Patients who are found to be resistant to the antiplatelet effects of aspirin, as determined by the Accumetrics Ultegra Aspirin Test, were found to have more than three times the risk of elevated levels of creatine kinase-MB (CK-MB) during coronary stenting, according to a study presented by researchers from the University of Hong Kong at the 2003 American Heart Association Scientific Sessions in Orlando, FL. Elevated CK-MB is associated with myonecrosis, or damage to the heart muscle, has been shown to correlate with adverse outcomes, including increased risk of cardiac death after coronary angioplasty.

 According to the American Heart Association, more than 800,000 people with coronary artery disease (CAD) undergo coronary stenting procedures each year, commonly following balloon angioplasty. Aspirin remains a cornerstone for the prevention of heart attack, stroke and other serious cardiovascular risks, with more than 23 million Americans taking aspirin to prevent cardiovascular disease and stroke. However, as many as 30 percent of aspirin users may be resistant to aspirin's antiplatelet-effects, and thus its protective benefits. This study adds to a growing body of research linking aspirin resistance to increased risk of cardiovascular events, and highlights the value of testing patients for aspirin resistance.

Researchers used the Accumetrics Aspirin Test, a point-of-care test that measures platelet function, to determine aspirin responsiveness in 136 patients scheduled for coronary stent procedure, and found that nearly 20 percent of these patients were aspirin-resistant and that these patients had an increased risk of adverse outcomes in spite of being pre-treated with both Aspirin and Plavix. Aspirin and Plavix are typically administered prior to the procedure to lessen complications associated with the coronary stenting procedure.

"Aspirin, along with Plavix, is the current standard of care for preventing serious complications associated with coronary stenting," says Wai-Hong Chen, MD, Division of Cardiology at the University of Hong Kong and lead investigator for this study. "The data showing elevated risks associated with aspirin resistance underscore how critical it is for physicians to determine if their patients are resistant to aspirin, in order to select the appropriate antiplatelet therapy."

In addition to this study, a growing body of research shows that patients who are resistant or not fully responding to aspirin are at increased risks for a cardiovascular and stroke related conditions. Previous studies have shown aspirin resistance to be associated with triple the risk of heart attack, stroke and death in patients with cardiovascular disease and at a greatly increased risk of vascular death in the two years following stroke.

The effectiveness of aspirin may vary from person to person, and the reason why certain patients do not completely respond to aspirin therapy is not yet fully understood. Resistance or reduced response to aspirin may be the result of a patient being insensitive to current aspirin dosage, concurrent use of NSAID therapies, genetic effects, elevated cholesterol, or patient non-compliance.

Once patients are identified as aspirin resistant, physicians may opt for an alternative approach to therapy, which may include increasing the dosage of aspirin or placing the patient on another antiplatelet medication.

Recently cleared by the FDA, the Accumetrics Aspirin test is the first rapid, (less than 10 minutes), point-of-care diagnostic test that can inexpensively test a patient's response or resistance to Aspirin. The system consists of a disposable assay device and bedside instrument that measures the degree to which a patients' platelets aggregate. The results are reported in Aspirin Reaction Units (ARUs) indicating to the physician whether or not aspirin is effectively inhibiting platelet function. These results help physicians make better informed treatment decisions quickly and cost-effectively. The Accumetrics test is now available at hospitals and physician's offices throughout the country.

"Millions of patients are prescribed aspirin to help prevent heart attacks and strokes. Doctors have traditionally been unable to determine inexpensively or quickly that taking aspirin is actually having the desired effect," says Dr. Daniel Simon, associate director, Interventional Cardiology and Bringham and Women's Hospital and professor of medicine at Harvard, who conducted one of the first studies using the Aspirin Test. "The Accumetrics Aspirin Test will aid physicians in determining the effectiveness of aspirin therapy in patients at risk for heart attack and stroke."