Planimetric assessment of anatomic valve area overestimates effective orifice area in bicuspid aortic stenosis

Background: Although the continuity equation remains the noninvasive standard, planimetry using; transesophageal echocardiography is often used to assess valve area for patients with aortic stenosis (AS). Not uncommonly, however, anatomic valve area (AVA(A)) obtained by planimetry overestimateS continuity-derived effective valve area (AVA(E)) in bicuspid AS. Methods: Transthoracic Doppler and transesophageal echocardiography were performed to obtain AVA(E) and AVA(A) in 31 patients with bicuspid AS (age 61 +/- 11 years) and 22 patients with degenerative tricuspid AS (age 71 +/- 13 years). Aortic root and left ventricular outflow tract dimensions and the directional angle of the stenotic jet were assessed in all patients. Using these data, a computational fluid dynamics model was constructed to test the effect of these variables in determining the relationship between AVA(E) and AVA(A). Results: For patients with tricuspid AS, the correlation between AVA(A) (1-15 +/- 0.36 cm(2)) and AVA(E) (1-13 +/- 0.46 cm(2)) was excellent (r = 0.91, P <.001, Delta = 0.02 0.21 cm(2)). However, AVAA was significantly larger (1-19 +/- 0.35 cm(2)) than AVAE (0.89 +/- 0.29 cm(2)) in the bicuspid AS group (r = 0.71, P <.001, Delta = 0.29 +/- 0.25 cm(2)). Computer simulation demonstrated that the observed discrepancy related to jet eccentricity. Conclusion: For a given anatomic orifice, functional severity tends to be greater in bicuspid AS than in tricuspid AS. This appears to be primarily related to greater jet eccentricity and less pressure recovery.