Intravascular ultrasound (IVUS) has become a common tool in today′s catheterization laboratory. It is recognized as an accurate method for high-resolution imaging throughout the entire epicardial coronary circulation. The latest generation of stand-alone ultrasound catheters provides reliable image quality and can access the majority of lesions approached by conventional angioplasty and stent equipment.
Careful IVUS follow-up studies during routine interventions have redefined the concept of restenosis. Recent work suggests that a significant contribution to late lumen narrowing following intervention is overall vessel contracture or “reverse" remodeling. In other words, intimal hyperplasia is not the sole culprit responsible for restenosis. Ultrasound studies have highlighted that the adventitia is clearly an active layer strongly influencing the vessel size during natural plaque development as well as following interventional therapies. Additionally, intracoronary ultrasound studies have provided strong evidence that plaque burden or residual plaque stenosis may play a critical role in determining which lesions are likely to develop restenosis.
Clearly scaffolding the intra-arterial surface with metal can significantly decrease vessel contracture and impact favorably on restenosis. However, the exact geometric configuration and axial position within the target segment of these metallic struts are often difficult to appreciate by conventional x-ray based imaging tools. Thus, IVUS has become widely used in today′s cath lab in the optimization of stent deployment. Early on, despite adequate deployment by angiography, ultrasound demonstrated incomplete expansion in the majority of stented segments. This finding lead to the adoption of high-pressure expansion techniques which has markedly improved subacute closure rates despite a reduction in anticoagulation protocols. Several trials are presently designed to determine if the ultrasound findings of incomplete expansion, incomplete apposition, and/or the presence of edge tears in the high-pressure deployment era impact on the short and long-term outcome of patients undergoing coronary stenting.
Recent studies have revealed that the length and size of the stent are related to the degree of intimal hyperplasia- longer lengths and smaller diameters dramatically increase the six-month restenosis rates. As experience grows with stenting, longer lesions in smaller vessels will be approached in the interventional suite and necessitate the need for accurate placement and geometric expansion. Undoubtedly, IVUS will continue to have an important synergistic role with regard to stent placement in today′s cath lab.