Assessment of effective orifice area of prosthetic aortic valves with Doppler echocardiography: An in vivo and in vitro study

Objectives: We sought to evaluate the Doppler assessment of effective orifi ce area in aortic prosthetic valves. The effective orifice area is a less f low-dependent parameter than Doppler gradients that is used to assess prost hetic valve function. However, in vivo reference values show a pronounced s pread of effective orifice area and smaller orifices than expected compared with the geometric area. Methods: Using Doppler echocardiography, we studied patients who received a bileaflet St Jude Medical valve (n 75; St Jude Medical, Inc, St Paul, Minn ) or a tilting disc Omnicarbon valve (n 46; MedicalCV, Incorporated, Inver Grove Heights, Minn). The prosthetic valves were also investigated in vitro in a steady-flow model with Doppler and catheter measurements in the diffe rent orifices. The effective orifice area was calculated according to the c ontinuity equation. Results: In vivo, there was a wide distribution with the coefficient of var iation (SD/mean x 100%) for different valve sizes ranging from 21% to 39% i n the St Jude Medical valve and from 25% to 33% in the Omnicarbon valve. Th e differences between geometric orifice area and effective orifice area in vitro were 1.26 +/- 0.41 cm(2) for St Jude Medical and 1.17 +/- 0.38 cm(2) for Omnicarbon valves. The overall effective orifice areas and peak cathete r gradients were similar: 1.35 +/- 0.37 cm(2) and 25.9 +/- 16.1 mm Hg for S t Jude Medical and 1.46 +/- 0.49 cm(2) and 24.6 +/- 17.7 mm Hg for Omnicarb on. However, in St Jude Medical valves, more pressure was recovered downstr eam, 11.6 +/- 6.3 mm Hg versus 3.4 +/- 1.6 mm Hg in Omnicarbon valves (P =. 0001). Conclusions: In the patients, we found a pronounced spread of effective ori fice areas, which can be explained by measurement errors or true biologic v ariations. The in vitro effective orifice area was small compared with the geometric orifice area, and we suspect that nonuniformity in the spatial ve locity profile causes underestimation. The St Jude Medical and Omnicarbon v alves showed similar peak catheter gradients and effective orifice areas in vitro, but more pressure was recovered in the St Jude Medical valve. The e ffective orifice area can therefore be misleading in the assessment of pros thetic valve performance when bileaflet and tilting disc valves are compare d.