This study evaluates the effects of Aspirin and thienopyridine resistance in relation to clinical cardiovascular outcomes as the genetic predictors of, and outcomes associated with aspirin and thienopyridine resistance in patients with peripheral arterial disease (PAD) currently remain unknown.

Although anti-platelet therapy is a cornerstone of PAD treatment, the investigators know very little about the prevalence, genetic determinants and clinical relevance of aspirin and thienopyridine resistance in PAD patients. The investigators expect to report on the prevalence of, and impact on outcomes from aspirin and/or thienopyridine (eg. clopidogrel) resistance, in patients who undergo peripheral arterial angiography/interventions (including carotid angiography/interventions) and operations. This study will provide important information on the utility of testing for aspirin and thienopyridine resistance and improve understanding of the genetic and pathophysiologic basis of anti-platelet therapy resistance in patients with cardiovascular disease, including PAD. Most importantly, this study will serve as the basis for a subsequent randomized prospective trial of different treatment options in PAD patients with aspirin/thienopyridine resistance.

Inclusion Criteria:

• patient undergoing PAD (carotid or lower extremity) angiography or intervention
• greater than or equal to 18 years of age

Exclusion Criteria:

• patient unable to take aspirin and thienopyridine for any reason (not excluded if take at least one of either medication)
• hematocrit less than or equal to 30%
• hematocrit greater than or equal to 52%

Patients enrolled between August 2010 and September 2012, with angiographically documented PAD involving carotid or lower extremity arteries. Patients may have been treated surgically or endovascularly at the discretion of the primary physician.