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Coronary catheterizationA coronary catheterization is a minimally invasiveprocedure to access the coronary circulationand blood filled chambers of the heartusing a catheter. It is performed for both diagnostic and interventional (treatment) purposes. Coronary catheterization is one of the several Cardiology diagnostic tests and procedures. Specifically, coronary catheterization is a visually interpreted test performed to recognize occlusion, stenosis, restenosis, thrombosisor aneurysmalenlargement the coronary arterylumens, heart chambersize, heart musclecontraction performance and some aspects of heart valvefunction. Important internal heartand lungblood pressures, not measurable from outside the body, can be accurately measured during the test. The relevant problems that the test deals with most commonly occur as a result of advanced atherosclerosis, atheromaactivity within the wall of the coronary arteries. Less frequently, other issues, valvular, heart muscleor arrhythmiaissues are the primary focus of the test. Coronary arteryluminalnarrowingreduces the flow reserve for oxygenated blood to the heart, typically producing intermittent anginaif very advanced; luminalocclusionusually produces a heart attack. However, it has been increasingly recognized, since the late 1980s, that coronary catheterization does not allow the recognition of the presence or absence of coronary atherosclerosisitself, only significant luminalchanges which have occurred as a result of end stage complications of the atheroscleroticprocess. See IVUSand atheromafor a better understanding of this issue.
HistoryCoronary catheterization was introduced in the late 1950s. One of the first, presumably because of ethical concerns and fellow physicians' fears, was performed by a physician on himself. Since the late 1970s, building on the pioneering work of Charles Dotterin 1964and especially Andreas Gruentzigstarting in 1977, coronary catheterization has been extended to more important uses: (a) the performance of less invasive physical treatment for anginaand some of the complications of severe atherosclerosis, (b) preventing heart attacksbefore complete damage has occurred and (c) research for better understanding of the pathology of coronary artery diseaseand atherosclerosis. Patient participationThe patientbeing examined or treated is usually awake during coronary catheterization, ideally with only local anaesthesiaand minimal general sedation, throughout the procedure. Performing the procedurewith the patientawake is safer as the patientcan immediately report any discomfort or problems and thereby facilitate rapid correction of any undesirable events. Medical monitors never tell the whole story; how the patient feels is often a most reliable indicator of procedural safety. In the early 1960s, cardiac catheterization frequently took several hours and involved significant complications for as many as 2-3% of patients. With multiple incremental improvements over time, simple coronary catheterization examinations are now commonly done in as little as 5-8 minutes, with multiple views, far better images and significant complication rates typically in the less than 0.0003% range. However, though the imaging portion of the examination is often brief, because of setup and safety issues, the patient is often in the lab for 20 to 45 minutes. Any of multiple technical difficulties, while not endangering the patient (indeed added to protect the patient's interests) can significantly increase the examination time. EquipmentCoronary catheterization is performed in a cardiac catheterization lab, usually located within a hospital. With current designs, the patient must lay relatively flat on a minimally padded narrow table which is designed to be radiolucent. The X-Raysource and imaging camera equipment are on opposite sides of the patient's chest and freely move, under motorized control, about the patient's chest position in space so that images can be quickly taken from multiple different angles. More advanced equipment, termed a bi-plane cath lab, uses two sets of X-Raysource and imaging cameras, each free to move independently, which allows two sets images to be performed with each injection of radiocontrastagent. The equipment and installation setup to perform such testing typically represents a capital expenditure of 2 to 5 million U.S. 2004 dollars, sometimes more, partially repeated every few years. Diagnostic Procedure DescriptionDuring coronary catheterization (often referred to as a cath by physicians), blood pressuresare recorded and X-Raymotion pictureshadow-grams of the blood inside the coronary arteriesare recorded. In order to create the X-raypictures, a physicianguides a small tube-like device called a catheter, typically ~2.0 mm (6-French) in diameter, through the large arteries of the body until the tip is just within the opening of one of the coronary arteries. By design, the catheteris smaller than the lumenof the arteryit is placed in; internal blood pressures are monitored through the catheterto verify that the catheterdoes not block blood flow. The catheteris itself designed to be radiodensefor visibility and it allows a clear, watery, blood compatible radiocontrastagent, commonly called an X-raydye, to be selectively injected and mixed with the blood flowing within the artery. Typically 3-8 cc of the radiocontrastagent is injected for each image to make the blood flowvisible for about 3-5 seconds as the radiocontrastagent is rapidly washed away into the coronarycapillariesand then coronaryveins. Without the X-raydye injection, the blood and surrounding heart tissuesappear, on X-ray, as only a mildly-shape-changing, otherwise uniform water density mass; no details of the blood and internal organ structure are discernable. The radiocontrastwithin the blood allows visualization of the blood flow within the arteries or heart chambers, depending on where it is injected. If atheroma, or clots, are protruding into the lumen, producing narrowing, the narrowingis seen as either a narrowingor increased haziness within the X-rayshadow images of the blood/dye column within that portion of the artery; this is as compared to adjacent, presumed healthier, less stenoticareas. See the single frame illustration of an coronary angiogramimage on the angioplastypage. For guidance regarding catheter positions during the examination, the physician mostly relies on detailed knowledge of internal anatomy, guide wire and catheter behavior and intermittently, briefly uses fluoroscopy and a low X-Raydose to visualize when needed. This is done without saving recordings of these brief looks. When the physician is ready to record diagnostic views, which are saved and can be more carefully scrutinized later, he activates the equipment to apply a significantly higher X-Raydose, termed cine, in order to create better quality motion picture images, having sharper radiodensitycontrast, typically at 30 frames per second. The physician controls both the contrast injection, fluoroscopyand cineapplication timing so as to minimize the total amount of radiocontrastinjected and times the X-Rayto the injection so as to minimize the total amount of X-Rayused. Doses of radiocontrastagents and X-Rayexposure times are routinely recorded in an effort to maximize safety. Though not the focus of the test, calcificationwithin the arterywalls, located in the outer edges of atheromawithin the artery walls, is sometimes recognizable on fluoroscopy (without contrast injection) as radiodensehalo rings partially encircling, and separated from the blood filled lumenby the interceding radiolucentatheroma tissue and endotheliallining. Calcification, even though usually present, is usually only visible when quite advanced and calcifiedsections of the artery wall happen to be viewed on end tangentiallythrough multiple rings of calcification, so as to create enough radiodensity to be visible on fluoroscopy. Catheterization to physically treat luminal diseaseBy changing the diagnostic catheterto a guiding catheter, physicians can also pass a variety of instruments through the catheterand into the arteryto a lesionsite. The most commonly used are 0.014 inch diameter guide wires and the balloon dilation catheters, see angioplasty. By injecting radiocontrastagent through a tiny passage extending down the balloon catheterand into the balloon, the balloon is progressively expanded. The hydraulic pressures are chosen and applied by the physician, according to how the balloonwithin the stenosisresponds. The radiocontrastfilled balloonis watched under fluoroscopy (it typically assumes a "dog bone" shape imposed on the outside of the balloon by the stenosisas the balloon is expanded), as it opens. As much hydraulicbrute force is applied as judged needed and visualized to be effective to make the stenosisof the arterylumenvisibly enlarge. Typical normal coronary arterypressures are in the <200 mmHg range (27 kPa). The hydraulicpressures applied within the balloon may extend to as high as 19000 mmHg (2,500 kPa). Prevention of over-enlargement is achieved by choosing balloons manufactured out of high tensile strength clear plastic membranes. The balloon is initially folded around the catheter, near the tip, to create a small cross-sectional profile to facilitate passage though luminalstenotic areas and designed to inflate to a specific pre-designed diameter. If over inflated, the balloon material simply tears and allows the inflating radiocontrastagent to simply escape into the blood. Additionally, several other devices can be advanced into the artery via a guiding catheter. These include lasercatheters, stentcatheters, IVUScatheters, Dopplercatheter, pressure or temperature measurement catheterand various clotand grinding or removal devices. Most of these devices have turned out to be niche devices, only useful in a small percentage of situations or for research. Stents, specially manufactured expandable stainless steel mesh tubes, mounted on a balloon catheter, are the most commonly used device beyond the balloon catheter. When the stent/balloon device positioned within the stenosis, the balloon is inflated which, in turn, expands the stentand the artery. The balloon is removed and the stentremains in place, supporting the inner arterywalls in the more open, dilated position. Current stents generally cost around $1,000 to 3,000 each U.S. 2004 dollars, the drug coated ones being the more expensive. Advances in catheter based physical treatmentsInterventional procedures have been plagued by restenosis due to the formation of endothelialtissueovergrowth at the lesion site. Restenosisis the body's response to the injury of the vessel wall from angioplastyand to the stentas a foreign body. As assessed in clinical trials during the late 1980 and 1990s, using only balloon angioplasty (POBA, plain old balloon angioplasty), up to 50% of patients suffered significant restenosis but that percentage has dropped to the single to lower two digit range with the introduction of drug-eluting stents. Sirolimus and tacrolimus are the two drugs used in coatings which are currently FDA approved in the United States. As opposed to bare metal, drug eluting stents are covered with a medicine that is slowly dispersed with the goal of suppressing the restenosis reaction. The key to the success of drug coating has been (a) choosing effective agents, (b) developing ways of adequately binding the drugs to the stainless surface of the stentstruts (the coating must stay bound despite marked handling and stent deformation stresses) and (c) developing coating controlled release mechanisms that release the drug slowly over about 30 days. External links
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Categories: Cardiology
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