How is supraventricular tachycardia diagnosed?
Diagnosis can usually be confirmed and other causes of a fast heart rate ruled out by using an electrocardiogram (ECG) during an episode of SVT. ECGs trace the rhythm and electrical activity of the heart. They record any abnormal findings in the heart's electrical impulses. Electrodes are placed on the chest, leg and arms and the results are printed on graph paper.
Sometimes a 24-hour ECG is used to show a change in rhythm over time.
Electrocardiograph (ECG): This traces the rhythm and electrical activity of your heart. It is a painless test and takes about five minutes to do. Small metal patches are put on your arms, legs, and chest and are connected to the ECG machine to take a reading. If an ECG is done during an episode of SVT, it can usually confirm the diagnosis and rule out other causes of a fast heart rate. (For example, a small area within a ventricle sometimes triggers a tachycardia. It is important to rule out a 'ventricular tachycardia' as this tends to be more serious than SVT, and has different treatments.)
The ECG between episodes of SVT is usually normal. So, doing an ECG between episodes of symptoms may not be much help. However, if SVT is suspected, you may be asked to wear a small portable ECG recorder. Some types record an ECG continuously over 24 hours. Others are designed so that you can switch it on to record when you have symptoms.
Ambulatory ECG: By the time you reach a medical facility, the symptoms will sometimes have stopped and the ECG will be normal. This is frustrating because an accurate diagnosis depends on capturing the rapid heartbeat on ECG. Ambulatory monitoring solves this problem by monitoring your heart over a period of time, usually 1-2 days. The ambulatory ECG is more likely to document any abnormal heart rhythms that you experience. You wear the monitor device, called a Holter monitor, while you go about your daily activities. You also keep a diary while you are wearing the device. If your health care provider finds any abnormalities on the ECG recording, these will be compared with what you were doing and feeling at the time.
Echocardiogram (ECHO): This is a noninvasive ultrasound examination of your heart. A small handheld device is passed over your chest. It transmits pictures of your heart walls and valves to a television screen. It also measures how well your left ventricle is pumping. The echo is used to screen for any problems in your heart structure, valves, or muscles.
Stress test: The stress test is an ECG done both at rest and while the heart is under stress, usually exercise on a treadmill or exercise bicycle. If you cannot exercise, you will be given a drug that will temporarily "stress" your heart. This test helps in the diagnosis of coronary heart disease, that is, blockage of your coronary arteries by fatty plaques (atherosclerosis). Coronary heart disease prevents your heart from getting enough blood, and this can cause abnormal heart rhythms.
Cardiac catheterization and coronary angiography: If your stress test result is abnormal or if you have chest pain, shortness of breath, or loss of consciousness, you may undergo cardiac catheterization under local anesthesia to assess disease in your heart and heart valves. Angiography is a type of imaging study that uses a dye in the arteries to highlight blockages and damage.
Electrophysiologic study: You may need this test if you have rapid heartbeat but your body does not tolerate treatment, or if your heart has created new electrical pathways that contribute to your abnormal rhythm. This test involves placement of several pacemaker electrodes into your heart chambers to record electrical activity. The electrodes are placed via a catheter that is threaded through the veins to the heart, under local anesthesia in the cardiac catheterization lab.
Blood tests may be performed to rule out thyroid disease and evidence of heart muscle damage (heart attack). Urine tests and additional blood tests may be preformed to rule out abnormal levels of drugs that can cause rapid heartbeat.