ECG detector/delineator (Wavedet)

ECG detector/delineator

Morphological characteristics of ECG (electrocardiographic) signal contain relevant information about electrical changes occurred in the heart.  Some of them are generated in the atria and others in the ventricles.  Looking at one single ECG beat it is easy to see at least three parts clearly distinguishable.

 

Principal segments and waves in a single heart beat electrical activity.

The first wave is named P wave which reflects the atrial depolarization.  Its presence in the beat is a symptom of the beat was generated in the sinus-atria node.  The second part is the qrs-complex.  As it is own name indicates it is composed of three waves, Q, R and S.  The underlying physiology of this complex is due to the ending of the atrial repolarization as well as the ventricles depolarization.  Moreover, the R wave peak is usually considered as the reference location of a heart beat usually named as fiducial point.  The final part of the heart beat consists of the repolarization of the ventricles and its representation on the ECG is registered at the T wave.

Each particular wave determined by their peaks and boundaries is crucial for advanced signal processing.   The better resolution either in detection (in case of peaks) or in the delineation (in the case of boundaries), the greater accuracy in the characterization of each physiological part in the ECG.  And it is suggested to check those marks generated once the automatic ECG detector/delineator was applied.

ECG Detector/Delineator included in BioSigBrowser are based on the wavelet transform.  Basically, it exploits the frequency content of each main wave decomposing them in different time-scale projections. Further details of accuracy and thresholds used by this algorithm can be found elsewhere {JP2004}.

As it was mentioned before, detection referrers to detect wave peaks whereas delineation means to find the boundaries of the waves.  And BioSigBrowser allows doing this by three ways.

  1. Single lead: The detection and delineation is done in a single lead using wavelet transform and using several sort of thresholds and time windows.
  2. Multi-lead: It is based on vectorcardiogram which is computed by three orthogonal leads. The loop, which is the graphical view of each orthogonal leads on the three axes, allows finding the maximum direction which is related with the projection of the electrical axes of the heart.  Then, a pseudo-lead can be generated as a projection of theses leads over this maximum direction and single lead approach can be applied to achieve one representative set of marks.  The marks obtained through this algorithm reflect the global electrical phenomena.  One of the advantages of this algorithm yields on the vectorcardiogram which is less affected by respiratory movements than single lead approach.  However, on the other hand, this ECG detection option is much time-consuming than single lead approach.

Single lead + rules: This third option combines the single lead approach, which is less time-consuming, and a set of post-processing rules.  Single lead approach is done over all desired leads and afterwards the post-processing rules are applied.  These rules are based on the consistency of marks meaning that they were grouped and as a result outliers are not considered.  Therefore, a unique set of marks looking for representing the whole electrical phenomena from the early mark from each single wave onset to the latest mark offset is obtained.

ECG Detector/Delineator setup interface.

External marks can be used for limiting the searching step of delineator.  These external marks, usually fiducial points, can be provided by some expert (clinician) or by other kind of ECG detector.

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