Stenting: New Diagnostic Tool Assesses Need without Patient Discomfort

A new tool called instantaneous wave-free ratio (iFR) showed benefits over fractional flow reserve (FFR) in diagnosing whether blocked arteries are the source of chest pain.

In a study presented this morning at ACC 2017 Scientific Sessions, Justin Davies, MBBS, PhD, (photo, left) a consultant cardiologist at Imperial College, London, said FFR is accurate but often not used because of patient discomfort.

The study, called DEFINE-FLAIR, found iFR offers accurate diagnosis but without being painful or causing shortness of breath in patients.

“Our study shows that it is safe to use either iFR or FFR technique, Davies said.

Using iFR also offers potential cost savings, researchers said.

The study had test sites in the United States, Europe, Africa, the Middle East, Asia and Australia.

It was the largest undertaking of its kind, and the first to assess how using iFR affects patients’ outcomes.

In a related study called IFR-SWEDEHEART, Matthias Gotberg, MD, PhD, (photo, right) a cardiologist at Skane University Hospital in Lund, Sweden, agreed. His study was also presented this morning.

“Our study shows that for cardiologists who currently use FFR, iFRprovides a similar clinical benefit but without patient discomfort,” Gotberg said, a finding that could benefit patients both by making the test less unpleasant and increasing the use of a valuable diagnostic tool.

Angiography alone can estimate the severity of a narrowed artery, but cannot accurately determine whether a stent is needed to widen it.

FFR, and iFR is far more precise, the researchers said.

The newer technique is less painful because it does not require a vasodilator drug.

In FFR a thin wire is threaded into the coronary artery and measures the loss of blood pressure across the narrowed area.

In iFR, there is also a thin pressure sensor wire, but the technique uses a mathematical algorithm to measure pressure in the artery only when the heart is relaxed and the coronary blood flow is high. That means the vasodilator is not needed.

In the DEFINE-FLAIR study, researchers enrolled 2,492 patients at 49 centers in 17 countries. Half got iFR and half FFR.

In the IFR-SWEDEHEART study, there were 2,037 patients treated at 15 centers in Sweden, Denmark, and Iceland. About half got FFR and half iFR.

There were no differences in either study’s results in terms of the composite primary endpin, both studies showed no significant differences in separate analyses of all-cause mortality, subsequent heart attack, or revascularization.

DEFINE-FLAIR showed a substantial reduction in symptoms of procedure-related adverse events: only 3% in iFR compared to 30.8% with FFR.

FFR patients had significantly higher rates of shortness of breath (20% vs 1% with iFR) chest pain (1.5% vs. 7.2%) heart rhythm disturbances (0.2% vs 4.8%) and serious adverse events. Those included severe shortness of breath or a need to cardiovert a patient (0.1% vs. 0.6%.)

Both studies also showed there was a substantial difference in the number of significant atherosclerotic lesions that needed stenting. They attributed that not to the relative accuracy of the two techniques, but to “subtle differences in the physiological basis of how the 2 approaches work and their slightly different thresholds for determining when stenting is required.

They suggested the difference does not mean FFR does a better job, but that using iFR and having fewer stents needed is a potential cost savings, as is the fact that iFR doesn’t require a vasodilator drug.

In IFR-SWEDEHEART, iFR picked up lesions in 29.2% of patients and FFR found them in 36.8% of patients.

A similar pattern was found in DEFINE-FLAIR in which 46 % of patients who had iFR had lesions that were bad enough to need stenting procedures and FFR determined that 50% of patients needed stents.

The comparisons also showed the iFR procedures were shorter at 40.5 minutes by about five minutes.

The two lead researchers are now collaborating on a follow-up analysis that will focus on primary outcomes in all 4,500 patients.

Both studies were published online today in the New England Journal of Medicine.

The studies were funded by Volcano-Philips (DEFINE FLAIR) and by a Colcano grant to the Uppsala Clinical Research Centre of Uppsala University (SWEDEHEART).