JACC: Noninvasive method detects ischemia-causing lesions

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A new technique that applies fluid dynamics theories to datasets from noninvasive coronary computed tomographic angiography (CCTA) to quantify fractional flow reserve (FFR) showed good correlation with FFR while proving more accurate than CCTA for detecting ischemia-causing coronary lesions, according to a study published Nov. 1 in the Journal of the American College of Cardiology. The feasibility of obtaining detailed functional information from anatomic datasets deserves further exploration, possibly beyond CCTA, recommended an editorialist.

While CCTA's performance as a diagnostic for identifying and excluding obstructive coronary stenoses is favorable, its predictive value for identifying lesions that cause ischemia has been less reliable. FFR, on the other hand, has been shown to be a useful tool for interventional cardiologists for assessing ischemia-specific lesions and for deciding to proceed to revascularization.

In an effort to achieve the benefits of both approaches, Bon-Kwon Koo, MD, PhD, of the department of medicine at Seoul National University Hospital in Seoul, South Korea, and colleagues applied computational fluid dynamics (CFD) to CCTA images to predict blood flow and pressure in coronary arteries to calculate lesion-specific FFR. The technique, which they call FFR CT, requires no additional scans, medications, or changes to protocols.

They used the international prospective DISCOVER-FLOW (Diagnosis of Ischemia-Causing Stenoses Obtained Via Noninvasive Fractional Flow Reserve) study, which enrolled patients with suspected or known coronary artery disease (CAD) at four sites. From that study group they identified 103 stable patients (159 vessels total) who were 18 years old or older, had undergone CCTA, invasive coronary angiography (ICA) and FFR between Oct. 13, 2009, and Jan. 14, 2011. Based on the CCTA, each had stenosis of 50 percent or greater in a major coronary artery and a diameter greater or equal to 2 mm.

The CCTAs and FFR CT evaluations were blinded. Ischemia was defined by an FFR and FFR CT of less than or equal to 80, and FFR was used as the reference standard for the diagnostic performance of CCTA and FFR CT.

They found that 56 percent of patients had one or more vessels with an FFR of less than or equal to 80. Based on per-vessel analysis, the new technique was more accurate and specific than CCTA stenosis (84.3 percent compared with 58.5 percent, and 82.2 percent compared with 39.6 percent, respectively) and had better positive and negative predictive values. FFR and FFR CT were well correlated.

“The results of the present study establish the feasibility of CFD modeling for noninvasive determination of the physiological consequences of CAD and support a utility for application of FFR CT in patients undergoing CCTA,” Koo and colleagues wrote.

They added that CCTA has been shown to overestimate CAD severity due to a high false positive rate, and the addition of their technique reduced the rate of false positives. “In this regard, the addition of FFR CT to CCTA might improve clinical decision-making and promote salutatory outcomes for individuals with CCTA-identified CAD,” they suggested. “[P]rospective outcomes studies are warranted.”

In an accompanying editorial, Stephan Achenbach, MD, of the department of cardiology at the University of Giessen in Giessen, Germany, commended Koo and colleagues for their study. “We learn that modern computational methods enable the simulation of complex disease manifestations during stress or exercise on the basis of three-dimensional morphology imaging obtained at rest and under baseline nonstress conditions,” Achenbach wrote.

Both Achenbach and the authors listed limitations to the study, including not being powered on a per-patient level and the potential for selection bias. Achenbach argued that several of the limitations were common in reports on novel techniques.

“In general terms: it seems to be possible to derive very detailed functional information from purely anatomic datasets—anatomy meets function,” Achenbach concluded. “This concept deserves and requires further investigation on a much broader scale and will most likely not remain limited to the relatively confined area of CCTA.”