Axial plaque redistribution (plaque shift) is recognized as one of the acute complications during percutaneous coronary intervention, sometimes resulting in additional procedures. Lumen encroachment after coronary intervention often looks ambiguous and is difficult to evaluate by angiography. Various potential factors, such as plaque redistribution, focal spasm, dissection, hematoma, thrombus or focal deposit of calcium, may be the reason for angiography’s limitations in elucidating this phenomenon. On the other hand, intravascular ultrasound (IVUS) can easily distinguish encroachment and provide accurate lumen area and plaque mass that cannot be assessed by angiography. This IVUS case report demonstrates longitudinal as well as cross-sectional IVUS images of axial plaque redistribution after sirolimus-eluting stent implantation for the treatment of bifurcation stenosis. Case Report A 72-year-old male with a history of hypertension, hyperlipidemia and a nuclear stress test demonstrating anterior and lateral ischemia was admitted for cardiac catheterization. Coronary angiography and IVUS examination revealed eccentric stenoses in the left anterior descending artery (LAD) and the left circumflex artery (LCx), just before the bifurcation of the first obtuse marginal branch (Figures 1 and 3, arrowhead). After successful LAD stent placement, the LCx was also stented using 13 mm sirolimus-eluting Cypher™ stent (Cordis Corp., Miami, Florida), jailing the obtuse marginal branch. Immediately after post-dilatation, however, the coronary angiogram showed a new significant stenosis at the distal adjacent segment (Figure 2, arrow). After intracoronary administration of nitroglycerin, IVUS examination with motorized pullback (0.5 mm/second) was performed for further investigation. IVUS imaging revealed a secondary critical lesion that was not observed before the interventional procedure (Figure 5, arrow, and Figure 6). Neither stent edge dissection nor hematoma was found. We believe that the most likely explanation is a significant plaque increase at the new lesion site resulting from axial plaque redistribution. The underlying mechanism is probably plaque extrusion from the stented segment, otherwise known as “plaque shift”. After an additional 13 mm sirolimus-eluting stent was implanted at the new lesion site, the patient experienced an uneventful course. Discussion Both stent implantation and subsequent balloon post-dilatation change the distribution of atherosclerotic plaque. Although recent studies have reported plaque redistribution as a consequence of stent deployment, it remains unclear where exactly the plaque mass is moved. Ahmed et al reported that most plaques could not be accommodated by further vessel expansion and dislodge into the reference segments.1 By contrast, Maehara et al found that most plaque shifting occurred from the middle to the distal stent zone.2 These two discordant findings may be associated with differences in lesion length in relation to the stent length, stent design, or simply differences in implantation techniques. The mechanism of additional lumen gain from stent deployment to final post-dilatation has been reported to result from axial plaque redistribution rather than vessel expansion.3 This finding indicates that the primary mechanisms of stent expansion may include both vessel expansion and plaque redistribution. With subsequent post-balloon dilatation, the additional lumen gain is proportional to more plaque redistribution rather than vessel expansion. In addition, due to the complex anatomy and plaque accumulation, axial as well as circumferential plaque redistribution often occurs during stenting, and subsequent balloon dilatation for bifurcation lesion subsets, resulting in additional dilatation and /or stenting to the main branch as well as the side branch.4 Recently, drug-eluting stents have demonstrated striking reductions in in-stent neointimal hyperplasia.5–7 In order to obtain “total vessel success”, attention must be paid to plaque modifications in the adjacent segment as well as the in-stent segment. Optimal drug-eluting stent implantation, including complete lesion coverage as well as appropriate pre- and post-dilatation, may be a warranted therapeutic technique not only in light its overall efficacy, but as a cost-saving therapy as well. In conclusion, this is the first IVUS case report in which axial plaque redistribution was visualized after drug-eluting stent deployment.
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