Letter by Bleiziffer et al Regarding Article, “Long-Term Outcomes After Valve Replacement for Low-Gradient Aortic Stenosis: Impact of Prosthesis-Patient Mismatch”
To the Editor:
With great interest, we read the article by Kulik and associates1 identifying patient-prosthesis mismatch (PPM) (defined as an effective orifice area [EOA] index below 0.85 cm2/m2) as an independent predictor of a higher incidence of congestive heart failure and impaired left ventricular mass regression after aortic valve replacement in patients with low-gradient aortic stenosis. In the study by Kulik et al, PPM was assessed by reference tables, although echocardiographic EOA index data were also available.
When analyzing large patient populations to investigate the impact of PPM on clinical outcome, echocardiographic EOA index data are often not available, and the EOA is only estimated by reference tables (based on echo or in vitro data) or by the use of the geometric orifice area, which is a fixed geometric parameter derived from the internal prosthesis diameter. One must be aware that these methods cannot detect all patients with severe or moderate PPM, and there are false-positive and false-negative categorizations. Pibarot et al2 demonstrated that the sensitivity and specificity to detect PPM are 73% and 80% when using echocardiographically derived reference tables (as done by Kulik et al1). Blackstone and associates3 used a geometric orifice area of <1.1 cm2/m2 to define “a prosthesis too small for patient size” and found no impact on long-term mortality. The indexed geometric valve area has been shown to be unrelated to hemodynamics or clinical outcomes.4
Hence, estimations of PPM based on reference tables and on the geometric orifice area yield low sensitivity and specificity, leading to incorrect categorization of patients in clinical studies. The effect of false categorization might outweigh that of inaccurate echocardiographic measurements, because the EOA value of the same prosthesis type and size can vary widely among patients. We are convinced that the potential impact of PPM on clinical outcomes after aortic valve replacement can only be detected if individual EOA index values are assessed by echocardiography in every patient. A study by Mohty-Echahidi and associates5 supports this thesis. They found a clear impact of PPM on mortality when PPM assessment was carried out by echocardiography for each individual patient.
In conclusion, Kulik and colleagues1 address a very important issue; we suggest, however, that use of echo-derived EOA index in their study would have more accurately identified patients with PPM.