Correspondence
Functional Severity of Coronary-Artery Stenoses
N Engl J Med 1996; 335:1687-1688November 28, 1996
- Article
To the Editor:
The words of warning against overreliance on angiographic findings in the coronary arteries in the editorial comments by Wilson (June 27 issue)1 were appropriate but not new.2 It is difficult to calculate the precise degree of flow impairment on the basis of angiographic images of an atherosclerotic artery.3 The paper by Pijls et al.,4 to which the editorial refers, lists the results of “quantitative coronary arteriography,” based on two-directional measurements made on the static images, down to the 1/100th of a millimeter. They did not separate the results for those with positive responses from those with negative responses to their invasive test, which measured the remaining flow reserve distal to the lesions. This supports my suspicion that, for this purpose, such labor-intense and time-consuming evaluation was a wasteful endeavor, since it did not add information to that obtained by simple visual inspection.
Analysis of the dynamic events seen with a cine film could have been used to identify a delay in contrast and collateral flow, but this approach can only mirror the situation that exists during angiography.5 Considering that the majority of patients with clinical symptoms of ischemic heart disease have multiple lesions, varying not only in severity but also in their shape, length, and location, and that they may or may not have a representative normal vessel segment, one is inclined to believe that the authors' technique would be applicable in a much greater number of patients than the small, highly selected group of patients with a single discrete stenosis of moderate severity that they studied. I also believe that the performance and interpretation of their invasive test would become accordingly more complex.
I am therefore skeptical about Wilson's conclusion that the angiographic findings should be evaluated on the spot with measurement of fractional flow reserve instead of with stress tests in order to facilitate the performance of angioplasty, thus reducing the costs and discomfort to the patient. In an elective evaluation for symptoms of coronary artery disease, the noninvasive stress test should be the first-line test.
5 ReferencesSven Paulin, M.D., Ph.D.
Beth Israel Hospital, Boston, MA 02215-54911
Wilson RF . Assessing the severity of coronary-artery stenoses. N Engl J Med 1996;334:1735-1737
Full Text | Web of Science | Medline2
Paulin S . Assessing the severity of coronary lesions with angiography. N Engl J Med 1987;316:1405-1407
Full Text | Web of Science | Medline3
Paulin S . Grading and measuring coronary artery stenoses. Cathet Cardiovasc Diagn 1979;5:213-218
CrossRef | Medline4
Pijls NHJ ,de Bruyne B ,Peels K , et al. Measurement of fractional flow reserve to assess the functional severity of coronary-artery stenoses. N Engl J Med 1996;334:1703-1708
Full Text | Web of Science | Medline5
Paulin S . Functional alterations in the coronary circulation as mirrored in the angiogram. Cardiovasc Intervent Radiol 1982;5:177-185
CrossRef | Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: We fully agree with Dr. Paulin that it would be desirable in patients with chest-pain syndromes and coronary stenoses who are undergoing elective surgery to demonstrate objective signs of ischemia by noninvasive tests before subjecting them to angioplasty. We emphasized this point in our paper several times.1 However, in clinical practice today, the noninvasive tests are often inconclusive, contradictory, or simply not performed. Data from a large insurance-claims data base showed that only 29 percent of percutaneous transluminal coronary angioplasty procedures were performed after such objective documentation of ischemia.2 Moreover, even the best noninvasive tests yield false negative results in a considerable number of cases, up to 30 percent in patients with stenosis of intermediate severity, as shown in our study.
Therefore, it is important to have methods available to determine in the catheterization laboratory whether a stenosis is functionally important — that is, associated with reversible ischemia — especially when other objective evidence of ischemia from noninvasive tests is lacking.1,3 Pressure-derived fractional flow reserve is a highly accurate index for that purpose, as demonstrated in our paper.
As Dr. Paulin remarks, measurement of fractional flow reserve can probably be used in a much greater number of patients than the selected group in our study, and some large multicenter studies are currently under way to test those expectations. Since fractional flow reserve is a specific index of the severity of epicardial stenoses and can easily be calculated on the spot, it is especially suitable when clinical decisions must be made about the need for epicardial interventions such as percutaneous transluminal coronary angioplasty and bypass surgery and to estimate to what extent a patient's condition may improve when the epicardial obstruction to flow is relieved.4,5
The data on quantitative coronary angiography in our study were presented to demonstrate that this anatomical information was not helpful for clinical decision making. This underscores the importance of functional evaluation of coronary stenoses in individual patients — as was done in our study by measuring intracoronary pressure — to reach the right clinical decision.
5 ReferencesNico H.J. Pijls, M.D., Ph.D.
Catharina Hospital, 5602 ZA Eindhoven, the NetherlandsBernard De Bruyne, M.D., Ph.D.
Cardiovascular Center, B-9300 Aalst, Belgium1
Pijls NHJ ,de Bruyne B ,Peels K , et al. Measurement of fractional flow reserve to assess the functional severity of coronary-artery stenoses. N Engl J Med 1996;334:1703-1708
Full Text | Web of Science | Medline2
Topol EJ ,Ellis SG ,Cosgrove DM , et al. Analysis of coronary angioplasty practice in the United States with an insurance-claims data base. Circulation 1993;87:1489-1497
Web of Science | Medline3
Wilson RF . Assessing the severity of coronary-artery stenoses. N Engl J Med 1996;334:1735-1737
Full Text | Web of Science | Medline4
De Bruyne B, Bartunek J, Sys SU, Pijls NHJ, Heyndrickx GR, Wijns W. Simultaneous coronary pressure and flow velocity measurements in humans: feasibility, reproducibility and hemodynamic dependence of coronary flow velocity reserve, hyperemic flow versus pressure slope index, and fractional flow reserve. Circulation (in press).
5
Pijls NHJ ,Herzfeld I ,De Bruyne B , et al. Evaluation of adequate stent deployment by measuring myocardial fractional flow reserve. Eur Heart J 1996;17:Suppl:518-518 abstract.
Web of Science | Medline
Author/Editor Response
I agree with Dr. Paulin that coronary artery disease often comes to clinical attention when it is more complex than was the case in the patients described by Pijls et al. The question addressed by their study, however, was whether a physiologic measurement of the flow impairment (fractional flow reserve) caused by a stenotic lesion was correlated with ischemia detected on noninvasive stress testing and with treatment outcome. They found that it was in a small group of patients. Although I agree that the study requires confirmation in a larger cohort of patients and that treatment should be randomized, the coronary anatomy of patients undergoing angioplasty is often similar to that reported in the study group. Hence, the report of Pijls et al. may be applicable to many patients undergoing angioplasty.
All the problems with angiographic analysis described by Dr. Paulin are important and underscore the need for a better approach. Noninvasive stress tests are the first-line tests for patients with suspected coronary disease, particularly for determining which patients should undergo coronary angiography. Noninvasive stress tests might also be used to guide for treatment because they show the potential to develop myocardial ischemia in a clinical situation, predict future coronary events, and when imaging methods are used, can identify the location of the ischemic myocardial bed. Since noninvasive stress tests detect myocardial ischemia primarily by detecting impairment of blood flow due to coronary-artery obstructions, it seems quite logical to think that a direct measurement of the hemodynamic obstruction caused by a stenosis might provide similar information in patients with discrete lesions typical of patients undergoing angioplasty. The study by Pijls et al. confirms that hemodynamic assessment of the severity of stenosis is linked tightly to the results of noninvasive stress tests.
In certain situations, noninvasive stress testing is not always possible or indicated before coronary angiography (e.g., in patients with unstable chest pain), nor is it always possible to assign the ischemia detected with noninvasive testing to a specific coronary lesion found on angiography. Therefore, the ability to assess the physiologic importance of an individual stenosis on the spot at the time of diagnostic angiography may obviate the need for a stress test and a return to the catheterization laboratory for angioplasty if the stress test suggests ischemia. The real question, however, is whether treatment based on the physiologic importance of coronary stenoses (whether assessed by means of hemodynamic measurements of stenoses or noninvasive stress testing) rather than on the angiogram correlates with better patient outcomes.
Robert F. Wilson, M.D.
University of Minnesota, Minneapolis, MN 55455
