Valve-in-valve transcatheter aortic valve implantation: the new playground for prosthesis-patient mismatch.

Transcatheter aortic valve implantation (TAVI) has become an established procedure for patients with aortic valve stenosis and significant comorbidities. One option offered by this technique is the implantation of a transcatheter valve inside a surgically implanted bioprosthesis. Many reports address the feasibility but also the pitfalls of these valve-in-valve (VIV) procedures. Review articles provide tables listing which valve sizes are appropriate based on the size of the initially implanted bioprosthesis. However, we previously argued that the hemodynamic performance of a prosthetic tissue valve is in large part a result of the dimensions of the bioprosthesis in relation to the patient's aortic outflow dimensions. Thus, the decision if a VIV TAVI procedure is likely to be associated with a favorable hemodynamic result cannot safely be made by looking at premade sizing tables that do not include patient dimensions and do not inquire about the primary cause for bioprosthetic valve stenosis. Prosthesis-patient mismatch (PPM) may therefore be more frequent than expected after conventional aortic valve replacement. Importantly, it may be masked by a potentially flawed method assessing its relevance. Such PPM may therefore impact significantly on hemodynamic outcome after VIV TAVI. Fifteen percent of currently published VIV procedures show only a minimal reduction of pressure gradients. We will address potential pitfalls in the current determination of PPM, outline the missing links for reliable determination of PPM, and present a simplified algorithm to guide decision making for VIV TAVI.