Fractional Flow Reserve
FFR is a diagnostic measure, performed by passing an angioplasty wire with a distal pressure sensor down a vessel that helps confirm whether a stenosis — seen as a narrowing on the angiogram — is sufficient to cause ischemia. FFR is a ratio of the mean distal coronary pressure (Pd) measured beyond the lesion divided by the mean proximal aortic pressure (Pa) conventionally measured during maximal hyperemia induced by adenosine administration. Mathematically the formula is: FFR = Pd / Pa.
Higher FFR values (1.0 being the highest) are likely to result in better patient outcomes. Values below 0.75 – 0.80 are generally considered to be strong surrogate indicators of inducible myocardial ischemia. This measurement is independent of changes in baseline hemodynamics and is highly reproducible. FFR can also be applied to patients with multi-vessel disease. Long and diffuse lesions or tandem lesions can also be interrogated with FFR.
The Value of FFR
Prior to FFR, coronary stenosis assessment was limited to a visual assessment of the angiogram with high intra and inter-observer variability. This is inherently flawed since atherosclerosis of the coronary arteries is a disease of the vessel wall. Luminal narrowing occurs after considerable plaque burden has already built up when the compensatory enlargement of the vessel (positive remodeling) can no longer accommodate any more plaque. Furthermore, lumen area is just one of many fluid dynamic factors that contribute to physiological reduction in flow during exercise stress. Physicians were more likely to review the angiogram through the lens of their respective specialty. Surgeons traditionally base their decisions on anatomy alone.
While the concept of FFR guided coronary artery bypass graft (CABG) surgery has to be validated with prospective outcome based studies, it would appear that with FFR’s physiologic data, a bypass may not be necessary when visual assessment suggests it is. Using anatomy alone limits treatment options and results in sub-optimal outcomes, whereas FFR provides the ability to evaluate and choose patient treatments based upon physiology.
A recent proof of concept study, RIPCORD, which compared FFR guided decision making to anatomy alone, confirmed the use of angiography alone led one in four stable CAD patients to receive the incorrect treatment (be it medical therapy, PCI or CABG). The study concluded that routine use of coronary physiology (FFR) in conjunction with angiograms resulted in better patient outcomes and reduced costs in the long term.
Dr. Nick Curzen, Ph.D., FRCP, FESC, who presented the RIPCORD results at the EuroPCR 2013 conference, admitted that “noninvasive cardiologists, interventionists, and surgeons often see things differently,” but asserted that “having FFR information will actually bring the three perspectives much more closely into alignment.” Further, a cardiologist in one of the conference sessions opined that “if I do more of this FFR, I'll do less stenting, and I'll be making less money,” whereby Curzen responded with “yes, but you'll be treating patients better."
A collateral benefit of FFR is the changing heart care paradigm. For example, historically clinicians treated all three coronary vessels if all three vessels showed visually significant stenosis; FFR frequently reveals that not all anatomic three-vessel disease is functionally three-vessel disease and in these cases not all vessels require treatment.
A Catalyst for the Heart Team Approach
The new Department of Cardiovascular Sciences was designed in 2007 at East Carolina Heart Institute around the concept of the heart team approach to valve disease and the accumulating data supporting FFR guided coronary treatment. Founding clinicians viewed their new department as an opportunity to do something novel at a level of integration previously only imagined. At the Heart Institute, cardiac surgeons and interventional cardiologists work together, physically, in the same department. Using coronary physiology measurements, like FFR, has enabled improved patient outcomes.
The use of FFR at ECHI, has crystallized a shared vision of the heart teams and broken down the traditional silos that often previously hampered cohesive and efficient patient care.
Within this new environment, populated with interventional cardiologists, noninvasive cardiologists and surgeons, discussions of CAD are conducted in a new framework where the crux becomes ischemia; its diagnosis, quantification and data supported treatment options. FFR, with its focus on accurate diagnosis, has fostered collegiality and commonality within the heart team and minimizes previous turf wars over what should be done and by whom. Interventional cardiologists are now beginning to think about surgical patients the same way they think about candidates for PCI, and are proactively performing FFR on vessels they believe will be tough calls for their surgeon teammates.
Readily adopted by the interventional cardiologists, FFR is viewed with skepticism by many heart surgeons elsewhere. Traditionally, the surgeon’s approach to revascularization had been exclusively based on the anatomical and the shift toward physiology to support treatment decisions was difficult at first. Now, surgeons at ECHI are increasingly requesting FFR data in deciding which vessels require bypassing and whether some patients shouldn’t go to bypass surgery.
With FFR, the case for surgery or PCI becomes an academic, data-driven decision; something clinicians and hospitals are embracing in this litigious society. The pressure wire and FFR support enhanced diagnosis and patient outcomes as clinicians realize that some visually significant lesions in the past predicted to be functionally significant were not, and conversely some visually underwhelming lesions were in fact physiologically significant. Further, intermediate graft longevity is linked to the functionality of the stenosis and grafting a nonfunctional stenosis results in a higher likelihood that the graft will not remain open.
At East Carolina Heart Institute, the interventional cardiologist and cardiac surgeon frequently review the angiograms and FFR data together to determine if the patient needs to undergo a stent procedure, bypass surgery, a combination of both or treat with medications alone. All risks and benefits are expressed to the patients jointly, by both the cardiac surgeon and the interventionists, to assist the patient in deciding the best option.
Benefits to the Hospital, Clinician and Patient
There are substantial benefits and efficiencies to be gained for patients and heart institutions by using FFR earlier in the triage process. The FAME study data clearly shows that FFR guided PCI yields superior clinical outcomes compared to anatomic based intervention alone with substantial cost savings.
FFR use has enabled East Carolina Heart Institute to pioneer new and improved ways to see, diagnose, treat and care for CAD patients. It has helped facilitate heart team efficiencies through reduced wait times, reduced doctor visits and fewer recurrences. Patients (and doctors) trust the values given with FFR more than just the angiograms and stress tests. From the hospital’s perspective, FFR will reduce healthcare costs in the long term by eliminating unnecessary stenting or coronary artery bypass grafting.
Advice for Others Adopting FFR
Surgeons and interventional cardiologists need to embrace FFR in their practice. For surgeons, it will help choose which lesions can be favorably approached with arterial conduits and which lesions can be earmarked to the interventional cardiologist or left alone. For the interventional cardiologist, first accept that angiography has limitations and that physiologic, functional driven intervention with FFR is the future. It will allow more appropriate and effective therapy for patients. Understand the technique, embrace it and build up experience rapidly.
Predictions for the Future of FFR
FFR is here to stay and its future is bright. With clinicians increasingly supplementing the angiogram with FFR, improved diagnostic information and patient outcomes ensue. Guideline and appropriate use committees are likewise recognizing the inherent limitations of angiography and incorporating the use of FFR, which will drive increased acceptance.
Technology is leading the way as FFR continues to grow, evolve and improve. Developments such as iFR, a new index of stenosis severity that may obviate the need for adenosine, improved wires and wireless instrumentation, intravascular ultrasound (IVUS) probes and co-registering FFR/iFR images onto angiograms in real time are all promising technologies that may enhance FFR guided decision making and if performed, PCI. Future clinical investigations and trials of coronary physiology guided therapy should further optimize the outcomes of PCI and CABG. In the long run, if used wisely, FFR will continue to facilitate improved outcomes for CAD patients.
Editor’s note: Ashesh Buch, M.D., MRCP, is an interventional cardiologist and assistant professor cardiology, Department of Cardiovascular Sciences at East Carolina Heart Institute at East Carolina University. Buch comes to ECU from the University of Wales. He has a medical degree from the University of Birmingham in the United Kingdom. He trained at University Hospitals of North Staffordshire NHS Trust in England and completed a fellowship in interventional cardiology at Washington (D.C.) Hospital Center.