951-74 Mechanisms of Balloon Angioplasty of In-Stent Restenosis: An Intravascular Ultrasound Study

Restenosis within tubular-slotted stents is usually treated with repeat PTCA. To understand the mechanisms of lumen enlargement after PTCA of in-stent restenosis, we used quantitative angiography (measurement of % diameter stenosis) and intravascular ultrasound to study 36 restenotic JJIS stents (7 native coronary and 29 vein graft) before and after repeat PTCA. Reference segment and pre- and post-PTCA measurement of external elastic membrane (EEM), stent, and lumen areas were used to calculate (1) plaque area, (2) neointimal hyperplasia (IH) area within the stent (stent—lumen area), (3) % area stenosis of lesion lumen area vs reference lumen area, (4) and % area stenosis of stent area vs reference lumen area.Pre-PTCAPost-PTCAPAngiographic % diameter stenosis63±1917±11<0.0001Reference lumen area (mm2)9.8±3.3Lesion EEM area (mm2)20.8±6.724.4±7.9<0.0001Stent area (mm2)7.4±3.19.9±3.7<0.0001Lesion lumen area (mm2)2.2±1.26.7±2.2<0.0001Lesion plaque area (mm2)18.6±6.518.0±6.7NSIH area within stent (mm2)5.3±3.33.2±2.5<0.0001% Area stenosis lumen vs reference76.1±14.031.0±22.0<0.0001% Area stenosis stent vs reference23.3±26.9-1.9±33.1<0.0001Pre-intervention, 80% of lesions had a minimum stent area less than the reference lumen area, compared to 50% post-PTCA (p=0.0028). Importantly, 55% of lumen enlargement after repeat PTCA was the result of additional stent expansion and 45% was the result of extrusion of tissue through the stent (decreased IH area within the stent). There was no evidence of compression of neointimal tissue post-PTCA (no change in overall plaque area). Dissections were uncommon (occurring in 17% of lesions after PTCA) and were minor in nature without clinical consequences. We Conclude:Instent restenosis appears to be the result of inadequate primary stent expansion and superimposed neointimal hyperplasia. The mechanism of successful PTCA of in-stent restenosis is a combination of additional stent expansion (increased stent area) and neointimal tissue extrusion through the stent. PTCA of in-stent restenosis results in a relatively high residual stenosis (angiographic % diameter stenosis=17±11 and ultrasound % area stenosis=31±22); this may contribute to more frequent repeat episodes of restenosis