The effective orifice area/patient aortic annulus area ratio: a better way to compare different bioprostheses? A prospective randomized comparison of the Mosaic and Perimount bioprostheses in the aortic position.

BACKGROUND AND AIM OF THE STUDY: The aim of this prospective, randomized study was to compare the hemodynamic performance of the Medtronic Mosaic and Edwards Perimount bioprostheses in the aortic position, and to evaluate prosthesis-specific differences in valve sizing and valve-size labeling.

METHODS: Between August 2000 and September 2002, 139 patients underwent isolated aortic valve replacement (AVR) with the Mosaic (n = 67) or Perimount (n = 72) bioprosthesis. Intraoperatively, the internal aortic annulus diameter was measured by insertion of a gauge (Hegar dilator), while prosthesis size was determined by using the original sizers. Transthoracic echocardiography was performed to determine hemodynamic and dimensional data. As the aim of AVR is to achieve a maximal effective orifice area (EOA) within a given aortic annulus, the ratio of EOA to patient aortic annulus area was calculated, the latter being based on annulus diameter measured intraoperatively.

RESULTS: Operative mortality was 2.2% (Mosaic 3.0%; Perimount 1.4%; p = NS). Upsizing (using a prosthesis larger in labeled valve size than the patient's measured internal aortic annulus diameter) was possible in 28.4% of Mosaic patients and 8.3% of Perimount patients. The postoperative mean systolic pressure gradient ranged from 10.5 to 22.2 mmHg in the Mosaic group, and from 9.4 to 12.6 mmHg in the Perimount group; it was significantly lower for 21 and 23 Perimount valves than for 21 and 23 Mosaic valves. The EOA ranged from 0.78 to 2.37 cm2 in Mosaic patients, and from 0.95 to 2.12 cm2 in Perimount patients. When indexing EOA by calculating the ratio of EOA to patient aortic annulus area to adjust for variables such as patient anatomy and valve dimensions, there was no significant difference between the two bioprostheses.

CONCLUSION: Comparisons of absolute EOA values grouped by the manufacturers' valve sizes are misleading because of specific differences in geometric dimensions. The EOA:patient aortic annulus area ratio provides a new hemodynamic index which may facilitate objective comparisons between different valve types.