Adenosine-induced Myocardial Blood Flow in Peripheral Artery Disease Patients

Inclusion Criteria: * Symptomatic lower extremity PAD defined by: * Symptoms at the time of screening including classic claudication, other exertional leg discomfort associated with physical limitations from PAD, AND Ankle brachial index (ABI) measurement at Visit 1 needs to be \< 0.90. OR, Prior lower extremity revascularization for symptomatic and haemodynamically significant PAD greater than 30 days prior to randomisation, irrespective of present leg symptoms and the Ankle Brachial Index (ABI). * Male and female ≥ 18 years of age and less than 60 yrs. * Subjects must be taking clopidogrel (75mg/day) for at least 30 days prior to entry to study. Exclusion Criteria: * Participation in another clinical study with an investigational product during the last 30 days. * History of ACS within the last 1 year. * Hypersensitivity or contraindications to clopidogrel or ticagrelor. * Need for chronic oral anticoagulant therapy or chronic low- molecular-weight heparin or long-term treatment with fondaparinux, warfarin, apixaban, rivoroxaban, and parenteral anticoagulants such as enoxeparin, and bivalirudin. * Life expectancy \< 6 months based on investigator's judgment. * Planned lower extremity revascularization (surgical or endovascular) in any vascular territory within the next 3 months or with current ischemic ulcers or gangrene. * Planned major amputation due to PAD within the next 3 months or major amputation due to PAD within the last 30 days. * Subjects who have suffered a stroke during the past 3 months. * Dementia likely to jeopardize understanding of information pertinent to study conduct or compliance to study procedures * Severe hypertension that may put the subject at risk. * Subjects considered to be at risk of bradycardic events (e.g., known sick sinus syndrome or second or third degree AV block unless already treated with a permanent pacemaker. * Known severe liver disease (e.g., ascites and/or clinical signs of coagulopathy). * Renal failure requiring dialysis * A known bleeding diathesis, haemostatic or coagulation disorder, or systemic bleeding, whether resolved or ongoing * History of previous intracranial bleed at any time, gastrointestinal bleed within the past 6 months, or major surgery within 30 days (if the surgical wound is judged to be associated with an increased risk of bleeding). * History of thrombocytopenia or neutropenia * Females of child-bearing potential (i.e., those who are not chemically or surgically sterilized, post-menopausal who are not willing to use an accepted method of treatment OR who have a positive pregnancy test at screening. * Concern for inability of the subject to comply with study procedures and/or follow-up (e.g., alcohol or drug abuse).