Objectives Assess seriate progress of vulnerable plaque (VP) formation fusing Optical Coherence Tomography (OCT) with histopathological test to confirm what we find in the OCT imaging of vulnerable plaque on established rabbit vulnerable plaque model. Providing early characteristics of the signals displayed by VP in order to prior recognise vulnerable people, in order to give accurate and reasonable therapy.
Method 23 New Zealand white rabbits were randomly divided into 4 groups after balloon injurying the intima with subsequently 1% high fat diet. Grouping: Examed at 4 time points: 6 (n=6), 8 (n=5), 10 (n=5), 12 (n=7) weeks. OCT and histopathological examination were performed at those time points to display each stage of vulnerable plaque. Serum blood fat test were collected, especially the low density lipoprotein (LDL-C) as a major predictor for the stability of the plaque.
Results There were 2 rabbits died separately in 6 and 8 weeks, and 3 died at 12 weeks. At 6th week (n=4), OCT showed that the intima were more and more thick with heterogeneously low and high signals. Part of the tissue was protruding into the lumen. The composition of this tissue vertified by pathology is lipid infiltration; At 8th week (n=3), the protruding area was increased. The cover of the region with low density was stripped with strong and high signal; At 10th week (n=5), signal of the cover upon the plaque were much thinner, while, pathology examination had proved that this signal represent the fibrous cap. Signal high bright region contain radial pattern that showed in the thin cap with lipid rich plaque was infiltrated with large macrophage; At 12th week (n=4), OCT showed the lumen area was severely stenosis due to the large protrusion or ringed-shaped plaque formation. Fibrous cap thickness were less than 65 μm (mean value=0.038±0.01 mm). While, 28.6% of the plaques were total occlusion lesion. Total Cholesterol (TC) was at 6 weeks 36.77±0.80 mmol/l, 8 weeks 38.10±1.92 mmol/l, 10 weeks 35.94±0.93 mmol/l, 12 weeks 35.36±1.30 mmol/l; Low density lipoprotein (LDL) was 26.79±4.64 mmol/l at 6 week, 20.72±2.07 mmol/l at 8 weeks, 19.83±1.96 mmol/l at 10 weeks, 19.83±1.96 mmol/l at 12 weeks.
Conclusion Balloon injury intima and subsequently high fat diet for 12 weeks can successfully establish the vulnerable plaque animal model. Plaques with large lipid core and thin cap were tend to rupture with subsequently thrombus. This process was the same as human beings, so that we can study the process of the vulnerable plaque formation using optical coherence tomography to display early stage imaging characteristics of the plaque. With the long time high fat diet, Total Cholesterol (TC) and Low Density Lipoprotein (LDL) had sharply increased which have a strong relativity with the stability of the plaque. Thus, we can use blood fat test to predict the stability changes of the plaque.