|Dr. Dennis W. Kim explains the importance of heart catheterization and other tests in the treatment of congenital heart disease.
If your doctor suspects your child may have been born with a heart defect or have acquired heart disease. in some other way, he or she may refer your child to a pediatric cardiologist.
The pediatric cardiologist may suggest tests to diagnose or rule out congenital (present at birth) or acquired heart disease. In some cases, these tests will be performed by a pediatric interventional cardiologist – a cardiologist with additional training in diagnosing and treating conditions through the use of thin, flexible tubes called catheters that are guided through the body’s arteries and veins. Interventional cardiology procedures are less invasive than surgery, requiring only a small puncture site in the skin.
Common tests that are used in diagnosing heart disease in children are listed below. These same tests are used for adult patients who may have undiagnosed congenital heart disease and for adults who acquire heart disease later in life.
An echocardiogram is a test that uses sound waves to create a moving picture of the heart. The picture can help doctors evaluate the heart’s structures, including the muscles and valves. Doctors may be able to see a hole in the wall that divides the left and right sides of the heart or a deformity of a heart valve, for example. The test allows doctors to see heart functioning such as:
- The motion of the muscular walls in the heart’s lower chambers, which provides insight into the heart’s pumping power;
- The size of heart structures, such as valves and pumping chambers;
- The flow of blood within the heart and blood vessels (which can be seen on a color Doppler echocardiogram). Seeing blood flow helps doctors identify and assess abnormalities;
- Pressure differences between one part of the heart and another based on how quickly blood is flowing.
Echocardiography uses ultrasound waves to make a picture of structures moving inside the heart. These harmless sound waves travel from an instrument, called a transducer, placed on the chest. You cannot hear these sound waves. As the sound waves reflect back from structures in the heart to the transducer, the echocardiogram machine receives and interprets them – and creates a picture of the heart’s internal structures. As the transducer continuously emits ultrasound waves, it also receives continuous feedback from the heart. The result is a picture of the heart muscles, valves and blood vessels in live action motion.
How Is an Echocardiogram Performed?
A gel is applied to the outside of the chest of the patient as he or she lies on a table. An “echo” technician moves the transducer over the child’s chest to collect different “views” of the heart. The test takes around 45 minutes to complete.
Is an Echocardiogram Safe?
There are no known risks associated with echocardiography and ultrasound exposure.
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An electrocardiogram, also called an ECG or EKG, is a quick, painless test that measures the heart’s electrical activity and records any disturbances in heart rhythm. It transforms the heart’s electrical activity into a tracing on paper. These tracings can help determine if the rhythm of the heart is normal and can give clues to if the heart’s chambers are enlarged or under strain. Certain patterns in the ECG may also be associated with certain types of congenital heart disease.
The Heart’s Electrical System
The individual muscle cells of the heart are capable of creating electrical impulses. Together, these individual cells generate the synchronized and rhythmic patterns that result in the coordinated pumping and filling of the heart. Besides the muscle cells, there is specialized tissue that help the electricity pass throughout the heart. Some of this tissue acts as the initiator of the electrical impulses; other tissue acts like electrical wiring to send the impulses between the upper and lower chambers.
The tissue that generates electrical activity is called the sinus node (or sinoatrial node). The sinus node, located high in the heart’s upper right chamber (atrium), generates an electrical impulse each fraction of a second. The impulse travels through the atrial muscles, causing them to contract. It then travels to the AV node (atrioventricular), which is located between the heart’s atria (upper chambers) and the ventricles (lower chambers). The AV node is the gatekeeper that regulates which impulses are passed to the lower chambers. It is typically the only pathway for electrical impulses to travel to the ventricles.
The AV node conducts the electrical impulses more slowly than other nodes to allow time for the ventricles to receive blood from the atria before they contract and send it out of the heart. If the electrical impulses traveling from the atria to the ventricles come early or late, the balance between blood filling the lower chambers and the timing of the heart’s contraction is disturbed. The AV node can prevent some of these extra impulses that may throw off the normal synchronized rhythm between the upper and lower chambers from going through to the lower chambers.
The electrical activity of the heart is very elegant and efficient. Since all heart tissue is capable of creating an electrical impulse, this creates a back-up system should one part of the normal conduction system fail. This is why it is very unusual for the heart to completely stop beating suddenly. If the sinus node were to fail, other areas of the atria can pick up, typically at a slightly slower rate. If that were to fail, specialized tissue in the area between the atria and ventricles will then activate, again usually at a slightly slower rate. If that were to fail, areas within the lower pumping chambers (ventricles) can then create the rhythm.
In some people, extra tissue is present that can function to create a short circuit between the chambers. This may result in the sudden episodic development of abnormally fast heart rates. These are sometimes called accessory pathways. In others, the signals from the top chambers are not passed through to the lower chambers, resulting in what is called heart block. This sometimes will require placement of a pacemaker. Other abnormal rhythms may be generated within the individual heart chambers. These can be detected on an electrocardiogram.
How Is an ECG Performed?
An ECG may be performed at rest or during exercise. During the ECG, small, sticky patches (electrodes) are placed on different areas of the chest and body. Wires leading from the patches to a computer carry a signal that traces the heart’s electrical activity on paper or on a computer. Doctors analyze the ECG to learn more about the heart’s rhythm and condition.
An ECG shows three “waves” of signals.
- The “P” wave indicates the electrical impulse in the upper chambers of the heart.
- The “QRS” wave records electrical activity in the lower chambers.
- The “T” wave reflects the heart’s electrical return to rest.
The shape and size of the waves, the time between each wave and the rate and regularity of beating provide valuable information to doctors. In addition to providing insight into the heart’s rhythm, the ECG helps doctors determine the size of the heart chambers, detect heart muscle damage, and identify abnormal levels of certain electrolytes, such as potassium and calcium, in the blood, which can contribute to abnormal ECG findings.
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| Is your doctor recommending heart catheterization for your child? Dr. James A. Kuo explains some of the reasons why.
A cardiac catheterization is a diagnostic procedure that provides detailed, x-ray pictures of the heart and its blood vessels. The pictures taken with contrast dye during this procedure are called angiograms. Interventional procedures to correct problems that are found can be performed at the same time. A cardiac catheterization is performed by a specially trained cardiologist, called an interventional cardiologist.
These procedures are performed at a hospital in a special room called the catheterization laboratory, or “cath lab.” The cath lab is equipped with an x-ray camera and a TV monitor (screen) on which the cardiologist views the child’s heart and arteries.
A pediatric or adult congenital catheterization procedure typically takes longer than an adult coronary catheterization procedure – generally about 2–3 hours. The patient is given medications for sedation by mouth or by injection prior to starting the procedure. Sometimes, an IV (intravenous line) is placed into a vein in the patient’s arm. The IV allows the patient to receive fluids and medications easily. If your child becomes anxious during the catheterization, he or she will receive more medications to help relax.
The patient may be sedated but awake (in the “twilight”) throughout the procedure or may be completely asleep under general anesthesia, depending on the procedure to be done. After the child has relaxed, the doctor will use a small needle to inject lidocaine, a local anesthetic, to numb the areas where the vessels will be entered. This initial needle prick could be the only discomfort experienced throughout the procedure. The procedure is typically painless. The heart itself does not contain pain receptors.
The femoral vein and artery in the groin – near where the leg bends from the hip – are the vessels doctors most commonly use to insert a catheter (a flexible tube that is smaller than the vessels) and thread it through the vessels to the heart, veins and peripheral arteries to perform the procedure. Sometimes a vein under the collar bone (subclavian vein) or in the neck (internal jugular) is used.
From this “access” point, the catheter is threaded through the veins and arteries to the heart. Because there are no nerves in the arteries, the patient will not feel the catheter or any pain during the catheterization procedure. A wide variety of specialized catheters in different sizes are available to be used for patients of all sizes – from newborn babies to adults.
The x-ray camera helps the physician guide the catheter to the heart. When the catheter is properly positioned, the cardiologist injects a contrast dye (radiographic contrast agent) through the catheter into the heart and its arteries. Most people do not feel the dye injection. However, some may feel a sensation of warmth in the chest, typically lasting only a few seconds. A few may feel lightheaded or nauseous.
When the x-ray beam passes through the dye, the arteries appear in black silhouette on a white background. The x-ray camera records a “movie” of the heart’s pumping chamber and arteries – a movie that can be recorded as a digital image or on 35mm film. This move of the heart provides critical information about the structure and functioning of the child’s heart.
Practical tips can help you know how to prepare your child for a cardiac catheterization and how to care for your child once you leave the hospital:
- Preparing Your Child for a Heart Catheterization
- What to Expect After a Cardiac Catheterization
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A computed tomography (CT) scan is a scan that uses x-rays to take detailed cross-sectional images of the body, including the arteries and beating heart. A contrast dye is injected into a vein. As this dye moves through the heart and blood vessels, the CT scan will take detailed pictures. These pictures can then be used to create a 3-D reconstruction of the heart and major blood vessels. Your doctor can use these images to identify problems with the heart or blood vessels and develop a treatment plan if necessary.
cMRI (cardiac MRI) is a scan that provides pictures of the heart and blood vessels inside the body using a magnetic field and pulses of radio wave energy. Unlike a CT scan, it does not use x-ray radiation. The MRI generates images of the heart and blood vessels, which can help your doctor assess the heart’s structure and function. In addition to providing information on anatomy, cardiac MRI can also provide information on how blood flows through the heart and vessels, how well the heart valves are functioning, how well the heart muscle is being supplied with blood, and if scars have formed within the heart muscle. Some kinds of stress testing can be performed with a cMRI as well. A cMRI scan takes longer to perform than a cardiac CT scan.
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There are different types of “stress tests” that can be used to evaluate the heart. The simplest is an exercise test, which is performed on a treadmill or stationary bicycle for people with suspected or known heart disease. The test records heart rate and blood pressure. Sticky electrodes are attached to the chest, shoulder and hip and are connected to a machine that records heart rate and blood pressure while your child is exercising. An echocardiogram [link to section on Echocardiogram above] may also be performed during and immediately after exercising (stress echocardiogram). Some problems with the heart are not seen when the heart is at a calm, resting state. Exercise testing allows doctors to “work” the heart and evaluate it during times of activity and stress. This is a non-invasive test, meaning nothing is put into the body during the test. Since the purpose of the test is to have your child exercise, it is important to have your child dress appropriately, including comfortable clothes and shoes meant for activity.
Other types of “stress testing” include giving medications by vein while performing an echocardiogram or cardiac MRI to make the heart work harder. Sometimes abnormalities may be more easily identified if the heart is made to intentionally work harder.
Occasionally, cardiac nuclear perfusion testing is performed in children. In this test, a small amount of radioactive compound is injected by vein and pictures of the heart are taken to see how well blood is being provided to the heart itself. These kinds of tests are only ordered after a detailed evaluation by your child’s cardiologist.
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Electrophysiology (EP) Study (Ablation Procedure)
An electrophysiology (EP) study is an invasive test to assess the heart’s electrical pathways. It is used to identify causes of abnormal heart rhythms (arrhythmias) and to provide therapies (called an ablation) to fix abnormalities in the electrical system of the heart.
An EP study is performed in the cardiac catheterization lab in a hospital. In this safe and controlled setting, your doctor intentionally will try to reproduce the abnormal rhythm. Special catheters (thin, flexible tubes) are inserted into the vessels in the leg and neck. These catheters sense the small electrical currents within the heart. Special ablation catheters can heat or freeze the abnormal areas of heart tissue to alter the ability of these areas to create arrhythmias. If successful, many children will no longer need to take medications to control their abnormal heart rhythms after an ablation procedure. Typically, an EP study is performed as an outpatient procedure and children will be able to go home the same day as their procedure.
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Pulse Oximetry Screening
|A pulse oximetry reading, such as the one shown here, indicates the percentage of hemoglobin in the red blood cells that contains oxygen. Normal is over 95%, while babies with heart defects can have saturations from 60% to 94%, or there may be a significant difference between saturations measured in the arms and legs. Babies who have a positive pulse oximetry screening should be evaluated by a pediatric cardiologist.
A pulse oximetry screen is a noninvasive (and painless) test performed on all newborn babies to determine the level of oxygen in their blood. This test uses rays of light of different wavelengths to measure the percent of hemoglobin (the part of blood that carries oxygen) that is filled with oxygen. Normally, a newborn baby should have an oxygen saturation level that is greater than 95%. Screening using pulse oximetry can detect some infants with congenital heart disease who otherwise may go undetected for a while. There are some congenital heart defects that cause a newborn baby to have lower oxygen saturation in the blood after birth. It often can be difficult to determine if a baby has cyanosis (bluish discoloration of the skin due to poor oxygen content of the blood) just by looking at him or her after birth.
How Is a Pulse Oximetry Test Performed?
The pulse oximeter has a lighted probe that is temporarily attached to the baby’s finger, ear lobe, or foot. Once the baby’s finger is attached to the probe (usually by a sticker), the red light of the probe reads the amount of oxygen carried by the blood. The oxygen level is tested in both arms and both feet. In some kinds of congenital heart disease, the numbers can be different in the arms compared to the legs. It also helps to validate the test to do it in all of the extremities. The time required to complete this test is approximately 1 to 5 minutes.
Is Pulse Oximetry Testing Safe?
Yes. There are no known risks associated with pulse oximetry testing. This is not a blood test so it does not require a needle stick. There is no radiation involved with this test as well. It simply temporarily shines a light through the skin to test how much of the blood contains oxygen.
Why Is Pulse Oximetry Testing Important?
Some congenital heart defects do not show signs within the first days or even weeks of life. Sometimes babies with significant congenital heart disease may not have a murmur after birth. Therefore, some babies may not show signs of significant congenital heart disease until after they become very sick. If healthcare providers discover a heart problem before a baby becomes ill, then the baby will have a better chance to do well with any necessary surgeries or procedures. Early diagnosis of the heart problem may also prevent damage to other organs that may occur when a baby becomes sick due to congenital heart disease.
While pulse oximetry screening cannot rule out all forms of congenital heart disease, it is a good starting point for evaluating many serious types of congenital heart defects. In 2011, the U.S. Department of Health and Human Services recommended the pulse oximetry screening should be included in the routine evaluation that all newborn babies undergo before they are discharged from the hospital after birth. More and more states are adopting this test as a routine procedure to be done on all newborn babies before they go home from the hospital.
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