Supraventricular Arrhythmia
Supraventricular Tachycardia
Supraventricular tachycardia is a group of rapid heart rhythms that arise above the ventricles, in the atria or the AV node region. In some forms, episodes start and stop suddenly.
On this page
Understanding SVT
What Is Supraventricular Tachycardia?
Supraventricular means “above the ventricles”. In SVT, the abnormal rhythm starts in, or depends on, the atria or the AV node region, and the heart rate becomes fast.
Episodes of rapid heart rhythm may be brief or may last longer. In some forms, episodes begin and end suddenly.
SVT is not one single arrhythmia. Several different mechanisms can cause it, and the mechanism influences the symptoms, the ECG findings and the treatment options.
Origin of the rhythm above the ventricles
Mechanism
How SVT Happens
In a normal rhythm, an electrical impulse starts in the sinus node, spreads through the atria, passes through the AV node and continues to the ventricles. Each impulse travels in one direction and then dies out.
In many forms of SVT, an impulse instead travels around an abnormal electrical circuit and returns to re-excite the same tissue again and again. This is called re-entry, and it can produce a fast, regular rhythm.
Reference
Normal Conduction
One impulse, one direction: the signal follows the normal route and then ends.
Mechanism
Re-entry Circuit
The signal travels around a loop and re-excites the tissue repeatedly, producing a rapid rhythm.
Types and mechanisms
Common Mechanisms of SVT
SVT is an umbrella term. Three mechanisms are described most often. Which one is present is established from the ECG and, where needed, an electrophysiology study.
AV nodal re-entrant tachycardia: a re-entry circuit in or near the AV node. It is one of the more common forms of SVT, and episodes often start and stop suddenly. Read the dedicated AVNRT page.
AVRT
AV re-entrant tachycardia: a circuit that uses the AV node and an additional electrical connection between the atria and ventricles, called an accessory pathway. Wolff-Parkinson-White (WPW) syndrome is the best-known example of an accessory pathway.
Atrial tachycardia
A rapid rhythm that arises from a small area in the atria, or from a circuit within the atria, and does not depend on the AV node to continue.
These mechanisms are described for context. A diagnosis for an individual patient is made by clinical assessment.
What patients may notice
Symptoms of SVT
Symptoms vary and usually occur during episodes. Many people feel well between episodes.
Sudden rapid heartbeat
A heartbeat that suddenly becomes fast.
Palpitations
Awareness of a pounding or fluttering heartbeat.
Dizziness
Feeling light-headed or unsteady.
Shortness of breath
Feeling breathless during an episode.
Chest discomfort
Pressure or discomfort in the chest.
Weakness
A feeling of tiredness or lack of strength.
Near-fainting or fainting
Occurs in some patients and needs medical assessment.
Fainting, chest pain or severe breathlessness need urgent medical care.
ECG
What SVT Can Look Like on an ECG
- A rapid rhythm during an episode
- Often a regular rhythm, depending on the mechanism
- Narrow QRS complexes (a narrow-complex tachycardia) are common in several forms of SVT
ECG interpretation depends on the mechanism and the clinical context. A recording made during symptoms is the most informative.
Assessment
How SVT Is Diagnosed
Diagnosis relies on documenting the rhythm. The tests used depend on how often episodes occur.
Clinical assessment
Review of symptoms, history and examination, with other tests where indicated.
A recording made during an episode can show the rhythm.
Continuous recording over a period of time, useful when episodes are frequent.
A device activated around the time symptoms occur, useful for occasional episodes.
Longer rhythm monitoring
Extended monitoring may be used when episodes are infrequent.
Considered when the diagnosis is unclear or ablation is being planned.
Intracardiac recording during an electrophysiology study
Electrophysiology study
The Role of an Electrophysiology Study
An EPS can be helpful when the diagnosis is uncertain or when catheter ablation is being considered. It may help to:
- Reproduce the rhythm under controlled conditions
- Identify the mechanism: AVNRT, AVRT or atrial tachycardia
- Identify the pathway or circuit involved
- Plan catheter ablation
Mapping
3D Mapping in SVT
3D electroanatomical mapping may be used where it is clinically useful, for example to map an atrial tachycardia or to locate an accessory pathway. Whether it is used depends on the mechanism and the procedure planned. Not every SVT procedure needs it.
3D electroanatomical map of an atrial chamber
Treatment
Treatment Approach
Treatment depends on how often episodes occur, how troublesome they are, the mechanism and patient preference. Not every patient needs the same approach.
Managing episodes
Some episodes stop on their own. Some people are taught techniques that may help, and episodes that need treatment can be treated by a medical team.
Medication
Medicines may be used to reduce episodes or control symptoms where clinically appropriate. The choice is individual.
Catheter ablation
In selected patients, ablation of the mechanism may be considered, depending on symptoms, the mechanism and patient preference.
This page does not replace medical advice. Anyone with an ongoing episode together with fainting, chest pain or severe breathlessness should seek urgent medical care.
Catheter ablation
Catheter Ablation for SVT
Catheter ablation treats the part of the mechanism that allows SVT to occur, such as a pathway or part of a circuit. Whether it is appropriate depends on clinical assessment.
EPS
The rhythm is studied from inside the heart.
Mechanism identification
The type of SVT is established.
Target pathway or circuit
The part of the mechanism to treat is identified.
Ablation
Energy is delivered to the selected area.
Reassessment
Electrical behaviour is checked again.
Procedure pathway
From Assessment to Follow-up
A general outline. The steps needed depend on the patient and the findings.
Assessment
Review of symptoms, history and examination.
Rhythm documentation
ECG or monitoring that records the rhythm.
EPS
Intracardiac recording and stimulation where appropriate.
Mechanism identification
The type of SVT and its circuit or pathway are identified.
Ablation when indicated
Treatment is delivered only if it is appropriate.
Reassessment
Electrical behaviour is checked again.
Recovery
Monitoring while the patient recovers.
Follow-up
A follow-up plan is explained.
Questions
Frequently Asked Questions
Is SVT dangerous?
SVT is often not life-threatening, but it can cause troublesome symptoms and, in some people, fainting. It should be assessed, and management depends on the person and the mechanism.
Why does my heart suddenly start and stop racing?
In some forms of SVT, a re-entry circuit can start and stop abruptly, which is why episodes may begin and end suddenly.
Is SVT the same as atrial fibrillation?
No. Atrial fibrillation is a different rhythm disorder with disorganised atrial activity. SVT usually refers to other rapid rhythms that arise above the ventricles.
What is the difference between AVNRT and AVRT?
Both involve re-entry. AVNRT uses a circuit in or near the AV node, while AVRT uses the AV node and an additional accessory pathway between the atria and ventricles.
How is SVT diagnosed?
By recording the rhythm during an episode, using an ECG, Holter monitoring or an event recorder, and sometimes an electrophysiology study.
When is an electrophysiology study recommended?
It may be considered when the diagnosis is unclear or when catheter ablation is being planned, after clinical assessment.
When is catheter ablation considered?
In selected patients, depending on symptoms, how often episodes occur, the mechanism and patient preference.
Does SVT always need treatment?
No. Treatment depends on symptoms, how often episodes occur and the mechanism.