Many cardiovascular events are clinical manifestations of underlying atherosclerotic disease. The progression of atherosclerosis, traditionally measured by angiography, is predictive of future clinical events and is a valid surrogate marker of cardiovascular (CV) disease. There is growing interest in using novel surrogate end points in clinical trials to expedite the development of new CV therapies. Innovative imaging technologies, such as intravascular ultrasound (IVUS), may carry advantages for the evaluation of coronary atherosclerotic burden and disease progression. Unlike angiography, which displays only the opacified luminal “silhouette,” IVUS provides transmural imaging of the entire arterial wall and permits both detection of early-stage atherosclerosis and accurate cross-sectional and even 3-dimensional quantification of plaques. Intravascular ultrasound is now used to guide therapeutic interventions and for diagnostic purposes, primarily for the evaluation of ambiguous lesions and left main coronary artery disease. In addition, clinical studies are using IVUS serially to measure plaque progression, which appears to be related to future CV events. Although the probative force of clinical end point studies still is stronger, IVUS is catching up. Currently, several trials of CV therapies use IVUS-determined plaque progression as the end point. The rationale for using IVUS-based surrogate end points in clinical trials is discussed in the present review. Key advantages of using IVUS-based surrogate end points versus clinical outcome include smaller patient numbers and substantially shorter trial durations; this reduces costs and may expedite the development and testing of new drugs. We expect in the near future a further increase of the use of IVUS-based surrogate end points in trials that evaluate novel CV therapies targeting on coronary atherosclerosis.
