Author : Dr Kendrick Shunk Interventional Cardiologist University of California San Francisco (UCSF) School of Medicine
2008-10-24
Cardiac Catheterization, Angioplasty and Stenting
If you think you may be having a heart attack, dial 911 immediately. Here are warning signs: American Heart Association
Cardiac catheterization with coronary angiography is a commonly performed diagnostic procedure in the US. Coronary angioplasty broadly describes a range of mostly mechanical treatments for coronary artery disease (CAD), or heart disease, and collectively referred to as percutaneous coronary intervention (PCI). As practiced currently, coronary angioplasty most often includes stent placement. It is estimated that more than 1,000,000 PCI procedures are performed annually in the US. The diagnosis of coronary artery disease (CAD) and an overview of CAD treatment options are discussed elsewhere. This knol focuses on specific aspects of cardiac catheterization and coronary angiography as an important diagnostic tool, as well as angioplasty and stenting as important therapeutic modalities for treatment of coronary heart disease.
Cardiac catheterization with coronary angiography:
The reasons why a cardiac catheterization may be ordered are discussed in more detail here (link, link), but for purposes of this discussion, let’s assume that it is important to obtain information about the status of your coronary arteries and that the potential value of that information for you and your doctor outweighs the risk of obtaining it at this time. Despite improvements that have led to an impressive safety record, cardiac catheterization is still an invasive procedure and does carry a finite risk of a complication. Fortunately, the risk of a serious complication such as stroke, heart attack, or death as a result of this procedure is very low (your cardiologist should quote you something in the 1 in 1000 to 1 in 10,000 range), but the risk of less serious complications, such as bleeding, are somewhat higher (perhaps in the range of 1 in 20 to 1 in 100). A full discussion of risks should take place between you and your cardiologist before proceeding.Cardiac Catheterization Procedure
In brief, cardiac catheterization is performed most commonly while you are awake, often with mild sedation, as follows:1) The groin area around the skin crease where the lower belly meets the upper thigh is cleaned and shaved for use as a tiny portal of entry to the femoral artery. Alternatively, sometimes the arm is used, either near the elbow crease (brachial artery) or near the wrist (radial artery).
2) Once in the catheterization laboratory (a.k.a. cath lab), the skin at the selected entry site is numbed with an injection of local anesthetic. From this point forward, there should be no pain.[AU: MOVE OK?]
3) A sheath (essentially just a small tube with a one-way hemostatic [acting to stop bleeding][AU: OK?] valve on the back end to prevent blood from escaping as various catheters are sequentially introduced) is inserted into the artery. The remainder of the procedure is performed through the sheath. The hole in the skin is typically about half the diameter of a pencil.
4) A long thin hollow tube (catheter) is fed into the sheath and advanced to the heart using X-ray guidance.
5) With the tip of the catheter in one of the arteries that supplies the heart muscle (coronary artery), a special iodine solution (contrast) is injected while an x-ray movie of the heart is recorded. The contrast blocks x-rays and thus provides an outline image of the artery. Multiple injections are recorded from various “camera” perspectives.
6) This catheter is removed and the same procedures repeated for any additional arteries or chambers that require angiography.
7) Certain other measurements, such as pressure recordings in various heart chambers are typically also obtained.
8) Once all the required information is gathered, all catheters are removed and the sheath is removed. (In some cases, it is clear that PCI needs to be performed and it may be appropriate to proceed directly using the same sheath before it is removed.)
9) Bleeding is stopped either by holding firm pressure for a period of time, or by using a closure device that either plugs, staples, or stitches the small hole in the artery.
Key Decisions after cardiac catheterization:
After cardiac catheterization with coronary angiography, the cardiologist will typically review the entirety of the data for a given patient. A this point, there are four possible outcomes of diagnostic cardiac catheterization with coronary angiography:1) Normal: The angiography will be entirely normal, usually indicating that the abnormal stress test or other concern prompting the catheterization was a “false alarm.”
2) PCI: A significant narrowing will be found in one or more of the coronary arteries that “fits” with the non-invasive studies, symptoms, and or other data and that narrowing appears amenable to PCI.
3) Bypass: Multiple areas of narrowing and/or narrowing in critical areas such as the left main coronary artery (a.k.a. the “widowmaker”) will be found, which are typically best treated with coronary artery bypass surgery (link).
4) Medical Therapy alone: Narrowings will be found, but none that are both severe and amenable to stenting or bypass; aggressive medical therapy alone will be recommended, without stenting or bypass surgery.
Sometimes this review and decision-making process can be accomplished while the patient is still on the table with the catheter in place, and sometimes it makes more sense to stop the procedure and allow the patient to recover and discuss the options at a later date. Features likely to influence the decision to proceed with PCI include:
1) Presence of an ongoing heart attack.
2) Involvement of only one coronary artery in a location that can be treated safely.
3) Presence of certain other conditions that would make coronary artery bypass surgery (link) a riskier choice, for example severe emphysema.
Percutaneous Coronary Intervention
Percutaneous Coronary Intervention refers to a variety of related procedures performed to improve blood flow through the coronary arteries, accomplished through a small entry point created in a peripheral artery, most commonly at the groin or wrist.Rationale for revascularization with Percutaneous Coronary Intervention (PCI)
Understanding the rationale behind percutaneous coronary intervention (PCI) requires some level of understanding of atherosclerosis (thickening and hardening of the walls of the artery)[AU:OK?], and medical therapies that are often the foundation of a multifaceted treatment plan for heart disease. In brief, although the heart is responsible for, among other things, pumping a supply of oxygenated blood to the entire body, the heart muscle itself still requires its own blood supply, and this supply comes from the 3 arteries that course over the surface of the heart muscle (myocardium). These are known as coronary arteries. These coronary arteries can become narrowed or blocked (stenosed), most commonly by the effects of cholesterol accumulating in and around the cells lining the artery wall (atherosclerosis). Depending upon a variety of factors, a strategy of mechanically restoring adequate blood flow to the downstream areas of myocardium (a.k.a. revascularizaion) may be appropriate, in addition to therapy with medications, diet, and lifestyle. In general, there are two ways of mechanically accomplishing revascularizaion, bypass surgery and/or PCI. Certain situations favor one over the other.
When physicians and patients think about the alternatives for treatment, there should always be consideration of the risk/benefit ratio for each and every alternative as well as a clear understanding that there are only two reasons to proceed with any therapy:
1) If it can be expected to extend life, and/or
2) If it can be expected to improve the quality of life.
In the case of coronary artery bypass surgery, there is evidence from clinical trials that in appropriately selected patients, it has the potential to do both. Other studies have supported the notion that PCI is particularly useful for a improving quality of life, generally by reducing episodes of chest pain and improving exercise tolerance. PCI can sometimes be a feasible alternative to bypass surgery in appropriately selected situations.
A Brief History of PCI (Much more is available elsewhere, see links below. )[AU: WHICH LINKS?]
PCI, which comprises balloon angioplasty and stenting, has been around for about 30 years. Using balloon angioplasty to treat a diseased coronary artery was pioneered in the late 1970s by Andreas Gruentzig. The basic mechanism by which balloon angioplasty works is by “cracking” the plaque and compressing it, thereby increasing the size of the channel for blood to flow through. Now that stents are available, performing balloon angioplasty alone (without a stent) is currently reserved for limited situations because the procedure carries a down side. Namely, the compressed plaque can recoil and abruptly re-close the vessel, requiring a repeat procedure. Also, the healing reaction to the balloon injury can cause scar tissue to proliferate and gradually re-narrow the vessel months later, a process known as restenosis.
Another type of PCI involves stents, which are small tubes of wire mesh used to prop open blood vessels on a more permanent basis. While “bare metal” stents largely solve the problem of abrupt plaque recoil, they do not entirely solve the restenosis problem.
More recently, stents that deliver medication (called drug-eluting stents) have been developed. These stents provide not only the scaffolding effect of the bare metal stents, but also have a drug/polymer coating, which allows medication to leach out into the surrounding vessel wall over the course of a couple of weeks. The medication is used for its ability to inhibit formation of scar tissue, and thereby reduce the risk of restenosis.
Currently, approximately 2/3 of the stents used in the US are of the drug-eluting variety and the remainder are bare metal.
“Lifestyle” Factors: Diet, Exercise, Tobacco
It should go without saying that PCI as a treatment for coronary artery disease is definitely not an alternative to proper diet, appropriate exercise, quitting smoking, or taking prescribed medications. Instead, it must be viewed as something that is sometimes needed in addition to all of these things.
The American Heart Association offers numerous recommendations aimed at coronary heart disease patients including recommendations for diet and lifestyle http://www.americanheart.org/presenter.jhtml?identifier=851 as well as exercise http://circ.ahajournals.org/cgi/reprint/CIRCULATIONAHA.107.185649. Specific exercise recommendations should be tailored to your specific situation by your physician, but in general, the goal should be aerobic exercise of a moderate intensity for about 30 minutes at least 5 times a week or of high intensity for longer than 20 minutes at least 3 times a week. Dietary goals should emphasize no more than appropriate total caloric intake with lower saturated fat and dietary cholesterol content, trans-fat intake of less than 1% of total calories, and for most people an increase in non-processed foods such as fresh fruits and vegetables and whole grains.
Tobacco use is a major contributor to CAD progression. Tobacco cessation (http://americanheart.org/presenter.jhtml?identifier=498 ) is of critical importance for anyone undergoing PCI.
Anyone undergoing PCI must have aggressive control of cholesterol levels in the blood. In addition to diet and exercise, this will almost always include the use of statins (cholesterol-lowering drugs) with a goal LDL of <70 mg/dL. A more detailed set of guidelines relating to cholesterol management is available (http://www.nhlbi.nih.gov/guidelines/cholesterol/atp3xsum.pdf) including discussion of alternatives to statins.
More information about medical therapy for coronary heart disease, which applies to patients who have undergone PCI, can be found here. (Link to CAD Tx)
The PCI Procedure:
Coronary artery angioplasty and stenting (PCI) may be performed as a stand-alone procedure, or it may immediately follow coronary angiography. In the latter case, the first 3 steps (which are the same as those for cardiac catheterization) have already occurred. There are numerous variations in the procedure, owing to the wide array of devices available, but in a typical case, the following will occur:1) The groin area around the skin crease where the lower belly meets the upper thigh is cleaned and shaved for use as a tiny portal of entry to the femoral artery. Alternatively, sometimes the arm is used, either near the elbow crease (brachial artery) or near the wrist (radial artery).
2) Once in the catheterization laboratory (a.k.a. cath lab), the skin at the selected entry site is numbed with an injection of local anesthetic.
3) A sheath (essentially just a small tube with a one-way “hemostatic” valve on the back end to prevent blood from escaping as various catheters are sequentially introduced) is inserted into the artery. The remainder of the procedure is performed through the sheath. The hole in the skin is typically about half the diameter of a pencil.
4) Blood thinning medications are administered to prevent clotting.
5) A guiding catheter of an appropriately selected shape is inserted through the sheath, and the tip of it is placed into the artery that needs the work.
6) Through this guiding catheter, a coronary guide wire (typically 0.014 inches in diameter) is advanced into the diseased artery beyond the main area of narrowing.
7) A small balloon is advanced over this wire to the place of narrowing, where it is inflated to several times atmospheric pressure in order to “crack” and compress the plaque.
8) This balloon is removed and a second balloon, this one with an appropriately sized stent compressed onto it, is advanced to the same spot.
9) This stent delivery balloon is inflated, which causes the compressed stent to enlarge and become permanently embedded into the wall of the artery. Shown below is a coronary stent that has already been expanded with a balloon.
10) The stent delivery balloon is removed, and if necessary, an additional balloon is used to ensure that the stent is adequately expanded and appropriately sized.
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Recovery after PCI:
As practiced in the US, PCI requires an overnight stay in the hospital following the procedure, typically in a hospital room that provides for continuous monitoring of the heart rhythm. Provided there are no complications, discharge to home the following day is usually appropriate. After the procedure, the following steps generally take place:1) Instructions will be given regarding what activities to avoid to allow healing of the groin site, what to watch for, and who to call with questions or problems.
2) Clopidogrel will almost always be prescribed at a dose of 75 mg per day for 12 months or longer.
3) Aspirin every day will almost always be prescribed.
4) Other medications, diet, and lifestyle changes may be required.
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Additional resources:
Working together, the American College of Cardiology and the American Heart Association (AHA) issue numerous relevant guidelines that pertain to heart disease. In many cases, other societies have signed on as well.www.americanheart.org
www.acc.org