October 26, 2011 (Seoul, South Korea) — Results of the Diagnosis of Ischemia-Causing Stenoses Obtained via Noninvasive Fractional Flow Reserve (DISCOVER FLOW) study show that the coronary stenoses that cause ischemia can be identified noninvasively with computer analysis of coronary computed tomography angiograms (CCTAs) .
"I think it's a potential game-changer, because for the first time you have the ability to look at coronary stenosis and ischemia simultaneously, [and] you have the ability to pinpoint the lesion that is causing the ischemia," DISCOVER FLOW senior investigator Dr James Min (Cedars-Sinai Medical Center, Los Angeles, CA) told heartwire. "You can imagine a scenario where somebody has an abnormal stress test and then you go in and you do an angiogram and see four or five stenoses, but you don't really know which one caused the ischemia." But this new "virtual fractional flow reserve" process — or FFRCT — can quantify the fractional flow reserve for each lesion with the data taken from a CCTA, thereby revealing which stenoses are causing ischemia and ought to be treated, as well as which stenoses do not need to be treated. "We've never before had this one-stop shop to . . . pinpoint the lesions that cause the ischemia noninvasively."
As reported by heartwire at EuroPCR 2011, in DISCOVER FLOW, Dr Bon-Kwon Koo (Seoul National University Hospital, Korea) and colleagues used computation of FFRCT to assess 159 vessels in 103 patients undergoing CCTA. Results of the study are published in the November 1, 2011 issue of the Journal of the American College of Cardiology.
All of the patients also underwent invasive CCTA and invasive catheter FFR imaging. Ischemia was defined as an FFR of ≤0.80 and anatomically obstructive coronary disease was defined as stenosis ≥50% as measured on the CCTA scan. The diagnostic performance of FFRCT and CCTA were assessed against invasive FFR as the reference standard. Of the patients in the study, 56% had at least one vessel with an FFR of ≤0.80.
Because only about half of stenoses over 50% actually cause ischemia, the specificity of traditional assessment of a stenosis by CCTA is below 50%. "The concern there is that you identify some high-grade stenoses that are angiographically confirmed, but the lesions don't actually cause ischemia." Fractional flow reserve measures how much of the blood flow is being blocked by a lesion, so it is about 25% more accurate than traditional CCTA at picking out lesions that cause ischemia, Min explained.
Per vessel diagnostic accuracy FFRCT and CCTA (reference for both was invasive FFR)
|Imaging technology||Accuracy (%)||Sensitivity (%)||Specificity (%)||Positive predictive value (%)||Negative predictive value (%)|
aIschemic defined as ≤0.80
bIschemia defined as stenosis ≥50%
FFRCT can assess stenoses from any CCTA scan — prospectively gated or retrospectively gated — without any additional imaging techniques or changes to the acquisition parameters. Just as computational fluid dynamics can predict the behavior of an airplane wing under different environmental parameters, FFRCT can measure the flow of blood through a stenotic coronary based on the specific geometry of the patient's coronaries and myocardium.
In an accompanying editorial , Dr Stephan Achenbach (University of Giessen, Germany) calls DISCOVER FLOW "an impressive first step into what needs to follow, the painstakingly detailed workup of whether this method will translate into clinical benefit when applied on a broader scale and which patient groups are the ones to most likely benefit from this additional analysis.
"It seems to be possible to derive very detailed functional information from purely anatomic data sets — anatomy meets function," Achenbach concludes. "This concept deserves and requires further investigation on a much broader scale and will most likely not remain limited to the relatively confined area of CCTA."
Proving FFRCT in patients
At the American Heart Association meeting in Orlando next month, Min will present results of a substudy from DISCOVER FLOW looking specifically at intermediate-grade stenoses (40%–69%), which present the most difficult treatment decisions. "If somebody sees a 90% stenosis or 10% stenosis, they are comfortable with what to do with that. But when you hit that 40% to 70% range — it's possible that those lesions are ischemic, but you don't know until you actually assess them," Min said.
DISCOVER FLOW was designed to evaluate the accuracy of FFRCT on a per-vessel basis, but the more important demonstration of its value will be its ability to guide treatment decisions for each patient. The DEFACTO trial, which finished enrollment at 17 centers about three weeks ago, is evaluating FFRCT per patient. "That's the big one," Min said. "DEFACTO will be the pivotal trial." Specifically, the 285-patient DEFACTO trial is assessing the ability of CCTA plus FFRCT to determine the presence or absence of at least one hemodynamically significant coronary stenosis in each trial subject. Invasive catheter FFR is the reference standard. Min expects that study to be completed in the first quarter of 2012.
Koo and Min have reported that they have no relationships relevant to the contents of this paper to disclose. Disclosures for the coauthors are listed in the paper. Achenbach has received research grants from Siemens and Bayer Healthcare; has received lecture honoraria from Siemens; is a consultant to Guerbet, Servier, and Circle; and is supported by research grant from Bundesministerium für Bildung und Forschung. The DEFACTO study is sponsored by HeartFlow.
Heartwire from Medscape © 2011 Medscape, LLC
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