Bimodal ECG-PCG Cardiovascular Disease Detection: a Close Look at Transfer Learning and Data Collection Issues

Early detection of cardiovascular diseases (CVDs) is crucial for minimizing their adverse impact on patients' health. Electrocardiograms (ECGs), which capture the heart's electrical activity, have been widely used to primarily evaluate heart conduction disorders. On the other hand, phonocardiograms (PCGs) recorded during cardiac auscultation, have been less explored, often being overlooked in favor of echocardiograms for detecting mechanical issues such as valvular diseases. However, due to their low cost and non-invasive nature, the analysis of both ECGs and PCGs can be easily integrated into preventive settings. Combining effectively the complementary information from these two modalities could significantly enhance the early detection of CVDs, where Machine Learning (ML) techniques can offer promising and cost-effective solutions. Progress in this area, however, has been limited by the lack of large enough datasets containing both ECG and PCG signals. One objective of this work is to analyze in-depth prior bimodal CVD detection research, identifying key issues to better address data collection and transfer learning limitations. We also propose a different approach to transfer learning for improving heart sound interpretation. Our findings confirm the effectiveness of using both signals to detect abnormal heart conditions. However, we also notice that even a refined transfer learning approach to enhance PCG interpretation is not enough to fully address the issues coming from the lack of bimodal data, indicating the need for further efforts in this direction. Ultimately, our bimodal approach achieved an overall AUROC of 96.4%, exceeding the performance of corresponding ECG-only and PCG-only models by approximately 3% and 10%, respectively. Compared to the other existing approaches, our method demonstrated superior AUROC performance while maintaining a relatively low false-negative rate, which is critical in CVD screening contexts.