The Role of Computed Tomography-Derived Fractional Flow Reserve (CT-FFR) and Myocardial Computed Tomographic Perfusion (CTP) in Patients Presenting With Chest Discomfort

Coronary artery computed tomographic angiography (CCTA) is a widely used, highly accurate technique for the detection of coronary artery disease (CAD), with sensitivity and negative predictive values of over 90% 1-4. Patients with normal CCTA findings have an excellent prognosis and do not require further testing for CAD 5. However, like invasive coronary angiography (CATH), CCTA is an anatomic test and, cannot reliably predict the impairment of flow (functional significance) of Coronary stenoses.

For this reason, in approximately 15-25% of patients, additional functional testing may be required after CCTA, usually in the form of stress testing 6-8. Stress testing is commonly done by exercise or pharmacologic stress with electrocardiographic monitoring and often, imaging of myocardial perfusion by nuclear scintigraphy (MPI) or detection of abnormal contraction by echocardiography. Furthermore, in patients with previously known CAD, CCTA alone is not an adequate test, because in most cases there are multiple lesions that are possible sources of ischemia. Over the last two decades the number of abnormal stress studies have decreased substantially from 40.9% in 1991 to 8.7% in 20099. This underscores the need for an accurate mechanism to identify which patients best benefit from invasive angiography.

Myocardial Computed Tomographic Perfusion (CTP) and Computed Tomography-Derived Fractional Flow Reserve (CT-FFR) have emerged as promising ways to identify ischemia when there is coronary disease identified by CCTA. The two tests provide different and perhaps complimentary information. Fractional Flow Reserve (FFR) measures the difference in flow created by a coronary stenosis before and after the administration of a vasodilator agent by measuring the drop in pressure across the stenosis. Coronary Flow Reserve (CFR) measures flow at maximum vasodilation versus flow at rest in a given arterial tree.

This is a prospective, observational study designed to evaluate the role of dynamic computed tomographic perfusion (CTP) and Computed Tomography-Derived Fractional Flow Reserve (CT-FFR) in patients presenting with chest discomfort.Patients with lesions greater than 50% will qualify to be a subject in the CTP study /CT-FFR 49. Those who agree to participate will be scheduled to have the CT-FFR and CTP performed within sixty days of the initial Coronary CTA procedure. A CTA will be performed at rest for FFR. The patient will then take approximately a 30 min break. Regadenoson will then be administered and the dynamic CT procedure will be done for perfusion. If patients are deemed to be appropriate for invasive angiography by the referring physician, coronary lesions between 40% and 80% will get a fractional flow measurement performed if indicated on a clinical basis. Stenosis in vessels less than 1.5 mm will be excluded from the study. The CT-FFR and CTP will be performed in these patients within 60 days of index coronary angiography.

The CT scanner to be used for this study is an Aquilion ONE ViSION edition 320-detector row scanner with 0.5-mm nominal width detector elements (Toshiba Medical Systems, Otawara, Japan). The scanner has a minimum rotation time of 275 ms. The CT acquisition software includes a novel dose reduction technology (Adaptive Iterative Dose Reduction 3D (AIDR 3D) Toshiba Medical Systems, Otawara, Japan).