Supraventricular Tachycardia

Michael C. Giudici MD, FACC, FACP, FHRS

 

Supraventricular Tachycardia (SVT) is a general term for cardiac arrhythmias that originate above the ventricles (the lower pumping chambers of the heart). There are many forms of supraventricular tachycardia, fortunately it is very rare that they are ever life-threatening.

 

Symptoms of SVT range from palpitations, dizziness, chest pressure, shortness of breath, and even loss of consciousness all the way to none at all. The way some people are “wired”, they can feel every beat of their heart and can tell if one single beat is out of synch. Other people may have a heart going over 150 beats per minute and have no symptoms at all!

 

The different supraventricular tachycardias are:

 

Atrial Fibrillation – This is, by far, the most common SVT. This can occur at all ages and tends to increase with age. In atrial fibrillation (AF), the top chambers of the heart are electrically going up to 400 beats per minute, but mechanically are just quivering and not pumping blood. The bottom of the heart tends to beat quite irregularly in AF and often too fast. The heart pumps less blood and clots may form in the top chambers which could travel through the bloodstream and cause a stroke. Management of AF usually includes medications like warfarin to prevent clots and medication to control the heart’s rate and/or rhythm. Other options for more definitive treatment of AF include catheter procedures to eliminate the irritable rhythms that produce AF – AF ablation, or pacemaker placement.

 

Atrial Flutter – This is a less common arrhythmia that usually runs in circles around the right atrium. The rate of the atrium is usually around 260-300 beats per minute and the ventricles beat anywhere from 75 to 150 beats per minute. Like AF, atrial flutter may result in blood clots and stroke, so warfarin is often required. Atrial flutter may be treated with medications like AF, but is more amenable to catheter ablation and is more easily cured than atrial fibrillation.

 

Focal Atrial Tachycardia – This is a relatively common arrhythmia in children and post-menopausal women. A single focus in either atrium decides to “be heard” and starts firing rapidly. This may be for a few beats (5 to 10) or may go on for minutes or hours. Some of these arrhythmias are relatively slow (120 to 130 beats per minute) and some may be over 200 beats per minute. These are treated with medications to suppress the focus, catheter procedures that search for the exact site of origin of the arrhythmia and ablate it with heat energy (radio-frequency) and cold energy (cryo-ablation). If all else fails, pacemakers can be useful to control the bottom of the heart.

 

Intra-atrial Re-entry Tachycardia – This is similar to Focal Atrial Tachycardia except that it involves a small circuit in the atrium rather than a single focus. Treatments are the same as in Focal Atrial Tachycardia.

 

SA Nodal Re-entry – This is Intra-atrial Re-entry that occurs near or even within the SA node. It is somewhat controversial that this arrhythmia truly exists. Many believe that it is only using the atrial tissue for its circuit and not the SA node. Treatments are the same as for focal atrial tachycardia.

 

Junctional Tachycardia – This is a relatively common arrhythmia in children, and rarely seen in adults. This is an automatic arrhythmia that originates in the Atrio-ventricular (AV) node. Usually the AV node gives rise to a junctional escape rhythm that is in the range of 35-50 beats per minute when the SA node gets too slow during sleep or when impulses aren’t getting through to the bottom of the heart (heart block). Junctional tachycardia has rates anywhere from 80 to 130 beats per minute. This can be quite difficult to treat as few medications are helpful. B-blockers and verapamil are the first choices with careful attention to electrolyte disturbances (high or low potassium or magnesium). The patients other medications should be reviewed as elevated levels of many drugs could be responsible.

 

AV Nodal Re-entrant Tachycardia (AVNRT) – This is the most common reason for someone to have the sudden onset of rapid, regular palpitations with rates of 160 to 220 beats per minute. Many persons are born with an extra piece of AV nodal tissue that conducts slightly slower than the normal AV node. If a premature beats comes at just the right time, it can block in the normal fast pathway, go down the slow pathway, and come back up the fast pathway and around in circles giving off impulses to both the atria and ventricles simultaneously.

 

Treatments can include maneuvers such as breath holding and “bearing down”, rubbing a carotid artery, putting one’s face in ice water, or rubbing your eyes, medicines that are taken acutely when an arrhythmia occurs or chronically to prevent frequent episodes, and catheter ablation where the slow pathway is mapped and eliminated.

 

Atrio-ventricular Re-entrant Tachycardia (AVRT) – This presents similarly to AVNRT but uses a pathway away from the AV node for one of the limbs of the circuit. About 3% of people can be born with a small muscle bundle that gets left behind in the formation of the heart. Muscle conducts electricity. If the accessory pathway can conduct from top to bottom, the resting ECG may be abnormal with delta waves. This is called Wolff-Parkinson-White Syndrome. This is one of the rare instances where a person could have a life-threatening form of SVT. If an accessory pathway conducts rapidly from atrium to ventricle and a person goes into atrial fibrillation, the pathway could conduct that very rapidly and cause ventricular fibrillation, which can be fatal. At least half of people with an accessory pathway only conduct from bottom to top, in which case the resting ECG is normal.

 

Another form of AVRT involves an unusual pathway called a Mahaim Fiber. This usually begins in the right atrium and runs along the back wall of the heart inserting in the distal right bundle. The tachycardia is always down the Mahaim Fiber and back up through the normal AV nodal tract. This tends to have a wider complex on ECG, but symptoms are similar to other AVRTs. Treatments for AVRT are medications or catheter ablation. When someone has obvious Wolff-Parkinson-White Syndrome, catheter ablation is usually performed earlier than in patients with normal baseline ECGs.

 

Permanent Form of Junctional Re-entrant Tachycardia (PJRT) – This is a relatively rare arrhythmia seen mainly in children and adolescents. It involves an accessory pathway very close to the AV node. Medications such as verapamil, flecainide, and b-blockers may be helpful, but catheter ablation is often required.

 

Inappropriate Sinus Tachycardia – This is an unusual arrhythmia seen mainly in young women. The sinus node will have rates in the 90’s, 100’s, 110’s, and 120’s at rest. Over time, this constant rapid rate can damage the heart and cause heart failure. Most of these respond to b-blockers, but on rare occasion, the only recourse is to ablate the sinus node which most commonly leads to slow heart rates and a need for permanent pacemaker placement.