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.