Purpose: To assess the geometry and area of the left ventricular outflow tract (LVOT) in non-stenotic and stenotic aortic valves and to determine the aortic valve area (AVA) in non-stenotic valves by magnetic resonance imaging (MRI) using a modified continuity equation.
Methods: Twenty patients (10 male, mean age 54.8 +/- 15 years) without known aortic valve disease and 10 patients (7 male, mean age 65.1 +/- 14 years) with moderate to severe aortic stenosis were included in this study. MRI was performed using a 1.5 T scanner (Philips Intera CV). AVA was assessed by planimetry on high quality SSFP cine sequences and used as reference standard. LVOT area was defined by calculating a circular area using the LVOT diameter from the 3 chamber view (3CV) and by planimetry. Peak flow velocity was assessed in the LVOT and the proximal aorta. AVA was calculated by a modified Gorlin equation, the continuity equation and a modified continuity equation using the planimetric LVOT area.
Results: Planimetric AVA ranged from 2.9 to 6.4 cm2 in patients with non-stenotic and from 0.3 to 1.3 cm2 with stenotic valves, LVOT area from 3.4 to 6.1 cm2 and from 2.6 to 6.5 cm2, respectively. The LVOT area based on the LVOT diameter derived from the 3CV was significantly underestimated in comparison to planimetry in non-stenotic and stenotic aortic valves (3.3 +/- 0.7 vs. 4.7 +/- 1.0 cm2, p < 0.0001; mean difference 1.1 +/- 0.12 cm2, CI 0.86-1.36 and 3.7 +/- 1.2 vs. 4.7 +/- 1.5 cm2, p < 0.05; mean difference 1.0 +/- 1.0 cm2, CI 0.24-1.71). The Gorlin formula showed a poor agreement with planimetry, whereas continuity equation and the modified continuity equation revealed a very good agreement. Planimetry of the LVOT displayed an elliptic shape of the LVOT in all patients with the minimum diameter perpendicular to the 3CV, which was the reason for the above mentioned underestimation.
Conclusion: The LVOT area calculated from the 3CV-LVOT diameter underestimates the LVOT area compared to planimetry due to an elliptic shape of the LVOT in patients with non-stenotic as well as with stenotic aortic valves. The modified Gorlin equation proved to be less useful to assess AVA in non-stenotic valves, whereas the continuity equation and a modified continuity equation displayed a very good agreement with planimetric area measurements.