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

Abstract

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-PTCA Post-PTCA P Angiographic % diameter stenosis 63 ± 19 17 ± 11 <0.0001 Reference lumen area (mm 2 ) 9.8 ± 3.3 Lesion EEM area (mm 2 ) 20.8 ± 6.7 24.4 ± 7.9 <0.0001 Stent area (mm 2 ) 7.4 ± 3.1 9.9 ± 3.7 <0.0001 Lesion lumen area (mm 2 ) 2.2 ± 1.2 6.7 ± 2.2 <0.0001 Lesion plaque area (mm 2 ) 18.6 ± 6.5 18.0 ± 6.7 NS IH area within stent (mm 2 ) 5.3 ± 3.3 3.2 ± 2.5 <0.0001 % Area stenosis lumen vs reference 76.1 ± 14.0 31.0 ± 22.0 <0.0001 % Area stenosis stent vs reference 23.3 ± 26.9 -1.9 ± 33.1 <0.0001 Pre-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.