A modified pseudo-bispectral MUSIC technique for on-line identification of abnormal atrial activations in noisy ECG signals

摘要

This paper presents a novel super-resolution weighted-noise/signal-subspace pseudo-bispectral MUSIC (WPBiMUSIC) technique to detect on-line the principal pseudo-bispectral peaks (PPBiPs) associated with abnormal atrial activations (P-waves) which can occur simultaneously with the QRS complex or the T-wave in arrhythmias cases. In the P-on-QRS case (P-wave(s) coincident with the QRS complex), the positions of the centre regions of the P-waves are manifested by small indentations on the QRS complex. Here the gold standard for P-wave identification is arguably expert clinician opinion. The alternatives to clinician opinion include inherently invasive imaging modalities such as echocardiography or an electrocardiogram (ECG) recorded directly from the atrium using an epicardial or endocardial electrode. Both alternatives require specialist equipment and interpretative expertise. The WPBi-MUSIC technique described in this paper offers higher resolution and achieves higher detection rate of the principal pseudobispectral peaks (PPBiPs) over and above that already obtained by employing a recently proposed novel decision strategy for P-wave detection based on second-order statistics (SOS) [1]. The proposed strategy in [1] is essentially based on the exploitation of the unique structural properties of the principal pseudo-spectral MUSIC peaks (PPPs) of the P-wave (or the entire PR interval including the P-wave), QRS complex, and the combined S-T segment and the T-wave. Results obtained previously have confirmed that most of the atrium and ventricle depolarisation-wave spectral energies (approximately 90%) are confined to two overlapping clusters inscribed by the top of the principal pseudo-spectral peaks (PPPs) and centred at 12 Hz and 15 Hz, respectively. In this paper, the super-resolution capability of the WPBi-MUSIC yields precise identification of anomalous P-waves particularly in the following two cases: (i) a small group of healthy male population studied, so far, has been found to produce total overlapping of the atrium and ventricle depolarisation-wave pseudo-spectral energies (the PPPs of the P-waves and the QRS complexes share the same frequencies), (ii) in some classes of arrhythmia, several successive abnormal atrial activations can be produced concurrently with the QRS complex over an 120 msec interval. Both require very high resolution to distinguish between very closely spaced PPPs. The results presented in this paper involve clinical trials and include 59 healthy volunteers, equivalent to 1600 hours of ECG recordings, sampled at 500 Hz. In addition, parallel observations of mechanical contractions of the atrium using Echocardiographic imaging and detected PPBiPs of the P-wave by processing the non-invasive ECG signals have been carried out to demonstrate the robustness of the WPBi-MUSIC technique in the worst scenarios of invisible P-waves. Where immediate decisions regarding, say second degree atrial-ventricular block, or different arrhythmia, must be taken.