Deep Learning for Cardiologist-level Myocardial Infarction Detection in Electrocardiograms
Zihui (Betty) Qin, Wenqi (Maggie) Zhao, Muyuan Zhao, Amartya (Marty) Mukherjee
This paper presents an approach to the detection of heart disease from ECG signals by fine-tuning the deep learning neural network, ConvNetQuake, in the area of scientific machine learning. A deep learning approach was used due to the model’s ability to be trained using multiple GPUs and terabyte-sized datasets. This, in turn, creates a model that is robust against noise. The purpose of this paper is to provide detailed analyses of the contributions of the ECG leads on identifying heart disease, to show the use of multiple channels in ConvNetQuake enhances prediction accuracy, and to show that feature engineering is not necessary for any of the training, validation, or testing processes.
Previous work and Motivation
The database used in previous works is the Physikalisch-Technische Bundesanstalt (PTB) database, which consists of ECG records. Previous papers used techniques, such as CNN, SVM, K-nearest neighbours, naïve Bayes classification, and ANN. From these instances, the paper observes several faults in the previous papers. The first being the issue that most papers use feature selection on the raw ECG data before training the model. Dabanloo, and Attarodi  used various techniques such as ANN, K-nearest neighbours, and Naïve Bayes. However, they extracted two features, the T-wave integral and the total integral, to aid in localizing and detecting heart disease. Sharma and Sunkaria  used SVM and K-nearest neighbours as their classifier, but extracted various features using stationary wavelet transforms to decompose the ECG signal into sub-bands. The second issue is that papers that do not use feature selection would arbitrarily pick ECG leads for classification without rationale. For example, Liu et al.  used a deep CNN that uses 3 seconds of ECG signal from lead II at a time as input. The decision for using lead II compared to the other leads was not explained.
The issue with feature selection is that it can be time-consuming and impractical with large volumes of data. The second issue with the arbitrary selection of leads is that it does not offer insight into why the lead was chosen and the contributions of each lead in the identification of heart disease. Thus, this paper addresses these two issues through implementing a deep learning model that does not rely on feature selection of ECG data and to quantify the contributions of each ECG and Frank lead in identifying heart disease.
1. Quantification of accuracies for single channels with 20-fold cross-validation, resulting highest individual accuracies: v5, v6, vx, vz, and ii
2. Quantification of accuracies for pairs of top 5 highest individual channels with 20-fold cross-validation, resulting highest pairs accuracies to fed into a the neural network: lead v6 and lead vz
3. Use 100-fold cross validation on v6 and vz pair of channels, then compare outliers based on top 20, top 50 and total 100 performing models, finding that standard deviation is non-trivial and there are few models performed very poorly.
4. Discussing 2 factors effecting model performance evaluation:
1） Random train-val-test split might have effects of the performance of the model, but it can be improved by access with a larger data set and further discussion
2） random initialization of the weights of neural network shows little effects on the performance of the model performance evaluation, because of showing a high average results with a fixed train-val-test split
5. Comparing with other models in other 12 papers, the model in this article has the highest accuracy, specificity, and precision
6. Further using 290 fold patient-wise split, resulting the same highest accuracy of the pair v6 and vz as record-wise split
1） Discuss patient-wise split might result lower accuracy evaluation, however, it still maintain an average of 97.83%
3.1: Data curation
Dataset: 549 ECG records total
290 unique patients
Each ECG record has a mean length of over 100s
3.2: ANN model
ConvNetQuake model + 1D batch normalization + Label-smoothing
- Input layer: 10-second long ECG signal
- Hidden layers: 8 * (1D convolution layer, Activation function: RELU, 1D batch normalization layer)
- Output layer: 1280 dimensions -> 1 dimension, Activation function: Sigmoid
Batch size = 10
Learning rate = 10^-4
Optimizer = ADAM
1.The paper introduced a new architecture for heart condition classification based on raw ECG signals using multiple leads. It outperformed the state-of-art model by a large margin of 1 percent.
2.This study finds that out of the 15 ECG channels(12 conventional ECG leads and 3 Frank Leads), channel v6, vz and ii contain the most meaningful information for detecting myocardial infraction.
3.This study also finds that recent advances in machine learning can be leveraged to produce a model capable of classifying myocardial infraction with a cardiologist-level success rate.
4.To further improve the performance of the models, access to larger labelled data set is needed.
5.The PTB database is small. It is difficult to test the true robustness of the model with a relatively small test set.
6.If a larger data set can be found to help correctly identify other heart conditions beyond myocardial infraction, the research group plans to share the deep learning models and develop an open source, computationally efficient app that can be readily used by cardiologists.
1.A detailed analysis of the relative importance of each of the standard 15 ECG channels indicates that deep learning can identify myocardial infraction by processing only ten seconds of raw ECG data from the v6, vz and ii leads and reaches cardiologist-level success rate.
2.Deep learning algorithms may be readily used as commodity software. Neural network model that was originally designed to identify earthquakes may be re-designed and tuned to identify myocardial infraction.
3.Deep learning does not require feature engineering of ECG data to identify myocardial infraction in the PTB database. This model only required ten seconds of raw ECG data to identify this heart condition with cardiologist-level performance.
4.Access to larger database should be provided to deep learning researchers so they can work on detecting different types of heart conditions. Deep learning researchers and cardiology community can work together to develop deep learning algorithms that provides trustworthy, real-time information regarding heart conditions with minimal computational resources.