Discussion:
HAART ring implantation has been shown to be a safe and effective valve-sparing approach to restore annular geometry in patients with AI with root or AAo enlargement1. To our knowledge, this report is the first to use 4D MRI to characterize flow patterns following HAART ring placement. Our analysis showed that flow velocities, WSS, and VEL increased following aortic repair, regardless of HAART implantation. While still poorly understood, higher flow velocities and VEL likely have adverse effects on ventricular loading and accelerate remodeling5,6. Moreover, increased area of elevated WSS is associated with greater rates of aortic dilation due to shear stress on native portions of aortic wall4.
Our series did demonstrate, however, that patients receiving HAART ring implantation displayed similar or improved WSS, VEL, and peak velocity profiles compared to subjects with aortic replacement alone. But, given the proximity to surgery, post-operative scans may have been acquired in the setting of ventricular ejection patterns before remodeling. It may be of value to study interval changes in flow patterns in the aortic root after allowing ample time for ventricular remodeling. Furthermore, grading of AS can be assessed through the degree of flow acceleration across the valve7. Flow acceleration was either reduced or similar in HAART patients when compared to control, suggesting the HAART ring does not contribute to AS.
Importantly, the increases in WSS, VEL, and peak velocity seen in our patients are not unexpected and are multifactorial. VSARR alone has previously been associated with increases in complex aortic blood flow, of which VEL is a marker8. We have previously speculated that this is, in part, due to the decreased compliance in Dacron grafts relative to physiologic tissue and absence of the Windkessel effect.
Our case series demonstrates while HAART patients may still be at elevated risk for abnormal aortic flow and remodeling, there may be a trend towards improved flow dynamics. Sample size and the short interval between surgery date and acquisition of post-surgery scans limit our ability to further characterize HAART ring alterations of flow. It would be worthwhile to analyze flow patterns at a longer interval to definitively rule out AS. Additionally, our work highlights serial 4D flow imaging as a valuable, noninvasive tool with minimal radiation exposure for post-operative evaluation of patients undergoing aortic surgery and for prognostication of need for future reintervention.