Accelerated atherosclerosis in saphenous vein bypass grafts: A spectrum of diffuse plaque instability☆
Section snippets
Structure and function of saphenous veins and arteries
There are several structural and functional differences between veins and arteries, which explain the greater susceptibility of veins to ischemic injury, lipid deposition, and thrombosis, leading to atherosclerosis and plaque vulnerability (Table 1).
Arterial injury
Vascular injury has been clearly identified as the critical inciting event in atherogenesis (Fig 1). Fuster et al proposed a unifying “response to injury” hypothesis describing 3 types of vascular injury progressing from functional endothelial changes (type I injury) to superficial injury to the vessel wall (type II injury) to deep medial injury (type III
Natural history of coronary artery bypass grafts and relationship to unstable plaque
The composition, vulnerability, and thrombogenicity of individual plaques vary greatly and are unrelated to stenosis severity.26, 27, 28, 29 Unifocal and multifocal plaque instability is recognized in the native coronary circulation as relatively distinct events occurring amidst long periods of plaque stability.30 It seems likely that SVG atherosclerosis represents the end of a continuum of plaque instability, in which diffuse, persistent vulnerable plaque passes through cycles of repetitive
Coronary angiography
Contrast angiography is the technique most commonly used to assess atherosclerotic plaque, but nearly all contemporary data about plaque stability are in the native arterial circulation, rather than vein grafts. Angiography is used to evaluate patients with acute coronary syndromes or progressive symptoms and is more useful for correlating the angiographic findings with the known clinical syndrome, rather than for predicting plaque vulnerability in a large population at risk. Angiography can
Magnetic resonance imaging (MRI)
MRI is a useful technique for imaging without ionizing radiation, and it can be repeated sequentially to follow patients over time. At present, high-resolution multicontrast MRI holds the most promise for identifying vulnerable plaque, by evaluating the lipid, fibrous, calcium, and thrombus content of atherosclerotic plaque.71, 72, 73 Coronary MR angiography can also evaluate patency of coronary arteries and bypass grafts. Unlike other imaging techniques, MRI has the potential to image and
Prevention of early SVG occlusion
Reduction in the extent of type III injury leading to early SVG occlusion may be accomplished by improved techniques of vein handling and harvesting. The availability of new platelet receptor antagonists and antithrombin agents is theoretically attractive because of the important role of platelets and thrombosis, but these potent agents are impractical in the perioperative period because of bleeding. Several clinical studies demonstrated that antiplatelet agents improve SVG patency during the
Conclusion
Plaque instability leading to plaque rupture is clearly implicated in the pathogenesis of acute coronary syndromes. Using angiographic criteria in native coronary arteries, there appears to be a spectrum of plaque behavior, including “normal” vessel, single or multiple stable plaques, and unifocal and multifocal unstable plaques. The principles underlying our understanding of multifocal plaque instability may be extended to our understanding of vein graft atherosclerosis, which represents the
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Address reprint requests to Robert D. Safian, MD, Director, Cardiac and Vascular Intervention, William Beaumont Hospital, Heart Center, 3rd Floor, 3601 West 13 Mile Road, Royal Oak MI 48073.