The heart is a 4-chamber muscle that functions like a blood pump, the 2 upper chambers are called atria, and the lower 2 chambers are the ventricles.
Supraventricular tachycardia (SVT) is a rapid rhythm of the heart that begins in the upper chambers. When patients experience changes in the normal sequence of electrical impulses and an abnormal heart rhythm occurs, they are said to have an arrhythmia .
The rhythm of the heart is usually controlled with a natural pacemaker (the sinoatrial node) in the upper right chamber that beats approximately 60 times per minute at rest and may increase with exercise.
The electrical impulses travel from the natural pacemaker through the atria, then pass through a filter called the atrioventricular (AV) nodule before running into specialized fibers that activate the ventricles.
The electrical impulses start at the sinoatrial node and travel through the atria to the AV node. The atria are above the ventricles, hence the supraventricular term.
From there, the electrical impulse travels through His fibers and Purkinje fibers to the left and right ventricles.
The term tachycardia refers to a fast heart rate of more than 100 beats per minute. Supraventricular tachycardia is often abbreviated as SVT (previously paroxysmal atrial tachycardia or TAP).
Symptoms during supraventricular tachycardia
- Loss of consciousness.
- Chest pain.
- Short of breath.
Typically, patients have symptoms of supraventricular tachycardia, but occasionally may not have symptoms. A common symptom during supraventricular tachycardia is palpitations or the sensation that the heart beats fast, flutters or runs.
This may take a few seconds or several hours. Occasionally, patients may have a feeling of shortness of breath or “air hunger” or pressure and pain in the chest.
Sometimes patients will feel dizzy or dizzy, and patients will rarely feel like they are about to faint. Loss of consciousness (also known as syncope ) during supraventricular tachycardia is rare.
Although such symptoms may be of concern, in general, supraventricular tachycardia is not a serious or life-threatening condition.
However, if any of these symptoms develop, you should seek immediate medical attention.
The electrocardiogram (ECG) provides an image of the heart rhythm and is recorded by placing adhesive or gel pads on the chest and extremities.
If the patient experiences this tachycardia during the (ECG), a clear diagnosis can be made. Other types of electrocardiographic monitors can be used to record the patient’s heart rhythm to help make a diagnosis of supraventricular tachycardia.
A 24-hour ambulatory holter monitor can be used to record the heart rate continuously for 24 hours. This type of monitor is particularly useful for documenting asymptomatic or very frequent rhythm abnormalities.
For those patients whose arrhythmias occur relatively little, event monitors or loops can be used.
An event monitor is attached to the patient’s wrist or chest whenever symptoms suggest supraventricular tachycardia.
Activating a button on the monitor will start a heart rate recording. The patient receives instructions on how to download this information to a computer that stores the results for later analysis through a special device placed over the mouthpiece of a telephone.
For patients who experience very short arrhythmias or who are accompanied by slight dizziness, an event monitor is not practical. In such cases, patients can use a loop monitor continuously for days or weeks.
The loop monitor continuously registers the heart rate, so that the patient only needs to press a button to keep a record of the rhythm for the next 1 to 2 minutes.
This allows to register even very transitory arrhythmias. The record of the loop monitor is downloaded using a telephone in the same way that the event monitor data is transmitted.
How is supraventricular tachycardia classified?
A TSV is classified medically according to the route taken by the electrical signal of the atria. A type of SVT (AV Nodal Reentrant Tachycardia or TRNAV) is produced because the electrical impulse travels in a circle using extra fibers in and around the AV node.
Another type of SVT occurs due to electrical conduction through additional fibers between the atria and the ventricles; This means of conduction is called a bypass or accessory way.
The electrical impulse travels through the AV node to the ventricle and back into the atrium through these additional fibers, producing the SVT called AV Reentraveal Tachycardia or TRAV.
Some patients are told they have Wolff-Parkinson-White syndrome (WPW), in which there is evidence of conduction through an accessory pathway from the atrium to the ventricle that can be detected on the ECG, even if they do not experience supraventricular tachycardia.
Diagram of Nodal AV Reentrant Tachycardia (TRNAV): The electrical impulse travels in a circle using extra fibers in and around the AV node.
Diagram of AV Reentrant Tachycardia (AVR): The electrical impulse travels through the AV node to the ventricles and back to the atrium through additional fibers that connect the atria and the ventricles.
Medications may be used to treat many patients with supraventricular tachycardia. The most common classes of medications are:
- Beta-blockers: These are commonly used to treat high blood pressure and other heart problems such as angina. In supraventricular tachycardia, they are used specifically to decrease conduction through the AV node to stop conduction during tachycardia.
- Calcium channel blockers: They are also used to treat high blood pressure and heart problems. Like Beta-blockers, they can be used to decrease conduction through the AV node. Examples of calcium channel blockers include Verapamil or Diltiazem.
- Antiarrhythmic agents : these agents are used to treat various arrhythmias and directly affect atrial or ventricular heart tissue.
They are more useful in supraventricular tachycardia that use an accessory or bypass or atrial tachycardia. You should talk to your doctor about the right medical therapy for you.
A special procedure called radiofrequency ablation (APR) has been developed as an alternative to medication to treat many patients with SVT.
During this procedure, special plastic tubes called catheters are inserted into a vein in the leg / groin area and advanced to the heart with a fluoroscope.
Catheters are used to record electrical signals from inside the heart. They can pinpoint the site from which the supraventricular tachycardia originates.
Radio waves (called radiofrequency energy) are administered at the tip of this catheter to the precise location of the supraventricular tachycardia, creating a small tissue coagulation of approximately 2 mm in diameter.
The procedure has a 90% to 95% chance of successfully treating supraventricular tachycardia, so that it does not recur or requires medication.
There is an approximately 5% chance that the supraventricular tachycardia will reappear, usually within the first 1 to 2 months.
The APR may entail the risks described below:
- Less than 1% risk of serious or life-threatening complications.
- Bleeding, bruising or infection at the catheter insertion site.
- Damage to the heart, lungs, blood vessels or nerves.
- Blood clots in the lungs.
- Allergic reactions.
- Adverse effects of sedatives or anesthetic agents, such as respiratory depression that requires the insertion of a breath.
The cardiologist will explain the complications and benefits of the APR and inform you if it is an appropriate treatment for your medical condition.
What can I do when I develop a supraventricular tachycardia?
You can discuss with your doctor the steps you can take when you develop supraventricular tachycardia.
For example, your doctor may instruct you to perform the Valsalva maneuver to try to stop supraventricular tachycardia yourself if you are not stunned, short of breath, chest pain or other serious symptoms.
To do this maneuver, first lie down, take a deep breath and hold it, and then lower it as if defecating.
If you feel quite stunned, you should go to bed and ask for help and for immediate transportation to a local hospital.
You may be taken to the emergency department of a local hospital. There, an ECG will be performed and an intravenous line will be started.
You may be given a small amount of a drug called adenosine that is quite effective in stopping TSV.
Adenosine can cause redness, a feeling of warmth and a sudden feeling of dyspnea for 30 seconds or less. It should be used with caution in patients with asthma.
Other medications such as verapamil, beta-blockers or diltiazem can also be given intravenously.