February 6th, 2013
FFR vs. iFR: All That Glitters Is Not Gold
The “Gold Standard”: Fractional flow reserve (FFR) is a pressure-derived index of coronary stenosis severity that has been validated for assessing the hemodynamic significance of stenoses that are of “intermediate” angiographic severity. In fact, FFR use during PCI carries a Class 1A recommendation from the European Society of Cardiology and a Class IIA recommendation from the American College of Cardiology, despite the fact that it requires additional instrumentation of the coronary arteries and pharmacologic vasodilation to induce maximal hyperemia.
Easier Money? The instantaneous wave-free ratio (iFR) is an alleged index of coronary stenosis severity that is independent of hyperemia. It is based on the hypothesis that coronary microvascular resistance is minimal during mid and late diastole (when coronary flow is maximal), so the administration of a vasodilator is unnecessary. It is thought that by avoiding the need to administer adenosine, iFR is more likely than FFR to expand the practice of pressure wire-guided decision making.
Convertible Currency? Unfortunately, the results of two new studies suggest that iFR is unlikely to replace FFR.
Using a simulation model to study the relationship between iFR and FFR, then validating their predictions with data from a large, multicenter cohort of humans, Johnson and colleagues found that:
- iFR systematically overestimates FFR, with wide limits of agreement that would often alter management decisions.
- In individual patients, iFR is not interchangeable with FFR.
In VERIFY, a prospective study of 206 consecutive PCI patients compared with a retrospective analysis of 500 archived pressure recordings, Berry and colleagues showed that:
- The diagnostic accuracy of iFR was only 60% compared with the FFR cut-off value of <0.80 (a value that has been validated in randomized trials for clinical management).
Pyrite (Fool’s Gold): The VERIFY authors conclude “…that iFR cannot be recommended for clinical decision making in patients with coronary artery disease.” Too bad, since iFR would be a convenient and quick use of a pressure-wire alone — without a vasodilator — to assess coronary stenosis severity.
With all the concerns of inappropriate PCI, do you feel compelled to use FFR to justify PCI?
In what percentage of patients with “intermediate” coronary stenoses do you use FFR?
Does the hassle associated with administering a vasodilator prevent you from measuring FFR in patients with intermediate stenoses?