Heart Rhythm Disorders: Supraventricular Tachycardia Diagnosis

  • Diagnosis

    Supraventricular tachycardia (SVT) is a rapid heartbeat that begins above the heart’s lower chambers (the ventricles) Figure 01. The heart relies on an organized sequence of electrical impulses in order to beat effectively. Any deviation from this normal sequence is known as "arrhythmia." Supraventricular tachycardia is an abnormally fast heart rhythm that begins in one of the upper chambers of the heart (atria), a component of the heart's electrical conduction system called the atrioventricular (AV) node, or both. Although supraventricular tachycardia (SVT) is rarely life-threatening, the symptoms—which include a feeling of a racing heart, fluttering or pounding in the chest or extra heartbeats (palpitations), or dizziness—can be uncomfortable.

    Click to enlarge: The heart

    Figure 01. The heart

    Supraventricular tachycardia happens when the normal electrical impulses that cause the heart to beat are interrupted. The most common cause of SVT is called re-entry, and occurs when a "short circuit" causes electrical impulses to circulate in a merry-go-round-like cycle that takes over the heart's normal rhythm.

    Although not everyone with SVT has symptoms, the most common type are heart palpitations—a feeling of a racing heart or fluttering or pounding in the chest. Other symptoms include:

    • dizziness
    • shortness of breath
    • chest pain
    • a pounding sensation in the throat or neck
    • weakness
    • fatigue
    • lightheadedness
    • fainting (especially in the case of underlying heart disease)

    Risk factors for SVT vary, but can include gender, age, and underlying disease. Depending on the type of SVT, the following things may be risk factors:

    • gender
    • age
    • abnormal heart structures
    • existing illness (such as long-term lung disease, diabetes, respiratory failure, inadequate oxygen intake, heart disease, low blood pressure, anemia, cancer, fever, and hyperthyroidism)
    • toxic reactions from the heart medication digoxin, or alcohol
    • exercise
    • pregnancy
    • emotions
    • pain
    • heart valve surgery.

    Your doctor will take a complete medical history to determine if your symptoms might indicate SVT. Heart palpitations are among the most common symptoms of many types of SVT. However, changes in heart rate can occur under normal circumstances without any underlying disease. That’s why it’s important to explain your symptoms in as much detail as possible. For example, be prepared to discuss:

    • when your symptoms began
    • how long they last
    • whether or not they stop and start or continue all the time
    • whether or not any particular activity, such as physical exercise, brings on or worsens symptoms
    • whether any activities relieve symptoms, including holding your breath or lying down
    • if your family has a history of heart disease
    • if you have been diagnosed with heart disease or any other illnesses

    A physical examination can help your doctor detect any factors that may be worsening your symptoms, and also determine your risk for possible complications. Your doctor can listen to your heart with a stethoscope. The sounds can reveal whether your heart is beating too fast, and if there is any sort of underlying heart disease.

    Your doctor will also want to measure your blood pressure, take your pulse, and look for signs of other diseases that can contribute to different forms of SVT, such as chronic lung or thyroid disease.

    Laboratory tests such as a complete blood count may be conducted to rule out or confirm other contributing illnesses such as anemia, hyperthyroidism, or metabolic disturbances.

    If your doctor suspects that you have SVT, he or she will want to confirm the diagnosis with an electrocardiogram (ECG) Table 01. An ECG is a test that gives your doctor important information about your heart’s rhythm and electrical impulses. The ECG can help pinpoint your particular type of tachycardia while revealing any damage to the heart muscle or other disturbances in conduction.

    The ECG is conducted in your doctor's office, and involves placing electrical leads on each arm and leg and across the chest when you are lying down. The leads can "sense" electrical impulses as they occur. The results are recorded on a sheet of paper as waves, which represent an impulse as it passes through the different stages of a heartbeat.

    Your doctor may want to confirm the results of your ECG with an event recorder or Holter monitor. An event recorder is used if your doctor suspects that you have occasional arrhythmias. Like an ECG, an event recorder records electrical impulses as they pass through different stages of a heartbeat. However, you must activate it yourself whenever you sense an arrhythmia. An event recorder looks like a small cassette recorder, and is worn under clothing on a shoulder strap or belt. If your arrhythmia occurs more often and your doctor wants to learn about your heart rate over a period of 24 to 48 hours, you may be asked to wear a device called a Holter monitor. The Holter monitor is a portable ECG machine that records heart rhythm continuously over a period of time. Similar to the event recorder, it is worn under clothing

    Your doctor may conduct an exercise stress test if he or she suspects that your tachycardia is related to physical activity. Exercise testing involves walking on a treadmill or pedaling an exercise bicycle at various speeds and levels of intensity while your doctor measures your heart rate, rhythm, and blood pressure.

    If the doctor suspects underlying heart disease, he or she may take a chest x-ray. A chest x-ray is usually reserved for people with symptoms—such as shortness of breath or chest pain—that are related to diseases that affect the heart structures. The x-ray can show calcium deposits, which can lead to valve disease, scarred muscle tissue, or blocked arteries. In addition, a chest x-ray can be used to learn if there is fluid in the lungs, which indicates congestive heart failure (a condition in which the heart cannot pump an adequate amount of blood) or lung problems.

    Other tests that can help your doctor pinpoint your type of SVT include vagal maneuvers and intravenous adenosine.

    • Vagal maneuvers are exercises that can help your doctor diagnose SVT. These maneuvers require your participation. In many cases, they can actually interrupt an arrhythmia or at least temporarily slow the heart rate. Vagal maneuvers include applying ice and cold water on the face, massaging the carotid artery (one of the two main arteries in the neck that carry blood from the aorta to the head), and the Valsalva maneuver.
    • Adenosine and verapamil are drugs that can stop arrhythmia. They are often used for diagnosis when vagal maneuvers don’t work.

    Table 1.  Common Tests for Diagnosing Supraventricular Tachycardia

    Test What's involved What it shows
    Electrocardiogram (ECG) Electrical leads are attached to cloth patches and placed on the arms and legs and across the chest. Conducted in the doctor's office. Takes about five minutes. May provide clues to the type of supraventricular tachycardia. Reveals damage to heart muscle. Shows other conduction disturbances.
    Event recorder Works the same as an electrocardiogram, but is a device worn on a shoulder strap or belt. Electrical leads are placed on the arms and legs and across the chest. Activated by the individual as an arrhythmia is occurring. May be worn for weeks. You can take the monitor off, but do not shower or bathe while wearing the monitor. Shows heart rhythms and electrical impulses. Can record abnormal heart rhythms that occurs less regularly
    Holter monitor Same as above but records heart rhythm continuously over a 24- to 48-hour period. Records heart rhythms and electrical impulses. Used to learn more about your heart rate over a longer period than a standard ECG.
    Exercise stress test Involves walking on a treadmill or pedaling an exercise bicycle at various speeds and levels of intensity. Takes between 30 to 40 minutes. Reveals tachycardias that are related to physical activity. Measures how well the heart functions during activities of varying types and intensity.
    Chest x-ray Conducted in the doctor's office or the hospital using an x-ray machine. Radiation exposure is minimal. Takes a few minutes. Reveals if heart or vessels leading to lungs are enlarged, or if there lung disease.
    Vagal maneuvers
    Diving reflex Immersing the face in ice water Interrupts arrhythmia and/or slows ventricle contractions to help diagnose the type of SVT. (Note that carotid sinus massage can significantly slow heart rate, and should only be done by a health care professional. It is not used in people with narrowing of the carotid artery or those with a history of stroke or heart attack.)
    Carotid sinus massage The doctor applies pressure on your carotid artery while you are lying down.
    Valsalva maneuver Requires you to hold your nostrils closed while forcefully attempting to breathe out, or bending over and straining as if having a bowel movement.

    Avoid any medications, food, physical activity, or emotional stress that may be responsible for your arrhythmia. If you experience an increased heart rate as a result of caffeine, alcohol, tobacco, decongestants, diet pills, or other medications, speak to your doctor about modifying your habits or replacing your medications. You should also discuss changing or stopping any physical activity that may be worsening your condition.

  • Prevention and Screening

    Avoid any medications, food, physical activity, or emotional stress that may be responsible for your arrhythmia. If you experience an increased heart rate as a result of caffeine, alcohol, tobacco, decongestants, diet pills, or other medications, speak to your doctor about modifying your habits or replacing your medications. You should also discuss changing or stopping any physical activity that may be worsening your condition.

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