Understanding those vital tests for your heart
Last week, Part 1 of this article discussed some of the important heart tests you should know about. These included blood tests, ECG, echocardiogram, and stress tests. Today, we will tackle the more complicated examinations like echocardiography, coronary angiogram, cardiac nuclear scan, cardiac CT scan, and cardiac magnetic resonance imaging.
Echocardiogram
An echocardiogram is an ultrasound of your heart and blood vessels. It’s a commonly used test that allows your doctor to see how well your heart is beating and pumping blood. It can be used to identify abnormalities in the heart muscle and valves as well as identify part of your heart muscle that has been damaged and weakened by a heart attack. An echocardiogram can also check the pumping function of your heart and fluid buildup around the heart.
The test uses ultrasound technology to generate detailed images of your heart’s structure and function. A device called transducer, which is gently pressed against your chest, transmits sound waves and collects the echoes reflected off tissues and fluids in your body. A computer uses this information from the transducer to create moving images on a video monitor (see illustration on Page D-2).
If more detailed views of your heart are necessary, your doctor may recommend a transesophageal echocardiogram. In this procedure, a flexible tube containing a transducer is guided down your throat and into your esophagus. From there, the transducer can obtain more detailed images of your heart. Your throat will be numbed, and you’ll have medications to make you relax. Sometimes, an echocardiogram is used in conjunction with a stress test, so your doctor can observe your heart function as it’s made to work harder during exercise or after administering a medication to make the heart work harder.
Coronary angiogram
If blood and ECG tests strongly suggest that your symptoms are caused by an urgent problem with the blood vessels that feed your heart (coronary arteries), a procedure called coronary angiogram can:
• Pinpoint where blockages are located in your coronary arteries.
• Show how many of your coronary arteries are blocked or narrowed by fatty plaques (atherosclerosis).
• Show how much blood flow is blocked through these blood vessels.
• Check the results of previous coronary bypass surgery.
• Check the blood flow through your heart and blood vessels.
During a coronary angiogram, a short tube (sheath) is inserted into a blood vessel in your groin or arm. A hollow, flexible, and longer tube (guide catheter) is then inserted into the sheath. Aided by x-ray images on a monitor, your doctor threads the guide catheter through the artery to reach your heart and its coronary arteries. This procedure is called cardiac catheterization.
With the catheter in place, your doctor also can measure pressures in your heart chambers and inject a special dye into the heart. The dye sharpens what can be seen in the monitor. A series of X-rays are taken while the dye flows through your blood vessels and heart. This helps your doctor to see how well the blood is flowing and to check for blockages, narrowed areas, and other abnormalities.
If necessary, your doctor can perform procedures to open up a blocked or narrowed artery, such as angioplasty or stent placement, during your coronary angiogram. The necessary tools are passed through the catheter used to inject the dye. Also, doctors can sometimes use the procedure to repair or replace damaged heart valves, eliminating the need for open-heart surgery.
Cardiac nuclear scan
Your doctor may request a cardiac nuclear scan if you’re having chest pains and your blood test and ECG results are inconclusive. This imaging test, which is often combined with a stress test, allows your doctor to see blood flow patterns to reveal clogged coronary arteries in detail and assess the efficiency of your heart’s pumping action.
During the test, a small amount of radioactive substance (tracer) is injected through an intravenous (IV) line into a vein in your arm or hand. After your body has absorbed the tracer, you lie on a table while a series of images is taken of your heart and blood vessels.
Pictures are usually taken while you’re at rest and after you’ve exercised — or after you’ve taken a medication to make your heart work harder — to see how your heart reacts to physical activity. The total time for the procedure is usually between two and four hours. If the test results are normal, this helps your doctor rule out coronary artery disease as a cause of your symptoms and may eliminate your need for hospitalization.
The test is typically performed using a type of imaging technology called single-photon emission computerized tomography (SPECT). A special gamma camera rotates around you, taking the pictures. The pictures are sent to a computer that uses the information to create 3-D images. Sometimes, other imaging techniques, such as positron emission tomography (PET) scanning, may be used to take the pictures. The PET scan is one type of nuclear stress test that’s particularly helpful for people who have very large chest sizes.
Some nuclear medicine scanners also have CT functions, which can take anatomic pictures of the heart. Combining nuclear images with CT images can give your doctor information about your heart’s blood flow and its anatomical structure all in one test.
Cardiac computerized Tomography scan
Cardiac computerized tomography (CT) scans can show the size and function of your heart muscle and check for certain valve problems. It can also be used to check the health of your arteries. For the test, you lie on a table inside a doughnut-shaped machine. An x-ray tube inside the machine rotates around your body and collects detailed images of your heart and chest.
A cardiac CT scan may be used to measure the amount of calcium in the walls of your coronary arteries. This is sometimes called a heart scan or coronary calcium scan, the results of which are expressed as a coronary calcium score. The calcium may be an early sign of coronary artery disease.
A coronary CT angiogram (CTA) is sometimes used in place of a traditional coronary angiogram to check for blocked or narrowed arteries. The advantage of a CTA is that no catheter has to be placed in your groin, and the dye that’s visible on the CT scan is injected through an IV line that’s placed in a vein in your hand or arm. CT images are taken while the dye flows through your blood vessels to your heart.
The disadvantage of this approach is that if a blockage in an artery is found, you’ll need a separate procedure (a traditional coronary angiogram) in order to fix the blockage. The type of dye used for a CTA is iodine-based. If you’re allergic to iodine or having kidney problems so that your kidneys can’t process the iodine correctly, your doctor may request a different imaging test.
Cardiac magnetic resonance imaging
Another way to look at the heart is using magnetic resonance imaging (MRI). This technique offers a movie-like imaging of the cardiovascular system. The scans are helpful in diagnosing unexplained heart failure, checking inflammation of the heart (myocarditis), and monitoring congenital heart disease. Cardiac MRI can also be used to evaluate coronary blood flow to the heart muscle and assess damage resulting from a heart attack. The images produced with MRI tend to be clearer and more detailed than with other imaging techniques, but you must lie very still. The procedure also takes longer than other imaging tests.
For cardiac MRI, you lie on a table inside a long tube-like machine that produces a very strong magnetic field. The magnetic field aligns atomic particles in some of your cells. Radio waves sent towards these particles are reflected back, as they produce signals that vary according to the type of tissue. These signals are converted to MRI images of your heart by a computer attached to the scanner.
Similar to CT angiography, MRI can be used together with an injected dye to assess blood flow to your heart (magnetic resonance angiography, or MRA). The dye used in MRA is usually gadolinium-based and, as such, may be an alternative to the CTA if you’re allergic to iodine. MRA doesn’t require catheterization either. The dye is injected intravenously through a vein in your arm or hand. However, gadolinium-based dyes aren’t recommended for those with significant kidney dysfunction.
Hearty news
Once you have completed all the various tests that your doctor has recommended, he will have a better picture of your overall heart health. Your doctor will then be able to plan out the most appropriate treatment program for you.
It is hoped that this two-part series on cardiovascular examinations has afforded you a good inside look at your heart and blood vessels and has given you a better understanding of the various tests used today to study the status and function of your heart.
