Correspondence
MRI Coronary Angiography
N Engl J Med 1993; 329:507-508August 12, 1993
- Article
To the Editor:
The study by Manning et al. on magnetic resonance imaging (MRI) coronary angiography (March 25 issue1) is an important first step toward identifying a noninvasive method of visualizing coronary anatomy. I am concerned, however, about the analysis performed in the study. Is it reasonable to exclude nine coronary segments from the analysis of the MRI studies because of technical limitations (uninterpretability and time constraints)? Should not MRI study of all 156 segments of coronary arteries intended for analysis have been compared with conventional methods according to “intention-to-analyze” principles? If all segments were uninterpretable, the sensitivity and specificity of MRI angiography would be zero.
I also wonder whether it is fair to compare two methods according to different standards. MRI coronary arteriography was judged according to its ability to identify a stenosis of 50 percent or more at any point in the imaged coronary tree. Conventional contrast coronary arteriography, on the other hand, has consistently provided submillimeter resolution of the entire coronary tree, giving information about the location, severity, and morphologic characteristics of stenoses. Thus, the best MRI angiogram is only 88 to 90 percent as good as the worst coronary angiogram. If MRI angiography were truly 88 to 90 percent as good as conventional coronary angiography, would this be adequate? Can we afford to be wrong more than 10 percent of the time in patients with coronary artery disease? I hope that current efforts in MRI angiography focus on improving the quality of the images.
1 ReferencesJohn A. Bittl, M.D.
Brigham and Women's Hospital, Boston, MA 021151
Manning WJ ,Li W ,Edelman RR . A preliminary report comparing magnetic resonance coronary angiography with conventional angiography. N Engl J Med 1993;328:828-832
Full Text | Web of Science | Medline
To the Editor:
Dr. Steinberg's editorial accompanying the preliminary report on MRI coronary angiography (March 25 issue)1 very appropriately points out that the clinical benefit of noninvasive MRI coronary angiography will be determined by its ability to identify those local arterial lesions that have important physiologic consequences. . . . Translating the appearance of anatomical lesions into a sense of their functional importance and consequences is extremely difficult2,3. Angiographic scoring is notorious for its imprecision and poor reproducibility4. These shortcomings hold for all in vivo imaging of the coronary arterial anatomy, whether it is obtained with conventional contrast angiography, transesophageal ultrasonography, ultrafast computerized tomographic (CT) scanning, or MRI angiography. Physicians must resist the temptation to identify the angiogram as the cornerstone of accurate diagnosis.
4 ReferencesSven Paulin, M.D., Ph.D.
Beth Israel Hospital, Boston, MA 022151
Steinberg EP . Magnetic resonance coronary angiography -- assessing an emerging technology. N Engl J Med 1993;328:879-880
Full Text | Web of Science | Medline2
Paulin S . Grading and measuring coronary artery stenoses. Cathet Cardiovasc Diagn 1979;5:213-218
CrossRef | Medline3
Paulin S . Functional alterations in the coronary circulation as mirrored in the angiogram. Cardiovasc Intervent Radiol 1982;5:177-185
CrossRef | Web of Science | Medline4
Paulin S . Assessing the severity of coronary lesions with angiography. N Engl J Med 1987;316:1405-1407
Full Text | Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: We disagree with Dr. Bittl's proposal that all 156 arteries (4 vessels in each of 39 patients) should be studied by “intention-to-analyze” principles. As we stated in our article, the left coronary system was not imaged in two patients (six vessels) because of time constraints. In both instances the MRI study was abbreviated because the patients were called early to the catheterization suite. It would be unfair to penalize the MRI technique for this unexpected scheduling event. We do agree that an option would have been arbitrarily to classify as “diseased” the additional three vessels that were thought to be uninterpretable by both independent observers. This would have done little to alter the data presented. One of the vessels had an angiographic stenosis, and two did not. All three patients were correctly classified as having coronary artery disease by MRI coronary angiography of other vessels. Thus, the data on sensitivity and specificity would have been unchanged.
We believe it was fair to compare MRI data with conventional contrast angiographic data. Contrast angiography is currently the angiographic standard by which patients are evaluated, and we used it to identify vessels with stenoses of 50 percent or more. Contrast angiography, however, has its own limitations. Visual estimation of the diameter of stenoses has substantial variability both between and within observers,1 and the angiographic appearance of stenoses may not correlate with their hemodynamic importance2. As our preliminary report stated, MRI coronary angiography also has limitations. There is currently inadequate spatial resolution for quantitative use of the method. Rather than identify angiographic stenoses, the gradient-echo technique described in our study distinguishes rapidly moving, laminar blood flow as a bright signal, whereas areas of turbulent or slow flow appear dark. Focal stenoses in the coronary arteries result in turbulence and signal voids (loss) on MRI examination.
We agree that although preliminary data suggest a good correlation with angiographic data, further improvements in software and hardware are needed. These will lead to improvements both in spatial resolution and in the accuracy of MRI for identifying coronary stenoses. In the future, improvements in image quality, coupled with MRI assessment of cardiac anatomy, function, and perfusion3 and coronary artery blood-flow velocity,4 may lead to the emergence of cardiac MRI as a powerful noninvasive tool for the evaluation of patients with suspected coronary artery disease.
4 ReferencesWarren J. Manning, M.D.
Robert R. Edelman, M.D.
Beth Israel Hospital, Boston, MA 022151
Fisher LD ,Judkins MP ,Lesperance J , et al. Reproducibility of coronary arteriographic reading in the Coronary Artery Surgery Study (CASS). Cathet Cardiovasc Diagn 1982;8:565-575
CrossRef | Medline2
Ganz P ,Abben R ,Friedman PL ,Garnic JD ,Barry WH ,Levin DC . Usefulness of transstenotic coronary pressure gradient measurements during diagnostic catheterization. Am J Cardiol 1985;55:910-914
CrossRef | Web of Science | Medline3
Wilke N ,Simm C ,Zhang J , et al. Contrast-enhanced first pass myocardial perfusion imaging: correlation between mycardial blood flow in dogs at rest and during hyperemia. Magn Reson Med 1993;29:485-497
CrossRef | Web of Science | Medline4
Edelman RR, Manning WJ, Gervino E, Li W. Noninvasive flow velocity quantification of human coronary arteries using fast, breath-hold magnetic resonance angiography. J Magn Reson Imaging (in press).
Author/Editor Response
Dr. Paulin quite appropriately points out that all currently available techniques for imaging the coronary arteries have shortcomings in their ability to demonstrate anatomy and to indicate the physiologic and functional consequences of anatomical narrowings. Noninvasive techniques available to detect resting or provokable ischemia also have limitations. As a result, these techniques are often used in combination, rather than as alternatives. Information about coronary anatomy and information about function are complementary, and physicians would like to have both. An adequate assessment of the clinical value of MRI coronary angiography should thus include an evaluation of its ability, as compared with that of available alternatives, to depict coronary anatomy and define the physiologic and functional consequences of coronary stenoses. If MRI coronary angiography is adopted for clinical use, then assessment of its value should also examine the extent to which it can be substituted for diagnostic alternatives, rather than be used in addition to them, as well as its effect on clinical and economic outcomes.
Earl P. Steinberg, M.D., M.P.P.
Johns Hopkins Medical Institutions, Baltimore, MD 21205
