44 I CARDIAC INTERVENTIONS TODAY I JULY/AUGUST 2008 COVER STORY A ccurate characterization of the degree of risk entailed in performing interventional proce- dures is the key to optimal clinical decision making. It has been recognized since the inception of percutaneous coronary intervention (PCI) that lesion morphology is a major determinant of both clinical and technical success and a predictor of compli- cations. It is intuitive that the way a lesion appears angiographically reflects its specific composition, which would suggest its likely response to mechanical manipu- lation and catheter-based treatment. In addition to identifying individual morphological factors that pre- dict success, a risk prediction model can be developed by combining these factors to facilitate quantification of risk. Risk models are useful in offering a realistic assessment to the patient and family, assisting the oper- ator to evaluate technical concerns, and providing an objective framework for benchmarking and quality assurance. In this article, the history of angiography-based risk assessment models for coronary interventions is reviewed in depth. The limitations inherent in a mor- phologic approach to PCI risk assessment are consid- ered, and the appropriate use of lesion classification in modern practice is described. Finally, we address the importance the practicing interventionist should place on existing analytic systems, which includes both mor- phologic characterization and clinical factors. THE AHA/ACC TASK FORCE CRITERIA In the early days of balloon angioplasty, when compli- cation rates were significantly higher than in contempo- rary practice, deciding which patients and stenoses to avoid and which to preferentially treat was a complex problem rendered even more difficult by the apparent randomness of relatively frequent adverse events. 1 Initially, balloon angioplasty had complication rates of 10% to 15%; in modern practice, PCI is associated with mortality and emergency bypass rates of less than 1%. 2 This marked improvement in PCI outcomes is primarily the consequence of advancements in technique, devices, adjuvant medical therapy, and improved case selection, all of which were developed to a large extent specifically to treat the difficult lesion types identified early in the angioplasty experience. The many innova- tions in PCI technique and the resultant delivery of pre- dictable and durable results are testaments to the his- torical value of these classification schemes. The first systematic attempt to identify angiographic factors predictive of increased risk was made by the National Heart, Lung, and Blood Institute Registry in 1984. 3 Faxon and coworkers found that circumflex artery location, lesion calcification, proximal tortuosity, eccentric geometry, and a severe stenosis were associat- ed with reduction in success, which was defined as ≥20% improvement in stenosis diameter. The severity of the lesion and its geometry were especially critical in the early experience; keep in mind that in 1983, a bal- loon could traverse a lesion in just 75% of cases when it was attempted. Hence, a subtotal lesion had just a 59% likelihood of success in that registry, and the success rate was only 37% for total occlusions. This background is important: improvements in technique throughout the evolution of PCI substantially altered the factors that predict success, producing the “moving target” rec- ognized today. Angiographic Characterization of Lesion Morphology Are the AHA/ACC and SCAI lesion classifications still useful? BY LLOYD W. KLEIN, MD, AND RONALD J. KRONE, MD