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High stress regions in saphenous vein bypass graft atherosclerotic lesions
R T Lee1, H M Loree, M C Fishbein
1Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.
Insights
Maximal stress in saphenous vein bypass graft lesions is significantly higher than in native coronary artery lesions. This finding suggests that reducing stress in bypass graft lesions may prevent plaque rupture.
Area of Science:
- Cardiovascular pathology
- Biomechanical analysis
- Atherosclerosis research
Background:
- Coronary artery bypass graft patency declines over time, often due to thrombosis.
- Plaque rupture is a known mechanism contributing to saphenous vein graft thrombosis.
Purpose of the Study:
- To test the hypothesis that maximal stresses in saphenous vein atherosclerotic stenoses exceed those in native coronary artery stenoses.
- To investigate the biomechanical factors contributing to plaque rupture in bypass grafts.
Main Methods:
- Finite element analysis was employed to determine stress distribution in 26 human lesions (14 native coronary, 12 saphenous vein grafts).
- Material properties were estimated from prior human tissue measurements.
- Lesions were from grafts placed an average of 9.8 years prior to study.
Main Results:
- Maximal circumferential stresses were significantly higher in saphenous vein lesions (median 352 kPa) compared to coronary artery lesions (median 104 kPa) (p=0.05).
- A strong correlation (r=0.83, p<0.001) was observed between maximal stress and the ratio of lumen area to fibrous cap thickness.
Conclusions:
- Saphenous vein bypass graft stenoses exhibit higher maximal circumferential tensile stresses than native coronary artery stenoses.
- Strategies aimed at reducing stress in bypass graft lesions, such as preventing lipid accumulation, may decrease the likelihood of plaque rupture.
Objectives:
Our aim was to test the hypothesis that maximal stresses in saphenous vein atherosclerotic stenoses are greater than those in native coronary artery stenoses.
Background:
The patency of coronary artery saphenous vein bypass grafts decreases with time, usually because of thrombosis. Plaque rupture has been described as one mechanism of vein graft thrombosis.
Methods:
Twenty-six nonruptured human lesions were studied. Fourteen lesions were from native coronary arteries, and 12 were from saphenous vein bypass grafts placed a mean +/- SD of 9.8 +/- 3.3 years before pathologic study. The finite element method was used to determine the distribution of stress in the lesion, using estimates of material properties from previous measurements of human tissues.
Results:
Maximal circumferential stresses were significantly higher in the saphenous vein lesions (median 352 kPa [interquartile range 161 to 475]) than in the coronary artery lesions (median 104 kPa [interquartile range 75 to 185]) (p = 0.05). Thin-walled cylinder formulations predict that stresses are proportional to the radius of the vessel and inversely proportional to the minimal wall thickness. In this study, there was a good correlation between the maximal stress in the 26 lesions and the ratio of the square root of lumen area to minimal fibrous cap thickness (r = 0.83, p < 0.001).
Conclusions:
Maximal circumferential tensile stresses in saphenous vein bypass graft stenoses are higher than in native coronary artery atherosclerotic stenoses. These data suggest that strategies that decrease stresses in bypass graft atherosclerotic lesions, such as prevention of lipid accumulation, could reduce the probability of plaque rupture in bypass grafts.