A simplified continuity equation approach to the quantification of stenotic bicuspid aortic valves using velocity-encoded cardiovascular magnetic resonance

OBJECTIVE: We aimed to compare velocity-encoded cine cardiac magnetic resonance (CMR) with an established echocardiographic method for noninvasive measurement of aortic valve area (AVA) using the continuity equation.

METHODS AND RESULTS: Twenty consecutive young adults with stenotic bicuspid aortic valves were examined with CMR and transthoracic echocardiography (TTE). CMR AVA was calculated by the continuity equation, dividing stroke volume by the aortic velocity-time integral (VTIAorta), the stroke volume measured both by ventricular volume analysis and by phase contrast velocity mapping at 4 levels (1 subvalvar and 3 supravalvar). Stroke volumes measured at all levels correlated well with those from volumetric analysis. The CMR AVAs calculated using volumetric analysis and VTIAorta from jet velocity mapping correlated and agreed well with TTE AVA measurements (R2 = 0.83). When CMR AVA was calculated more rapidly using volume flow and VTIAorta both measured from the same trans-jet velocity acquisition, R2 was 0.74, with a bias and limits of agreement of 0.02 (-0.44, 0.47) cm2.

CONCLUSIONS: Continuity equation calculation of the AVA using CMR velocity mapping, with or without ventricular volumetric measurement, correlated and agreed well with the comparable and widely accepted TTE approach.