(Circulation. 1995;91:1607-1608.)
© 1995 American Heart Association, Inc.
Articles |
Noninvasive Coronary Arteriography— Here at Last?
From the Division of Cardiac Radiology of the Department of Radiology and the Cardiac Unit of the General Medical Service, Massachusetts General Hospital, Boston, Mass.
Correspondence to Robert E. Dinsmore, MD, Founders 202, PO Box 9657, Massachusetts General Hospital, Boston, MA 02114.
Key Words: Editorials • magnetic resonance imaging
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Noninvasive coronary arteriography has long been the Holy Grail of cardiologists and radiologists interested in diagnostic imaging. Over the years, newly emerging technology such as digital subtraction angiography and ultrasonography, has been applied to this goal, but success has been elusive. Recently, the clinical need for a noncatheter coronary angiogram has diminished for the majority of patients referred to the catheter laboratory who have a high likelihood of flow-limiting coronary lesions. For these patients, who are now frequently candidates for catheter-based intervention, the added expense of a noninvasive study would be difficult to justify. However, other patients would benefit from a noninvasive coronary angiogram if it could reliably identify or exclude clinically significant coronary lesions. Recent reports have indicated that this may now be possible. Preliminary studies suggest that magnetic resonance angiography (MRA) can demonstrate the coronary arteries, detect coronary stenoses, and quantify coronary blood flow velocity.1 2 3 The quality of published magnetic resonance imaging (MRI) images already far outstrips previous noninvasive studies of coronary arteries. One study, using rapidly acquired breath-hold gradient-echo MRA of the four main epicardial arteries, correlated with coronary cineangiography in 39 patients, found a sensitivity for identification of at least 50% stenoses in individual patients of 97% and specificity of 70%.1 Nonetheless, the ultimately disappointing experience, following initial optimism, with other noninvasive methods suggests the need for caution in interpreting these early reports.
A number of difficult technical problems remain before coronary MRA is ready for general clinical use. Compared with cineradiography, the resolution of rapid acquisition MRA is poor, and it has not been possible to identify coronary stenoses by defining their borders or to assess branches beyond the main coronary arteries. Improvement in gradient coils and surface coils can be expected to improve MRA signal-to-noise ratios, and hence spatial resolution, to approximately 1.0 mm. In contrast, cineangiograms currently have greater than 3.0 line-pair/mm resolution. Thus, the possibility of accurate anatomic definition of stenoses with MRA cannot realistically be forecast at present.
Because of this problem, MRA techniques that identify coronary lesions by local signal loss due to the flow shear associated with turbulent blood flow have been used, as in the study cited above.1 However, turbulence occurs with even minor changes in arterial diameter or geometry, and local signal loss may also result from other causes, including motion. Experience with MRA of peripheral arteries, which are technically less challenging because of their larger size and limited motion, has shown the difficulty in distinguishing flow-limiting from milder stenoses.4 Therefore, it appears doubtful that MRA of the small mobile coronary arteries with tortuous, variable distribution will have a high enough specificity, eg, in comparison with stress testing,5 6 to be generally useful for evaluation of cardiac ischemic disease. It could be used for screening patients with a low likelihood of any abnormality, for whom coronary angiography may nonetheless be indicated, such as patients with atypical chest pain and younger patients undergoing cardiac valve surgery, or for suspected coronary anomalies.
These shortcomings have been addressed by MRI studies of coronary flow velocity.2 3 The results of these studies suggest that each area of signal loss detected by MRA could be further analyzed with coronary stenosis flow velocity mapping2 or by measurement of flow reserve.3 Measurements so far have been done only in large proximal branches, and the use of either method to study smaller, often tortuous, branches will be a formidable technical challenge. The stenosis flow velocity approach requires precise localization of the stenosis, with measurement of a flow velocity–time profile in and proximal to the stenosis. The flow reserve method would require measurements of each questionable arterial branch before and after administration of a vasodilator, since flow reserve in a major artery may remain normal in the presence of significant branch stenosis. Change in flow velocity alone without measurement of arterial diameter may not accurately reflect change in flow reserve. However, accurate measurement of branch diameter changes is problematic because of resolution limitations.
For these reasons, coronary MRA of all clinically relevant branches, including those as small as 1.5 to 2.0 mm in diameter, in an acceptable time and with sufficient specificity for patients likely to have ischemia cannot be anticipated in the near future. A more immediately promising use of coronary MRA may be for instances in which the clinical question is limited to one or a few major vessels.
This approach is exemplified by the report of Hundley et al,7 which appears in this issue of Circulation. These authors focused on a single clinically important arterial segment—the infarct-related artery—in survivors of myocardial infarction. The questions posed are within the present capability of the method: Is flow distal to the culprit lesion antegrade, retrograde, or absent? For this study, multiple fast field echo sequences, with cine MRI, were obtained, using presaturation pulses to determine the direction of flow, with an average examination time of less than 1 hour. A preliminary study of 18 patients correctly identified the presence or absence of antegrade flow in all cases; in one case, collateral flow to a 1-mm-diameter distal branch was not detected.
Although recent evidence suggests that even late restoration of antegrade flow after myocardial infarction is beneficial,8 9 further study of the significance of the open artery is needed. Nonetheless, the importance of having a reliable noninvasive test of the circulation distal to the culprit lesion has increased. The MRA method described by Hundley et al7 needs additional confirmation and comparison with other noninvasive markers of reperfusion. However, these initial results suggest that this could be the first successful application of a noninvasive coronary angiogram to an important clinical problem.
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Footnotes |
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The opinions expressed in this editorial are not necessarily those of the editor or of the American Heart Association.
Received January 12, 1995; accepted January 13, 1995.
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References |
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TopIntroductionReferences |
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1. 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.
2. Keegan J, Firmin D, Gatehouse P, Longmore D. The application of breath hold phase velocity mapping techniques to the measurement of coronary artery blood flow velocity: phantom, data and initial in vivo results. Magn Reson Med. 1994;31:526-536. [Medline] [Order article via Infotrieve]
3. Poncelet BP, Weiskoff RM, Wedeen VJ, Brady TJ, Kantos H. Time of flight quantification of coronary flow with echo-planar MRI. Magn Reson Med. 1993;30:447-457. [Medline] [Order article via Infotrieve]
4.
Atlas SW. MR angiography in neurologic disease.
Radiology. 1994;193:1-16.
5.
Quiñones NA, Verani MS, Haichin RM, Mahmarian JJ,
Suarez J, Zoghbi WA. Exercise echocardiography versus 201 Tl single
photon emission computed tomography in evaluation of coronary artery
disease. Circulation. 1992;85:1026-1031.
6.
Marwick T, Willemart B, D'Hondt AM, Baudhuin T, Wijns W,
Detry JM, Melin J. Selection of the optimal nonexercise stress for the
evaluation of ischemic regional myocardial dysfunction and
malperfusion. Circulation. 1993;87:345-356.
7.
Hundley WG, Clarke GD, Landau C, Lange RA, Willard JE, Hillis
LD, Pesh RM. Noninvasive determination of infarct artery patency by
cine magnetic resonance angiography. Circulation. 1995;91:1347-1353.
8. Cigarroa RG, Lange RA, Hillis LD. Prognosis after acute myocardial infarction in patients with and without residual anterograde coronary blood flow. Am J Cardiol. 1989;64:155-160. [Medline] [Order article via Infotrieve]
9. Lavie CJ, O'Keefe JH, Chesebro JH, Clements JP, Gibbons RJ. Prevention of late ventricular dilatation after acute myocardial infarction by successful thrombolytic reperfusion. Am J Cardiol. 1990;66:31-36. [Medline] [Order article via Infotrieve]
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