Ischemia episode detection in ECG using kernel density estimation, support vector machine and feature selection

School of Information and Communications, Gwangju Institute of Science and Technology 1, , Oryong-dong, Buk-gu, Gwangju, Republic of Korea. .
BioMedical Engineering OnLine (Impact Factor: 1.43). 06/2012; 11(30):30. DOI: 10.1186/1475-925X-11-30
Source: PubMed


Myocardial ischemia can be developed into more serious diseases. Early Detection of the ischemic syndrome in electrocardiogram (ECG) more accurately and automatically can prevent it from developing into a catastrophic disease. To this end, we propose a new method, which employs wavelets and simple feature selection.
For training and testing, the European ST-T database is used, which is comprised of 367 ischemic ST episodes in 90 records. We first remove baseline wandering, and detect time positions of QRS complexes by a method based on the discrete wavelet transform. Next, for each heart beat, we extract three features which can be used for differentiating ST episodes from normal: 1) the area between QRS offset and T-peak points, 2) the normalized and signed sum from QRS offset to effective zero voltage point, and 3) the slope from QRS onset to offset point. We average the feature values for successive five beats to reduce effects of outliers. Finally we apply classifiers to those features.
We evaluated the algorithm by kernel density estimation (KDE) and support vector machine (SVM) methods. Sensitivity and specificity for KDE were 0.939 and 0.912, respectively. The KDE classifier detects 349 ischemic ST episodes out of total 367 ST episodes. Sensitivity and specificity of SVM were 0.941 and 0.923, respectively. The SVM classifier detects 355 ischemic ST episodes.
We proposed a new method for detecting ischemia in ECG. It contains signal processing techniques of removing baseline wandering and detecting time positions of QRS complexes by discrete wavelet transform, and feature extraction from morphology of ECG waveforms explicitly. It was shown that the number of selected features were sufficient to discriminate ischemic ST episodes from the normal ones. We also showed how the proposed KDE classifier can automatically select kernel bandwidths, meaning that the algorithm does not require any numerical values of the parameters to be supplied in advance. In the case of the SVM classifier, one has to select a single parameter.

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    • "The features used in our method are fewer in number but are more closely related to medical indicators than the previous methods. The method proposed byPark et al. in 2012has also shown high sensitivity of 94.1%[25]. Identical with the method proposed by Park et al., our method is designed with carefully specified features which are highly correlated with the clinical evidences observed in the ECG signals from patients with myocardial ischemia, such as ST elevation or the changes of T waves. "
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    • "They have compared their results with MIT/BIH database and obtained a sensitivity of 99.53% and a positive predictivity of 99.73 and a sensitivity of 99.7% and a positive predictivity of 99.68%. Park et al. (2012) proposes a wavelet interpolation filter to remove motion artefacts around the ST-segment of stress ECG. Inoue and Miyazaki (1998) "
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