Coronary artery disease

The clinical problem

Fractional flow reserve is the accepted measure of whether a coronary stenosis is functionally significant. It is the ratio of pressure downstream of the narrowing to pressure upstream, measured under maximal flow, and a value below 0.8 is generally treated. Obtaining it requires an invasive procedure with its own cost and risk, which is why it is measured in only a minority of cases where it would be informative.

Computing the same ratio from a coronary CT scan removes that barrier. The difficulty is that the answer depends on the boundary conditions — how much flow the heart muscle downstream demands — which the image does not show directly, and on solving pulsatile flow in a geometry that varies from patient to patient.

What we build

Vessel geometry is segmented from the CT scan and meshed. Flow is driven by a lumped-parameter model of the coronary circulation whose parameters are set from the myocardial volume the vessel supplies, so that flow demand follows anatomy rather than a population average.

Because a full three-dimensional simulation of a pulsatile cycle takes hours, we calibrate one-dimensional models against a small number of three-dimensional runs. The reduced model retains the geometry-dependent pressure–flow relationship and reproduces the waveforms at a fraction of the cost, which is what makes parametric and per-patient studies feasible.

Chronic total occlusion

When a coronary artery is completely blocked, flow reaches the downstream muscle through collateral vessels. Whether opening the occlusion helps depends on how much relief those collaterals already provide. We generated 45,000 virtual cases spanning collateral number and diameter, and found that diameter, not number, governs the hemodynamic relief — a single wide collateral does more than many narrow ones.