Letter by House et al regarding article, "Prosthesis-patient mismatch in bovine pericardial aortic valves: evaluation using 3 different modalities and associated medium-term outcomes".

The proverbial gold standard for evaluating prosthesis-patient mis-match (PPM) is the effective orifice area index. This is attributable to the inverse relationship that exists between the effective orifice area index and mean gradient. 1 Other tools have been promoted to identify PPM but have not withstood scrutiny. 1 In a recent edition of Circulation: Cardiovascular Imaging, Chacko et al 2 propose applying the American Society of Echocardiography guidelines for prosthetic valves to exclude the presence of PPM. In these guidelines, there is a useful algorithm for the evaluation of high transprosthetic gradients. 3 This algorithm was specifically created to assist in the evaluation of aortic prostheses with elevated peak velocities exceeding 3 m/sec. A common pathogenesis of velocities exceeding 3 m/sec is PPM, although this is not the exclusive reason for increased velocities. In addition, PPM is not invariably associated with velocities exceeding 3 m/sec, as demonstrated in low-flow states. These low-flow states can occur with reduced left ventricular ejection fraction (LVEF; ie, classical low-flow) but also with preserved LVEF (paradoxical low-flow). 4 The authors did exclude patients with LVEF <50%, with the goal of creating a hemodynamically similar cohort. However, it has been well established that a normal LVEF is not synonymous with a normal stroke volume, and that a large proportion (10%–35%) of patients with preserved LVEF have in fact reduced transvalvu-lar flow. 4 This paradoxical low-flow state is often associated with pseudonormalization of transvalvular flow velocities and gradients in patients with native aortic valve stenosis, leading to underestimation of stenosis severity. The same concept applies to patients with prosthetic heart valves, such that patients with preserved LVEF who have reduced stroke volume can have PPM even with flow velocities <3 m/sec. Similar to what is observed in patients with paradoxical low-flow, low-gradient aortic stenosis, these patients with preserved LVEF and concomitant low-flow, low-gradient PPM likely have worse prognosis compared with those with normal flow and elevated gradient PPM. Not taking into account this phenomenon of velocity/gradient pseudonormalization associated with paradoxical low-flow obviously led to a significant underestimation of the true incidence of PPM in this series. Although the American Society of Echocardiography guidelines algorithm provides a useful template to guide the investigation of potential pathogeneses of increased transprosthetic velocities, it is unlikely that it was intended for the comprehensive evaluation of PPM. In particular, this algorithm does not address the case of patients with paradoxical low-flow who …