The inner lining of a blood vessel (the endothelium) keeps blood from leaking out. When the endothelium is cut or damaged, platelets form a blood clot (or thrombus) to prevent excessive bleeding. Platelets are small cells transported in blood that react to damaged endothelium by sticking together to “plug up” the damaged area, and stop the bleeding.
Platelets play a major role in the progression of a heart attack. Plaques cause the blockage of coronary arteries in those with atherosclerosis. Heart attacks are usually caused by a plaque rupturing and releasing its contents into the bloodstream. When platelets encounter the released materials they assume that the endothelium is damaged. The platelets quickly form a thrombus that can block blood flow through the artery. Heart muscle, which needs blood flow to survive, is then damaged and a heart attack results.
As noted above, the disruption of plaques can occur during a heart attack. It can also occur during a balloon-and-stent surgical procedure. In this case, the inflation of a balloon inside a coronary artery can cause tiny tears to the plaque and endothelium, causing platelets to quickly form a thrombus.
Platelets are critical in preventing bleeding in areas both inside and out of the coronary artery. When you cut your finger, it is the platelets that stop the blood flow by forming a clot. When the platelets are inhibited, you bleed more easily and for a longer time. There is a fine balance in preventing platelets from forming a thrombus and causing dangerous bleeding elsewhere.
Medications such as aspirin and clopidogrel (plavix) can prevent platelets from forming a thrombus. This combination of pills is used in most people after a balloon-and-stent procedure to prevent thrombus formation inside the stent and in other coronary artery segments. Your doctor may recommend taking aspirin and Plavix for life if you’ve had a balloon and stent procedure.
This is not a recommendation to be taken lightly. If the medications are stopped prematurely, stents can develop sudden life-threatening closure due to thrombus formation. Alternatively, the medications increase your chance of life-threatening bleeding during fairly routine surgery. Many surgeons hesitate to operate on those taking aspirin and Plavix. You should discuss the pros and cons of Plavix use with your doctor prior to starting any drug regimen or undergoing a procedure requiring the use of this powerful “anti-platelet” medication.
Another platelet inhibitor called prasugrel has also been evaluated. A study in the New England Journal of Medicine compared the use of Plavix and prasugrel after stent placement. While prasugrel was better at reducing thrombus formation inside stents, it also caused more bleeding complications than Plavix. It is not yet clear if the additional benefit of this newer, more powerful agent, will outweigh the added risks.
Sources:
Wiviott, SD, Braunwald, E, McCabe CH, et. al., Prasugrel versus Clopidogrel in Patients with Acute Coronary Syndromes. New England Journal of Medicine. November 15, 2007: 357(20): 2001-15.