The Clinical Implications of Body Surface Area as a Poor Proxy for Cardiac Output

Background: Prosthesis-patient mismatch (PPM), routinely used to characterize the degree of hemodynamic obstruction caused by a prosthetic heart valve, is associated with adverse patient outcomes after aortic valve replacement (AVR). In the common definition of PPM, the opening area of the valve is related to the patients’ cardiac output, by indexing effective orifice area (EOA) with body surface area (BSA). The aim of this study is to assess the implications of using BSA as a proxy for cardiac output. Methods: 744 patients with normal LV function underwent echocardiographic assessment after surgical AVR. To validate the use of BSA as a proxy for cardiac output, the relation between these variables was analyzed. The effects of BSA on the classification of PPM (EOAi < 0.85 cm²/m²) and the presence of hemodynamic obstruction (mean gradient ≥ 20 mmHg and/or Doppler velocity index < 0.35) were estimated. Results: There was a weak correlation between BSA and cardiac output (r: 0.29, 95% CI: 0.22;0.35), and cardiac output was not proportional to BSA (Cardiac output = 1.5 x BSA +1.9). As a result, the increased risk of patients with a large BSA to be labelled with PPM (OR: 5.2, 95% CI: 2.5,11 per m² BSA), was not reflected by a significantly higher risk of hemodynamic obstruction (OR: 1.5, 95% CI: 0.5,4.9 per m² BSA). Conclusions: The current definition of PPM results in a systematic overestimation of hemodynamic obstruction in patients with a larger BSA, and we recommend cautious use in this subgroup. Abbreviations: AVR: Aortic valve replacement; BMI: Body mass index; BSA: Body surface area; EOA: Effective orifice area; EOAi: Indexed effective orifice area; LVOT: Left ventricular outflow tract; PERIGON: PERIcardial SurGical AOrtic Valve ReplacemeNt Pivotal Trial; PPM: Prosthesis-patient mismatch; TTE: Transthoracic echocardiography; VARC-2: Valve Academic Research Consortium-2.