Hemodynamic flow signatures: a novel paradigm for the evaluation of transcatheter aortic valve performance

A new paradigm for understanding transcatheter aortic valve (TAV) success is emerging, which hinges on whether a device reinstates physiological aortic flow. Limitations of echocardiography prevent complex flow assessment. Meanwhile, 4-dimensional flow cardiac magnetic resonance offers superior quantification of time-resolved 3-dimensional flow dynamics, permitting assessment of systolic flow displacement (reflecting eccentricity), systolic flow reversal ratio (reflecting conduit inefficiency), wall shear stress, and energetic efficiency. Abnormal aortic flow can persist after TAV replacement, despite reduction in transvalvular gradient. Persistent nonphysiological flow is thought to increase energy losses, reduce left ventricular ejection efficiency, and impair optimal afterload reduction, which theoretically may limit left ventricular reverse remodeling. Restoration of near-normal flow is a plausible therapeutic target for evaluating TAV performance. However, whether physiological flow restoration post-TAV replacement may enhance left ventricular mass reduction, increase TAV durability, and improve patient-relevant outcomes is unknown, and further research is crucial. Future clinical translation of cardiac magnetic resonance flow metrics also depends on automated extraction of systolic flow displacement and systolic flow reversal ratio, and postprocessing standardization. This review provides a perspective on 4-dimensional flow cardiac magnetic resonance for evaluating aortic flow post-TAV replacement, which may have the potential to refine TAV platform selection, inform next-generation device design, and hypothetically predict left ventricular recovery.