The use of aspirin therapy as a primary prevention strategy for heart attacks
October 22nd, 2008
Many patients at risk of premature heart disease are recommended to take low dose aspirin regularly (usually 75 mg in a coated or dispersible formulation) as an anticlotting agent to lessen the risk of future heart attacks. Such patients, who have not yet had a heart attack or stroke, in treatment called primary prevention, are believed to be in a high risk category usually because of a raised cholesterol, diabetes, cigarette smoking or hypertension or a combination of these factors.
A new study, from the University of Dundee, has shown, in 1276 subjects, that aspirin does not significantly reduce the risk of a heart attack for people with diabetes. The paper is an important one as it appears to contradict previous evidence regarding the use of aspirin for primary prevention, given that aspirin can cause stomach bleeding in susceptible people. “No benefit” means no difference over 7 years in heart attacks or strokes. The population studied was an unselected group of Type 1 and Type 2 patients with diabetes over the age of 40 years – and would have included people both at low and high risk for future heart disease.
How does this square with previous evidence and advice? In 2004, the American Diabetes Association published a position statement on the use of aspirin in diabetes. The main studies which informed this statement focussed on primary prevention were:
• The US Physicians’ Health Study (using 325 mg aspirin every other day in male physicians) showed a significant reduction in heart attack of 4% compared to 10.1% taking placebo. This gave a relative risk reduction of 0.39 for diabetic men on aspirin therapy
• Early Treatment Diabetic Retinopathy Study (ETDRS) – was a mixed primary and secondary study as 49% of the type 1 and type 2 men and women with diabetes had a history of cardiovascular disease. (The relative risk for heart attack in the first 5 years for those taking aspirin was 0.72 (CI 0.55 – 0.95) There was a significant reduction in heart attack in those taking aspirin.
• The Hypertension Optimal Treatment (HOT) Trial, using 75 mg aspirin daily in 18790 people with hypertension also showed benefits for aspirin with reduction of cardiovascular events by 15% and heart attack by 36%.
So the advice at that time was clear: Use aspirin therapy as a primary prevention strategy in men and women with Type 1 or Type 2 diabetes at increased cardiovascular risk, including those over 40 years of age with additional risk factors. Might the effect in the US Physicians Study have resulted from restricting the study to men? Canadian researchers, analysing 113,000 patients studied in many clinical trials, reported in 2007 that in primary prevention at least, there was a suggestion that women are less sensitive to the protective effects of aspirin.
However, there is no doubt of the protective effect of aspirin in ALL people who have already suffered either a heart attack or stroke (secondary prevention). In those who have not, the need for aspirin therapy should be carefully discussed with your doctor as the decision will depend on a number of factors including a proper assessment of risk and knowledge of the presence of potential risks for use of aspirin (including previous bleeding from the stomach, a bleeding tendency, liver disease or aspirin allergy). In my practice, the prescription of aspirin increases with increasing risk of a future cardiovascular event. People with diabetes have increased risk, and stratifying this risk is likely to lead to a definition of a population who will be protected by aspirin therapy sufficiently to outweigh the risks of gastrointestinal haemorrhage. In our clinic, we assess our patients with diabetes intensively for premature coronary artery disease using carotid ultrasound, detailed lipoprotein assessment, coronary artery calcification scores and peripheral arterial Doppler studies if pulses are absent. Despite the results of this recent study, I will not be changing my advice to recommend aspirin therapy where there is already evidence of arterial thickening and it is my proposition that such patients should be treated in the same way as if they had already had a heart attack (secondary prevention).
Dr Ralph Abraham - Oct 08
