Background: Transthoracic echocardiography (TTE) is routinely used to calculate aortic valve area (AVA) by continuity equation (CE). However, accurate measurement of the left ventricular outflow tract (LVOT) can be difficult and flow acceleration in the LVOT may lead to miscalculation of the AVA.
Objective: The aim of our study was to compare AVA measurements by standard TTE, cardiac magnetic resonance imaging (MRI) and a hybrid approach combining both techniques.
Methods: AVA was calculated in 38 patients (age 73±9 years) with standard TTE, cine-MRI planimetry and a hybrid approach: Hybrid Method 1: TTE-derived LVOT measurement in the CE numerator was replaced by the MRI assessment of the LVOT and AVA was calculated: (LVOT(MRI)/*LVOT-VTI(TTE))/transaortic-VTI(TTE). Method 2: We replaced the SV in the numerator by the MRI-derived SV and calculated AVA = SV(MRI)/ transaortic-VTI(TTE).
Results: Mean AVA derived by TTE was 0.86 cm(2)±0.23 cm(2) and 0.83 cm(2)±0.3 cm(2) by MRI- planimetry, respectively. The mean absolute difference in AVA was 0.03 cm(2) for TTE vs. MRI planimetry. AVA calculated with method 1 and method 2 was 1.23 cm(2)±0.4 cm(2) and 0.92 cm(2)±0.32 cm(2), respectively. The mean absolute difference between TTE and method 1 and method 2 was 0.37 cm(2) and 0.06 cm(2), respectively (p<0.001).
Conclusion: MRI-planimetry of AVA and hybrid method 2 are accurate and showed a good agreement with standard TTE measurements. Therefore, hybrid method 1 is a reasonable alternative if poor acoustic windows or LVOT flow accelerations limit the accuracy of TTE, particularly in patients at high risk for an invasive hemodynamic study.