Instantaneous wave-free ratio (iFR)

Instantaneous wave-free ratio (iFR)

Fractional flow reserve (FFR) is quite popular now for the assessment of intermediate coronary lesions to decide on whether revascularization is needed or not. It involves measurement of pressure proximal and distal to the lesion after inducing maximal hyperemia with adenosine. FFR became popular after the results of FAME I (Fractional Flow Reserve versus Angiography for Guiding PCI in Patients with Multivessel Coronary Artery Disease trial I) and FAME II (Fractional Flow Reserve versus Angiography for Guiding PCI in Patients with Multivessel Coronary Artery Disease trial II) results were published. But the additional cost and procedural time are often of concern to the operators, as well as potential problems with the use of adenosine.

It was to overcome this that the instantaneous wave free ratio (iFR) was introduced, in which translesional pressure gradient in a specific diastolic interval is measured. This period has a constant microvascular resistance and results similar to FFR can be achieved without inducing hyperemia with adenosine [1]. RESOLVE study showed that iFR less than 0.84 corresponded to FFR less than 0.80 and iFR above 0.94 corresponded to FFR above 0.80. In their Frame of Reference article in JACC [2], Kerin MJ et al asks whether iFR is the new standard of care for coronary physiology or whether it produces more questions than answers! The recent iFR-SWEDEHEART [3] and DEFINE-FLAIR [4] studies have demonstrated the non inferiority of iFR compared to FFR. iFR was associated with lower procedure times and avoided the adenosine related effects, leave alone, the extra cost of adenosine.

References

1. Sen S, Escaned J, Malik IS, Mikhail GW, Foale RA, Mila R, Tarkin J, Petraco R, Broyd C, Jabbour R, Sethi A, Baker CS, Bellamy M, Al-Bustami M, Hackett D, Khan M, Lefroy D, Parker KH, Hughes AD, Francis DP, Di Mario C, Mayet J, Davies JE. Development and validation of a new adenosine-independent index of stenosis severity from coronary wave-intensity analysis: results of the ADVISE (ADenosine Vasodilator Independent Stenosis Evaluation) study. J Am Coll Cardiol. 2012;59:1392–1402.

2. Kern MJ, Seto AH. Is Instantaneous Wave-Free Ratio a New Standard of Care for Physiologic Assessment of Coronary Lesions? More Questions Than Answers. Circulation. 2017;136:2295-2297.

3. Götberg M, Christiansen EH, Gudmundsdottir IJ, Sandhall L, Danielewicz M, Jakobsen L, Olsson SE, Öhagen P, Olsson H, Omerovic E, Calais F, Lindroos P, Maeng M, Tödt T, Venetsanos D, James SK, Kåregren A, Nilsson M, Carlsson J, Hauer D, Jensen J, Karlsson AC, Panayi G, Erlinge D, Fröbert O; iFR-SWEDEHEART Investigators. Instantaneous wave-free ratio versus fractional flow reserve to guide PCI. N Engl J Med. 2017;376:1813–1823.

4. Davies JE, Sen S, Dehbi HM, Al-Lamee R, Petraco R, Nijjer SS, Bhindi R, Lehman SJ, Walters D, Sapontis J, Janssens L, Vrints CJ, Khashaba A, Laine M, Van Belle E, Krackhardt F, Bojara W, Going O, Härle T, Indolfi C, Niccoli G, Ribichini F, Tanaka N, Yokoi H, Takashima H, Kikuta Y, Erglis A, Vinhas H, Canas Silva P, Baptista SB, Alghamdi A, Hellig F, Koo BK, Nam CW, Shin ES, Doh JH, Brugaletta S, Alegria-Barrero E, Meuwissen M, Piek JJ, van Royen N, Sezer M, Di Mario C, Gerber RT, Malik IS, Sharp ASP, Talwar S, Tang K, Samady H, Altman J, Seto AH, Singh J, Jeremias A, Matsuo H, Kharbanda RK, Patel MR, Serruys P, Escaned J. Use of the instantaneous wave-free ratio or fractional flow reserve in PCI. N Engl J Med. 2017;376:1824–1834.