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. It is performed for both diagnostic and interventional (treatment) purposes.
Coronary catheterization is one of the several cardiology diagnostic tests and procedures. Specifically, through the injection of a liquid radiocontrast agent and illumination with X-rays,[1] angiocardiography allows the recognition of occlusion, stenosis, restenosis, thrombosis or aneurysmal enlargement of the coronary artery lumens; heart chamber size; heart muscle contraction performance; 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 relevant problems that the test deals with most commonly occur as a result of advanced atherosclerosis – atheroma activity within the wall of the coronary arteries. Less frequently, valvular, heart muscle, or arrhythmia issues are the primary focus of the test.
Coronary artery luminal narrowing reduces the flow reserve for oxygenated blood to the heart, typically producing intermittent angina. Very advanced luminal occlusion usually 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 atherosclerosis itself, only significant luminal changes which have occurred as a result of end stage complications of the atherosclerotic process. See IVUS and atheroma for a better understanding of this issue.
Indications for cardiac catheterization include the following:
Equipment[edit]
Coronary catheterization is performed in a catheterization lab, usually located within a hospital. With current designs, the patient must lie relatively flat on a narrow, minimally padded, radiolucent (transparent to X-ray) table. The X-ray source and imaging camera equipment are on opposite sides of the patient's chest and freely move, under motorized control, around the patient's chest so images can be taken quickly from multiple angles. More advanced equipment, termed a bi-plane cath lab, uses two sets of X-ray source and imaging cameras, each free to move independently, which allows two sets of images to be taken with each injection of radiocontrast agent. The equipment and installation setup to perform such testing typically represents a capital expenditure of US$2–5 million (2004), sometimes more, partially repeated every few years.
Advances in catheter-based physical treatments[edit]
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 developed significant restenosis; but that percentage has dropped to the single to lower two-digit range with the introduction of drug-eluting stents. Sirolimus, paclitaxel, and everolimus are the three 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 stent struts (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. One of the newest innovations in coronary stents is the development of a dissolving stent. Abbott Laboratories has used a dissolvable material, polylactic acid, that will completely absorb within 2 years of being implanted.
Radiation dosage[edit]
Angiography[edit]
Imaging in coronary angiograms is performed via fluoroscopy using X-rays, which pose a potential for increasing the patient's risk of radiation-induced cancer. The risk increases with the exposure time, consisting of 1) time guiding the probe into and out of the heart and 2) time illuminating the contrast agent to perform the angiogram. Absorbed radiation is also a function of body mass index, with obese patients having twice the dose of normal-weight patients; exposure to the operator was also doubled.[8] Coronary angiograms can be done either transradial (through the wrist) or transfemoral (through the groin).[9] The transradial route results in somewhat greater patient and operator exposure. Overall, patient exposure can range from 2 millisieverts (equivalent of about 20 chest x-ray plates) to 20 millisieverts.[10] For a given patient, exposure can vary within an institution and between institutions by up to 121%.[11]
Radiation exposure to the operator can be reduced by the use of protective equipment. Exposure to the patient can be reduced by minimizing fluoroscopy time.