Detecting paroxysmal atrial fibrillation from normal sinus rhythm in equine athletes using Symmetric Projection Attractor Reconstruction and machine learning

Figures

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  Figure 1. Flowchart of the overall methodology from the raw data to final classification. ECG = electrocardiogram; SPAR = Symmetric Projection Attractor Reconstruction.

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  Figure 2. The 20-second electrocardiogram (ECG) sub-strip and its corresponding attractor for 2 different control subjects (a, b) and 2 different paroxysmal atrial fibrillation (PAF) subjects (c, d). Subtle differences in the rotation of the central core region of the attractor could be observed between the control and PAF groups for most subjects. This figure illustrates the differing appearance of equine ECGs and also that the attractor is independent of any vertical shift of the signal, since the resulting image remains centered on the origin of the (v,w) plane (see Aston and colleagues21 for further details).

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  Figure 3. Posterior probability scores for likelihood of a paroxysmal atrial fibrillation (PAF) diagnosis by subject for the 48 subjects of dataset 2, with control subjects in blue and PAF subjects in red. a: Results for initial model trained using features derived from only dataset 1 (91 subjects). b: Results for revised model trained using features derived from the combined dataset 1 and dataset 2 (91 + 48 subjects), but trained on only dataset 1 data.

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  Figure 4. Mean posterior probability scores for likelihood of a paroxysmal atrial fibrillation (PAF) diagnosis over 1000 stratified repeated random sampling cross-validation runs for dataset 3, with control sub-strips/subjects in blue and PAF sub-strips/subjects in red. a: Classification of each 20-second sub-strip record (1251 sub-strips, 9 per subject). b: Classification of subject (139 subjects).

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  Figure 5. Density profiles for the attractors of dataset 3 (139 subjects, 1251 attractors) for (a) r density, (b) θ arm densities, (c) θ core densities, where r is the distance from the center of the attractor and θ reflects the angular movement around the attractor. Control records are shown in blue, paroxysmal atrial fibrillation records are shown in red. The solid lines correspond to the mean for each class of the data, the dotted lines correspond to the mean plus standard deviation, and the shaded regions indicate the data between the 5th and 95th percentiles.

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  Figure 6. The θ core density profiles of the attractors for (a) the 6 paroxysmal atrial fibrillation (PAF) subjects with the (originally) 256 Hz electrocardiograms (ECGs), (b) the 13 PAF subjects with 500 Hz ECGs, and (c) the 6 PAF subjects with the (originally) 256 Hz ECGs after the signals were multiplied by -1. The solid lines correspond to the mean for each class of the data, the dotted lines correspond to the mean plus standard deviation, and the shaded regions indicate the data between the 5th and 95th percentiles.