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The instantaneous wave-free ratio (iFR) remained comparable to fractional flow reserve (FFR) as a tool to help decide whether patients with stable angina or acute coronary syndrome need revascularization, the iFR-SWEDEHEART group reported.

Clinical outcomes at 5 years were not significantly worse if operators had relied on iFR instead of FFR:

• Combined all-cause death, myocardial infarction (MI), and revascularization: 21.5% vs 19.9%, respectively (HR 1.09, 95% CI 0.90-1.33)
• All-cause death: 9.4% vs 7.9% (HR 1.20, 95% CI 0.89-1.62)
• MI: 5.8% vs 5.7% (HR 1.00, 95% CI 0.70-1.44)
• Unplanned revascularization: 11.6% vs 11.3% (HR 1.02, 95% CI 0.79-1.32)

"The study confirms the long-term safety and efficacy of revascularization guided by iFR compared with FFR," concluded Matthias Götberg, MD, PhD, of Skane University Hospital and Lund University in Sweden, in his presentation at the Transcatheter Cardiovascular Therapeutics (TCT) meeting held in Orlando, Florida, and broadcast online.

Götberg reported that study results were consistent across various prespecified subgroups.

iFR is an index of coronary physiology, its main advantage over FFR being instant measurement that doesn't require adenosine administration.

Yet this index is no replacement for FFR, according to Shmuel Banai, MD, of Tel Aviv Sourasky Medical Center in Israel, during a TCT press conference. He stressed the importance of laying a wire down to measure microvascular resistance, coronary flow reserve, and other physiological parameters in a full study of the patient's microvasculature.

"We wish people are doing that, but they're not," countered press briefing moderator Roxana Mehran, MD, of Mount Sinai School of Medicine in New York City.

The reluctance to adopt FFR in the U.S. has been attributed to the need for adenosine, which can be costly and feel mildly unpleasant for patients -- or even cause bradycardia or heart block.

Götberg's registry-based randomized had 2,037 people enrolled from 2014 to 2015 at 15 sites across Sweden, Iceland, and Denmark. Eligible patients had suspected stable angina (62%), unstable angina (20%), or non-ST-segment elevation MI (17%)

Participants randomized to iFR or FFR had an average age of 67, and three in four were men.

Stenting was deferred if iFR and FFR were above 0.89 and 0.80, respectively.

The group that underwent iFR had more lesions evaluated (mean 1.55 vs 1.43 with FFR, P=0.002) but fewer significant lesions (29.2% vs 36.8%, P<0.0001), Götberg reported.

iFR and FFR groups shared similar proportions of patients who ultimately underwent percutaneous coronary intervention (PCI; 44%) and coronary artery bypass grafting (CABG; 10%).

Study authors had previously reported that iFR met noninferiority against FFR and was a better experience for patients in a 1-year report.

Critics of iFR-SWEDEHEART have noted that it doesn't inform clinicians which patients need physiological assessment, and that the study lacked a third arm of patients managed without physiology.

Nevertheless, given that results stayed reassuringly stable over time, it may be time for the guidelines to green-light iFR as a tool evaluating candidates for PCI in multivessel disease, suggested Giuseppe Tarantini, MD, PhD, of the University of Padova in Italy, during the press conference discussion.

Another physiological index not requiring adenosine, the angiography-derived quantitative flow ratio, also proved its mettle against angiography alone in the FAVOR III trial, also reported at this year's TCT.

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