Drug-coated stents used to prop open blocked arteries may cause potentially fatal blood clots in rare cases, said experts at the World Cardiology Congress (WCC) in Barcelona. Safety concerns were raised when a Swiss-Dutch study presented at the WCC said recipients of drug-coated stents were at increased risk of potentially-fatal thrombosis (blood clots). The study tracked 8,146 patients. Two other Swiss studies also reported that drug-coated stents had higher risk of thrombosis compared to bare-metal stents that are not medicated.
Drug-coated stents are preferred over bare-metal stents by many interventionists because they bring down risk of artery re-blockage (restenosis) from about 25 per cent to less than 10 per cent. Drug-coated stents have been implanted in almost 60 lakh people worldwide since they were introduced in 2000, with about 1.5 lakh people using them in India since June 2002.
According to the Interventional Council of India, 60 per cent of the 65,000 stents implanted in India last year were drug-coated.
But now cardologists say the drug-coated therapy may be too aggressive. Bare metal stents allow a thin layer of cells to grow over them to make a biological lining. The medicines in the drug-coated ones, however, prevent tissue growth to could block the arteries from growing. While too much tissue growth is bad, a thin layer of cells is essential to cover the exposed metal, which if not covered can cause clotting and block arteries.
“When the polymer used to deliver the medicines in drug-coated stents is too aggressive, it remains on the stent for over six months to a year and continues to prevent cell-coating from forming. This increases risk of long-term clotting. New generation drug-coated stents are using less-aggressive bio-stable polymers to overcome this problem,” says Swaminathan Jayaraman, CEO of the Bangalore-based Vascular Concepts, the manufacturers of Pro-Nova.
While there has been a shift away from using drug-coated stents in the US, cardiologists in India say these devices cannot be ignored in India because they bring down risk of restenosis. “Since most Indians have diffused heart disease with multiple and longer blockages, and complications such as diabetes, they cannot undergo repeat procedures, so I’d still recommend drug-coated stents for the main arteries,” says Dr Purshotam Lal, director of interventional cardiology at Metro Heart Institute and a member of the health ministry’s expert committee set up to regulate cardiovascular devices (including stents) in India.
“The clotting risk usually occurs from six months to a year after implantation, but may remain for up to three years if the patient does not take blood-thinning medicines such as aspirin and clopidogrel. The patient has to continue taking both drugs for at least a year and longer if he has risk factors such as diabetes,” says Dr Ashok Seth, Chairman & Chief Cardiologist Max Devki Devi Heart and Vascular Institute.
This is not the first time the drug-coated stents have come under a shadow: In 2003, the US Food and Drug Administration issued a warning after receiving more than 290 reports of blood clots in Cypher patients, with more than 60 deaths associated to the device. The Taxus stent has been linked to a life-threatening mechanical defect that caused three deaths and severa complications, which has resulted in a recall of over 1 lakh of the medical devices.The FDA, however, did not ask for drug-covered stents to be withdrawn.