A new study published in JAMA sheds further light on a controversial question – whether or not to prescribe low-dose aspirin (81-100mg) for the primary prevention of vascular disease (strokes and heart attacks).
Primary prevention means preventing a negative medical outcome prior to the onset of disease, in this case preventing the first heart attack or stroke. Secondary prevention refers to treatments given to patients who have already had their first heart attack or stroke in order to reduce the risk of subsequent events.
The evidence strongly supports the efficacy of aspirin for the secondary prevention of both heart attacks and strokes. Aspirin has two effects which likely contribute to this protective effect. First, aspirin is an anti-platelet agent – it reduces the stickiness of platelets, which are cell fragments in the blood that clump together to stop bleeding. They can also clump together around an ulcerated cholesterol plaque on an artery, forming a thrombus, resulting in blockage or embolus (the clot traveling downstream) and causing either a heart attack or stroke.
Other anti-platelet agents, such as clopidogrel, are also effective in preventing stroke and heart attack.
Of course, platelets exist for a reason, and blocking their action increases the risk of bleeding or can make bleeding worse when it occurs. Therefore determining the optimal dose and target population are important to maximize the benefit of aspirin or other anti-platelet agent while minimizing the bleeding risk. (more…)
A new review published in the BMJ once again opens the question of the risks vs benefits of daily aspirin as a prevention for heart attacks and strokes. The reviewers looked at nine randomized trials involving over 100,000 patients and found that aspirin is effective in reducing heart attacks and strokes, but also increases the risk of gastrointestinal bleeding and that in some patients this risk outweighs the benefit.
This is an old and enduring controversy, and one with significant public health ramifications. Aspirin is an anti-platelet agent – it inhibits platelets, the cell fragments in the blood that are the first line against bleeding, from aggregating (clumping together). Platelets aggregate in order to quickly stop bleeding from damaged veins or arteries. But they can also aggregate around cholesterol plaques in arteries, causing a large thrombus (blood clot) that can block off the artery, or that can break off and lodge in a downstream artery (an embolus) and cause a stroke or heart attack.
By inhibiting platelet aggregation daily aspirin reduces the risk of forming a thrombus or embolus, and thereby reduces the risk of heart attack or stroke. Of course, the real story is always more complex than our straightforward explanations. There is some research to suggest that the anti-inflammatory effects of aspirin may also be important to their role in reducing vascular risk. The relative contribution of anti-platelet and anti-inflammatory effects have not been fully teased out. Further, the anti-inflammatory effects of daily aspirin may have non-vascular benefits, like reducing the risk of some cancers.