Coronary Catheterization
A coronary catheterization is a minimally invasive procedure to access the coronary circulation and blood filled chambers of the heart using a catheter. A catheter is a tube that can be inserted into a body cavity duct or vessel. Catheters thereby allow drainage or injection of fluids or access by surgical instruments. The process of inserting a catheter is catheterization. The patient is usually awake during coronary catheterization, ideally with only local anaesthesia and minimal general sedation so that he/ she can immediately report any discomfort.
The main problems that the test deals with occur as a result of advanced atherosclerosis, atheroma activity within the wall of the coronary arteries. The test also deals with other issues like valvular, heart muscle or arrhythmia.
Specifically, coronary catheterization visually interprets and recognizes occlusion, stenosis, restenosis, thrombosis, heart chamber size, heart muscle contraction performance, aneurysmal enlargement the coronary artery and some aspects of heart valve function. Important internal heart and lung blood pressures, not measurable from outside the body, can be accurately measured during the test.
The narrowing of the Coronary artery luminal reduces the flow reserve for oxygenated blood to the heart, typically producing intermittent angina if very advanced; luminal occlusion usually produces a heart attack. Coronary Catheterization is used for both diagnosis and treatment.
Even though Coronary Catheterization was first discovered accidentally in the late 1950s, it has been extended to significant use only since the late 1970's. It was then that Coronary Catheterization was used for: (a) less invasive physical treatment for angina and some of the complications of severe atherosclerosis, (b) preventing heart attacks before complete damage has occurred and (c) research for better understanding of the pathology of coronary artery disease and atherosclerosis.
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, it has been increasingly recognized, since the late 1980s, that coronary catheterization does not allow the recognition of the presence or absence of coronary atherosclerosis itself, only significant luminal changes which have occurred as a result of end stage complications of the atherosclerotic process.
Procedure
Coronary catheterization is performed in the cardiac catheterization lab of 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-Ray source 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 cardiac catheterization lab, uses two sets of X-Ray source and imaging cameras, each free to move independently, which allows two sets images to be performed with each injection of radiocontrast agent.
Diagnostic procedures
During coronary catheterization, blood pressures are recorded and X-Ray motion picture shadow-grams of the blood inside the coronary arteries are recorded. In order to create the X-ray pictures, a physician guides 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 catheter is smaller than the lumen of the artery it is placed in; internal/ intraarterial blood pressures are monitored through the catheter to verify that the catheter does not block blood flow.
The catheter is designed to be radiodense for visibility and it allows the clear, watery, blood compatible radiocontrast agent, the
X-Ray dye, to be selectively injected and mixed with the blood flowing within the artery. Without the X-Ray dye injection, the blood and surrounding heart tissues appear, 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 radiocontrast within 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 narrowing is seen as either a narrowing or increased haziness within the X-ray shadow images of the blood/dye column within that portion of the artery; this is as compared to adjacent, presumed healthier, less stenotic areas.
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-Ray dose 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-Ray dose, termed cine, in order to create better quality motion picture images, having sharper radiodensity contrast, typically at 30 frames per second. The physician controls both the contrast injection, fluoroscopy and cine application timing so as to minimize the total amount of radiocontrast injected and times the X-Ray to the injection so as to minimize the total amount of X-Ray used. Doses of radiocontrast agents and X-Ray exposure times are routinely recorded in an effort to maximize safety.
Therapeutic procedures
By changing the diagnostic catheter to a guiding catheter, physicians can also pass a variety of instruments through the catheter and into the artery to a lesion site. The most commonly used are 0.014 inch diameter guide wires and the balloon dilation catheters. By injecting radiocontrast agent through a tiny passage extending down the balloon catheter and into the balloon, the balloon is progressively expanded. The hydraulic pressures are chosen and applied by the physician, according to how the balloon within the stenosis responds. The radiocontrast filled balloon is watched under fluoroscopy as it opens. As much hydraulic brute force is applied as judged needed and visualized to be effective to make the stenosis of the artery lumen visibly enlarge.
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 luminal stenotic areas and designed to inflate to a specific pre-designed diameter. If over inflated, the balloon material simply tears and allows the inflating radiocontrast agent to simply escape into the blood.
Additionally, several other devices can be advanced into the artery via a guiding catheter. These include laser catheters, stent catheters, IVUS catheters, Doppler catheter, pressure or temperature measurement catheter and various clot and grinding or removal devices.
Advances in catheter based physical treatments
Interventional procedures have been plagued by restenosis due to the formation of endothelial tissue overgrowth at the lesion site. Restenosis is the body's response to the injury of the vessel wall from angioplasty and to the stent as 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 significantly with the introduction of drug-eluting stents. 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.
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