Ann Thorac Surg 1995;59:1532-1533
© 1995 The Society of Thoracic Surgeons
INVITED COMMENTARY
Robert O. Bonow, MD
Division of Cardiology, Northwestern University Medical School, Wesley 524, 250 E Superior St, Chicago, IL 60611-2950
 |
Introduction
|
|---|
See also page 1528.
Over the past two decades, thallium-201 imaging has emerged as an important method for the evaluation of myocardial perfusion, ischemia, and viability in patients with coronary artery disease. The diagnostic and prognostic information gained from thallium imaging is readily integrated into management decision making and can be used to identify patients who are candidates for myocardial revascularization. The mechanisms underlying thallium uptake by the myocardium, and subsequent washout from the myocardium, have been well described in experimental models of ischemia and infarction, and these have been applied successfully to patients with ischemic heart disease. In particular, the rate of thallium washout from the myocardium is directly related to myocardial blood flow. Thallium defects on initial stress images that improve or normalize on late resting (redistribution) images, which represent ischemic, jeopardized myocardium, do so because of the faster washout rate of thallium from the normal compared with the ischemic myocardium. However, the mechanisms underlying thallium defects that are not apparent on initial stress images but appear on the redistribution images (termed ``reverse redistribution''), and the clinical interpretation of this phenomenon, remain controversial. Although this is not an infrequent clinical observation, there are no good experimental models of this condition to permit in-depth laboratory investigation. Reverse redistribution is relatively common among patients with recent myocardial infarction, especially after reperfusion therapy. A possible explanation for reverse redistribution in this setting is restoration of normal perfusion to an admixture of fibrotic and viable myocardium, with more rapid washout of thallium from the viable myocytes in this region compared with regions with normal transmural flow to normal myocardium. Indeed, recent studies support the concept that myocardial regions with reverse redistribution represent viable myocardium, as such regions demonstrate metabolic activity on positron emission tomography [1, 2].
This article by Watarida and associates demonstrating thallium reverse redistribution after myocardial revascularization adds further support to this explanation of the phenomenon. Patients manifesting reverse redistribution after coronary artery bypass grafting had successful revascularization of regions that had undergone previous myocardial infarction and had residual wall motion abnormalities. These regions represented predominantly viable myocardium, as evidenced by postoperative restoration of regional wall motion. It is also noteworthy that reverse redistribution was apparent only after successful revascularization of myocardium with inducible ischemia before operation, as manifested by reversible thallium defects, and systolic dysfunction, as manifested by regional wall motion abnormalities. This is an important observation that confirms the hypothesis that reversible defects on preoperative thallium imaging identify viable but dysfunctional myocardium with the potential for substantial improvement in regional function after revascularization.
|
References
|
|---|
- Marin-Neto JA, Dilsizian V, Arrighi JA, et al. Thallium reinjection demonstrates viable myocardium in regions with reverse redistribution. Circulation 1993;88:1736–45.[Abstract/Free Full Text]
- Soufer R, Dey HM, Lawson AJ, Wackers FJT, Zaret BJ. Relationship between reverse redistribution on planar thallium scintigraphy and regional myocardial viability: a correlative PET study. J Nucl Med 1995;36:180–7.[Abstract/Free Full Text]
Top
Introduction
References