CTA Becomes a One-stop Shop with FFR Measurement

AuntMinnie | Using CT to measure cardiac fractional flow reserve (FFR) — measuring the shape and speed of blood flow in the heart and coronary arteries — is a potential game changer that could turn everyday coronary CT angiography (CCTA) scans into a one-stop cardiac assessment tool, taking over some imaging tasks from other modalities.

CT-based FFR measurements can accurately show the functional impact of any coronary artery stenosis without the need for extra radiation, risk, drugs, or special imaging procedures, according to a presentation by Dr. James Min, from Cedars-Sinai Medical Center, at the International Society for Computed Tomography (ISCT) annual meeting in San Francisco in June.

Traditionally, fractional flow reserve measurements have been performed during invasive coronary angiography, a technique that has emerged as the only accurate way to gauge lesion-specific ischemia or the hemodynamic significance of coronary artery stenosis, Min said. For guiding therapy, FFR measurements are preferable to stress myocardial perfusion imaging (MPI) because the latter doesn’t permit the assessment of lesion-specific ischemia. As a standalone test, CCTA is fine for anatomy, but it’s less accurate in gauging the physiological impact of stenosis.

Moreover, FFR-guided coronary revascularization improves the long-term clinical outcome of patients with coronary artery disease (CAD), Min said. And it’s the ischemia-guided measurement tool that has been shown to result in event-free survival.

“FFR is defined by the ratio of maximum myocardial blood flow in a diseased artery to blood flow in the hypothetical case that the artery is normal,” Min said. “But FFR is an invasive technique that requires a pressure wire to come past an epicardial stenosis to measure the pressure at maximal hyperemia and measure the pressure in the proximal aorta simultaneously.”

CCTA correlates very favorably with angiographic estimates of coronary artery stenosis, of course, “but it’s fairly unreliable in its prediction of which lesions are ischemic and which lesions are not,” said Min, who is co-director of cardiac imaging and director of imaging research at Cedars-Sinai. “So the question then arises whether or not we can determine fractional flow reserve from CTA, and it appears that we can,” he said.

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