Mark M. Levinson, MD
Hutchinson Hospital, Hutchinson Kansas
Coronary Angiography is the name for a diagnostic x-ray procedure designed to visualize the small nutrient arteries of the heart. These tiny blood vessels are only 1 to 3 millimeters in diameter. Thus it takes special x-ray equipment and techniques to obtain images of sufficient quality for diagnosis and surgical decision making.
The credit for "inventing" coronary angiography is given primarily to Dr. Mason Sones, working at the Cleveland Clinic in the 1950's. Dr. Sones accidently injected angiography dye into the mouth of the coronary arteries for the first time in a living patient during an attempt to visualize other cardiac structures. Aware of the significance of this observation, Dr. Sones went about designing equipment and techniques to routinely x-ray the various coronary arteries in human patients. Since that initial discovery, there have been tremendous refinements in angiographic equipment, technique and safety. Coronary angiography has become the cornerstone for both diagnosis and treatment of coronary artery disease (CAD) worldwide.
In this test, the patient is brought to the x-ray (or radiology) procedure room where specialized fluoroscopic equipment is available. The patient must lay motionless on the x-ray table, with their hands to the side or overhead. It is normal for a patient to be apprehensive and nervous during this procedure. The team in the catheterization laboratory (or cath lab) will commonly administer medications designed to relax the patient and relieve both pain and anxiety during the procedure. A sterile area is prepared in the groin by cleansing the skin with topical antiseptic agents and covering the region with sterile drapes. The skin is "numbed" with local anesthesia (similar to the Novocaine injection used by a dentist). The cardiologist places a needle into the main artery in the upper leg, called the femoral artery. Through this needle, a flexible wire is passed and threaded backward into the arterial tree until the wire reaches the main aorta (as confirmed by x-ray fluoroscopy). Over the wire, a long plastic tube (also known as angiogram catheter) is threaded into the aorta. The initial wire serves as a guiding system to ensure that the catheter tracks into the aorta properly.
The angiogram catheter is maneuvered into position just above the outlet valve of the left ventricle, (also known as the aortic valve). With careful maneuvering, the tip of the catheter can be positioned at the mouth of the main coronary arteries. Once positioned, specialized contrast agent, or angiogram dye is selectively injected into the mouth of the coronary artery while continuous x-ray images are exposed onto movie film. During the actual injection, the patient notices a flushing sensation starting in the chest and migrating to the head and sometimes the entire body. This sensation is a side effect of the dye matierial, and occurs to a varying degree in all patients. The flushing sensation is bothersome, but is short-lived. It is not an allergic reaction.
As the dye travels down the branches of the coronary artery itself, continouous images are exposed onto movie film. The composite roll of images is known as a cineangiogram. In most modern cath labs, the cardiologist can also see the preliminary results immediately on the overhead video screen. Digitized images are also saved on computer and replayed onto the video screen as needed. In nearly all cases, multiple views from different angles are necessary in order to ascertain the precise location and severity of the coronary artery blockages. In some views, a blockage may not initially appear to be that severe. However, from another angle of view, the artery may appear nearly occluded. Thus it is important for the cardiologist to rotate the fluoroscopy equipment and obtain pictures from multiple views.
After completion of the coronary angiogram procedure, the cardiologist reviews the final images on a specialized projector, making measurements of each blockage seen. Blockages in the channel of an artery are rated by percentage (i.e. the percent of the flow channel that is obstructed). For blockages that involve less than 50% of the vessel diameter, intervention is usually not necessary. In general terms, when plaque buildup is blocking more than 50% of the vessel diameter, the blockage is considered clinicially significant. However, most blockages are not considered serious until they reach at least 75% narrowing of the diameter of the artery. At this point, there will always be significant impairment of blood flow. Such lesions are clinically important and thus candidates for treatment.
Below is an example of a 99% blockage in the most important coronary artery, the left anterior descending (LAD). The normal parts of the coronary vessels are clearly seen as smooth unbroken white channels against the black background of the undyed tissues.
Here is a view of the right coronary artery (RCA) demonstrating two high grade (> 90%) blockages.
Depending on lesion size, shape, length, location and other factors, some blockages can be treated without bypass surgery. (Consult The Learning Center for educational presentations on angioplasty, atherectomy , and other such techniques). However, there are many patients in whom the blockages cannot be easily or safely modified by such techniques. Coronary Artery Bypass Grafting (CABG) is the mainstay of treatment for such patients. For example, in patients with multiple high grade blockages, it is more effective to restore circulation throughout the heart with bypass surgery. If the cardiologist feels that surgery is warranted, the films and clinical situation are reviewed by a consulting surgeon. The surgeon utilizes the cineangiogram images to plan both the location and number of potential bypass grafts needed in order to optimize that patients surgical result.