USING NOVEL CARDIOVASCULAR MAGNETIC RESONANCE 4D FLOW HEMODYNAMIC IMAGING TO INVESTIGATING VENTRICULAR AORTIC COUPLING

Abstract

<h3>Introduction</h3> Ventricular-aortic-coupling (VAC) is a mechanism of growing interest in heart disease and aging. It has been postulated that aortic stiffness could lead to progressive systolic and indirectly diastolic dysfunction. VAC is important to understand the interaction of cardiac contractility and compliance with the arterial system. Studies have reported anesthetic dose and rate of infusion are associated with ventricular-arterial uncoupling. This can be confounded further in patients with severe hemodynamic disorders such as septic shock, however, the relationship between the ventricular and arterial systems is still not fully understood. With 4D-flow cardiovascular magnetic resonance (CMR) imaging, the images of the thoracic cavity can be acquired in a single acquisition. Our goal was to investigate the relationship between intraventricular and aortic hemodynamics in a healthy population, using modern measures of 4D-Flow analysis and myocardial deformation. <h3>Methods</h3> 40 healthy participants were recruited to undergo a 3-Tesla CMR scan. A 4D-flow acquisition of the thoracic cavity was acquired and blood flow in the left ventricle were assessed for direct flow (blood that enters and leaves the ventricle during one heartbeat) and retained inflow (blood that enters the LV during diastole but is not ejected during the same cardiac cycle). From the same acquisition, 4D-pulse wave velocity (PWV) was calculated of the aorta. Systolic and diastolic ventricular function were assessed by peak systolic global longitudinal strain (GLS) and early diastolic strain rate from standard function cines. <h3>Results</h3> Participants (62.5% male) were aged from 21 to 63 years. Mean aortic PWV was 6.1±1.4m/s, LV direct flow fraction was 44.8±12.0% and retained inflow fraction was 25.6±6.3%. GLS was -17.1±2.0% and diastolic strain rate was 0.94±0.24/s. Increasing age was related to three parameters: Increase in aortic PWV (r=0.415, p=0.001), decrease in retained inflow (r=-0.575, p=0.001) and in early diastolic strain rate (r=-0.637, p<0.001). There was no association between systolic measures of GLS and direct flow fraction with age. When comparing flow results to ventricular strain, both a high aortic PWV (β=0.615, p=0.017) and reduced direct flow fraction (β=-0.06, p=0.048) were independently correlated with attenuated GLS, even when accounting for age. Diastolic strain rate was also independently linked to a high aortic PWV indicating aortic stiffness (β=0.024, p=0.001), and there was a correlation with the retained inflow fraction (r=0.408, p=0.031), however this was not significant when accounting for age. <h3>Conclusion</h3> Advanced measures of 4D-flow have shown that aortic pulse wave velocity as a measure of aortic stiffness and intraventricular hemodynamics are associated with reduced diastolic and systolic left ventricular deformation in a healthy control population. These modern quantitative measures should now be implemented in patient cohorts to investigate the role of VAC in cardiovascular disease, and how it may be impacted in an anesthetic setting.