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To Stent or Not To Stent: Fractional Flow Reserve (FFR) Trumps Angiography in Diagnosing Blockages up to 90%

Fractional Flow Reserve    

June 23, 2010 -- The FAME study, published in January 2009, showed that using Fractional Flow Reserve (FFR) instead of standard angiography to determine whether or not to stent a blocked coronary artery resulted in one-third fewer stents being placed and, more importantly, resulted in almost one-third fewer serious adverse cardiac events, such as heart attack and death.

These results have remained intact, even after two years of follow-up.

Now, an ancillary study of the FAME data, has been published in the June 22 issue of the Journal of the American College of Cardiology and, as the authors conclude:

"In patients with multivessel CAD, coronary angiography is an inappropriate tool to identify ischemia-producing stenoses as detected by the FFR. This discrepancy between angiographic and functional stenosis severity is not only present in the 50% to 70% stenosis range but also in the 71% to 90% stenosis range."

Angiography, long considered the "gold standard" in diagnosing coronary artery disease, is now being labeled as inappropriate and inaccurate by those who are utilizing a new technique for determining ischemia. (The authors also note that noninvasive stress testing is similarly inaccurate in determining ischemia in multivessel disease.)

An angiogram is a shadow image of the coronary artery, produced by X-rays and contrast dye to show if any blockages exist. When a cardiologist sees a blockage greater than 50%, he or she often decides to open the artery using balloon angioplasty and places a stent to hold the artery open.

Criticism has been leveled at this diagnostic method and has been labeled as the "oculo-stenotic reflex" -- if you see a blockage (stenosis) you automatically assume it needs to be stented. However, this is not always the case.

    Angioplasty.Org Image

The FAME study refuted this methodology for patients with multivessel coronary disease (narrowings in more than one artery). Using a catheter to measure the blood pressure on both sides of the blockage, called the fractional flow reserve (FFR), cardiologists were able to determine more accurately whether the plaque build-up was actually causing significant ischemia (loss of blood flow). When guided by FFR, less stents were placed and outcomes for the patients were better by 28%, when compared to stent placement guided only by the angiogram.

What the authors of this week's JACC paper have shown is that the advantage of FFR-guided stent placement exists not only in what might be called "intermediate lesions" of 50-70% (as measured by angiography) but also in more severe blockages. Two-thirds of the coronary narrowings in the 50-70% range were measured by FFR as being functionally insignificant. In other words, only one out of three blockages in this range was causing ischemia; placing a stent in two-thirds of these lesions was not only unnecessary, but could result in more adverse events.

However, even in the more severe range of 71-90% blockages, one out of five stenoses were measured by FFR as being functionally insignificant -- no stent needed. It was only in the range of 91% or greater narrowing that virtually all of the lesions were significant and the patient would benefit from stenting.

The implications of these studies are wide-ranging. The authors show that many patients diagnosed with triple-vessel disease may in fact only have one or two vessels causing a problem. They also note that if many of the angioplasty vs. .surgery studies had used FFR instead of angiography to determine whether or not to use a stent, the improved results may have favored angioplasty more. Likewise, the COURAGE trial may also have shown a greater benefit for angioplasty and stenting.

Andreas Gruentzig
Andreas Gruentzig holding
his original balloon catheter

Interestingly enough, the original balloon catheter, as designed by Andreas Gruentzig, the inventor of coronary angioplasty, had a built-in capacity to measure coronary pressures. Gruentzig insisted on this feature to determine if the balloon had sufficiently opened the artery. He was a strong proponent of documenting the results of his procedures and of using intracoronary blood pressures as a guide for dilatation.

But as balloon angioplasty grew and started being applied in more complex and sophisticated cases, the relatively bulky pressure measurement designs had to be discarded by catheter manufacturers in order to create balloons of smaller and smaller profile, balloons which could reach into narrower arteries and negotiate more tortuous coronary anatomy.

Until now, that is. Today, specialized FFR catheters are manufactured by two companies: Volcano Corporation and St. Jude Medical (which funded this week's JACC study, as well as the original FAME trial). But despite the clear advantages shown in these studies, FFR is still only utilized in 10-15% of all percutaneous coronary interventions (PCI). Both companies feel that this is changing and that, with the advances in design and the integration of FFR technology into the cath lab, this new diagnostic tool will be adopted by cardiologists in increasing numbers, resulting in better outcomes for patients and potentially lower costs (less stents) for the healthcare system.

Reported by Burt Cohen, June 23, 2010