Ticagrelor has been shown to significantly reduce the rate of cardiovascular disease (CVD) events and death compared with clopidogrel in patients having prior acute coronary syndrome. A number of outcome studies have demonstrated the risk of major CVD events increased with blood viscosity. Stroke patients and those with stroke risk factors were shown to have chronically elevated blood viscosity relative to healthy controls. Based on prior observations, the rationale for this study is to demonstrate that both aspirin-ticagrelor and ticagrelor monotherapy will be superior to aspirin monotherapy in the reduction of whole blood viscosity at the end of each 4 week treatment period.~The primary objectives for this study is to: (1) Compare the effect of aspirin-ticagrelor with aspirin in a double blind, randomized, cross-over study design (weeks 1-4, weeks 6-10, and weeks 12-16) on blood viscosity at both low (5 s-¹) and high (300 s-¹) shear rates at the end of each 4-week treatment period; and (2) to compare the effect of ticagrelor mono-therapy with aspirin in a double blind, randomized, cross-over study design (weeks 1-4, weeks 6-10, and weeks 12-16) on blood viscosity at both low (5 s-¹) and high (300 s-¹) at the end of each 4-week treatment.~The secondary objectives for this study include: (1) a determination as to whether there are differences in low and high shear rate dependent viscosity with treatment by ticagrelor alone and combination aspirin-ticagrelor. Additionally, investigated will be the effect of the treatment on peripheral arterial blood flow using pulse volume recordings, ankle brachial index, and toe pressures.~The general approach to evaluation of drug efficacy will be through blood samples collected with a standard venipuncture for viscosity testing. Blood viscosity will be measured using an automated scanning capillary tube viscometer across a physiologic range of shear rates of 1-1000 s-1 in increments of 0.1 s-1. Blood viscosity levels at 5 s-1 will be reported as low-shear viscosity, and blood viscosity measurements at 300 s-1 will be reported as high-shear viscosity. Additionally, pulse volume recordings will be simultaneously obtained at the level of the ankle, metatarsal and toe bilaterally according to standard protocol, and Continuous-wave Doppler will be used to determine ankle-brachial indices or toe-brachial indices, and flow velocity profiles.
The hypothesis being that both aspirin-ticagrelor and ticagrelor monotherapy will be superior to aspirin monotherapy in the reduction of whole blood viscosity at the end of each 4 week treatment period. Study participants will be randomized into 3 groups, and each group will receive each of 3 treatments in the cross-over study. At the end of each individual 4 week treatment period the investigators will determine whether there are differences in low and high shear rate dependent viscosity and investigate the effect of the treatment on peripheral arterial blood flow using pulse volume recordings, ankle brachial index and toe pressures. Subjects will be eligible if they have ankle-brachial index less than or equal to 0.85, or if a patient's blood vessels are calcified, patients will have toe-brachial index less than or equal to 0.6 performed using continuous-wave Doppler.