A Pitfall of Fractional Flow Reserve Measurement

   ABSTRACT: Fractional flow reserve is a simple and efficient tool to assess the severity of an intermediate lesion in order to determine the optimal therapy. However there are some limitations to its use. We observed that in patients with an occluded artery, FFR measurements in the vessel supplying collaterals can be underestimated leading to inappropriate therapy. J INVASIVE CARDIOL 2010;22:E110–E111    Key words: chronic total occlusion, FFR, lesion severity, multivessel disease, percutaneous coronary intervention, stenosis severity    Fractional Flow Reserve (FFR) measurement provides a simple and efficient means of determining the severity of angiographically intermediate lesions. The use of FFR was recently shown to be of clinical benefit in patients with multivessel disease.¹ We have recently observed that in multivessel disease patients with a chronic total occlusion, FFR measurement could be abnormal despite the lack of significant or intermediary stenosis because of large collaterals to an occluded artery.    Case Report. A 44-year-old male with dyslipidemia and active smoker was referred to our institution for cardiac catheterization. He suffered exertional angina refractory to medical therapy (CCS 2). He had a history of myocardial infarction treated by percutaneous coronary intervention with stent implantation in the mid segment of the right coronary artery (RCA) 6 months before. At that time the left anterior descending artery was totally occluded at the ostium with collateral flow from the distal RCA, grade II on the Rentrop scale. Stress echocardiography showed inferior and septal wall ischemia with a lack of viability in the anterior wall. Angiography showed a mild atheroma of the circcumflex artery in addition to the lesions described above, and the RCA angiogram showed no instent restenosis in a significant or intermediary lesion (Figure 2B). The lack of significant stenosis was confirmed by intravascular ultrasound of the RCA (Figure 1A). In order to understand the mechanism of ischemia of the inferior and septal segments, FFR measurement was performed in the distal RCA and showed a significant pressure drop 0.72. Pull-back analysis confirmed the lack of focal pressure drop consistent with the lack of significant or intermediate stenosis of the RCA visible angiographically (Figure 1A).    Total coronary occlusion was considered unsuitable for PCI and patient was managed with medical treatment.    Discussion. Pressure-based myocardial fractional flow reserve (FFR) is a validated tool to assess coronary stenosis severity and in particular the functional value of angiographically intermediary stenosis. Its use to help guide therapy was shown to be of clinical benefit in patients with multivessel disease.² FFR is defined as the maximal blood flow to the myocardium supplied by that artery in the presence of a stenosis, divided by the theoretical normal maximal flow in the same arterial distribution. It can be easily derived from the ratio of the mean distal coronary artery pressure to the aortic pressure during maximal vasodilatation. A FFR value 1 Contrarily to coronary flow reserve, FFR is not influenced by hemodynamic parameters such as pulse rate and blood pressure. However the validity of FFR to assess stenosis severity in the presence of major collaterals branches is not established. In the case described above, FFR was 3 In our case, the patient had documented ischemia by stress echocardiography in the territory of the occluded artery (LAD) confirming the coronary steal. Werner et al had described different profiles of microvascular function in collateralized arteries in the absence of donor artery stenosis, they studied FFR in the donor artery, collateral and microvascular resistance at baseline and after induced hyperemia, before and after recanalization of the occluded artery and showed that 56 arteries from 26 patients (46%) had coronary steal with reduced FFR in the donor artery, patients without microvascular dysfunction in the collateralized artery (54%) had a normal FFR in the donor artery.³    The interpretation of FFR in patient with major collaterals to an occluded coronary artery may be skewed and could lead to inappropriate therapy unless careful pull-back analysis is performed to confirm the lack of focal pressure drop.

References

1. Pijls NH, van Schaardenburgh P, Manoharan G, et al. Percutaneous coronary intervention of functionally nonsignificant stenosis: 5-year follow-up of the DEFER Study. J Am Coll Cardiol 2007;49:2105–2111. 2. FAME Study Investigators. Fractional flow reserve versus angiography for guiding percutaneous coronary intervention. N Engl J Med 2009;360:213–224. 3. Werner GS, Fritzenwanger M, Prochnau D, et al. Determinants of coronary steal in chronic total coronary occlusions donor artery, collateral, and microvascular resistance. J Am Coll Cardiol 2006;48:51–58.

_________________________________________________ From the Hôpital Universitaire Nord de Marseille, Département de Cardiologie, Marseille, France. The authors report no conflicts of interest regarding the content herein. Manuscript submitted October 26, 2009 and final version accepted November 25, 2009. Address for correspondence: Laurent Bonello, MD, Hôpital Universitaire Nord de Marseille, Département de Cardiologie, chemin des Bourrely, Marseille, 13015 France. E-mail: laurentbonello@yahoo.fr