What is percutaneous coronary intervention?
Percutaneous coronary intervention (PCI) is a group of procedures that open partial or complete obstructions of coronary arteries caused by the build-up of atherosclerotic plaque. These procedures include balloon angioplasty, coronary stenting, and coronary atherectomy.
These procedures are performed in the cardiac catheterization laboratory. During the procedure, the patient is given gentle sedation and local anesthesia. Special guiding catheters are advanced from the leg (or rarely from the arm) and guided to the arteries of the heart. Through these hollow catheters, a small guidewire is then advanced into the coronary artery with the partial or complete blockage. A long narrow balloon is then advanced over these small guidewires into the area of the blockage. Once in place, these balloons can be inflated. The inflated balloon compresses the plaque against the wall and thereby decreases the blockage of blood flow through the inside of the artery. The balloon is then deflated and the catheter is removed. This process is called an angioplasty.
Usually, an angioplasty is followed by placement of a stent in the same area of the blockage. A stent is a mesh tube made out of metal. This metal tube can be expanded inside the artery by another special balloon. Once expanded, the stent becomes imbedded into the wall of the artery. The purpose of the stent is to reduce the risk of another blockage forming in this area where an angioplasty was performed. Some blockages and arteries are not suitable for a stent and the cardiologist performing the procedure will discuss this with patient.
On some occasions, a coronary artery may be filled with plaque that has become “calcified” (as hard as stone). In this case, a rotational atherectomy device (“rotoblator”) may be used. A rotoblator is a coronary catheter with a burr at its end that is rotated very quickly (approximately 50,000 rpm), and can act to break up the calcium in the arterial wall. There are many other instruments and tools used by the interventional cardiologist to assist in these procedures.
Who is a candidate for an angioplasty?
There are three types of patients that may benefit from an angioplasty. The first type of patient that benefits from an angioplasty is one that is having a myocardial infarction (or heart attack) due to a sudden and complete blockage in artery. An angioplasty for this type of patient is often life saving.
Another type of patient that may benefit form an angioplasty is one that is experiencing unstable angina (or acute coronary syndrome). Patients with unstable angina have a recent onset of anginal symptoms (chest pain, shortness of breath) or a change in their chronic anginal symptoms due to a new blockage or progression of their existing blockages. Evidence has shown that the long-term outcomes of these patients is improved by relieving these blockages, either by angioplasty or coronary bypass surgery. Your cardiologist will help you determine which treatment would be best for you.
The final type of patient that may benefit from an angioplasty is one with chronic stable angina. While an angioplasty has never been shown to improve long-term survival in patients with chronic and stable symptoms, it has been shown to improve their symptoms. This may be important for patients whose activities have become limited due to symptoms of chest pain and shortness of breath.
What is restenosis?
In patients undergoing an angioplasty, a percentage of them will develop “restenosis”. This is a term used to describe a re-narrowing of their coronary artery at the site of their previous angioplasty procedure.
Why does restenosis occur?
After treatment of an occlusive plaque by balloon angioplasty, stenting or rotablation, a healing process then follows, with the development of scar tissue at that site. In some cases, the development of scar tissue is an overly exuberant process, and significant narrowing of the angioplasty site occurs with consequences similar to when that site had been narrowed by plaque.
How often does restenosis occur?
When using balloon angioplasty alone to treat a narrowing, the restenosis rate is generally 30-40%. When using a bare metal stent, the overall rate of restenosis is 20%. When using a drug-eluting stent, the restenosis rate is less than 10%. A patient who develops restenosis may have this treated with a repeat angioplasty. On occasion in patients with recurrent restenosis, coronary bypass surgery will be required. The risk of restenosis varies from patient to patient depending on the location within the coronary circulation of the treated plaque and by other factors such as the presence of diabetes or renal (kidney) failure. The occurrence of restenosis following a PCI generally occurs between six weeks and eight months following the procedure. As a general rule, if restenosis has not developed by one year following the procedure, the future likelihood of restenosis is extremely low.
What is the difference between a bare metal stent and a drug-eluting stent?
In recent years, stent technology has advanced such that the stainless steel stents we have traditionally been using can now be coated with a polymer impregnated with certain medications that would reduce the rate of restenosis. Due to the fact that these “drug-eluting stents” succeeded in reducing the rate of restenosis by more than 50% of the rate associated with the traditional “bare metal stents,” they rapidly gained in popularity after their FDA approval in 2003. Unfortunately, in some cases these medicated stents are so effective that too little scar tissue is formed, leaving some metal still exposed long after the procedure is performed, which may lead to blood clot formation in the stent. In rare instances, patients having drug-eluting stents have developed heart attacks caused by acute closure of their stents by the development of blood clots months or even years after placement of their stents. Fortunately, formation of a blood clot on the exposed metal can be prevented by a patient taking the combination of aspirin and clopidogrel (Plavix), which both inhibit platelet clotting function. Therefore, patients having drug-eluting stents placed are now requested to take their “dual anti-platelet therapy” for a prolonged period of time. Currently, the general recommendation is one year of clopidogrel therapy and indefinite use of aspirin, but, in some cases, both medications are continued long-term after the placement of a drug-eluting stent. The advantage of having a drug-eluting stent placed is the significantly lower chance of developing restenosis. The disadvantage, however, is the requirement for prolonged dual anti-platelet therapy, which carries an increased bleeding risk.
What happens after a PCI?
Following a PCI, the patient generally remains in the hospital overnight and is released on the following day. The PCI patient must remain on medications long-term, some of which are to reduce the risk of the development of future cardiovascular disease and some of which are to protect against the development of blood clot formation within the stent. There is no medical therapy to prevent restenosis. Generally, a patient will undergo a stress test six months following the PCI to rule-out the development of restenosis. They should continue to be followed long-term under a cardiologist’s care.