The Virtual Cardiac Stress Test
Coronary computed tomography (CT) angiography represents the technical evolution in cardiac imaging due to its high diagnostic value in coronary artery disease as a less invasive technique. Diagnostic performance of coronary CT angiography is significantly enhanced with the development of multislice CT scanners.
Coronary CT angiography has undergone remarkable technological advancements in safety and image quality that, when paired with results from recent comparative effectiveness trials, have led many to conclude that it should be more broadly performed and serve as the first test in many patients with stable chest pain concerning for possible coronary artery disease (CAD).
The Virtual Cardiac Stress Test (VCAST) developed by Kardiolytics Inc. is another advancement in this area. It offers an automatic CT analysis workflow that can be handled by the physician with very limited support from the radiologist, comprehensive volumetric analysis consisting FFRct and EFR which supports clinical decisions, and plaque analysis including classification, and volume quantification.
Overview of Technology
We use artificial intelligence (AI) to create a three-dimensional surface model of the stenotic coronary arteries. This model reflects the actual state of coronary vessels of the patient along with existing atherosclerotic lesions. The geometry of this model is used to create the reconstructed model of "idealized" coronary vessels, of a hypothetically healthy patient, without atherosclerotic stenosis.
This model is generated based on the numerical virtual reconstruction of the artery geometry and involves the removal of existing stenoses. The cross-sectional area of the vessel at the location of the stenosis is reproduced on the basis of approximation of the cross-sectional area before and after the stenosis.
Computational modeling of blood pressure and flow
The Kardiolytics Inc. developed a non-invasive method, based on CT images and computational fluid dynamics to evaluate the hemodynamic significance of coronary stenosis under higher-intensity physical exercise conditions. Increased physical exertion, can elicit cardiovascular abnormalities that are not present at rest, and it can be used to determine the stage of coronary heart disease.
The VCAST is a comparative method in which the flow energy losses in stenotic and normal, hypothetically healthy models of coronary arteries are compared, therefore the numerical calculations of pressure and flow conditions are carried out in two stages:
- The Computational Fluid Dynamics simulation of the coronary pressure and blood flow in stenotic and normal model
- In second step VCAST compares symulation results of the stenotic and normal model of coronary arteries
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The VCAST results
Summary of the analysis includes:
- 3d model of complete coronary artery tree
- identification of coronary plaques
- results of pressure and flow across the entire coronary tree,
- relative flow parameters analysis in relation to corresponding hypothetical normal (healthy) coronary arteries,
- assessing hemodynamic significance of the stenosis (single or multiple) itself,
- prediction the personalized effects of revascularization.
The VCAST Report
The Report of the test contains:
- the general information about the patient,
- information about the location and shape of atherosclerotic lesions, degree of stenosis, type of plaques, the hemodynamic effect of revascularization therapy that facilitating the selection of the stent diameter
- images of FFRSTEN and FFRREC distribution, the Fractional Flow Reserve calculated as the ratio of average total pressure measured in stenotic model after the stenosis vessel in the distal section of the to the average pressure in the aorta, for stenotic and reconstructed models respectively.
- image of EFR distribution, defined as the ratio of total flow energy losses in the branch of the stenotic model to the flow energy losses in the branch of the virtually reconstructed coronary vessel without atherosclerotic changes.
Localization of atherosclerosis lesions
FFR, the Fractional Flow Reserve, is calculated as the ratio of average pressure measured in stenotic model after the stenosis in the distal section of the vessel to the average pressure in the aorta.
EFR, the Energy Flow Reference index, is defined as the ratio of total flow energy losses in the branch of the stenotic model to the flow energy losses in the branch of the virtually reconstructed coronary vessel without atherosclerotic changes.
Left Coronary Artery (LCA):
- proximal segment of the Left Anterior Descending (pLAD) - stenosis of 50%
- proximal section of the first Diagonal branch (pD1) - stenosis of about 82% , hemodynamically significant.
- distal section of the first Diagonal branch (dD1) - minimal stenosis of about 70% , hemodynamically significant.
- proximal segment of the Ramus Intermedius (RI) branch - stenosis of 70% with no non-calcified atherosclerotic plaque.
Right Coronary Artery (RCA):
- proximal segment of the Right Coronary Artery (RCA) - stenosis of 35 %
- middle segment of the Right Coronary Artery (mRCA) and at the junction of RCA with the Right Ventricular Artery (RVA), middle plaques with stenosis up to 40 % .
- middle segment of the Right Coronary Artery (RCA) - two sequential stenosis of ~30-40 %