A new study revealed that patients who are resistant to aspirin are four times more predisposed to have heart attack, stroke or even die from a pre-existent heart condition.

The study, done by researchers at the University Health Network Division of Cardiovascular Surgery, Toronto General Hospital, reviewed all the available data on patients, aspirin and heart problems because there has been relatively little research in this area. Research is so ambiguous that there is no method of accurately determine who is and is not aspirin resistant.

“We were unable to determine which platelet function test best identifies aspirin-resistant patients,” Dr. Michael R. Buchanan, Ph.D., of McMaster University and colleagues reported in the January 18 online edition of the British Medical Journal.

The researchers identified 20 studies, involving 2,930 patients with cardiovascular disease, all of whom had been prescribed 75-325 mg aspirin daily as a way of preventing clots from forming in the blood. About 28 percent were classified as aspirin resistant.

The study found that patients who are labeled “aspirin resistant” have blood cells, also known as platelets that are not affected in the same way as those patients who are responsive to the drug. These patients were at a greater risk of suffering from a heart attack, stroke or even dying. Specifically, the study found that 39 percent compared to 16 percent of aspirin sensitive patients suffered some sort of cardiovascular event.

The study also revealed that other drugs prescribed for thinning the blood such as Clopidogrel or Tirofiban, did not actually provide any sort of benefits to these patients.

Dr. Buchanan and colleagues said that more research is needed to figure out the best way to identify aspirin-resistant patients. They also say aspirin resistance “is a biological entity that should be considered when recommending aspirin as antiplatelet therapy.”