What is cardiovascular disease (CVD)?

Cardiovascular disease (CVD) includes conditions that are associated with the heart (cardio) and blood vessels (vascular). It includes heart attack, ischemic stroke, heart failure, arrhythmia, heart valve problems, and peripheral artery disease.It is the leading cause of death in the United States and is becoming the number one cause of death in the world. More than 900,000 deaths in the United States in 2014 were associated with cardiovascular disease. Many of the CVD cases, especially heart attack, stroke and peripheral artery diseases are related to a process called atherosclerosis. This is a condition where plaques build up in the walls of arteries leading to narrower arteries and blood clot formation. It ultimately obstructs blood flow in the blood vessels. When blood flow is obstructed in arteries of the heart it causes a heart attack. If blood flow is blocked in the blood vessels of the brain due to blood clots it leads to an ischemic stroke. There are numerous risk factors for cardiovascular disease. Examples of the risk factors include high blood pressure, smoking, and high LDL level (bad cholesterol), obesity, physical inactivity, poor diet, and diabetes mellitus.

What is the difference between primary prevention and secondary prevention for CVD?

Primary prevention is prevention of a stroke or heart attack in people who have never had a heart attack or stroke. Secondary prevention is any strategy used to prevent another heart attack or stroke from occurring. 

How does aspirin prevent heart attacks and strokes?

Aspirin is an anti-platelet agent. It irreversibly blocks the action of cyclooxygenase-1 (COX 1) enzyme which reduces the production of thromboxane A2 by platelets. Thromboxane A2 is a chemical that activates platelets and causes them to aggregate to form a clot. By blocking COX-1 aspirin inhibits platelet aggregations and the formation of a blood clots. Reducing the ability of blood to clot reduces the risk of stroke or heart attacks caused by blood clots in the brain or heart. 

Should Aspirin be used for primary prevention of strokes or heart attacks?

The FDA does not believe that there is enough evidence supporting the use of aspirin for primary prevention of cardiovascular disease. Recently the FDA denied a request from one of the aspirin manufacturers, Bayer HealthCare, to market aspirin for patients with no prior history of cardiovascular disease. After reviewing available clinical trial data for aspirin for primary prevention for cardiovascular disease, the FDA concluded that aspirin does not have clinical benefits to prevent a first cardiovascular event that outweigh the risk of bleeding. However, the FDA stated that they are still waiting for results of additional clinical trials that are underway, which may or may not change the guidelines for aspirin usage in the next few years.

What is the efficacy of aspirin in secondary prevention of stokes and heart attacks?

There are numerous clinical trials that prove the benefits of aspirin therapy in patients with a history of heart attacks and strokes. The benefits of long-term aspirin therapy are best demonstrated by the Antithrombotic Trialists Collaboration’s meta-analysis. This analysis of secondary prevention studies included a total of 16 secondary prevention trials; 6 trials of patients with previous myocardial infarction, 10 trials of patients with stroke or transient cerebral ischemia, and those who had contributed in 2002 Antithrombotic Trialists Report. More than 60,000 patients were included in this analysis of the long-term benefits and risks of aspirin therapy. 

The analysis compared cardiovascular events in patients allocated to aspirin therapy versus control. It showed that 4.3% of patients experienced major coronary events per year amongst those receiving aspirin versus 5.3% per year without aspirin therapy. The data also showed that 2.08% of patient experienced an ischemic stroke per year with aspirin therapy versus 2.54% per year without aspirin therapy. Additionally, serious vascular events were observed in 6.7% of patients per year with aspirin therapy, versus 8.2% per year without aspirin therapy. Overall, the study concluded that aspirin therapy significantly reduced serious vascular events, with a non-significant increase in hemorrhagic stroke. 

The FDA and major guidelines for managing CVD recommend taking aspirin 75 to 325 mg daily for patients with previous cardiovascular events in addition to other preventative measures for CVD. There is much less evidence supporting the use of aspirin for primary prevention. Patients who are at high risk for strokes or heart attacks but have never had an event and are taking aspirin for primary prevention should discuss this recommendation with their physician and ask about other preventive measures. An aspirin a day is not always beneficial. 

References

FDA Information for Consumers 

Lopez AD, Mathers CD, Ezzati M, Jamison DT, Murray CJ. Global and regional burden of disease and risk factors, 2001: systemic analysis of population health data. Lancet. 2006;367(9524):1747.

Hennekens CH, Dyken ML, Fuster V. Aspirin as a therapeutic agent in cardiovascular disease: a statement for healthcare professionals from the American Heart Association. 1997;96(8):2751.

Antithrombotic Trialists’ (ATT) collaboration, Baigent C, Blackwell L, Collins R, Emberson J, Godwin J, Peto R, Bursing J, Hennekens C, Kearney P, Meade T, Patrono C, Roncaglioni MC, Zanchetti A. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participants data from randomized trials. Lancet.