Efficacy of FPA in swine models could open the door for more accurate CAD testing in humans

A new lab technique could cut testing time and improve the accuracy of coronary artery disease (CAD) diagnoses according to new research published in Radiology. 

First-pass analysis (FPA) technology could change the field of CAD diagnosis, Sabee Molloi, PhD, and co-authors wrote in the study, and eliminate the need for less accurate, more copious tests like fractional flow reserves, cardiac MRIs, single-photon emission CTs or PET scans. FPA combines computed tomographic (CT) angiography and dynamic CT perfusion data by using just two whole-heart volume scans and one contrast material injection. Molloi and colleagues found FPA to be a valuable method to enable accurate, low-dose vessel-specific morphologic and physiologic assessment of CAD in six swine models.

Unlike other testing techniques, FPA indicates good detection of microsphere perfusion values of less than 1 mL/min/g at maximal hyperemia in the left anterior descending artery (LAD), Molloi et al. explained. The technique also measures quantitative perfusion in the left circumflex artery, right coronary artery and all three coronary arteries combined, while limiting testing to just two first-pass volume scans and one injection.

“The FPA technique models the entire myocardium as one compartment; therefore, the vascular, interstitial and cellular compartments are lumped together,” the authors wrote. “As a result, partial diffusion of contrast material from the vascular space into the interstitial and cellular compartments does not affect the FPA technique.”

The researchers studied six male Yorkshire swine in an animal care committee-approved retrospective trial. The FPA technique was tested in the pigs between April 2015 and October 2016, according to the paper, at which point four to five intermediate-severity stenoses were generated in the LAD and 20 contrast material-enhanced volume scans were acquired per stenosis.

Not all volume scans were used for FPA perfusion—just two—but in each case scans were used for maximum slope model (MSM) perfusion measurement, which uses small tissue volumes of interest to generate myocardial time-attenuation curves.

Molloi and colleagues were able to validate the FPA technique in the animals through FPA and MSM perfusion measurements in all three coronary arteries combined. The CT dose and size-specific dose estimates per two-volume FPA perfusion measurement were 10.8 and 17.8 mGy, respectively, the authors wrote, and mean heart rate and mean arterial pressure were 78.6 beats per minute and 73.4 mmHg.

“The FPA technique performed better than the MSM technique in perfusion measurement, demonstrating higher slope of agreement and higher concordance correlation as compared with microsphere perfusion measurement,” Molloi and co-authors said in the paper, noting the FPA technique also performed better than MSM to detect significant stenoses.

The MSM technique did demonstrate higher sensitivity and negative predictive value, they wrote, though such high sensitivity and negative predictive value can lead to a slew of false-positive findings.

Still, the authors said, the FPA technique proved to be a less complicated, more accurate way of detecting CAD in affected patients.

“The FPA technique has the potential to reduce the radiation dose and contrast material dose associated with CT-based CAD work-up, making comprehensive assessment of CAD more accessible to and effective in patients in need,”  they wrote. “(It) has the potential to be used for accurate, low-dose vessel-specific morphologic and physiologic assessment of CAD.”