Stanford Cardiac Arrhythmia Service

Supraventricular Tachycardia

Supraventricular tachycardia (SVT) is a rapid heart rhythm of the upper heart chambers. 
In supraventricular tachycardia electrical signals travel from the upper chambers of the heart to the lower chambers of the heart.

SVTs are usually 150-250 beats per minute but can be both slower or faster.  Commonly, supraventricular tachycardia results in symptoms such as rapid heart beating, dizziness, shortness of breath, or chest discomfort.

In normal rhythm, the electrical impulse starts in the upper heart chambers and then travels through the A-V node, which is like a staircase connecting the top and bottom floors of a building. 

There are several common types of supraventricular tachycardia. The most common type of SVT is called A-V nodal Reentry.  In AV nodal reentry, the electrical impulse travels in and around the A-V node.   The electrical signal goes  and around like a race car going around a racetrack.  The electrical signal may continue going around this pathway, causing the tachycardia to continue. 

The second most common form of SVT uses a second connection between the upper and lower heart chambers, a second staircase.  In this second type of tachycardia, the electrical signal goes down one staircase from the top chamber to the bottom chamber and then takes the second staircase from the bottom chamber and back up to the upper chamber.  The electrical signal continues to take this path as the tachycardia persists.

The third form of SVT called atrial tachycardia is like a flashing light occurring from a place within the upper chambers.  The electrical signal comes from this place and continues to spread throughout the upper heart chambers.

The electrical signal in SVT starts in the upper chamber and then travels down the A-V node connecting the top and bottom chambers.  When the lower heart chamber is activated by the electrical signal reaching it, the lower chamber beats and pumps blood to the rest of the body.  The heart rate during the SVT is the rate that the lower heart chamber beats.

SVTs are not felt to be life-threatening themselves. Patients with SVTs may have a wide range of symptoms.  Particularly when SVTs are brief or not too rapid patients may not be aware that they have an SVT.   Most commonly patients describe a rapid heart sensation, often as if their hearts are pounding out of their chests.  Patients also describe shortness of breath, chest discomfort, or dizziness or lightheadedness. 

For many patients, most or all episodes of SVT stop on their own.  The duration ranges widely from seconds to minutes and occasionally hours.

In some patients, an intervention is required to stop the SVT.  Patients are frequently taught to bear down as if they are having a bowel movement in order to increase the pressure within the chest cavity to try to stop the SVT episode.  This action called a vagal maneuver works by causing the body’s control system called the autonomic nervous system to put the breaks on conduction through the A-V node, the staircase described above connecting the upper and lower heart chambers. Other techniques such as placing one’s head in cold water is not used frequently any longer. In some patients, the SVT does not stop on its own and the patient seeks emergency care by calling 911.  The patient may be given a medication through an intravenous (IV) called adenosine, which causes a strong flushing sensation that lasts about 30 seconds..  In some cases the medication is given more than once.  Patients frequently ask about the potential consequences of staying in the tachycardia for prolonged periods of time, for example, many hours.  For many patients, there may be a significant decrease in the ability of the heart to pump blood throughout the body during the episode of SVT.  The consequences of decreased blood being pumped through the body will vary based on the patient’s overall condition, their degree of hydration, and specific medical conditions such as heart disease.   Some patients may experience impairment of kidney function. Patients with artery problems of the heart could have a heart attack.   Patients should discuss their physician an appropriate time to call 911 if the SVT does not stop on its own. Frequently, 30 minutes is a reasonable time period but in some patients with other heart problems, it may be a shorter period of time.

Most patients with SVT do not have any other significant problems of the heart. However, there are a number of heart conditions and medical conditions that are associated with SVTs particularly the ones called atrial tachycardias.  Patients who are born with specific heart conditions, called congenital heart disease, prior heart surgery, or with heart valve problems are more likely to have these arrhythmias.

The Treatment of Supraventricular Tachycardias

The most commonly used medications for the treatment of supraventricular tachycardias include medications that affect the ability of the A-V node, the staircase between the upper and lower heart chambers, to conduct.  These medications include the beta-blocking agents (see section on beta-blocking agents), calcium channel agents (see section on Calcium channel blocking agents), or digoxin.   These medications are used to treat any of the three most common types of supraventricular tachycardia.  Most commonly patients take these medications on a daily basis in order to prevent the episodes of supraventricular tachycardia from occurring.   In selected cases, patients may be given doses of short acting versions of one of these three types of medications (beta-blocking agents, calcium channel blocking agents, or digoxin) to take after the onset of an episode of the supraventricular tachycardia.  This strategy is usually for patients that have longer episodes that do not usually terminate within a few minutes since these medications usually take 10-20 minutes to act.  Patients also should not have symptoms of dizziness or lightheadedness since these medications may decrease the blood pressure which already may be low and may worsen these symptoms.  Patients are usually are begun on one of the medications  (beta-blocking agents, calcium channel blocking agents, or digoxin) at a starting dose.  If patients continue to have episodes of supraventricular tachycardid and the medications are well tolerated without significant side effects, the next step may be to increase the dose of the medications.  If an increased dose is not tolerated, one option would be to return to the initial dose of the medication or decrease it and to add a low dose of another of the three categories of medication.

Patients that are felt to atrial tachycardias based on ECGs obtained during the supraventricular tachycardia are often treated with the same antiarrhythmic medications that are used to treat atrial fibrillation (see also section on treatment of atrial fibrillation).  These medications may include flecainide, propafenone, sotalol, dofetilide, amiodarone, or dronedarone. 

Many patients with supraventricular tachycardia do not need treatment with daily medications. . Such patients have brief episodes of supraventricular tachycardia, that often last less than one or two minutes, occur infrequently such as once every several months or a few times a year,  and are not  associated with symptoms such as dizziness or lightheadedness.  Patients that have frequent episodes of supraventricular tachycardia such as weekly will typically be treated with daily medications.  Patients with severe symptoms such as near passing out or passing out even though the episodes are infrequent are usually treated with daily medications.  Patients that require termination of the supraventricular tachycardia with the medication adenosine are often treated with daily medications.  For patients with other medical problems such as artery problems of the heart or heart failure, it may be particularly important to prevent supraventricular tachycardias.

Catheter ablation is a technique that serves as an alternative for medications for supraventricular tachycardia.  Catheters are narrow plastic tubes, usually 2-3 mm in diameter, that are inserted into the body and advanced to the heart chambers.  Ablation refers to the killing of islands of cells responsible for the heart rhythm problems.   The catheters are most commonly inserted into the femoral artery or vein (groin area – see figure) and advanced to the heart using fluoroscopy, a weak form of X-ray, to guide the catheters. Once the catheter is position in the heart it is used to record electrical signals from within the heart.  Measurements of the electrical conduction within the heart are made.  The catheters positioned in the heart are used to deliver minute electrical impulses to the heart.  These impulses may be used to trigger or induce the supraventricular tachycardia.  In some cases a medication similar to adrenaline called isoproterenol is used to help produce the tachycardia. After the supraventricular tachycardia has been produced, it is possible to determine the location from which the supraventricular tachycardia, a process called mapping. The location of the supraventricular tachycardia is determined by comparing the timing of the electrical signals recorded from the various catheter positions within the heart.   There are several technologies that may be used to assist in the mapping process.  These technologies use magnetic sensors or electrical impulse measurements in order to create a GPS-like map of the electrical activation of the heart. This electrical activation map helps to determine the site at which catheter ablation should be performed.

The location of the catheter ablation depends on the type of supraventricular tachycardia.  In the most common type of supraventricular tachycardia, A-V nodal reentrant tachycardia a region of heart cells outside the A-V node proper is targeted for ablation.  For patients with accessory pathways, the ablation is performed at the region between the atrium and ventricles where conduction is not usually present.  Atrial tachycardias may be present in nearly all parts of the atria.  In some cases atrial tachycardias and accessory pathways may exist on the left side of the heart.  These cases may sometimes require a puncture of the wall separating the right atrium and the left atrium, a process called transseptal catheterization.

There are two energy sources that are commonly used for catheter ablation of supraventricular tachycardias.  These include catheter cryoablation and radiofrequency energy.  Catheter cryoablation may be selected when the location of the site to be ablated is close to the normal electrical system of the heart in order to minimize the risk of damage to it (See section on Catheter Cryoablation).

Most patients with supraventricular tachycardia that are felt to require daily treatment with medications are given the option of either having a catheter ablation or receiving daily medications.  For patients previously not treated with medications, either option is reasonable as a first choice.   The choice is largely left to patient preference.  Some patients may prefer to be treated with medications while other patients may prefer a procedure.  For patients for whom one or more medications have been tried but supraventricular tachycardias still recur, options include increasing the dose of the medications, trying a different medication, combining two or more medications, or proceeding with catheter ablation. 

In 90% or more patients, it is possible to produce the supraventricular tachycardia. However if it is not possible to produce the tachycardia, it usually is not possible to treat the patient with catheter ablation. Sometimes there are indirect clues to the type and location of the site to be ablated even if it cannot be produced but this is not always the case.   For most supraventricular tachycardias catheter ablation is highly successful with initial success being 90% or more. However, difficulty producing the supraventricular tachycardia prior to the ablation may make it more difficult to tell reliably that the supraventricular tachycardia has been successfully treated.   Even if the supraventricular tachycardia is successfully treated, the supraventricular tachycardia may recur, sometimes upt to 10-15% or more.  The recurrence may be lower if the tachycardia was very easily produced prior to the ablation and may be higher if the structures are so close to the normal electrical system of the heart such as the A-V node that there were regions of the heart that were avoided to prevent damage to these structures.   Generally there is a very low risk of damage to this system requiring a pacemaker, usually 1% or less. However, in some cases the location of the supraventricular tachycardia origin may be so close to the normal electrical conduction system that this risk may be much higher.   Overall, there is a 1% or less risk of serious or life-threatening complications with catheter ablation of supraventricular tachycardia, including stroke, heart attack, death, damage to the heart or lungs requiring surgery, and puncture of the heart.  For some arrhythmias that require treatment on the left side of the heart the risks are slightly higher but are still within this range.

Patients are usually observed overnight in the hospital following catheter ablation.  Patients usually are instructed to avoid exercise or lifting objects more than 10 pounds in weight for one week, particularly to allow the femoral (groin) blood vessels at the site of catheter insertion to heal and avoid bleeding.  It is particularly important for patients to report any symptoms such as chest pain, shortness of breath, bleeding at the site of entry, fever, cough, or neurological symptoms such as weekness, dizziness, or trouble with vision or speech if these symptoms are new or increasing after discharge.   Having some chest discomfort after the procedure is not unusual but typically it improves rather than worsens after the ablation.  

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