Valve replacement for severe calcified aortic stenosis (AS) is currently the second most frequently performed cardiac operation. In these patients, the insertion of a small size prosthesis is an issue of concern, because the incomplete relief of left ventricular obstruction might have the same consequences as native AS—namely, high trans-aortic pressure gradients and increased left ventricular afterload leading to persistent left ventricular hypertrophy and persistent symptoms. Valve prosthesis–patient mismatch (PPM) has been described when the implanted prosthesis is too small according to the patient’s body size, resulting in high postoperative gradients.1 Pibarot and colleagues have underscored the negative impact of PPM on early postoperative survival, especially in case of preoperative left ventricular dysfunction.2 In addition, the same authors have proposed a strategy, based on the projected indexed effective orifice area (EOA) of the prosthesis, to eventually indicate more complex interventions (that is, aortic root enlargement) in case of anticipated mismatch. In contrast, several authors have failed to demonstrate any impact of PPM on postoperative outcome3^–5 and thus the clinical relevance of PPM has been largely debated. More recently, the issue of mismatch in the mitral position was also addressed.6^–8 From a clinical standpoint, the main issues could be summarised as follows: Is PPM a clearly defined entity and is it predictable? Is there reasonably convincing evidence that the negative impact of mismatch may justify more complex surgical interventions? Is there evidence that such a preventive strategy improves patient’s outcome?

WHAT IS THE DEFINITION OF MISMATCH IN THE AORTIC POSITION?

In most studies, prosthesis–patient mismatch is defined according to the projected EOA taken from published in vivo reference values for each type and size of prosthetic valves and indexed to the patient’s body surface area.2–5 9^–13 A currently accepted definition is the following: no PPM if the projected …