Stent Treatment for Coronary Artery Disease
Consequently, restricts or partially blocks the blood flow to the heart. During exercise a blocked artery is unable to expand and the heart is deprived of oxygen (myocardial ischemia). Symptoms develop causing chest pain or pressure (angina), leading to a heart attack called myocardial infarction. Major risk factors of coronary artery disease related to smoking, high cholesterol (Attributed to meat, eggs, and other animal products), lacking of exercise, obesity, stress, and hormone replacement.
Drugs are available to treat coronary artery disease including: Cholesterol medication, aspirin, Beta Blockers (Drugs slow heart rate and decrease blood pressure. Thus decreasing heart demand for oxygen), Nitroglycerin (Opening coronary arteries and reducing heart demand for blood), Calcium channel blockers (Medication relaxes surround coronary arteries, thus increasing blood flow to the heart), and Angiotensin-converting enzyme (ACE) inhibitors (Decreases blood flow and may lead to preventing progression of coronary artery disease). Aggressive treatment for coronary artery disease includes: Balloon Angioplasty, use of stents that are non – medicated, medicated or gene coated, significantly treat coronary artery disease.
In 1977 balloon angioplasty (PTCA) was the first method to unblock an artery. A catheter was inserted either in femoral artery in leg or radial artery in the arm, and passed through until it reached the blocked artery in the heart. Prior to the surgical procedure, the patient is administered a mild sedative through an intravenous line. During the procedure, an X-ray would help the surgeon guide the catheter to the location. Upon reaching the block artery, a balloon mounted at the end of the catheter would be inflated for about 30 to 60 seconds, opening the blocked passage. Successful opening of coronary arteries is 90% and 40% requiring the procedure to be repeated in the future.
Researchers developed a stent (mesh tube), kept an artery open. During the expansion of the artery, a stent would be implanted to support the new stretched open position. Appears like a scaffold, keeping the vessel open. Eighty percent of angioplasty patients will have a stent implanted. The procedure usually takes between one and half to two and half hours. Approximately twenty percent of patients that had stents implanted, arteries can re-close (Resenosis), and require the procedure to be repeated.
In April 2003, the Food and Drug Administration, approved drug coated or eluting stent to open clogged arteries. Cordis Corporation, a Johnson & Johnson company marketed CYPHER – Sirolimus – eluting Coronary Stent. The development of a coated stent, slowly releases CYPHER into the tissue around the stent (naturally occurring substance), reduces or stops restenosis. During a study, medicated coated stents, shown restenosis rate was reduced to 8.9 percent. However the cost for coated stents is three times more than non – coated stents but cost effective.
In March 2006, Boston Scientific received FDA approval for medicated TAXUS coated stents, preventing arteries from narrowing after being implanted. The market for coated stents worldwide is $2.5 billion, and nearly six million people have an implanted medicated coated stents. Both Johnson & Johnson and Boston Scientific coated stents cost under $3,000 a piece.
In April 2006, Boston Scientific reported approximately 27 cases of TAXUS coated stents, doctors had complication during stenting procedure, in most cases balloons used for implanting a stent seemed to stick to the coating on the stent, creating potential blockage. In some cases, surgery was required to have the balloons removed. The company had no plans to change the manufacturing to address this problem, since a large number of successful medicated stents had been implanted, and considered a minor problem. Guidant Corporation (Purchased by Boston Scientific Corporation in 2006) will seek FDA approval for an experimental drug coated stent device called Promus. During European cardiology conference in September 2006, Promus test results will be shown. If Promus gets approval from the FDA, enable Boston Scientific to offer stents with both types of coating, currently available from the two leading manufactures of stents. Also, Abbott Laboratories will manufacture Promos stents.
Researchers are studying gene – coated stents, may prove to stimulate the growth of new blood vessels and restore blood to the heart. According to Dr. Robert J. Levy, chairman of pediatric cardiology at the Children’s Hospital of Philadelphia said: “This is the first study to demonstrate successful delivery of a gene vector from a bare metal stent.” The new technique causes less inflammation than stents with polmer coatings. Proven successful in tests with cell cultures and rodents. The findings was published online in December 2005, issue of the ‘Proceedings of the National Academy of Sciences.’ Implication of the results may help treat other diseases with implantable medical devices, delivering gene therapy. Chemical and biological engineer David L. Lynn and his team, developed a method to coat stents with film of nanostructured layers of DNA and cationic polymers. The DNA is released into the surrounding cells by the polymers. The application of gene – coated stents prevents restenosis. The findings of David Lynn and his team, presented at the American Chemical Society’s national meeting held in San Francisco, in September 2006
Researchers at Kaisher Permanete, one of the biggest U.S. health and hospital systems, examined link between drug coated stents and fatal blood clots. In September 2006, During the World Congress of Cardiology meeting in Barceleona, several studies by Kaiser Permanete presented findings of medicated – coated stents: Delay the healing around a stent and create a risk of blood clots, which may cause a heart attack. Calvin Weinberger, chief cardiologist for 8.5 million members of Kaiser Permanete said: “stents are widely overused, even among Kaiser doctors who feel pressure to implant them to keep up with consumer demand.”
A week prior to the Barcelona meeting, Boston Scientific Corporation provided information that an internal study of 3,500 patients found, Taxus stents increased the risk of blood clots, but not the risk of heart attack or death, compared with a non – coated medicated stent. During the World Congress Cardiology meeting, REALITY trial investigators, including Dr. San Raffaele Hospital and Cenro Cuoro Columbus Hospital in Milan Italy, showed CYPHER Stent patients had one percent chance developing a blood clot compared 2.5 percent of Taxus stent patients. Cordis Corporation sponsored the REALTIY trial. CYPHER stents are available in more than 80 countries and longest clinical follow up studies compared to any drug stent competition.
