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January 31, 2019

Checking pulse manually on the wrist at the Cardiovascular Institute of the South.

Imagine watching TV or waking from a deep sleep and suddenly realizing that your heart is racing uncontrollably.  You haven’t done anything to warrant an increased heart rate, yet it is thundering out of control.  You can feel it pounding in your chest and begin trying to calm yourself by taking some deep breaths.  Still, with no signs of slowing down, you begin to think that something may be terribly wrong.  You may even find yourself in the emergency room as your heart continues to race, and here a doctor may well tell you that you are experiencing an episode of SVT, or supraventricular tachycardia. 

What is SVT?

SVT is a rapid, irregular heart rate that occurs as the result of improperly functioning electrical impulses which control heart rhythm.  In addition to the four chambers that pump blood throughout the body, the heart is also equipped with an electrical system that coordinates how and when these chambers contract.  The hub for this system is the sinoatrial (SA) node.  Sitting at the top of the heart in the right atrium, the SA node is responsible for coordinating the electrical signals that maintain a steady heart rhythm.  During SVT, however, this system malfunctions and the rhythm becomes irregular, with a resting heart rate that can range from 100 to over 200 beats per minute.

Types of SVT

Due to the complexity of the heart’s electrical system, there are multiple areas in which the electrical “misfire” may occur.  Its precise location will determine the specific type of SVT involved.  Options include:

  • Atrioventricular Node Re-Entrant Tachycardia (AVNRT) – AVNRT is the most commonly occurring form of SVT, accounting for about 60% of all cases. In the condition, an abnormal electrical connection within the AV node can cause the electrical impulse to get stuck, circling around the same circuit rather than traveling normally throughout the heart.
  • Atrioventricular Reciprocating Tachycardia (AVRT) – In those with AVRT, the heart is equipped with a secondary, or “accessory,” electrical pathway between one of the upper and lower chambers of the heart. When the signal gets caught in this pathway rather than the normal conduction system, SVT can occur. The condition known as Wolff-Parkinson-White Syndrome falls into this category.
  • Atrial Tachycardia (AT) – In instances of AT, an electrical impulse outside of the SA node occurs repeatedly, causing the current to circle the atria over and over again. This is the least common form of SVT and is often seen in conjunction with heart disease.

Treatment Options for SVT

SVT alone is not a life-threatening condition, and its treatment will depend largely on the frequency and severity with which it occurs.  During an active episode, there are a handful of treatments which may be used to bring the heart rate back to normal.  These include:

  • Carotid Sinus Massage – This very specific technique of massaging the carotid artery in the neck can help release chemicals to slow the heart. If done incorrectly, however, it can contribute to blood clots.  Therefore, this treatment should only be performed by a physician.
  • Vagal Maneuvers – These maneuvers can work by stimulating the vagus nerve and temporarily slowing conduction through the AV node. Most commonly, patients are instructed to hold their breath and strain as though having a bowel movement for several seconds.  Other techniques include immersing the face in ice water, coughing, and gagging.
  • Cardioversion – If SVT does not respond to vagal maneuvers or continues for more than 30 minutes, patients should seek emergency medical attention. In these cases, cardioversion may be used to restore a normal heart rhythm.  This may be accomplished chemically through intravenous medications like Adenosine or Verapamil, or it may be done through an electric shock delivered to the heart through patches or paddles placed on the chest.

If SVT is a recurring problem, additional measures may be taken to help control the heart rhythm and prevent future episodes.  These include:

  • Medication – Prescription medications to control heart rhythm include beta blockers, calcium channel blockers and Digoxin. In order to avoid complications and future episodes, it is important to take these medications exactly as prescribed by your physician.
  • Catheter Ablation – Catheter ablation is a safe and effective SVT treatment which can prevent the occurrence of future episodes without the need to rely on medication. During the outpatient procedure, the heart is put into SVT and the source of the erratic electrical impulse identified.  This connection is then ablated through a source such as heat, preventing its ability to conduct electrical signals in the future.

SVT can be a frightening condition.  Fortunately, it can be easily and safely treated.  If you are suffering from arrhythmia of any kind, it is important to seek the attention of a cardiology specialist known as an electrophysiologist.  These physicians specialize in the heart’s electrical system and can help you identify the cause of your arrhythmia, as well as potential treatment options.

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