone

“…Compared with other rhythm classification algorithms, the PSR algorithm can provide higher values for the specificity and sensitivity and a shorter calculation time [22,24]. In this method, a two-dimensional phase space diagram divided into a 40 × 40 grid is reconstructed with signal x(t) on the x-axis and x(t + ) on the y-axis ( is a delay time constant) to identify a dynamic variation rule in the ECG waveforms.…”

“…Amman et al used the coherent line removal algorithm for removal of periodic CC artifact. Unfortunately, the SR/VF rhythms identification performance of this algorithm was not presented while only SNR-improvement was offered [22].…”