TCT: IVUS falls short for lesion measurement; stick to FFR

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IVUS provides 2D information of the obtuse marginal artery.
Source: Craig A. Thompson, MD

MIAMI—“You can’t use IVUS [intravascular ultrasound] to determine whether a lesion is less or equal to 0.8. For that determination, you need to use FFR [fractional flow reserve],” explained Gregg W. Stone, MD, as one of the take-home messages from the VERDICT F1RST/VERDICT PILOT trials, presented Oct. 22 at 2012 Transcatheter Cardiovascular Therapeutics (TCT) conference.

While this wasn’t a clinical outcomes trial, the VERDICT investigators conducted a prospective, multicenter study examining the correlation between IVUS and FFR parameters in intermediate lesions to improve on prior analysis that have examined this relationship, explained Stone, of Columbia University Medical Center and New York-Presbyterian Hospital in New York City.

Prior studies have had limitations, as most were retrospective, and IVUS and FFR methodologies are not standardized, he added.  

This VERDICT F1RST trial enrolled 234 patients with 241 lesions at 10 sites in four countries. They examined only one lesion per major vessel, with a diameter stenosis of >40 to <80 percent and a reference vessel diameter (RVD) of >2.5 mm. Also, the researchers enrolled multiple vessels in the same patient, but only one lesion per vessel. They excluded patients with STEMI in the previous 24 hours, with left main disease, ostial, bifurcation, thrombus, calcification, angulation or tortuosity. “These were pretty straightforward lesions,” Stone said. Also, FFR was assessed with IV adenosine, followed by virtual histology-IVUS (VH-IVUS).

“At the same time we were running VERDICT PILOT, the VERDICT F1RST trial was ongoing as well,” Stone said. “Thus, we decided to pool our data and systemize in order to have a trial with much greater power to examine subgroups.”

VERDICT PILOT was a multicenter, nonrandomized, nonblinded study that enrolled 282 patients, 202 intermediate coronary lesions, with a diameter stenosis of >40 to <80 percent, and a RVD 2.75 mm to 4 mm in sites in the U.S. and Europe.

The major differences between the trials were that the RVD was >2.5 mm in PILOT vs. >2.75 mm in F1RST, and F1RST did not exclude patients with wall motion abnormalities.

Overall, both trials assessed the minimum luminal cross-sectional area (MLA) and FFR in 544 intermediate lesions in 516 patients from 24 centers in nine countries.

“The optimal cutoff was 2.9 mm2. There was a rough correlation between FFR and IVUS, but it wasn’t great,” Stone said.

There were 20.6 percent of the values that were true-positive, and 45.4 percent that were true-negative. “There were a lot of patients that had an FFR of greater than 0.8 and a MLA of less than 2.9mm2,” he reported. “Surprisingly, 10.5 percent of all patients had false-negative—and this quadrant has been fairly absent in previous studies.”

The positive-predictive value was 46.7 percent—similar to other studies—but the negative-predictive value was worse than other studies at 81.3 percent.

Another finding, according to Stone, was that left anterior descending (LAD) arteries were much more likely to have a positive FFR, than non-LAD. Circumflex arteries were far less likely to have a positive FFR.

Thus, the researchers concluded that FFR was independently related to vessel location, vessel size and lesion severity. Also, plaque burden and composition had minimal correlation with FFR.

Stone said that the variable with the strongest and most accurate correlation to FFR of <80 was MLA (<2.9 mm2 or less). The optimal MLA cutoff varied with vessel characteristics.

VERDICT F1RST confirmed the findings from prior studies that there is only a modest correlation between IVUS MLA and FFR, Stone said. “Indeed, the false-negative rate was higher and negative predictive of 81.3 percent was lower in the present study than in prior reports,” he noted.

Based on these findings, Stone reiterated: “Don’t fool yourself into thinking that you can use IVUS in most cases.”

Volcano sponsored both trials.