Utility of Fractional Flow Reserve Measurement in Demonstrating Chronic Ischemic Myocardium in Chronic Total Occlusions of Coronary Arteries

 Disclosures: Dr. Shaw and Dr. Varghese report no conflicts of interest regarding the content herein. Dr. George reports he is a consultant for Maquet and Abiomed. The authors can be contacted via Dr. Jon George at georgej@deborah.org.

Case

A 56-year-old male with history of coronary artery disease, ischemic cardiomyopathy, hypertension, and dyslipidemia presented to the hospital with acutely decompensated systolic heart failure and evidence of myocardial injury, approximately one month after suffering an anterolateral ST-elevation myocardial infarction, and subsequent percutaneous coronary intervention (PCI) with stenting to his left anterior descending coronary artery (LAD). Serum troponin on current presentation was only trivially elevated and the 12-lead electrocardiogram demonstrated non-specific T-wave changes, consistent with his recent anterolateral myocardial infarction. Coronary angiography demonstrated a patent stent in the LAD, mild disease in a non-dominant left circumflex coronary artery (LCX), and chronic total occlusion (CTO) of a dominant right coronary artery (RCA) (Figure 1). The distal RCA and its branches were filled by septal collaterals from the LAD (Figure 2). The inferior wall demonstrated severe hypokinesis by echocardiography, but was deemed viable from collateral perfusion. The patient was optimized medically and discharged home in 48 hours, with plans for PCI of the RCA CTO in the future, given his ischemic cardiomyopathy and recurrent heart failure. 

Ten days later, the patient was brought to the catheterization laboratory for PCI. Bilateral common femoral arterial access was obtained. The ostium of the RCA was engaged using an 8 French AL (Amplatz left) 1 guide with side holes, and a 6 French EBU (Extra Back Up) 3.5 guide (Medtronic) was used to engage the left main coronary artery. Simultaneous dual coronary contrast injection confirmed a long occlusion from the proximal to mid RCA with a small segment of reconstitution in the mid vessel, and patent right posterior descending artery (RPDA) and right posterolateral (RPL) branch (Figure 3). A short 2 mm balloon was inflated in the conus branch to serve as an anchor for the poorly supported RCA guide (Figure 4). A Corsair catheter (Asahi Intecc) with a Pilot 200 guide wire (Abbott Vascular) was used to cross subintimally through the proximal RCA occlusion to the mid vessel (Figure 4). Next, a CrossBoss catheter (Boston Scientific) was advanced through the mid-distal occlusion, with subintimal tracking to the bifurcation of the RPDA and RPL branch (Figure 5). A StingRay balloon catheter (Boston Scientific) was then used to occupy the subintimal space and re-enter the true lumen of the RPDA with the StingRay guide wire (Figure 6). Intraluminal position was confirmed by injection through an over-the-wire balloon. An Aeris wire (St. Jude Medical) for fractional flow reserve (FFR) measurement was then advanced first into the EBU guide in the left coronary system to equalize pressures, and subsequently into the distal RPDA for FFR measurement in the distal reconstituted RCA perfused by collateral blood flow. Resting FFR was measured at 0.50, consistent with under-perfused myocardium, despite robust collateralization from the LAD (Figure 7). The entire occluded segment of RCA was then pre-dilated with a 2.5 x 20 mm Emerge balloon (Boston Scientific) and stented in overlapping fashion with Promus (Boston Scientific) everolimus-eluting platinum chromium stents from distal to proximal (2.75 x 38 mm, 2.75 x 38 mm, 3 x 38 mm, and 3 x 16 mm). Final angiogram showed good angiographic result with TIMI-3 flow (Figure 8). A final post-revascularization FFR measurement was significantly improved at 0.94 (Figure 9).

Discussion

Until recently, the prevailing attitude toward well-collateralized CTOs was that collateral filling of the distal occluded vessel was sufficient for myocardial perfusion of the associated territory. This sentiment was further driven by the results of the COURAGE trial, which did not demonstrate a difference in death or myocardial infarction in patients with stable angina who were treated with optimal medical therapy with or without revascularization.¹ However, the nuclear sub-study of COURAGE showed that in patients with moderate to severe ischemia in at least 10% of the myocardium, morbidity and mortality benefit was seen in the revascularized group.² Advances in interventional techniques and devices, and the continued improvement of drug-eluting stents, have led to a shift in the general approach to CTOs, favoring coronary revascularization in symptomatic patients with demonstrable hibernating or ischemic myocardium.³

FFR is an invasive ischemic evaluation modality, which involves the passage of a pressure guide wire across a coronary lesion to measure the pressure in the vessel distal to the lesion in comparison to the pressure in the aorta. FFR value is derived from the ratio of the mean distal coronary artery pressure to the aortic pressure during maximal vasodilation.⁴ The FAME study concluded that routine measurement of FFR in patients undergoing PCI significantly reduces major adverse cardiac events at 1 year.⁵ The FAME 2 trial demonstrated that an FFR value <0.8 represents significant inducible ischemia even in stable coronary disease.⁶ The utility of FFR to measure physiological significance of collateralized myocardial segments has been previously demonstrated.⁷

With increased interest in revascularizing CTOs percutaneously, recent evidence has emerged that well-collateralized CTOs still demonstrate persistent chronic myocardial ischemia. In a recent study, Sachdeva et al performed FFR measurement in vessel segments distal to CTOs to evaluate the robustness of collateral flow.⁸ Resting ischemia was present in most patients, with inducible ischemia present in all patients after maximal hyperemia (mean FFR 0.45). This suggests that despite excellent collateral filling distal to a CTO, the myocardium subtended by the occluded vessel remains chronically ischemic and might benefit from revascularization.

The technique of FFR measurement in CTOs differs from the traditional approach by virtue of having to cross the occluded segment with an FFR guide wire. The guide wire is normalized in the contralateral guide to equalize the aortic and FFR guide wire pressures. After crossing of the CTO segment, the FFR guide wire is advanced into the distal collateralized CTO vessel through a 1.2-1.5 mm over-the-wire balloon. FFR measurements are recorded in the distal CTO vessel at baseline without inducing hyperemia after withdrawal of the balloon into the guide. If the CTO is recanalized via a retrograde approach, all retrograde devices occupying the collaterals will have to be removed prior to FFR measurement in order to allow adequate collateral filling of the distal CTO segment and facilitate measurement of true perfusion pressures. Upon completion of revascularization, a final FFR measurement is recorded post-intervention using the same technique.

In the case described herein, there was echocardiographic evidence of myocardial viability in the distribution of the distal RCA. After successful subintimal crossing of the RCA CTO, an FFR of the distal RCA demonstrated severe baseline ischemia with a resting FFR of 0.35, despite robust collateralization from the LAD septal perforators. Angioplasty and stenting of the RCA led to near resolution of the FFR gradient, potentially resulting in significant improvement of heart failure symptoms. 

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