CTA provides morphologic information of coronary anatomy and is capable of detecting the presence of atherosclerotic lesions. It is, however, limited in its ability to detect myocardial ischemia as morphologic information alone is not enough to predict the physiological significance of coronary luminal stenosis. That's important because the benefits of revascularization are highest in patients who have coronary stenoses that are flow-limiting and hemodynamically significant.

Invasive angiography and CT angiography are limited in delineating flow-limiting lesions that can be detected, however, by perfusion imaging or invasive FFR. A single test that could noninvasively calculate the severity of a lesion and its hemodynamic significance is desirable for the management of patients with symptomatic CAD.

There has been limited evidence regarding CT perfusion imaging (CTP) and most of what exists was performed using 64-row multidetector computed tomography (MDCT) systems. CORE320 is the acronym for a study designed by investigators at Johns Hopkins University, Baltimore, Maryland: the combined coronary atherosclerosis and myocardial perfusion evaluation using 320-row detector CT.¹

This multicenter, multinational, prospective study included 381 patients with suspected CAD who had been referred for clinically indicated coronary angiography. Noninvasive CT evaluation of coronary lesion severity (by CTA) + hemodynamic significance (by CTP using a 320-row detector CT) was compared to invasive angiography + single photon emission CT (SPECT) and analyzed on a per-patient and per-vessel basis.

Revolutionizing Patient Management?

In originally reporting the design of the trial, the authors wrote: "If successful, the technology could revolutionize the management of patients with symptomatic CAD."

Investigators reported results of CORE320 at ESC 2012 and found that combined CTA and CTP was capable of detecting hemodynamically significant stenoses (50% or 70%), as defined by invasive angiography with an associated SPECT perfusion defect. Furthermore, combined CTA and CTP was superior to CTA alone for correctly identifying flow-limiting and functionally relevant obstructive CAD and predicted revascularization with accuracy similar to invasive coronary angiography + SPECT.

Specifically, the patient-based diagnostic accuracy (area under the curve [AUC]) of combined CTA and CTP for detecting or excluding flow-limiting CAD was 0.87 (95% CI 0.83-0.91), and 0.89 (95% CI 0.86-0.93) when the invasive angiography stenosis reference standards were >50% and >70% respectively. CTP increased the diagnostic accuracy of CTA alone to delineate flow-limiting disease (AUC 0.87 vs. 0.81; p < 0.001). The combination of CTA and CTP had similar diagnostic power to the combination of ICA and SPECT myocardial perfusion imaging (MPI) in identifying revascularized patients at 30 days (p = 0.13).

In presenting the study results, principal investigator Joao A. C. Lima, MD, listed several open issues and potential limitations:

• Who should have this test?
• Who should go directly to invasive angiography based on clinical information?
• What is the role of CT versus invasive FFR measurement at the time of angiography?
• Stress CTP is an additional study after CTA and requires additional radiation and contrast.
• The 320-row detector CT systems are not widely available yet, and the data from CORE320 may not apply to 64-row CT.
• Concerns and considerations that need additional consideration include exposure to radiation and contrast, plus cost effectiveness.

Overall, he said, "We found the addition of CT myocardial perfusion to CT angiography allows clinicians to distinguish between anatomic and flow limiting stenoses in patients with suspected coronary disease."

Reference

1. Vavere AL, Simon GG, George RT, et al. J Cardiovasc Comput Tomogr. 2011;5:370-81.

Keywords: Myocardial Perfusion Imaging, Coronary Artery Disease, Myocardial Ischemia, Cost-Benefit Analysis, Area Under Curve, Coronary Stenosis, Coronary Angiography, Tomography, Emission-Computed, Single-Photon, Multidetector Computed Tomography, Baltimore, Cytidine Triphosphate, Hemodynamics

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