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Turbulence mapping: a new CMR approach for assessment of aortic stenosis
Journal of Cardiovascular Magnetic Resonance volume 15, Article number: P110 (2013)
Pressure loss estimation based on the simplified Bernoulli equation frequently misclassifies the severity of aortic stenosis. Consequently, several investigators have on the basis of fluid dynamics theory derived pressure loss indices aimed at improving the clinical approach to pressure estimation [1–3]. However, CMR may offer a stronger alternative. The primary cause of pressure loss in aortic stenosis is dissipation of turbulent kinetic energy (TKE) into heat. New CMR methods permit direct estimation TKE . We sought to evaluate the relationship between CMR-measured TKE and previously described pressure loss indices.
27 patients under evaluation for aortic valve replacement were enrolled. The patient population represents a broad range of aortic stenosis and aortic dilation. Aortic valve area was 1.6 ± 1.7 cm2 (mean ± std dev), range: 0.4 - 6.4 cm2. Peak velocity was 3.7 ±1.4 m/s, range 2.0 - 7.5 m/s. Maximum aortic diameter was 4.1 ± 0.8 cm, range 3.0 - 6.1 cm.
TKE was estimated using a novel 4D Flow CMR method, as described in . A measure of the total TKE (TKEtot) was obtained by integrating the TKE per voxel across the ascending aorta. Each subject had clinical echocardiography and computed tomography studies done close to the CMR study.
TKEtot was compared against three pressure loss indices (iPL) derived from the literature [1–3] (see table in figure 1). These indices represent different approaches to estimate pressure loss effects based on data obtainable with noninvasive imaging. The underlying theory has been compared favorably with catheter-based measurements in select settings [1–3].
Scatter plots for TKEtot vs iPL1, iPL2, and iPL3 are shown in Figure 2. Correlation for TKEtot vs iPL1, TKEtot vs iPL2, and TKEtot vs iPL3 was 0.65, 0.87, 0.92, respectively. The slope was significantly different from zero in all cases.
This study used a novel CMR flow imaging method to measure the total TKE in the ascending aorta of patients with aortic stenosis. Strong correlation was found between TKE and pressure loss indices derived from fluid dynamics theory. By directly measuring the source of irreversible pressure loss, TKE mapping allows new avenues for evaluation of aortic stenosis with CMR. Future work will include a comparison between CMR-measured TKE and catheter-based pressure measurements.
Swedish Heart-Lung Foundation
Swedish Brain Foundation
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Dyverfeldt, P., Hope, M.D., Tseng, E.E. et al. Turbulence mapping: a new CMR approach for assessment of aortic stenosis. J Cardiovasc Magn Reson 15, P110 (2013). https://doi.org/10.1186/1532-429X-15-S1-P110
- Aortic Valve
- Turbulent Kinetic Energy
- Aortic Stenosis
- Pressure Loss
- Aortic Dilation