Computed Tomography-Based Assessment of Transvalvular Pressure Gradient in Aortic Stenosis

Figures

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  Figure 1. Central illustration describing the present study's design. The aim of this study was to validate a CT-based model for estimation of transvalvular pressure gradients (TPGCT). CT images and pressure waveforms of 84 patients with aortic stenosis were investigated in this retrospective study. TPGCT was calculated using a reduced-order model requiring the aortic flow rate (Q) and the aortic valve area (AVA) as input. AVA was calculated by segmentation of the aortic valve leaflets, and Q was calculated from volumetric assessment of the left ventricle. For validation, invasively measured TPGcatheter was calculated from pressure measurements in the left ventricle as well as the ascending aorta.

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  Figure 2. Comparison of heart rate and transvalvular pressure gradient distributions between both methods. (A) Box plots showing the measured heart rate during CT (left) and catheterization (right). (B) Box plots showing the distributions of TPGCT (left) and the TPGcatheter (right). The box defines the range from the 25th to 75th percentile, whereas the whiskers indicate the inner 99% assuming normal distribution. Values outside this range are marked as outliers using red crosses. All individual values and their correspondence between both methods are shown as connected dots.

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  Figure 3. Bland–Altman plot visualizing the differences between the catheter-based measurements of the pressure gradient and the non-invasive estimations using the power law model (Top) or Doppler echocardiography (Bottom). Data are presented as difference of both methods against the average of both methods. The value of the average prediction error is indicated by a solid line, whereas the dashed lines indicate the average prediction error ±1.96 times the standard deviation of this error.

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  Figure 4. Scatter plot comparing the catheter-based measurements of the pressure gradient against the non-invasive estimation using the reduced-order model (Left) and echocardiography (Right). The linear regression is shown as a dashed line.

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  Figure 5. Comparison of the model's prediction error (TPGcatheter – TPGCT) based on four different possible error sources using box plots: (A) comparison of patients who have absolute heart rate difference between catheterization and CT equal or below 10 bpm and patients whose difference exceeded that threshold. (B) Comparison of cases, where the dynamic CT had 10 or less phases per heartbeat and those with more phases. (C) Comparison of patients who had no or a mild mitral insufficiency and those with moderate insufficiency. (D) Comparison between female and male patients.