There are many diagnostic procedures that can help doctors make a rapid, precise diagnosis. They include electrocardiography (ECG), stress testing, electrophysiologic testing, tilt table testing, radiologic procedures (x-rays), ultrasonography (including echocardiography), magnetic resonance imaging (MRI), radionuclide imaging, positron emission tomography (PET), cardiac catheterization, central venous catheterization, angiography, and computed tomography (CT). Fluoroscopy is used infrequently. Blood tests to measure levels of sugar (to test for diabetes), cholesterol, and other substances are often performed.
Most of these procedures carry very small risk, but the risk increases with the complexity of the procedure and the severity of the heart disorder.
Electrocardiography is a quick, simple, painless procedure in which the heart's electrical impulses are amplified and recorded on a piece of paper. This record, the electrocardiogram (ECG), provides information about the part of the heart that triggers each heartbeat (the pacemaker), the nerve conduction pathways of the heart, and the rate and rhythm of the heart.
Usually, an ECG is obtained if a heart disorder is suspected. It is also obtained as part of a routine physical examination for most middle-aged and older people, even if they have no evidence of a heart disorder. It can be used as a basis of comparison with later ECGs if a heart disorder develops.
|ECG: Reading the Waves
An electrocardiogram (ECG) represents the electrical current moving through the heart during a heartbeat. The current's movement is divided into parts, and each part is given an alphabetic designation in the ECG.
Each heartbeat begins with an impulse from the heart's pacemaker (sinus or sinoatrial node). This impulse activates the upper chambers of the heart (atria). The P wave represents activation of the atria.
Next, the electrical current flows down to the lower chambers of the heart (ventricles). The QRS complex represents activation of the ventricles.
The electrical current then spreads back over the ventricles in the opposite direction. This activity is called the recovery wave, which is represented by the T wave.
Many kinds of abnormalities can often be seen on an ECG. They include a previous heart attack (myocardial infarction), an abnormal heart rhythm (arrhythmia), an inadequate supply of blood and oxygen to the heart (ischemia), and excessive thickening (hypertrophy) of the heart's muscular walls.
Certain abnormalities seen on an ECG can also suggest bulges (aneurysms) that develop in weak areas of the heart's walls. Aneurysms may result from a heart attack. If the rhythm is abnormal (too fast, too slow, or irregular), the ECG may also indicate where in the heart the abnormal rhythm starts. Such information helps doctors begin to determine the cause.
To obtain an ECG, an examiner places electrodes (small round sensors that stick to the skin) on the person's arms, legs, and chest. These electrodes measure the magnitude and direction of electrical currents in the heart during each heartbeat. The electrodes are connected by wires to a machine, which produces a record (tracing) for each electrode. Each tracing shows the electrical activity of the heart from different angles. The tracings constitute the ECG. ECG takes about 3 minutes, is painless, and has no risks.
Exercise Stress Testing
Testing the heart during exercise can help identify coronary artery disease. In coronary artery disease, blood flow through the coronary arteries (which supply blood to the heart muscle) is partly or completely blocked. If the coronary arteries are only partly blocked, the heart may have an adequate blood supply when the person is resting but not when the person exercises. Thus, testing the heart during exercise can help identify coronary artery disease. Because exercise stress testing specifically monitors how the heart is functioning, the testing helps doctors distinguish between problems due to a heart disorder and those due to other problems that limit exercise, such as lung disorders, anemia, and poor general fitness.
Exercise testing has two components. Exercise or a drug is used to stress the heart, making it beat faster, and the person is tested for signs of inadequate blood flow to the heart. The person is also monitored for symptoms that suggest coronary artery disease, such as low blood pressure, shortness of breath, and chest pain.
To stress the heart, most people walk on a treadmill or pedal an exercise bicycle. People who cannot use their legs can use an arm crank. Gradually, the pace of the exercise and the force required to do it (workload) are increased. The ECG is monitored continuously, and blood pressure is measured at intervals. Usually, the person being tested is asked to keep going until the heart rate reaches between 80% and 90% of the maximum for age and sex. If symptoms, such as shortness of breath or chest pain, become too uncomfortable or if significant abnormalities appear on the ECG or blood pressure recordings, the test is stopped sooner. Testing takes about 30 minutes. Exercise stress testing has a small risk; the chance of its causing a heart attack or death is 1 in 5,000.
People who cannot exercise can be evaluated using pharmacologic stress testing. For this procedure, a drug, such as dipyridamole, dobutamine, or adenosine, is injected to simulate the effects of exercise on blood flow.
Most commonly in stress testing, ECG is used to check for reduced blood flow in coronary arteries. Sometimes more accurate but more expensive tests, such as echocardiography and radionuclide imaging, are performed as part of stress testing (see Diagnosis of Heart and Blood Vessel Disorders: Radionuclide Imaging).
No test is perfect. Sometimes, these tests show abnormalities in people who do not have coronary artery disease (a false-positive result), and sometimes tests do not show any abnormalities in people who have the disease (a false-negative result). In people without symptoms, especially younger people, the likelihood of coronary artery disease is low, despite an abnormal test result. In such cases, a positive result is usually more likely to be false than true. These false-positive results may cause considerable worry and medical expense. For these reasons, most experts discourage routine exercise stress testing (such as for screening purposes before an exercise program is begun or during an evaluation for life insurance) in people who do not have symptoms.
Continuous Ambulatory Electrocardiography
Abnormal heart rhythms and inadequate blood flow to the heart muscle may occur only briefly or unpredictably. To detect such problems, doctors may use continuous ambulatory ECG, in which the ECG is recorded continuously for 24 hours while the person engages in normal daily activities.
For this procedure, the person wears a small battery-powered device (Holter monitor) held on with a shoulder strap. The monitor detects the heart's electrical activity through electrodes attached to the chest and records the ECG. While wearing the monitor, the person notes in a diary the time and type of any symptoms. Subsequently, the ECG is run through a computer, which analyzes the rate and rhythm of the heart, looks for changes in electrical activity that could indicate inadequate blood flow to the heart muscle, and produces a record of every heartbeat during the 24 hours. Symptoms recorded in the diary can then be correlated with changes in the ECG.
If necessary, the ECG can be transmitted by telephone to a computer at the hospital or doctor's office for an immediate reading as soon as symptoms occur.
An event monitor is used when a person must be monitored longer than 24 hours. It is similar to a Holter monitor, but it records only when the user activates it—that is, when symptoms occur. If symptoms occur so rarely that they cannot be captured during 24-hour monitoring, an event monitor may be placed under the skin for up to a year. A small magnet is used to activate this monitor.
Continuous Ambulatory Blood Pressure Monitoring
If the diagnosis of high blood pressure is in doubt (for example, if the measurements taken in the office vary too much), a 24-hour blood pressure monitor may be used. The monitor is a portable battery-operated device, worn on the hip, connected to a blood pressure cuff, worn on the arm. This monitor repeatedly records blood pressure throughout the day and night over a 24- or 48-hour period. The readings determine not only whether high blood pressure is present but also how severe it is.
Electrophysiologic testing is used to evaluate serious abnormalities in heart rhythm or electrical conduction. Testing is performed in the hospital. After injecting a local anesthetic, a doctor inserts a catheter with tiny electrodes at its tip through an incision, usually in the groin, into a vein or sometimes an artery. The catheter is threaded through the major blood vessels into the heart chambers, using fluoroscopy (a continuous x-ray procedure) for guidance. The catheter is used to record the ECG from within the heart and to identify the precise location of the electrical conduction pathways.
Usually, a doctor intentionally provokes an abnormal heart rhythm during testing to find out whether a particular drug can stop the disturbance or whether an operation will help by eliminating abnormal electrical connections within the heart. If necessary, a doctor can quickly restore a normal rhythm with a brief electrical shock to the heart (cardioversion). Although electrophysiologic testing is an invasive procedure and an anesthetic is required, the procedure is very safe: The risk of death is 1 in 5,000. This procedure usually takes 1 to 2 hours.
Tilt Table Testing
Tilt table testing is usually recommended for people who experience fainting (syncope) for an unknown reason and who do not have a structural heart disorder (such as aortic valve stenosis). Typically, a person is tilted at a 60° to 80° angle on a motorized table for 15 to 20 minutes while blood pressure and heart rate are continuously monitored. If blood pressure does not decrease, the person is given isoproterenol (a drug that stimulates the heart) intravenously in a dose large enough to accelerate the heart rate by 20 beats per minute, and the test is repeated. The procedure produces many false-positive results; that is, it often appears to indicate a heart disorder when none is present. This procedure takes 30 to 60 minutes and is very safe.
Anyone thought to have a heart disorder has chest x-rays taken from the front and the side (see Common Imaging Tests: Plain X-Rays). The x-rays show the shape and size of the heart and outline blood vessels in the lungs and chest. Abnormal heart shape or size and abnormalities such as calcium deposits within heart tissue are readily seen. Chest x-rays also can detect information about the condition of the lungs, particularly whether blood vessels in the lungs are abnormal and whether there is fluid in or around the lungs.
X-rays can detect enlargement of the heart, which is often due to heart failure or a heart valve disorder. The heart does not enlarge when heart failure results from constrictive pericarditis, in which scar tissue forms throughout the sac that envelops the heart (pericardium).
The appearance of blood vessels in the lungs is often more useful in making a diagnosis than the appearance of the heart itself. For instance, enlargement of the pulmonary arteries (the arteries that carry blood from the heart to the lungs) and narrowing of the arteries within the lung tissue suggest high blood pressure in the pulmonary arteries, which may lead to thickening of the muscle of the right ventricle (the lower heart chamber that pumps blood through the pulmonary arteries to the lungs). X-rays of other parts of the body may be taken to detect blockages in other blood vessels.
Spiral (helical) computed tomography (CT) may be used to detect structural abnormalities of the heart, the sac that envelops the heart (pericardium), major blood vessels, lungs, and supporting structures in the chest. Typically, a dye that can be seen on x-rays (radiopaque dye or contrast agent) is injected into the person's vein. The person is asked not to breathe during a scan so that the image will not be blurred.
Newer electron beam CT, previously called ultrafast or cine-computed tomography, is used mainly to detect calcium deposits in arteries that supply blood to the heart (coronary arteries), an early sign of coronary artery disease. This type of scanning is not widely available.
Computed tomography angiography (CTA—see Diagnosis of Heart and Blood Vessel Disorders: Angiography of Peripheral Blood Vessels) is a type of CT that is used to produce three-dimensional images of the major arteries of the body, except the coronary arteries. The images are similar in quality to those produced by conventional angiography (see Common Imaging Tests: Computed Tomography). CTA can be used to detect narrowing of the arteries supplying organs and aneurysms and tears in major arteries. CTA can also detect clots that have broken off within an artery, traveled through the bloodstream, and lodged in the small arteries of the lungs (pulmonary emboli).
Unlike conventional angiography, CTA is not an invasive procedure. The radiopaque dye is injected into a vein rather than into an artery as in angiography. CTA usually takes less than 1 to 2 minutes.
Fluoroscopy is a continuous x-ray procedure that shows the heart beating and the lungs inflating and deflating on a screen. However, fluoroscopy, which involves a relatively high dose of radiation, has been largely replaced by echocardiography and other procedures. Fluoroscopy is still used as a component of cardiac catheterization and electrophysiologic testing.
Echocardiography and Other Ultrasound Procedures
Ultrasonography (see Common Imaging Tests: Ultrasonography) uses high-frequency (ultrasound) waves bounced off internal structures to produce a moving image. It uses no x-rays. Ultrasonography of the heart (echocardiography) is one of the most widely used procedures for diagnosing heart disorders because it is noninvasive, harmless, relatively inexpensive, and widely available and because it provides excellent images. Ultrasonography is also used in the diagnosis of disorders affecting blood vessels in other parts of the body.
Echocardiography can be used to detect abnormalities in heart wall motion and to measure the volume of blood being pumped from the heart with each beat. This procedure can also detect abnormalities in the heart's structure, such as defective heart valves, birth defects, and enlargement of the heart's walls or chambers, as occurs in people with high blood pressure, heart failure, or impairment of the heart's muscular walls (cardiomyopathy). Echocardiography can also be used to detect pericardial effusion, in which fluid accumulates between the two layers of the sac that envelops the heart (pericardium), and constrictive pericarditis, in which scar tissue forms throughout the pericardium.
The main types of ultrasonography are M-mode, two-dimensional, Doppler, and color Doppler. In M-mode ultrasonography, the simplest technique, a single beam of ultrasound is aimed at the part of the heart being studied. Two-dimensional ultrasonography, the most widely used technique, produces realistic two-dimensional images in computer-generated "slices." Stacking the slices together can re-create a three-dimensional structure.
Doppler ultrasonography shows the direction and velocity of blood flow and thus can detect turbulent flow due to narrowing or blockage of blood vessels. Color Doppler ultrasonography shows the different rates of blood flow in different colors. Doppler ultrasonography and color Doppler ultrasonography are commonly used to help diagnose disorders affecting the heart and the arteries and veins in the trunk, legs, and arms. Because these procedures can show the direction and rate of blood flow in the chambers and blood vessels of the heart, they enable doctors to evaluate the structure and function of these parts. For example, doctors can determine if the heart valves open and close properly, if and how much they leak when closed, and if blood flows normally. Abnormal connections between an artery and a vein or between heart chambers can also be detected.
The ultrasound waves are emitted by a handheld recording probe (transducer). For echocardiography, the examiner places gel on the chest over the heart and moves the probe over that area. The probe is connected to a monitor that displays an image. The image is recorded on a videocassette, a computer disk, or paper. By varying the placement and angle of the probe, doctors can view the heart and nearby major blood vessels from various angles and thus get an accurate picture of heart structure and function. Echocardiography is painless and takes 20 to 30 minutes.
If doctors need to obtain greater clarity or to analyze the aorta or structures at the back of the heart (particularly the left atrium or left ventricle), transesophageal echocardiography can be used. For this procedure, a probe is passed down the person's throat into the esophagus and stomach. The probe records signals from just behind the heart. Transesophageal echocardiography is also used when regular echocardiography is difficult to perform because of obesity, lung disorders, or other technical problems.
Magnetic Resonance Imaging
With magnetic resonance imaging (MRI—see Common Imaging Tests: Magnetic Resonance Imaging), a powerful magnetic field and radio waves are used to produce detailed images of the heart and chest. This expensive and sophisticated procedure is used predominantly for the diagnosis of complex heart disorders that are present at birth (congenital) and to differentiate between normal and abnormal tissue.
MRI has some disadvantages. It takes longer to produce MRI images than computed tomography (CT) images. Because of the movement of the heart, the images obtained with MRI are fuzzier than those obtained with CT. However, newer MRI scans that are timed to match specific parts of the ECG (called gated MRI) are much clearer than conventional MRI scans.
Magnetic resonance angiography (MRA) is a type of MRI that focuses on blood vessels rather than organs. MRA produces images of blood vessels and blood flow similar in quality to those produced by conventional angiography but is not an invasive procedure (see Diagnosis of Heart and Blood Vessel Disorders: Angiography of Peripheral Blood Vessels). MRA can be used to detect bulges (aneurysms) in the aorta, narrowing of the arteries supplying the kidneys (renal stenosis), and a narrowing or blockage in the arteries that supply blood to the heart (coronary arteries) or the arms and legs (peripheral arteries).
In radionuclide imaging (see Common Imaging Tests: Radionuclide Scanning), a tiny amount of a radioactive substance (radionuclide), called a tracer, is injected into any vein. The amount of radiation the person receives is tiny—less than that produced by most x-rays. The tracer emits gamma rays, which are detected by a gamma camera. A computer analyzes this information and constructs an image to show the different amounts of tracer taken up by tissues.
Radionuclide imaging of the heart is particularly useful in the diagnosis of chest pain when the cause is unknown. If the coronary arteries are narrowed, radionuclide imaging is used to learn how the narrowing is affecting the heart's blood supply and function. Radionuclide imaging is also used to assess improvement in blood supply to the heart muscle after bypass surgery or similar procedures and may be used to help determine a person's prognosis after a heart attack.
Different tracers are used depending on which disorder is suspected. For evaluating blood flow through heart muscle, the tracers typically used are technetium-99 sestamibi or thallium-201, and images are obtained after the person has an exercise stress test (see Diagnosis of Heart and Blood Vessel Disorders: Exercise Stress Testing). The amount of tracer absorbed by the heart muscle cells depends on the blood flow. At peak exercise, an area of heart muscle that has an inadequate blood supply (ischemia) absorbs less tracer—and produces a fainter image—than neighboring muscle with a normal supply. In people unable to exercise, an intravenous injection of a drug, such as dipyridamole, dobutamine, or adenosine, may be used to simulate the effects of exercise on blood flow. These drugs divert the blood supply from abnormal to normal blood vessels, depriving the area with inadequate blood flow even further.
After the person rests for a few hours, a second scan is performed, and the resulting image is compared with that obtained during exercise. Doctors can then distinguish areas of the heart where inadequate blood flow is reversible (usually caused by narrowing of the coronary arteries) from areas where it is irreversible (usually caused by scarring due to a previous heart attack).
If a heart attack may have occurred very recently, technetium-99m is used instead of thallium-201. With technetium, damage due to a heart attack can be detected after 12 to 24 hours and up to about 1 week. Unlike thallium, which accumulates primarily in normal tissue, technetium accumulates primarily in abnormal tissue. However, because technetium also accumulates in bone, the ribs somewhat obscure the image of the heart.
A specialized type of radionuclide imaging called single-photon emission computed tomography (SPECT) can produce a series of computer-enhanced cross-sectional images. A three-dimensional image can also be produced. SPECT provides more information about function, blood flow, and abnormalities than does conventional radionuclide imaging.
Positron Emission Tomography
In positron emission tomography (PET—see Common Imaging Tests: Positron Emission Tomography), a substance necessary for heart cell function (such as oxygen or sugar) is labeled with a radioactive substance (radionuclide) that gives off positrons (electrons with a positive charge). The labeled nutrient is injected into a vein and reaches the heart in a few minutes. PET is used to determine how much blood is reaching different parts of the heart muscle and how different parts of the heart muscle process (metabolize) various substances. For example, when labeled sugar is injected, doctors can determine which parts of the heart muscle have an inadequate blood supply because those parts use more sugar than normal.
PET scans produce clearer images than do other radionuclide procedures. However, the procedure is very expensive and not widely available. It is used in research and in cases in which simpler, less expensive procedures are inconclusive.
Cardiac Catheterization and Coronary Angiography
Cardiac catheterization used with coronary angiography is the most accurate method of diagnosing coronary artery disease. Used together, the two procedures are the only way to directly measure the pressure of blood in each chamber of the heart and to obtain an image of the interior of coronary arteries. These procedures are performed to determine whether angioplasty or coronary artery bypass surgery is technically feasible. They may be performed to confirm the diagnosis of other heart disorders, to determine the severity of a heart disorder, or to detect the cause of worsening symptoms.
More than a million cardiac catheterizations and angiographic procedures are performed every year. They are relatively safe, and complications are rare. With cardiac catheterization and angiography, the chance of a serious complication—such as stroke, heart attack, or death—is 1 in 1,000. Fewer than 0.01% of people undergoing these procedures die; most of those who die already have a severe heart disorder or other disorder. The risk of complications and death is increased for older people.
Cardiac catheterization is used extensively for the diagnosis and treatment of heart disorders that are not due to disease of the coronary arteries. Cardiac catheterization can be used to measure how much blood the heart pumps out per minute (cardiac output) and to detect birth defects of the heart and tumors, such as a myxoma.
In cardiac catheterization, a thin catheter (a tubular, flexible surgical instrument) is inserted into an artery or vein through a puncture made with a needle or a tiny incision. A local anesthetic is given to numb the insertion site. The catheter is then threaded through the major blood vessels and into the heart chambers. The procedure is performed in the hospital and takes 40 to 60 minutes.
Various instruments may be placed at the tip of the catheter. They include instruments to measure the pressure of blood in each heart chamber and in blood vessels connected to the heart, to view or take ultrasound images of the interior of blood vessels, to take blood samples from different parts of the heart, or to remove a tissue sample from inside the heart for examination under a microscope (biopsy).
When a catheter is used to inject a dye that can be seen on x-rays, the procedure is called angiography. When a catheter is used to widen a narrowed heart valve opening, the procedure is called valvuloplasty. When a catheter is used to clear a narrowed or blocked artery, the procedure is called angioplasty (see Understanding Percutaneous Coronary Intervention (PCI)).
If an artery is used for catheter insertion, the puncture or incision site must be steadily compressed for 10 to 20 minutes after all the instruments are removed. Compression prevents bleeding and bruise formation. However, bleeding occasionally occurs at the incision site, leaving a large bruise that can persist for weeks but that almost always goes away on its own.
Because inserting a catheter into the heart may cause abnormal heart rhythms, the heart is monitored with electrocardiography (ECG). Usually, doctors can correct an abnormal rhythm by moving the catheter to another position. If this maneuver does not help, the catheter is removed. Very rarely, the heart wall is damaged or punctured when a catheter is inserted; immediate surgical repair may be required.
Cardiac catheterization may be performed on the right or left side of the heart.
Catheterization of the right side of the heart is performed to obtain information about the heart chambers on the right side (right atrium and right ventricle) and the tricuspid valve (located between these two chambers). The right atrium receives oxygen-depleted blood from the body, and the right ventricle pumps the blood into the lungs, where blood takes up oxygen and drops off carbon dioxide. In this procedure, the catheter is inserted into a vein, usually in an arm or the groin. Pulmonary artery catheterization (see Diagnosis of Heart and Blood Vessel Disorders: Pulmonary Artery Catheterization), in which the balloon at the catheter's tip is passed through the right atrium and ventricle and lodged in the pulmonary artery, is sometimes performed during certain major operations and in intensive care units.
Catheterization of the left side is performed to obtain information about the heart chambers on the left side (left atrium and left ventricle), the mitral valve (located between the left atrium and left ventricle), and the aortic valve (located between the left ventricle and the aorta). The left atrium receives oxygen-rich blood from the lungs, and the left ventricle pumps the blood into the rest of the body. The left side is catheterized more often than the right. For example, catheterization of the left side is performed when coronary artery disease has been detected (to determine the extent of the disease) or is suspected (to confirm the diagnosis). This procedure is usually combined with coronary angiography to obtain information about the coronary arteries.
For catheterization of the left side of the heart, the catheter is inserted into an artery, usually in an arm or the groin. Less commonly, the catheter is inserted into a vein in the groin and threaded into the right side of the heart (as in catheterization of the right side). The catheter is then threaded into the left side by puncturing the wall (septum) separating the right atrium from the left.
Coronary Angiography ():
This procedure provides information about the coronary arteries, which supply the heart with oxygen-rich blood. Coronary angiography is similar to catheterization of the left side of the heart, and the two procedures are almost always performed at the same time. After injecting a local anesthetic, a doctor inserts a thin catheter into an artery through an incision in an arm or the groin. The catheter is threaded toward the heart, then into the coronary arteries. During insertion, the doctor uses fluoroscopy (a continuous x-ray procedure) to observe the progress of the catheter as it is threaded into place. After the catheter tip is in place, a radiopaque dye, which can be seen on x-rays, is injected through the catheter into the coronary arteries, and the outline of the arteries appears on a video screen and is recorded on a tape or disk. Usually, motion picture techniques that produce continuous images are used; this procedure is then called cineangiography. It provides clear pictures of the heart chambers and coronary arteries as they move.
Coronary angiography is seldom uncomfortable and usually takes 30 to 50 minutes. It is performed as an outpatient procedure unless the person is very ill.
When the radiopaque dye is injected into the aorta or heart chambers, the person has a temporary feeling of warmth throughout the body as the dye spreads through the bloodstream. The heart rate may increase, and blood pressure may fall slightly. Rarely, the dye causes the heart to slow briefly or even stop. The person may be asked to cough vigorously during the procedure to help correct such problems, which are rarely serious. Rarely, mild complications, such as nausea, vomiting, and coughing, occur. Serious complications, such as shock (see Shock), seizures, kidney problems, and sudden cessation of the heart's pumping (cardiac arrest), are very rare. Allergic reactions to the dye range from skin rashes to a rare life-threatening reaction called anaphylaxis (see Allergic Reactions and Other Hypersensitivity Disorders: Anaphylactic Reactions). The team performing the procedure is prepared to treat the complications of coronary angiography immediately.
Risk of complications is higher in older people, although it is still low. Coronary angiography is essential when angioplasty or coronary artery bypass surgery is being considered (see Coronary Artery Disease: Percutaneous Coronary Intervention).
Ventriculography is a type of angiography in which x-rays are taken as a radiopaque dye is injected into the left or right ventricle of the heart through a catheter. It is performed during cardiac catheterization. With this procedure, doctors can see the motion of the left or right ventricle and can thus evaluate the pumping ability of the heart. Based on the heart's pumping ability, doctors can calculate the ejection fraction (the percentage of blood pumped out by the left ventricle with each heartbeat). Evaluation of the heart's pumping helps determine how much of the heart has been damaged.
Pulmonary Artery Catheterization
Pulmonary artery catheterization is a useful measure of overall heart function in people who are critically ill, particularly when fluids are being given intravenously. Such people include those who have severe heart or pulmonary disorders (such as heart failure, heart attack, abnormal heart rhythms, or pulmonary embolism when these disorders are accompanied by complications), those who have just undergone heart surgery, those who are in shock (see Shock), and those who have severe burns.
Pulmonary artery catheterization is also performed to measure pressure in the right heart chambers and to estimate pressure in the left heart chambers, the amount of blood the heart pumps per minute (cardiac output), resistance to blood flow in the arteries that carry blood from the heart (peripheral resistance), and the volume of blood. This procedure can provide useful information about cardiac tamponade (see Cardiac Tamponade: The Most Serious Complication of Pericarditis ) and pulmonary embolism (see Pulmonary Embolism (PE): Pulmonary Embolism).
As in right heart catheterization, a catheter with a balloon at its tip is inserted into a vein, usually in the neck (under the collarbone) or an arm, and is threaded toward the heart. The tip of the catheter may be passed through the superior vena cava or inferior vena cava (the large veins that return blood to the heart from the upper and lower parts of the body) and through the right atrium and right ventricle to the pulmonary artery. The balloon at the catheter's tip is lodged in the pulmonary artery. A chest x-ray is taken or fluoroscopy may be used to make sure the tip is placed correctly.
The balloon is inflated to temporarily block the pulmonary artery, so that pressure in the capillaries of the lungs (pulmonary capillary wedge pressure) can be measured. This measurement is an indirect way to determine pressure in the left atrium. Blood samples can be taken through the catheter, so that the oxygen and carbon dioxide levels in the blood can be measured.
The procedure may cause many complications, but they are usually rare. They include an air pocket between the layers of membranes covering the lungs (pneumothorax), abnormal heart rhythms (arrhythmias), infection, damage or clotting in the pulmonary artery, and injury to an artery or vein.
Central Venous Catheterization
In central venous catheterization, a catheter is inserted into one of the large veins of the neck, upper chest, or groin. This procedure is most often used to give intravenous fluids or drugs when a catheter cannot be inserted into an arm or a leg vein (peripheral intravenous catheter). Central venous catheterization is occasionally used to monitor central venous pressure (pressure in the superior vena cava, the large vein that returns blood to the heart from the upper part of the body). Central venous pressure reflects the pressure in the right atrium when it is filled with blood. This measurement helps doctors estimate whether the person is dehydrated and how well the heart is functioning. But it has largely been replaced by pulmonary artery catheterization.
Angiography of Peripheral Blood Vessels
Angiography of the peripheral arteries (those of the arms, legs, and trunk—except those supplying the heart) is similar to coronary angiography, except the catheter is threaded to the artery being investigated (see Common Imaging Tests: Angiography). Angiography may be done to detect narrowing or blockage of an artery, a bulge (aneurysm) in an artery, or an abnormal channel between an artery and a vein (arteriovenous fistula). Angiography is often done to determine whether angioplasty (Understanding Percutaneous Coronary Intervention (PCI)) or coronary artery bypass grafting (Coronary Artery Bypass Grafting) is needed.
Angiography of the aorta (aortography) can be used to detect abnormalities (such as an aneurysm or a dissection) in the aorta. It can also be used to detect leakage of the valve between the left ventricle and the aorta (aortic regurgitation).
Digital subtraction angiography may be done before selective angiography to detect and visualize problems such as narrowing or blockage of an artery. However, this type of angiography is seldom adequate to determine whether surgery (with or without angioplasty) is needed. Digital subtraction angiography is not used for coronary arteries because it is unnecessary; clear images of these arteries can be obtained when a radiopaque dye is injected directly into a coronary artery.
In digital subtraction angiography, images of arteries are obtained before and after a radiopaque dye is injected, and a computer subtracts one image from the other. Images of tissues other than the arteries (such as bones) are thus eliminated. As a result, the arteries can be seen more clearly, much less dye is required, and the procedure may be safer than standard angiography.
Last full review/revision April 2006 by Paul H. Tanser, MD