Author + information
- Published online May 6, 2019.
- John McB. Hodgson, MD∗ ()
- Case Western Reserve University, Cardiac Intensive Care Unit, MetroHealth Medical Center, Cleveland, Ohio
- ↵∗Address for correspondence:
Dr. John McB. Hodgson, Case Western Reserve University, Cardiac Intensive Care Unit, MetroHealth Medical Center, 2500 MetroHealth Drive, Cleveland, Ohio 44109.
- computational fluid dynamics
- coronary artery disease
- coronary physiology
- fractional flow reserve
- percutaneous coronary intervention
“. . . what has been done will be done again;
there is nothing new under the sun.” (1)
Since Mason Sones discovered selective coronary contrast injections (October 30, 1958), the coronary angiogram has been the cornerstone for assessing coronary artery disease and guiding patient therapy. An entire subspeciality of invasive and interventional cardiology has developed around the coronary angiogram. Specific professional societies (e.g., Society for Cardiac Angiography and Interventions) were formed (first meeting June 5, 1978). Specialized fellow training (circa 1985) and board exams (1999) were developed and an era of unprecedented innovation and advancement in the treatment of coronary artery disease was born (2).
Unfortunately, the coronary angiogram is flawed. Although the x-ray imaging equipment has improved through the years, providing better resolution, the fundamental problem of imaging a complex 3-dimensional structure in 2 dimensions continues to plague accurate interpretation. It is well appreciated that visual interpretation of the angiogram is widely variable among different operators, even when proximal stenosis in large vessels are involved (3,4). To overcome this problem, and to move toward a more physiologic approach to the assessment of coronary artery stenosis, multiple techniques have been tried to measure coronary blood flow, or parameters closely related to blood flow (e.g., velocity, pressure gradients) (5).
Many of us tried to use coronary flow reserve, either by digital angiography (6,7) or by coronary velocity measurements (8). We soon learned that there were too many confounding influences to allow accurate determination of the physiologic significance of individual lesions. We also tried simple translesional pressure gradient measurements (9), but the major breakthrough came with Nico Pijl’s work on fractional flow reserve (FFR) (10). Subsequent advancements have largely revolved around modifications of the FFR technique and translating the invasive measurement of FFR to noninvasive imaging. The use of cardiac computed coronary tomography with complex computer flow modeling has allowed a true noninvasive assessment of FFR suitable for routine use (11).
In this issue of iJACC, Gosling et al. (12) explore the application of computational flow dynamics (CFD) to invasive coronary angiograms. Their proof-of-concept study shows that with certain limitations, such an approach might be able to yield FFR estimates from routinely acquired angiograms. I was initially quite skeptical of this approach. A careful read of the paper will allow an understanding of the numerous assumptions (e.g., distal boundary conditions, flow behavior) and anatomic limitations (quality of the angiogram, overlap, tortuosity, branches, and so on). Undoubtedly, as has occurred with computed coronary tomography–based measures of FFR, the technique described by Gossling et al. (12) can be refined and simplified. Given sufficient computer processing power, it could provide estimates in near real time. There may be some practical advantages of this approach compared with computed coronary tomography–FFR: for example, motion artifacts, calcium blooming, and misalignment would not be encountered. Other investigators have recently reported similar techniques to assess FFR from the invasive angiogram (albeit using simpler techniques) (13).
More importantly, why do I need a complex analysis of the coronary angiogram to estimate the FFR, when I can easily pass a pressure wire and measure it directly! After all, I am already in the catheterization lab! Then it dawned on me: I am a “believer,” but most invasive operators are (sadly) not. I would not hesitate to measure the FFR or to use intravascular imaging tools to better assist me in interpreting the basic angiogram. In many Asian countries, the use of FFR or intravascular imaging is common (>80%); however, in the United States and Europe, these tools are used in ≤20% of procedures (14). Thus the need for an assessment tool that can be used by the many operators who are either uncomfortable (or uninterested) in performing measurements that enhance our ability to gauge the significance of coronary angiographic lesions.
As Gossling et al. (12) point out, use of FFR to assess and guide stenosis treatment is superior to using visual angiographic assessment alone. Their technique performs simulated stent placement; this feature will allow operators new paradigms in planning percutaneous coronary intervention. For example, for multiple lesions, being able to identify which lesion is more physiologically important might minimize unnecessary stenting.
The ability to provide an estimate of FFR in all 3 major coronary vessels in near real time becomes attractive to every angiographer from a public health perspective. An objective FFR measurement based on angiographic computational flow dynamics could provide an initial screening tool to assist in the planning of appropriate therapy for individual patients. This could also provide many new insights for patients with multivessel disease. This method might not be accurate in patients with nonideal microvascular resistance assumptions, such as patients with prior infarction or ventricular hypertrophy. Appropriate trials would need to be performed to assess this strategy; however, I personally find it hard to believe that the “more informed” strategy would not provide better patient outcomes.
Yet another analysis of the benefit of image-guided intervention has just been published (15). Although a welcome addition to the scientific publications, I have to agree with Gary Mintz that this analysis may be ignored, as have the many preceding it (16). So, if we cannot beat them, we will have to join them! By providing a tool in the catheterization lab that rapidly estimates the FFR for major epicardial arteries from routine angiograms, we may finally be able to get a majority of invasive operators “on board.” Although the work of Gossling et al. (12) is not “new under the sun,” it may finally penetrate the darkness of visual angiographic interpretation. Only time will tell!
↵∗ Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of iJACC or the American College of Cardiology.
Dr. Hodgson has received consulting and speaking fees from Philips Volcano.
- 2019 American College of Cardiology Foundation
- ↵Book of Ecclesiastes 1:9 (NIV).
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