Carotid Pulse Arrival Time as a Potential Biomarker for Ascending Thoracic Aortic Aneurysm: Proof-of-Concept Studies

Abstract Monitoring of ascending thoracic aortic aneurysm by contrast CT presents major cost, health, and patient availability issues, especially for patients in rural areas. Although CT is expected to remain the gold standard for patient monitoring, these issues make it attractive to explore an alternative monitoring modality that could be done more often, possibly even at home, and could be used to screen whether the full CT is necessary. Such a tool would not only help reduce the number of CT scans needed for stable patients, it would also have the potential to be used more often than the usual 6-12 month frequency of surveillance CT, meaning that a potential problem could identified sooner. In this exploratory project, we will determine whether carotid pulse arrival time (cPAT) has the potential to be such a monitoring tool. cPAT is easily measured via surface tonometry, and electrical-impedance-based methods are even simpler and less costly. cPAT is also a direct measurement of flow through the ascending thoracic aorta, unlike the standard pulse wave velocity measurements that test wave speed between, e.g., the carotid and femoral arteries. The appeal of cPAT is clear, but it is not clear that the measurement is sensitive enough to measure significant changes in the ascending aorta. Thus, we will use two Specific Aims to assess the potential of cPAT as a monitoring tool. First, we will perform an experiment on a large cross-sectional cohort to determine whether cPAT results are consistent with the empirical expected pulse wave velocity based on age and blood pressure, testing whether cPAT can measure a population-level trend that one would expect to see. Second, we will perform computer simulations of fluid-structure interaction flow in the ascending aorta, using realistic geometries based on patient scans. These simulations, which will include longitudinal patient scans and artificially enlarged aneurysms, will allow us to assess how much of a change in vessel properties could be detected given the time resolution of the cPAT. Together, these two Aims will determine whether a larger-scale study is merited on whether cPAT can be an effective monitoring tool.