Thrombus Organization Plays No Major Role in Late Neointimal Formation After Angioplasty in Porcine Coronary Arteries

Thrombus organization has been suggested to play a major role in late neointimal formation after coronary angioplasty. We sought to describe the time sequence of lesion formation after angioplasty in porcine coronary arteries and to quantify the relation between early thrombosis and late neointimal formation. Deep vessel wall injury was induced by conventional balloon angioplasty in the circumflex (CX) and right coronary (RCA) arteries and by retraction of a chain-encircled balloon in the left anterior descendent artery (LAD). Lesions were assessed by histomorphometry at days 0, 1, 4, 7, 14, 28, and 56 after angioplasty. A response-to-injury index (lesion area/injury length) was determined for each artery. Angioplasty led to rupture/removal of media. Thrombus was present at the exposed adventitia at days 0, 1, and 4. From day 7, neointima was observed on the luminal side of the arterial wall. All thrombus had disappeared at day 28, at which only neointima was observed. Histomorphometry revealed that lesion formation after angioplasty was a gradually increasing process from day 0 to day 28 with no further growth from day 28 to day 56. Maximal thrombus size (day 4, RCA: 0.07 ± 0.04 mm, CX: 0.23 ± 0.16 mm, LAD: 0.15 ± 0.11 mm) was significantly smaller than late neointimal formation (day 28, RCA: 0.68 ± 0.18 mm, CX: 0.63 ± 0.23 mm, LAD: 0.71 ± 0.18 mm) in all three arteries (p < .03). Lesion formation after angioplasty is a gradually increasing process for 4 weeks. Maximal thrombus size is about four times smaller than late neointimal formation. Thus, thrombus organization plays no major role in late neointimal formation.