CT angiography and non-invasive fractional flow reserve have improved diagnostic accuracy for coronary obstructions

Image: CC/T. Heston MD

Key study points:

1. Noninvasive FFR_CT plus CT is associated with improved diagnostic accuracy of obstructive coronary artery disease over CT angiography alone.

Primer:  Chest pain is among the most common presenting complaints in a hospital emergency room.  The physician evaluating a patient presenting with chest pain must answer two questions: 1) does the patient have obstructive coronary disease, and 2), if so, what is the patient’s risk for cardiovascular events?  The answers to these questions will inform whether medical therapy and/or revascularization therapy are indicated.  The recommended work-up depends on the pre-test probability of disease, with low-risk, intermediate-risk and high-risk patients undergoing expectant management, noninvasive testing and invasive cardiac catheterization respectively.

Noninvasive tests to date provide information on either the anatomy of the coronary arteries (CT angiography) or their function by assessing perfusion or wall motion function (exercise treadmill testing, stress MRI, stress echo, nuclear stress tests). A noninvasive test that is both sensitive for anatomic lesions and specifically functional regarding ischemia has been elusive.  

Fractional Flow Reserve (FFR) (coronary artery pressure distal to a stenosis / aortic pressure) provides functional information but its determination requires an invasive coronary angiogram (ICA). 

This [multicenter diagnostic performance] study by Min et al evaluates the accuracy of a new noninvasive FFR computed from CT (FFR_CT) compared to the reference standard of invasive FFR determined by conventional coronary angiography.  Data were drawn from the DeFACTO study, which spanned 17 centers in 5 countries including 288 stable patients with known/suspected coronary artery disease who underwent CT, ICA, FFR and FFR_CT. The study was well-blinded with independent core laboratories performing, analyzing and interpreting each modality.

252 patients had adequate FFR_CT images that were compared with invasive FFR.  Comparing each patient’s FFR_CT plus CT against the standard of invasive FFR revealed an accuracy of 73% (95% CI 67%-78%) with a sensitivity of 90%, specificity of 54%, positive predictive value of 67% and negative predictive value of 84%.  CT angiography alone was found to have an accuracy of 64% with a sensitivity of 84% and specificity of 42% in this study.  Thus, FFR_CT plus CT was associated with improved diagnostic accuracy over CT alone. 

In sum: FFR_CT plus CT was associated with improved diagnostic accuracy over CT angiography alone (73% vs 64%), even though the study did not meet its pre-specified primary endpoint of a 95% CI with a lower bound exceeding 70%. 

One limitation of this study is possible understatement of the accuracy of CT angiography alone.  Prior studies in CT angiography used a standard of invasive angiography alone, and have demonstrated a higher diagnostic accuracy than this study which used both invasive angiography and FFR as standards for comparison.  Using more stringent standards in this study may have biased the results by understating the accuracy of CT.  Another limitation is that results of such a study performed in tightly controlled core laboratories might not translate to real clinical practice.  Resource utilization and patient outcomes following FFR_CT should be investigated.  Other future studies could assess the utility of FFR_CT in patients with varying pre-test probabilities of CAD, thus revealing how this technology may best be applied to clinical practice.  

More background information:

1. Blankstein R, Devore AD. Selecting a noninvasive imaging study after an inconclusive exercise test. Circulation. 2010;122:1514–1518. [An overview of noninvasive tests for CAD]
2. Tonino PA, De Bruyne B, Pijls NH, et al; FAME Study Investigators.  Fractional flow reserve vs angiography for guiding percutaneous coronary intervention.  N Engl J Med. 2009;360(3):213-224
3. Koo BK, Erglis A, Doh JH, et al.  Diagnosis of ischemia-causing coronary stenoses by noninvasive fractional flow reserve computed from coronary computed tomographic angiograms: results from the prospective multicenter DISCOVER-FLOW (Diagnosis of Ischemia-Causing Stenoses Obtained Via Noninvasive Fractional Flow Reserve) study.  J Am Coll Cardiol. 2011;58(19):1989-1997

Click to read the study in JAMA

Written by MP

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