In the September issue of Vascular Disease Management, Drs. Koleilat and Gray present an article on the utilization of fractional flow reserve (FFR) to assess the hemodynamic significance of lesions in the peripheral arterial system. They utilize the same basic equipment used by interventional cardiologists performing fractional flow reserve to determine the hemodynamic importance of coronary lesions to guide coronary interventional therapy, but they apply it to the peripheral arterial vasculature. Instead of using vasoactive drugs, which may have side effects, to induce a hyperemic state and therefore demonstrate gradients, he creates a hyperemic state by simple external cuff compression of the calf for a minute to induce ischemia resulting in subsequent hyperemia during reperfusion. 

There are many limitations to conventional peripheral angiography that this technique has the potential to solve. Many angiograms are performed only in anterior-posterior projections where eccentric lesions or lesions at areas of overlapping vessels may not be visualized. Dense dystrophic calcification may obscure ideal initial assessment as well as postinterventional assessment of treatment success. Lesions that are hemodynamically significant may not be assessed as significant, and some “borderline” lesions that are not limiting flow may be inappropriately treated. This may result in suboptimal hemodynamic gain in lesions that should be treated but aren’t as well as inappropriately treated insignificant lesions resulting in longer-than-needed segment treatment zones and occasionally “full metal jackets.” Multiple angulated subtracted angiographic views may be helpful in overcoming some of angiography’s shortcomings, but these add radiation exposure, contrast risk, and may not always adequately discern between lesions requiring therapy or not, and when additional therapy is needed beyond the index procedure. 

Hemodynamic assessment may have the potential to become even more important as drug eluting balloons and other drug-eluting therapies are utilized more frequently. A deep dissection following DEB with normal subsequent hemodynamics may require no additional treatment with stents or atherectomy. Hemodynamically insignificant index lesions potentially will be less likely to have interventions performed. These factors could therefore lessen overall procedural costs while potentially improving quality outcomes, as demonstrated by the COURAGE trial in coronaries.¹

Before interventionalists completely accept FFR as the “gold standard” in guiding peripheral interventions, further evaluation is needed. Peripheral arterial intervention is different than coronary intervention, and peripheral arterial hemodynamics are substantially different than coronary hemodynamics. What is effective in the coronaries may not be in the peripheral arterial system. Coronary flow occurs in diastole, while peripheral arterial flow is throughout the cardiac cycle. Flow is shunted away from the legs at rest and is minimal. The heart has high flow at rest that increases further with exertion. Small-diameter coronary vessels have far greater absolute flow than large-diameter femoral arteries. This results in greater velocity of flow making gradients more obvious. Without substantial augmentation of flow, interventionalists may incorrectly deem peripheral arterial lesions with no or minimal gradient to be insignificant, resulting in failure to achieve optimal outcomes.

The potential advantage of this type of assessment is promising and warrants further study. Before there can be widespread adoption by interventionalists, longer term follow-up and correlation with outcomes will be needed. Various arterial segments such as femoral, popliteal, and infrapopliteal will need individual correlation. And ultimately, cost effectiveness must be established. 

Reference

1. Boden WE, O'Rourke RA, Teo KK, et al; COURAGE Trial Research Group. Optimal medical therapy with or without PCI for stable coronary disease. N Engl J Med. 2007;356(15):1503-1516.