Characteristics of the wrist derived ptohoplethysmography signal : the impact of aortic valve stenosis

Aortic valve stenosis (AS) is the second most prevalent valvular heart disease in developed countries, and its impact on the healthcare system is expected to increase due to the aging western population. The disease monitoring process of AS using echocardiography imposes high costs and burdens on healthcare professionals and patients. In addition, it remains challenging to anticipate to the unpredictable nature of disease deterioration. Therefore, a noninvasive tool to remotely monitor AS progression could improve disease management and make the follow-up trajectory more efficient. Photoplethysmography (PPG), a technique often used in wearable devices, offers potential as it correlates with various physiological measurements affected by AS. The aim of this study is to investigate the association between AS and the PPG signal. We conducted an observational, prospective, multicenter study in patients undergoing a transcatheter aortic valve implantation (TAVI). The TAVI procedure offers a valuable clinical situation to unravel the effect of aortic valve obstruction on the characteristics of PPG signals. By comparing the PPG signal characteristics before and after valve implantation in patients with severe AS, it can be explored how resolving the valve obstruction impacts the signal. PPG data were acquired during the TAVI procedure and an algorithm was developed to select 300 consecutive and good-quality cardiac cycles from these data. Subsequently, the PPG signal characteristics of 156 patients were compared before and after valve implantation. The study demonstrated a significant increase after valve placement in the PPG features: systolic amplitude, area under the curve, upstroke, downstroke, (b+e)/a ratio, and the b/a ratio. A significant decrease after valve placement was found for the PPG features: crest time, e/a ratio, notch time, and the pulse width of the PPG signal at different heights. Significant differences after valve implantation suggest that these PPG signal characteristics could be used as potential indicators of AS progression, such as a decreased systolic amplitude or an increased crest time. An observational, prospective, single-center study was established to overcome the limitations of the TAVI study. The design and rationale of the study were described in Chapter 5. This study focuses on acquiring data during a transthoracic echocardiogram (TTE) to prevent bias introduced by surgical conditions and explore subtle differences in aortic valve function between patients. Patients with and without AS will be equipped with a wristband incorporating a PPG sensor during their TTE examination. The PPG signal characteristics will be compared between patients with AS and patients without AS. Currently, 71 patients have been included, of which 9 with severe AS, 9 with moderate AS, 1 with mild AS, and 4 with a stenotic bicuspid valve. This study contributes to the development of a remote monitoring device for AS that could potentially be used to reduce the number of unnecessary hospital visits and an earlier diagnosis of disease deterioration. To summarize, the TAVI study showed promising results indicating the potential of PPG in AS monitoring. These findings emphasize the need for further investigation under nonsurgical conditions, with native valves, and interpatient comparisons, which led to the establishment of the DETECT-REMOTE study. The combination of the results of both studies will contribute to a better understanding of the association between AS and the wrist-derived PPG signal and its potential clinical applications.