Background:
Left ventricular outflow tract (LVOT) measurement by Echo falsely assumes circular LVOT with implications for aortic valve area (AVA) determined using continuity equation. In this study, we investigated the utility of combining Echo Doppler and computed tomography (CT) based LVOT area for precise AVA assessment.
Methods:
AVA-echo was calculated using continuity equation and standard echocardiography techniques. CT-LVOT area was measured by 3 independent readers. Blinded measurements were obtained in candidates for percutaneous aortic valve replacement. AVA-CT was calculated using CT-LVOT area and echo Doppler measurements. The inter-observer variability for CT-LVOT area and correlation between AVA-echo and AVA-CT was analyzed using intra-class (ICC) and Spearman correlation coefficient.
Results:
Complete data for 66 patients was analyzed. The ICC for CT derived LVOT measurement by three observers was 0.96 demonstrating excellent reliability. The LVOT area by echo was significantly smaller than that obtained by CT (3.43±0.8 vs. 4.45±1.2 cm2, p<0.0001) and showing moderate correlation (r=0.66, p=0.006). Similarly, the AVA-echo was significantly lower compared to AVA-CT (0.76±0.46 vs. 0.97±0.53 cm2, p<0.0001). The correlation coefficient for AVA-echo and AVA-CT was 0.7 (p < 0.0001), 0.4 (p=0.06) and 0.9 (p<0.0001) for AVA-echo of 0.8 cm2 respectively. The regression analysis showed that AVA-CT could be predicted by applying a correction factor to the AVA-echo as AVA-CT = AVA-echo x 1.1+0.14.
Conclusion:
CT provides accurate and reliable LVOT assessment. Combining CT-LVOT and echo Doppler measurements result in a larger AVA compared to AVA-echo representing a true anatomic measurement. These findings have important implications for grading of aortic stenosis and management of patients with moderate to severe aortic stenosis.
Modified continuity equation using left ventricular outflow tract three-dimensional imaging for aortic valve area estimation
