Cardiac catheterization

Definition

Cardiac catheterization (also called heart catheterization) is a diagnostic and occasionally therapeutic procedure that allows a comprehensive examination of the heart and surrounding blood vessels. It enables the physician to take angiograms, record blood flow, calculate cardiac output and vascular resistance, perform an endomyocardial biopsy, and evaluate the heart's electrical activity. Cardiac catheterization is performed by inserting one or more catheters (thin flexible tubes) through a peripheral blood vessel in the arm (antecubital artery or vein) or leg (femoral artery or vein) under x-ray guidance.

Purpose

Cardiac catheterization is most commonly performed to examine the coronary arteries, because heart attacks, angina, sudden death, and heart failure most often originate from disease in these arteries. Cardiac catheterization may reveal the presence of other conditions, including enlargement of the left ventricle; ventricular aneurysms (abnormal dilation of a blood vessel); narrowing of the aortic valve; insufficiency of the aortic or mitral valve; and septal defects that allow an abnormal flow of blood from one side of the heart to the other.

Symptoms and diagnoses that may be associated with the above conditions and may lead to cardiac catheterization include:

• chest pain characterized by prolonged heavy pressure or a squeezing pain
• abnormal results from a treadmill stress test
• myocardial infarction (heart attack)
• congenital heart defects
• valvular disease

Cardiac catheterization with coronary angiography is recommended in patients with angina (especially unstable angina); suspected coronary artery disease; suspected silent ischemia and a family history of heart attack; congestive heart failure; congenital heart disease; and pericardial (lining outside the heart) disease. Catheterization is also recommended for patients with suspected valvular disease, including aortic stenosis (narrowing) or regurgitation, and mitral stenosis or regurgitation.

Patients with congenital cardiac defects are also evaluated with cardiac catheterization to visualize the abnormal direction of blood flow associated with these diseases. In addition, the procedure may be performed after acute myocardial infarction (heart attack); before major noncardiac surgery in patients at high risk for cardiac problems; before cardiac surgery in patients at risk for coronary artery disease; and before such interventional technologies and procedures as stents and percutaneous transluminal coronary angioplasty (PTCA) or closure of small openings between the atria (upper chambers), called atrial septal defects.

Left- and right-side catheterization

Cardiac catheterization can be performed on either side of the heart to evaluate different functions. Testing the right side of the heart allows the physician to evaluate tricuspid and pulmonary valve function, in addition to measuring blood pressures and collecting blood samples from the right atrium, right ventricle (lower chamber), and pulmonary artery. Catheterization of the left side of the heart is performed to test the blood flow in the coronary arteries, as well as the level of function of the mitral and aortic valves and left ventricle.

Coronary angiography

Coronary angiography, which is also known as coronary arteriography, is an imaging technique that involves injecting a dye into the vascular system to outline the heart and coronary vessels. Angiography allows the visualization of any blockages, narrowing, or abnormalities in the coronary arteries. If these signs are visible, the cardiologist may assess the patient's readiness for coronary bypass surgery, or a less invasive approach such as dilation of a narrowed blood vessel by surgery or the use of a balloon (angioplasty). Because some interventions may be performed during cardiac catheterization, the procedure is considered therapeutic as well as diagnostic.

Outpatient catheterization

Cardiac catheterization is usually performed in a specially designed cardiac catheterization suite in a hospital, so that any procedural complications may be handled rapidly and effectively. Cardiac catheterization may also be performed on patients presenting to the emergency department with chest pain or chest injuries. The procedure may be performed on an outpatient basis, depending on the patient's pre- and post-catheterization condition. As of 2000, however, the American Heart Association (AHA) and the American College of Cardiology (ACC) issued a joint statement denying approval of the use of separate cardiac catheterization laboratories that are not part of a hospital, on the grounds that a small number of patients having the procedure on an outpatient basis will have unexpected reactions or complications.

Demographics

Coronary artery disease is the first-ranked cause of death for both men and women in the United States. More than 1.5 million cardiac catheterizations are performed every year in the United States, primarily to diagnose or monitor heart disease. There is an expected growth to more than three million procedures by 2010.

Description

Cardiac anatomy

The heart consists of four chambers separated by valves. The right side of the heart, which consists of the right atrium (upper chamber; sometimes called the right auricle) and the right ventricle (lower chamber), pumps blood to the lungs. The left side of the heart, which consists of the left atrium and the left ventricle, simultaneously pumps blood to the rest of the body. The right and left coronary arteries, which are the first vessels to branch off from the aorta, supply blood to the heart. The left anterior descending coronary artery supplies the front of the heart; the left circumflex coronary artery wraps around and supplies the left side and the back of the heart; and the right coronary artery supplies the back of the heart. There is, however, a considerable amount of variation in the anatomy of the coronary arteries.

Catheterization procedure

The patient lies face up on a table during the catheterization procedure, and is connected to a cardiac monitor . The insertion site is numbed with a local anesthetic, and access to the vein or artery is obtained using a needle. A sheath, a rigid plastic tube that facilitates insertion of catheters and infusion of drugs, is placed in the puncture site. Under fluoroscopic guidance, a guide-wire (a thin wire that guides the catheter insertion) is threaded through a brachial or femoral artery to the heart. The catheter, a flexible or preshaped tube approximately 32–43 in (80–110 cm) long, is then inserted over the wire and threaded to the arterial side of the heart. The patient may experience pressure as the catheter is threaded into the heart. The contrast agent, or dye, used for imaging is then injected so that the physician can view the heart and surrounding vessels. The patient may experience a hot, flushed feeling or slight nausea following injection of the contrast medium. Depending on the type of catheterization (left or right heart) and the area being imaged, different catheters with various shapes and ends are used.

The radiographic/fluoroscopic system has an x-ray subsystem and video system with viewing monitors that allow the physician to observe the procedure in real time using fluoroscopy as well as taking still x rays for documentation purposes. Most newer systems use a digital angiography system that allows images to be recorded, manipulated, and stored digitally on a computer.

The procedure usually lasts about two or three hours. If further intervention is necessary, an angioplasty, stent implantation, or other procedure can be performed. At the end of the catheterization, the catheter and sheath are removed, and the puncture site is closed using a sealing device or manual compression to stop the bleeding. One commonly used sealing device is called Perclose, which allows the doctor to sew up the hole in the groin. Other devices use collagen seals to close the hole in the femoral artery.

During cardiac catherization, a catheter is fed into the femoral artery of the upper leg (A). The catheter is fed up to coronary arteries to an area of blockage (B). A dye is released, allowing visualization of the blockage (C). (

Illustration by GGS Inc.

)

Diagnosis/Preparation

Before undergoing cardiac catheterization, the patient may have had other noninvasive diagnostic tests, including an electrocardiogram (ECG), echocardiography , computed tomography (CT), magnetic resonance imaging (MRI), laboratory studies (e.g., blood work), and/or nuclear medicine cardiac imaging. The results of these noninvasive tests may have indicated a need for cardiac catheterization to confirm a suspected cardiac condition, further define the severity of a previously diagnosed condition, or establish the need for an interventional procedure (e.g., cardiac surgery).

Patients should give the physician or nurse a complete list of their regular medications, including aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), because they can affect blood clotting. Diabetics who are taking either metformin or insulin to control their diabetes should inform the physician, as these drugs may need to have their dosages changed before the procedure. Patients should also notify staff members of any allergies to shellfish containing iodine, iodine itself, or the dyes commonly used as contrast agents before cardiac catheterization.

Because cardiac catheterization is considered surgery, the patient will be instructed to fast for at least six hours prior to the procedure. A mild sedative may be administered about an hour before the procedure to help the patient relax. If the catheter is to be inserted through the groin, the area around the patient's groin will be shaved and cleansed with an antiseptic solution.

Aftercare

While cardiac catheterization may be performed on an outpatient basis, the patient requires close monitoring following the procedure; the patient may have to remain in the hospital for up to 24 hours. The patient will be instructed to rest in bed for at least eight hours immediately after the test. If the catheter was inserted into a vein or artery in the leg or groin area, the leg will be kept extended for four to six hours. If a vein or artery in the arm was used to insert the catheter, the arm will need to remain extended for a minimum of three hours.

Most doctors advise patients to avoid heavy lifting or vigorous exercise for several days after cardiac catheterization. Those whose occupation involves a high level of physical activity should ask the doctor when they could safely return to work. In most cases, a hard ridge will form over the incision site that diminishes as the site heals. A bluish discoloration under the skin often occurs at the point of insertion but usually fades within two weeks. The incision site may bleed during the first 24 hours following surgery. The patient may apply pressure to the site with a clean tissue or cloth for 10–15 minutes to stop the bleeding.

The patient should be instructed to call the doctor at once if tenderness, fever, shaking, or chills develop, which may indicate an infection. Other symptoms requiring medical attention include severe pain or discoloration in the leg, which may indicate that a blood vessel was damaged.

Risks

Cardiac catheterization is categorized as an invasive procedure that involves the heart, its valves, and coronary arteries, in addition to a large artery in the arm or leg. Cardiac catheterization is contraindicated (not advised) for patients with the following conditions:

• A bleeding disorder, or anticoagulation treatment with Coumadin (sodium warfarin); these may adversely affect bleeding and clotting during the catheterization procedure.
• Renal insufficiency or poor kidney functioning (especially in diabetic patients), which may worsen following angiography.
• Severe uncontrolled hypertension.
• Severe peripheral vascular disease that limits access to the arteries.
• Untreated active infections, severe anemia, electrolyte imbalances, or coexisting illnesses that may affect recovery or survival.
• Endocarditis (an inflammatory infection of the heart's lining that often affects the valves).

Radiation hazards

Cardiac catheterization involves radiation exposure for staff members as well as the patient. The patient's dose of radiation is minimized by using lead shielding in the form of blankets or pads over certain body parts and by choosing the appropriate dose during fluoroscopy. To monitor staff members' exposure to radiation, they wear radiation badges that detect exposure and lead aprons that shield the body. The radiographic/fluoroscopic system may be equipped with movable lead shields that do not interfere with access to the patient and are placed between staff members and the source of radiation during the procedure.

Morbidity and mortality rates

As with all invasive procedures, cardiac catheterization involves some risks. The most serious complications include stroke and myocardial infarction. Other complications include cardiac arrhythmias, pericardial tamponade, vessel injury, and renal failure. One study demonstrated a total risk of major complications under 2% for all patients. The risk of death from cardiac catheterization has been demonstrated at 0.11%. The most common complications resulting from cardiac catheterization are vascular related, including external bleeding at the arterial puncture site, hematomas, and pseudoaneurysms.

The patient may be given anticoagulant medications to lower the risk of developing an arterial blood clot (thrombosis) or of blood clots forming and traveling through the body (embolization).

The risk of complications from cardiac catheterization is higher in patients over the age of 60; those who have severe heart failure; or those with advanced valvular disease.

Allergic reactions related to the contrast agent (dye) and anesthetics may occur in some patients during cardiac catheterization. Allergic reactions may range from minor hives and swelling to severe shock. Patients with allergies to seafood or penicillin are at a higher risk of allergic reaction; giving antihistamines prior to the procedure may reduce the occurrence of allergic reactions to contrast agents.

Normal results

Normal findings from a cardiac catheterization will indicate no abnormalities in the size or configuration of the heart chamber, the motion or thickness of its walls, the direction of blood flow, or motion of the valves. Smooth and regular outlines indicate normal structure of the coronary arteries.

The measurement of intracardiac pressures, or the pressure in the heart's chambers and vessels, is an essential part of the catheterization procedure. Pressure readings that are higher than normal are significant for a patient's overall diagnosis. Pressure readings that are lower, other than those resulting from shock, are usually not significant.

The ejection fraction is also determined by performing a cardiac catheterization. The ejection fraction is a comparison of the quantity of blood ejected from the heart's left ventricle during its contraction phase with the quantity of blood remaining at the end of the left ventricle's relaxation phase. The cardiologist will look for a normal ejection fraction reading of 60–70%.

Abnormal results are obtained by viewing the still and live motion x rays during cardiac catheterization for evidence of coronary artery disease, poor heart function, disease of the heart valves, and septal defects.

The most prominent sign of coronary artery disease is narrowing or blockage (stenosis) in the coronary arteries, with narrowing greater than 50% considered significant. A clear indication for intervention by angioplasty or surgery is a finding of significant narrowing of the left main coronary artery and/or blockage or severe narrowing in the high left anterior descending coronary artery.

A finding of impaired wall motion is an additional indicator of coronary artery disease, an aneurysm, an enlarged heart, or a congenital heart problem. Using an ejection fraction test that measures wall motion, cardiologists regard an ejection fraction reading under 35% as increasing the risk of complications while also decreasing the possibility of a successful long- or short-term outcome from surgery.

Detecting the difference in pressure above and below the heart valve can verify the presence of valvular disease. The greater the narrowing, the higher the difference in pressure.

To confirm the presence of septal defects, measurements are taken of the oxygen content on both the left and right sides of the heart. The right heart pumps unoxygenated blood to the lungs, and the left heart pumps blood containing oxygen from the lungs to the rest of the body. Elevated oxygen levels on the right side indicate the presence of a left-to-right atrial or ventricular shunt . Low oxygen levels on the left side indicate the presence of a right-to-left shunt.

Alternatives

Other methods of visualization are available that limit radiation exposure, by using ultrasound imaging to observe the coronary arteries. Imaging of general cardiac architecture and valvular function can be visualized by noninvasive cardiac ultrasound. Cardiac ultrasound and Doppler ultrasound can be used together to observe valvular insufficiency and stenosis. Areas of poor myocardial function can also be evaluated by ultrasound.

Nuclear medicine scans of the heart can show the perfusion of blood to a region of the myocardium. If blockages of the coronary artery exist, blood flow will be reduced. By adding a radioactive marker to the blood, images are generated to show areas of poor perfusion. Combined with exercise, these tests can accurately demonstrate cardiovascular disease. However, the imaging process can take several hours, and the patient is still internally exposed to high levels of radiation.

Resources

books

Bennett, J. Claude, and Fred Plum, eds. "Cardiac Catheterization and Angiography." In Cecil Textbook of Medicine. 20th ed. Vol. 1. Philadelphia: W. B. Saunders Company, 1996.

"Diagnostic Cardiovascular Procedures: Invasive Procedures." In The Merck Manual of Diagnosis and Therapy , 17th ed, Ed. Mark H. Beers, and Robert Berkow. Whitehouse Station, NJ: Merck Research Laboratories, 1999.

Segen, Joseph C., and Joseph Stauffer. "Cardiac Catheterization." In The Patient's Guide To Medical Tests: Everything You Need To Know About The Tests Your Doctor Prescribes. New York: Facts On File, Inc., 1998.

periodicals

Norris, Teresa G. "Principles of Cardiac Catheterization." Radiologic Technology 72, no. 2 (November-December 2000): 109–136.

Scanlon, Patrick J, et al. ACC/AHA Guidelines for Coronary Angiography 33, no. 6 (May 1999): 1756–1824.

Segal, A. Z., et al. "Stroke as a Complication of Cardiac Catheterization: Risk Factors and Clinical Features." Neurology 56 (April 2001): 975–977.

organizations

American College of Cardiology. Heart House, 9111 Old Georgetown Road, Bethesda, MD 20814-1699. (800) 253-4636. http://www.acc.org .

American Heart Association National Center. 7272 Greenville Avenue, Dallas, TX 75231. (800) AHA-USA1. http://www.americanheart.org .

other

Cardiology Channel. Cardiac Catheterization. http://www.cardiologychannel.com/cardiaccath/ .

Jennifer E. Sisk, MA Allison J. Spiwak, MSBME