Patient – prosthesis mismatch
Patient – prosthesis mismatch is often noted in aortic position, that too after surgery for aortic stenosis. In aortic stenosis the aortic root is not dilated and the left ventricle is hypertrophied. Hence often a lower size of prosthetic valve has to be chosen, which can lead to patient – prosthesis mismatch. In aortic regurgitation, a dilated aortic root often allows a good sized prosthesis to be chosen.
To put it simply, a prosthetic valve too small for the patient’s body surface area produces patient-prosthesis mismatch. It produces an increase in transvalvar gradient, but imaging studies like echocardiogram, fluoroscopy or computed tomography will show absences of thrombotic masses and normal valve opening angles. Measurement of the orifice area and calculating the indexed area with respect to body surface area will differentiate it from other causes of prosthetic valve dysfunction which can also increase the gradient. Absence of pannus or thrombus reducing the orifice area should also be documented by imaging studies.
In patients with small aortic annulus, surgeons sometimes resort to aortic root widening procedures to accommodate larger sized prosthetic valves to avoid mismatch. But these procedures require extra skill and increases the surgical time and hence the possible periprocedural morbidity.
Stentless bioprosthesis are less likely to have patient prosthesis mismatch. They have better valve orifices and lesser transvalvar gradients compared to stented bioprosthesis.