Nico H. J. Pijls

Noninvasive fractional flow reserve derived from coronary CT angiography : clinical data and scientific principles

Fractional flow reserve derived from coronary computed tomography angiography enables noninvasive assessment of the hemodynamic significance of coronary artery lesions and coupling of the anatomic severity of a coronary stenosis with its physiological effects. Since its initial demonstration of feasibility of use in humans in 2011, a significant body of clinical evidence has developed to evaluate the diagnostic performance of coronary computed tomography angiography-derived fractional flow reserve compared with an invasive fractional flow reserve reference standard. The purpose of this paper was to describe the scientific principles and to review the clinical data of this technology recently approved by the U.S. Food and Drug Administration.

Validation of Fractional Flow Reserve in Animals

During maximum vasodilation, which corresponds with minimal myocardial resistance, distal coronary pressure divided by aortic pressure equals maximum myocardial blood flow divided by the normally expected value as it would be if no epicardial lesion were present1,2. The theoretical background of the concept of fractional flow reserve and its experimental validation have been provided in the preceding chapters. So far, however, pressure-derived fractional flow reserve has been validated in an open chest dog model against the ratio of epicardial hyperemic flow velocity in the presence of a stenosis to hyperemic flow velocity in the absence of a stenosis.

Practical Set-up of Coronary Pressure Measurement

The present chapter aims at providing the reader with the practical aspects of coronary pressure measurements in humans. The technical requirements, equipment, “tips and tricks” of the procedure itself, and methods to induce hyperemia are reviewed. Potential pitfalls to be aware of, are discussed in chapter 6.

Assessment of Collateral Blood Flow by Coronary Pressure Measurement

Although the importance and protective role of the collateral circulation of the heart have been recognized for decades, no methods have been available so far for quantitative assessment of collateral blood flow in conscious humans1–4.

Pitfalls in Coronary Pressure Measurement

As with every new technique, the cardiologist starting to perform coronary pressure measurements by wire technology will face some potential pitfalls which may lead to erroneous results or misinterpretation of data. Most of these pitfalls are easily recognized, a few are more tricky. There are some pitfalls specifically related to the equipment, to the guiding catheter used, to the use of the different hyperemic stimuli, and to specific physiologic or pathophysiologic conditions. Most of these pitfalls are easily avoided once the operator is aware of them.

FFR in Some Specific Conditions

An essential prerequisite for the calculation of FFR from aortic and coronary pressure is to obtain the measurements under conditions of maximum hyperemia. Only in this situation it can be assumed that the resistance of the vascular bed is minimal and therefore equal to the resistance in the same vascular bed but not depending on an epicardial stenosis. This condition has been demonstrated in animals (chapter 7) and in humans (chapter 8). Only when the resistance of the vascular bed depending on an epicardial stenosis equals the resistance of the same vascular bed but without stenosis, these resistances can be cancelled in the calculation of FFR2. It has been shown in animals and in humans, in the physiological range of aortic pressure, that the relation between myocardial flow and driving pressure is linear during maximum microvascular vasodilation3–4 This implies that, during maximum hyperemia, the ratio of two myocardial flows (which corresponds to the definition of FFR) equals the ratio of their respective driving pressures. The key point with respect to FFR is not the slope but the linearity of the pressure-flow relation under conditions of maximum vasodilation. When maximum hyperemia is not achieved the relation between hyperemic flow and driving pressure is curvilinear, and thus, the ratio of these (‘non-hyperemic’) flows does not equal the ratio of their respective driving pressures.

Fractional Flow Reserve for Evaluation of Coronary Interventions

Are there any values of myocardial fractional flow reserve (FFR myo ) after a coronary intervention, indicating that the result of the procedure was excellent, moderate, or insufficient ?

Stenting of bifurcation lesions

We agree that an RCT cannot be compared with a retrospective analysis. However, we do not agree on the note of natural selection bias. On the contrary, we believe that our analysis is completely unbiased because literally all patients admitted for bifurcation stenting in the year 2013 were included. In a randomised controlled trial with strict inclusion and exclusion criteria, the population is more selected.

INFLUENCE OF LESION LOCATION ON THE DIAGNOSTIC ACCURACY OF ADENOSINE-FREE CORONARY PRESSURE WIRE MEASUREMENTS: THE CONTRAST (CAN CONTRAST INJECTION BETTER APPROXIMATE FFR COMPARED TO PURE RESTING PHYSIOLOGY?) SUBSTUDY

Several adenosine-free coronary pressure wire indices have been proposed to assess the functional significance of coronary artery lesions; however, there is a theoretical concern that lesion location and the amount of myocardium interrogated may affect diagnostic performance.nnIn a total of 763

THE IMPACT OF EJECTION FRACTION ON FRACTIONAL FLOW RESERVE: INSIGHTS FROM THE FAME (FRACTIONAL FLOW RESERVE VERSUS ANGIOGRAPHY FOR MULTIVESSEL EVALUATION) TRIAL

Fractional flow reserve (FFR)-guided percutaneous coronary intervention (PCI) significantly improves outcomes compared with angio-guided PCI in patients with multivessel coronary artery disease. However, there is a theoretical concern that patients with reduced left ventricular ejection fraction (EF