|Year : 2020 | Volume
| Issue : 1 | Page : 3-4
A new contestant enters the race for noninvasive fractional flow reserve evaluation, iFRCT
Richard Bayer II1, Stefan Baumann2, U Joseph Schoepf1
1 Department of Radiology and Radiological Science, Division of Cardiovascular Imaging, Medical University of South Carolina, Charleston, SC, USA
2 First Department of Medicine-Cardiology, University Medical Centre Mannheim, Mannheim, Germany
|Date of Submission||14-Mar-2020|
|Date of Acceptance||16-Mar-2020|
|Date of Web Publication||4-Apr-2020|
Prof. U Joseph Schoepf
Department of Radiology and Radiological Science, Division of Cardiovascular Imaging, Medical University of South Carolina, Charleston, SC
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bayer II R, Baumann S, Schoepf U J. A new contestant enters the race for noninvasive fractional flow reserve evaluation, iFRCT. Cardiol Plus 2020;5:3-4
|How to cite this URL:|
Bayer II R, Baumann S, Schoepf U J. A new contestant enters the race for noninvasive fractional flow reserve evaluation, iFRCT. Cardiol Plus [serial online] 2020 [cited 2020 May 31];5:3-4. Available from: http://www.cardiologyplus.org/text.asp?2020/5/1/3/281944
The assessment of the functional significance of coronary artery disease (CAD) has been an important topic in both invasive and noninvasive cardiac imaging over the past decade. While invasive coronary angiography remains the gold standard for coronary artery luminal assessment, the decision to proceed with revascularization is no longer governed by subjective visual assessment of luminal stenosis. Prior data have demonstrated significant interobserver variability in the interpretation of coronary angiograms, while others have demonstrated a poor correlation between visual angiographic assessment and objective lesion-specific ischemia., It was with the Fractional Flow Reserve versus Angiography for Guiding Percutaneous Coronary Intervention trial that patient outcomes were improved when fractional flow reserve (FFR) was utilized to guide coronary revascularization. In addition, it has been demonstrated that coronary lesions without hemodynamic functional significance, as determined by FFR, can have intervention safely deferred. Within this patient population, the annual rates of myocardial infarction are <1%. As such, FFR has a Class I indication for the assessment of lesion-specific ischemia to guide revascularization by the European Society of Cardiology and Class IIa recommendation for the American College of Cardiology.,
In addition to FFR, an instantaneous wave-free ratio (iFR) is an alternative invasive method to assess the functional significance of coronary stenoses. FFR utilizes adenosine to reduce and minimize intracoronary resistance. Under these conditions, minimized and constant intracoronary resistance, pressure, and flow are proportional. Thus, decreased pressure across a coronary lesion corresponds to a decrease in the flow. Utilizing similar principles, iFR utilizes an interval of time during diastole when intracoronary resistance is constant and low, similar to conditions obtained with adenosine infusion. During this time interval, the transtenotic pressure gradients reflect the functional significance of the stenosis. These iFR pressure gradients are obtained without the need for intravenous adenosine administration. Prior studies have demonstrated that a revascularization strategy guided by iFR is noninferior to FFR., As such, iFR also carries a Class I indication for the assessment of lesion-specific ischemia by the European Society of Cardiology.
While FFR and iFR allow for the assessment of lesion-specific ischemia once the patient has proceeded for invasive evaluation, many patients undergo invasive angiography only to reveal nonobstructive disease. As such, a method to determine the functional significance of coronary lesions prior to invasive angiography is attractive. This would allow for more efficient use of catheterization laboratories, focusing resource utilization on patients where intervention is appropriate. This is the premise behind coronary CT angiography (CCTA)-derived FFR. Noninvasive CT-based FFR utilizes methods such as computational fluid dynamics (FFRCFD-CT) and artificial intelligence-based machine learning (FFRML-CT) to calculate FFR values from standard CCTA datasets. FFRCFD-CT has demonstrated high diagnostic accuracy for the diagnosis of functionally significant CAD when compared to invasive FFR. In addition, FFRML-CT has been shown to have a similar performance in detecting lesion-specific ischemia when compared to FFRCFD-CT. Most importantly, in clinical practice, CCTA with selective FFRCFD-CT had similar outcomes to that of planned ICA while resulting in lower costs. More recently, given the increased use of iFR, FFRML-CT has been shown to have excellent diagnostic performance when compared to iFR.
The article by Zhang et al. seeks to expand the existing evidence of noninvasive FFR utilizing a new technique that calculates a CCTA-derived iFR (iFRCT). In this article, iFRCT was compared to invasive FFR in 114 patients with 115 myocardial bridges (MBs). Their results demonstrated good diagnostic accuracy of iFRCT with a sensitivity of 0.90, a specificity of 0.73, and an accuracy of 0.79 when compared to invasive FFR.
The concept of iFRCT, as presented, represents an interesting and novel technique for the noninvasive evaluation of hemodynamically significant CAD. It is interesting that the authors elected to evaluate this technique in patients with myocardial bridging and not more traditional atherosclerotic coronary lesions. An MB is often considered a normal variant, and invasive functional assessment of MBs remains a source of controversy. In addition, there are data that suggest because of the changes in intracoronary pressure related to vessel compression during systole that FFR may be less accurate in determining real hemodynamic significance when compared to iFR. This would suggest that in this particular patient population, a more appropriate comparison of iFRCT might have, in fact, been invasive iFR itself. Moreover, one of the benefits to iFR is that infusion of adenosine, which can result in adverse procedural symptoms (chest pain, shortness of breath, etc.), is not needed. However, with noninvasive CT-derived FFR (FFRCFD-CT and FFRML-CT), hyperemia is simulated and similarly does not require the infusion of adenosine. Given that both FFRCFD-CT and FFRML-CT have shown high diagnostic performance when compared to invasive reference standards, the benefit of an iFRCT approach remains unclear. Furthermore, the authors state that the modeling software for iFRCT is complex and time consuming but do not provide the time required to obtain results or how this compares to the other noninvasive FFR techniques. Finally, the study represents a small single-center trial and will require additional larger prospective trials to validate the results.
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