Clinical Implications of Peripheral Plaque Morphology

Advances in the pathophysiology of Peripheral Arterial Disease (PAD) have been limited by the inaccessibility of the blood vessels to precise diagnostic interrogation. Traditional methods for studying disease in the peripheral arterial blood vessels have significant limitations. The development and refinement of IVUS (Intravascular Ultrasound) has provided a powerful in vivo method to assess plaque morphology. The potential of IVUS to quantify the structure and geometry of normal and atherosclerotic peripheral arteries will allow one to characterize specific lesions and to distinguish which plaques will or will not lead to complications.

Three primary hypotheses will be tested in this study: (1) IVUS combined with advanced digital image and signal processing provides a sensitive method to determine plaque geometry and composition in the human peripheral artery wall; (2) IVUS can discern specific arterial wall morphology, providing data that can be used to identify plaques that predispose the patient to late complications; and (3) IVUS-derived plaque structure can be used to predict responders and non-responders to pharmacologic therapy and percutaneous endovascular interventions.

These hypotheses will be tested as follows: (1) custom engineered IVUS analysis software will be used to describe the geometry, composition, and spatial component relationships of the vessel, (2) the morphology of lower extremity arterial plaque, as determined by IVUS, will be correlated with baseline clinical characteristics of subjects, and (3) the effects on plaque morphology after long term treatment with antihyperlipidemics will be determined.

There are three arms of the trial. (1) IVUS of Amputation Specimens: Histological sections of fresh arterial segments from amputation specimens will be correlated with IVUS derived radiofrequency data to quantify arterial plaque burden and composition (dense calcium, fibrous, fibro-fatty, and necrotic core components). (2)Observational Study: Patients undergoing standard lower extremity angiography for PAD will be studied with IVUS at the same sitting. IVUS finding will be correlated with demographic factors (age, gender, and race) and symptom severity (claudication, rest pain, tissue loss). Patients will be followed up for up to five years, and the occurrence of ischemic events (worsening of leg ischemia, need for intervention and re-intervention, and distant complications such as MI and stroke) will be reconciled with the arterial wall at the baseline examination. (3) Randomized Clinical Trial: A randomized, double-blinded clinical trial of high-dose atorvastatin vs. low dose atorvastatin will be performed in patients with intermittent claudication, based on our hypothesis with statin therapy will result in stabilization or regression of lower extremity arterial plaque, differences best assessed with high resolution imaging studies. Enrollment goals were not met due to treatment paradigm that has shifted to aggressive LDL control, therefore the overwhelming majority of patients were excluded due their existing statin therapy. On 6/25/08 the protocol and informed consent were amended to reflect elimination of the Randomized arm of this study and the restructuring of this arm to a Cohort Observational arm, correlating patients' current statin dosages with LDL levels and plaque morphology. This is the current design for this arm.