The reason behind why patients who are on aspirin still have heart attacks is an important topic in cardiovascular disease.
The VerifyNow(TM) is a simple test that was designed to measure whether aspirin therapy was working in patients with coronary artery disease, the number one killer in the Western world. Aspirin blocks an important enzyme, COX-1, in platelets that prevents them from sticking together to form blood clots. These clots can block blood flow in the heart's arteries causing heart attacks and death. COX-1 converts a molecule, arachidonic acid to thromboxane A2, and it is the latter molecule that triggers platelet clumping.
Patients on aspirin treatment who have sticky platelets after stimulation with arachidonic acid are termed "aspirin resistant" and this is the method used in the VerifyNow(TM) test. However, other molecules in the blood stream, in addition to arachidonic acid can trigger platelets to stick together and may also cause heart attacks.
To date, it is unknown whether patients who have sticky platelets after stimulation with arachidonic acid also have a similar response after stimulation with other molecules. Our study suggests that patients with aspirin resistance not only have highly sticky platelets after stimulation by arachidonic acid, but also have a similar response to other molecules that stimulate platelets to clump together. The platelets of these patients therefore have a tendency to clump in response to multiple stimuli. We studied one hundred ten patients with a history of coronary artery disease that were treated with aspirin.