**8. Patient-prosthesis mismatch**

Prosthesis‐patient mismatch (PPM) is that a smaller than expected effective orifice area (IEOA) in relation to the patient's body surface area (BSA) will result in higher transvalvar gradients. It is condition that occurs when the valve area of a prosthetic valve is less than the area of that patient's normal valve.[46] Several authors suggest that prosthesis-patient mismatch occurs at an IEOA of 0.85 cm<sup>2</sup> /m2 .[46,47] Transvalvular gradients begin to rise substantially at IEOAs below this value, and these elevated gradients potentially cause increased left ventricular work that prevents adequate regression of left ventricular hypertrophy. Several factors including age, body mass index (BMI), and pre-operative status of left ventricular function may poten‐ tially influence the effect of PPM on post-operative outcomes.[46] PPM is associated with a significant reduction in cardiac index during the postoperative course. The incidence of congestive heart failure was significantly higher in patients with PPM.[48] Several studies reported that early mortality is significantly increased in patients with PPM.[47, 48, 49, 50]

The projected indexed EOA should be systematically calculated at the time of the operation to estimate the risk of PPM. PPM can be avoided by using a simple strategy at the time of operation. Pibarot suggested that surgeon first calculate the patient's BSA from his or her weight and height. Than multiply BSA by 0.85 cm<sup>2</sup> /m2 , the result being the minimum EOA that the prosthesis to be implanted should have to avoid PPM, and than choose the prosthesis and the reference values for the different types and sizes of prosthesis.[46, 47]

Due to concerns over PPM, stentless bioprosthetic valves, which generally have a larger EOA sizefor- size compared with mechanical or stented bioprosthetic valves, have been increasingly utilized for AVR. In initial evaluation, stentless valves had better hemody‐ namics and improved survival rates relative to stented biological or mechanical valves and were more durable than stented biological valves. Stentless valves may be preferred in patients with a small aortic root, and arguments have been made that wider utilization of stentless valves may minimize PPM. Stentless valves also appear to have better hemo‐ dynamic profiles than stented valves during exercise testing. Technical reasons for not im‐ planting stentless valves include extensive aortic root calcification, coronary ostia opposed by 180, presence of the two coronary ostia in close proximity, or unusual disproportion between the sinotubular junction and the aortic annulus. Whereas stented valves allow perfect valve mounting within the aortic annulus, thus reducing the risk of implanting an incompetent valve, postoperative AR and limited durability remain a concern with the free-hand stentless valve insertion technique. This issue may be circumvented with full aortic root replacement using a stentless porcine root.[3.49,50]
