What a New Meta-Analysis Reveals About Fractional Flow Reserve Assessment with Computed Tomography

Computed tomography (CT)-derived fractional flow reserve (FFR) values greater than 0.90 may help rule out significant coronary artery disease (CAD), according to a new meta-analysis of 43 studies.

For the meta-analysis, recently published in the Journal of the American Heart Association, researchers reviewed FFR data from 5,236 patients (7,291 blood vessels). Seventy percent of the cohort were men, 36 percent were current or past smokers, 63 percent had hypertension and the median body mass index ranged between 25 to 30, according to the study. The meta-analysis authors also noted a high prevalence of other common cardiovascular risk factors such as diabetes and hypercholesterolemia.

Overall, the study authors found that FFR-CT demonstrated a per-vessel level accuracy rate of 82.2 percent, an 80.9 percent sensitivity rate and an 83.1 percent specificity rate. The accuracy rate with FFR-CT is above 90 percent for ruling out hemodynamically significant CAD when the FFR-CT value is > 0.90, according to the researchers. They also found a 90 percent accuracy rate in diagnosing hemodynamically significant CAD when the FFR-CT value is < 0.49.

“FFR-CT could be an effective gatekeeper to invasive angiogram, helping avoid complications from invasive procedures,” wrote lead meta-analysis author Thomas I. Faulder, a medical student at the College of Medicine and Denistry at James Cook University in Townsville, Australia, and colleagues.

However, the researchers pointed out that the diagnostic capability varies with FFR-CT value measurements. For patients with FFR-CT values ranging between 0.70 and 0.80, the meta-analysis authors noted an accuracy rate of 67 percent.

In the findings from studies that compared FFR-CT to invasive FRR assessment, the researchers said 17.8 percent of vessels (1,047 out of 5,883) were misclassified by FFR-CT. These misclassified vessels by FFR-CT included 459 stenoses (median FFR value of 0.75) that were deemed insignificant and 588 vessels (median FFR value of 0.86) that were deemed hemodynamically significant, according to the research findings.

The meta-analysis authors also pointed to FFR-CT values > 0.90 for 1,374 vessels with a 94 percent correlation (1,283 vessels) to invasive FFR assessments > 0.8. The researchers added that the remaining 91 vessels reclassified as hemodynamically significant by invasive FFR had a median FFR value of 0.76.

“Therefore, for FFR‐CT values >0.9, there is a 90% chance that invasive angiogram can be safely deferred. Although there is a 10% chance the lesion will be hemodynamically significant, the majority of these lesions will have invasive FFR between 0.70 and 0.79,” explained Faulder and colleagues.

(Editor’s note: For related content, see “Study: CCTA-Derived Fraction Flow Reserve Can Predict MI and Mortality Risks in Patients with Stable Angina,” “AMA Issues New Code for AI Estimates of CCTA-Based Fractional Flow Reserve” and “HeartFlow Gets New CPT Reimbursement Code for CT-Based Fractional Flow Reserve.”)

The researchers emphasized caution in assessing the accuracy of FFR-CT in patients with a recent ST-elevation myocardial infarction (STEMI) or those with severe aortic stenosis. While the meta-analysis findings showed a slightly higher accuracy rate for FFR-CT in cases of severe aortic stenosis, Moxon and colleagues said this non-significant finding was based on two studies with small cohorts and different methodologies.

The meta-analysis authors noted a 13 percent lower FFR-CT accuracy in patients with recent STEMI in contrast to those with suspected or known CAD (70 percent vs. 83 percent).

“FFR-CT assumes a normal vasodilatory response but a reduced vasodilator response in the microvasculature has been observed up to 6 months following myocardial infarction, possibly reducing FFR‐CT accuracy,” pointed out Faulder and colleagues.

In regard to limitations with the meta-analysis, the researchers acknowledged varying degrees of stenosis severity at different sites (ranging from left anterior descending to right coronary artery) utilized for the assessment of FFR-CT in the reviewed studies. Faulder and colleagues also noted the risk of bias with 22 of the studies in the meta-analysis having co-authors who had relationships with manufacturers of software utilized to calculate FFR-CT.