Myocardial stiffness measured by natural shear wave imaging correlates with poor exercise performance in Fontan patients

Background Ventricular stiffness – a key aspect of diastolic function - is a major contributor to Fontan failure. Traditional echocardiography fails to reliably assess diastolic function in single ventricles or to explain reduced functional capacity among patients post-Fontan. Shear waves (SW), generated by valve closure, offer a novel echo-based marker of myocardial stiffness. However, whether they relate to functional capacity in Fontan patients is unexplored. Purpose We measured myocardial SW velocities at rest in adults with a Fontan circulation and investigated their relation to VO2peak as a marker of exercise capacity. Methods This ongoing single-center study includes both adults post-Fontan and healthy volunteers (HV). Participants underwent high frame rate echocardiography using a research scanner capturing images at 1200 frames/second. Natural SWs were tracked along the ventricular septum after mitral valve closure in HV, or after atrioventricular valve closure in patients. If the septum was absent, SWs were tracked along the anterior wall of the dominant ventricle. An anatomical M-mode line was drawn from base to apex to generate color-coded acceleration maps. SWs appeared as tilted green bands, and their slope -indicating propagation velocity- was estimated semi-automatically. Patients underwent blood sampling for NT-proBNP and cardiopulmonary exercise testing on a supine bicycle combined with peripheral venous pressure (PVP) measurement via a venous catheter inserted into a peripheral vein in the arm. PVP correlates with mean pulmonary arterial pressure in Fontan patients, and a PVP/cardiac output (CO) slope > 3 is associated with worse clinical outcome. Results Fifty patients and 117 matched-HV were recruited. The mean age of Fontan patients was 32.4±9.3 years and 44% were female. Natural SW velocities were measurable in all HV and in 47 (94%) of patients. SW velocities were higher in Fontan compared to HV (6.0±1.3 m/s vs 3.4±0.6 m/s, p<0.001) and increased with age (r=0.46, p=0.001, Fig. 1A) and time since Fontan palliation (r=0.48, p=0.001). SW velocities correlated strongly with VO2peak values (r=-0.75, p<0.001, Fig. 1B), and correlated significantly with steeper PVP/CO slopes (r=0.49, p=0.001) and elevated NT-proBNP (r=0.49, p=0.001) (Fig. 1C-D). Notably, univariable regression analysis revealed that VO2peak was significantly associated with age, sex, NT-proBNP levels, PVP/CO slopes, and SW velocities. In the multivariable regression model that included all these variables, only SW velocities maintained a significant independent association withVO2peak (Table 1). Conclusion Natural SW imaging in adults post Fontan palliation is feasible. SW velocities correlated strongly with elevated NT-proBNP, elevated PVP/CO slope and reduced exercise capacity. These preliminary results of an ongoing study confirm the potential of natural SW imaging for the assessment of ventricular stiffness in adults post-Fontan in a larger cohort.