A noninvasive test for fractional flow reserve derived from CT (FFRCT) is a better predictor of revascularization and major adverse cardiac events (MACE) than CT angiography (CTA), according to a study in JACC: Cardiovascular Imaging. FFRCT could also prevent unnecessary invasive coronary angiographies (ICAs), the study’s authors wrote.
Researchers analyzed 181 patients across 69 North American sites. The mean age of the study population was 62 and the patients were 36 percent women. Seventy-six percent of all patients were considered at intermediate risk for obstructive coronary artery disease (CAD) based on a risk score.
Over an average follow-up of 29 months, the researchers analyzed the composite endpoint of coronary revascularization and MACE—defined as death, nonfatal MI or hospitalization for unstable angina. FFRCT less than or equal to 0.80 was associated with a 4.3-fold risk of a patient meeting that endpoint, while severe CTA stenosis was associated with a 2.9-fold risk.
“In patients referred to ICA after CTA, we demonstrate that retrospectively obtained FFRCT has a better predictive value for the composite outcome of coronary revascularization or MACE than severe stenosis (≥70 percent) on CTA,” wrote Michael T. Lu, MD, with Massachusetts General Hospital and Harvard Medical School, and colleagues. “Furthermore, our data suggest that adding information on FFRCT to coronary CTA may improve the efficiency of referral to ICA by lowering the number of invasive angiograms, decreasing the proportion of ICA without ≥50 percent stenosis, and increasing the rate of subsequent coronary revascularization.”
Among patients with an FFRCT less than or equal to 0.80, 61 percent received coronary revascularization and 11 percent experienced a MACE. Sixteen percent of patients above that FFRCT cutoff required revascularization and four percent experienced a MACE.
Importantly, the sites participating in the study had no knowledge of the FFRCT results and couldn’t use them in their clinical decision-making.
More than four million Americans with stable chest pain receive noninvasive diagnostic testing for suspect CAD each year, according to the authors. HeartFlow, the maker of the first noninvasive FFRCT technology, appears to be gathering momentum with its product, which allows clinicians to view a simulated, three-dimensional model of a patient’s coronary blood flow.
The company recently announced CMS, beginning in 2018, will reimburse hospitals $1,450.50 for performing the technical component of the test on Medicare patients.
In an accompanying editorial in JACC: Cardiovascular Imaging, a pair of physicians from Ohio State University agreed “if FFRCT results are available, they should be used by interventional staff in revascularization decision making.”
However, they were troubled that half of the potential patients were excluded from the trial, mostly because they didn’t meet guidelines for standard CTA, including administration of nitroglycerin and high image pixel resolution.
“One would hope that use of nitroglycerin is standard practice for coronary CTA. However, other acquisition compromises that render FFRCT infeasible such as thicker slice collimation for obese patients still afford delivery of CTA alone with its favorable benefit-risk ratio to such patients,” wrote Subha V. Raman, MD, and Karolina M. Zareba, MD. “We do not know if this retrospective analysis would hold for the subjects in the stress testing arm of (the trial): Would functional test results have worked as well? It is also not clear why 50 nondiagnostic CTAs were excluded, because FFR overcomes CTA limitations such as calcification in many of these instances.”
Other barriers to broader application of FFRCT analysis, according to Raman and Zareba, include algorithmic improvements, faster turnaround times for results and potential high costs associated with only one vendor having clinically approved software.