Intravascular imaging modalities, including intravascular ultrasound (IVUS) and optical coherence tomography (OCT), can detect less extensive stent malapposition due to their high resolution and the ability to provide the cross-sectional images of the vessel. On IVUS examination, PSS was recognized as stent malapposition, which was defined as separation of stent struts from the arterial wall with evidence of blood flow behind the strut except for a vessel bifurcation. Stent malapposition in late phase is formed by positive arterial remodeling, dissolution of residual thrombus or plaque debris, and chronic stent recoil [9, 10]. Previous IVUS studies showed that late acquired stent malapposition with positive remodeling was seen in 5–13 % of lesions treated with DES [11–13], and the stent malapposition was associated with the occurrence of LST. [6] On OCT examination, PSS was recognized as cavities between and outside the stent struts (Fig. 16.3). These cavities, uncovered struts, and red thrombus were frequently observed in the lesions with PSS compared with those without PSS. These findings suggested that PSS was associated with delayed healing and could be a risk factor for stent thrombosis.

Coronary angioscopy, the intravascular imaging of a different dimension, permits the direct visualization of the intimal surface and provides an opportunity to understand pathogenesis and clinical implication of PSS. We presented angioscopic images in two cases of PSS observed by coronary angiography. The first case is 77-year-old female with unstable angina pectoris who was treated with a paclitaxel-eluting stent (PES, 2.5 mm diameter × 20 mm long) at midportion of the left anterior descending artery 6 years ago. Follow-up coronary angiography showed no restenosis, but contrast staining outside the proximal site of stent segment, which is named PSS (Fig. 16.4). On coronary angioscopic examination, the struts at the proximal site of stent segment were exposed similar to immediately after implantation of the stent. Blood flow was observed behind stent struts. These findings showed that the struts were not covered by neointima and malapposed. Additionally, red thrombus on yellow plaque behind the malapposed struts was found. In the second case, 78-year-old female with stable angina pectoris was treated with SES (3.5 mm diameter × 18 mm long) implantation at midportion of right coronary artery 6 years ago. VLST unfortunately occurred during clinical follow-up in this case, and emergency coronary angiography at the time of VLST showed the occlusion of proximal site of the stent segment. After performing thrombus aspiration, coronary angiography showed TIMI-3 flow and appearance of PSS at proximal site of the stent segment (Fig. 16.5). Similar to the first case, coronary angioscopy showed that struts were uncovered and malapposed within the segment of PSS. There was red thrombus on yellow plaque behind the malapposed struts.