Supraventricular Tachycardia

What is Supraventricular Tachycardia?

Supraventricular tachycardia (SVT) is a rapid arrhythmia originating in the atria of the heart. The heart rate or pulse rate is between 150 and 250 per minute. It is caused by electrical loops or foci of increased excitation potential within the atria. There are various subtypes. These include AVNRT, AVRT, Atrial Tachycardia, Atrial Flutter and Nodal tachycardias.

What is AVNRT?

AVNRT is a type of supraventricular tachycardia. In this disease, there are fast and slow pathway(s) in an area called the AV node. The electrical impulse usually starts to rotate in these pathways following a premature beat, and there is a heartbeat in each round of these rotations. They appear as sudden onset of rapid heartbeats.

They end spontaneously or with some maneuvers. Patients notice that these palpitations can stop when they cough or strain. Sometimes they last for a long time, do not stop and cause you to go to hospital. They are usually not life-threatening, but can pose a risk if there is other underlying heart disease, such as heart failure, coronary artery disease or serious valve problems.

What is AVRT?

AVRT is a type of SVT caused by an extra conduction pathway between the atria and ventricles that should not normally exist. This pathway causes an electrical short circuit. Each electrical cycle leads to a heartbeat and the person again feels a regular heart palpitation.

What is Atrial Tachycardia?

Atrial tachycardia is caused by a focus or electrical loop inside the atria. The patient feels a regular or irregular heart palpitation. It tends to be more resistant.

What is Nodal Tachycardia?

Nodal Tachycardia is a type of supraventricular tachycardia that originates in the area between the atrium and ventricle called the AV node. It can occur for no apparent reason, but can also occur due to medication or after heart surgery.

What are the Symptoms of SVT?

SVT can cause symptoms such as sudden onset and termination of palpitations, dizziness, fainting, feeling faint, fainting, sweating, chest pain and shortness of breath. The symptoms may be more serious if you have heart failure, coronary artery disease or valve disease.

What Causes SVT?

Supraventricular tachycardia is caused by electrical loops in the atria or foci with an increased potential to emit impulses. It usually starts spontaneously for no apparent reason.

How is SVT Diagnosed?

To diagnose supraventricular tachycardia, ECG recordings are needed, especially at the time of palpitations. ECGs taken at this time can reveal the type of palpitations, that is, where in the heart they originate. Treatment is planned accordingly. If the palpitations are short-lived or somehow cannot be captured by ECG, then we try to capture them with devices called holters or event recorders.

In a holter, a device is attached to the person. This device stays on the person for a few days and records the heart rhythm. Which we call event recorder devices, record in 2 ways. First, when there is a palpitation that meets the specified parameters, the device automatically records this attack. Secondly, when a person feels a complaint, he presses the button on the device and the ECG is recorded.

In recent years, it has become easier to take an ECG during palpitations with the effect of ECG-capturing watches. Single-channel ECGs that can be obtained in 5-6 seconds with watches are very helpful in the diagnosis of arrhythmia. Currently, device algorithms only try to recognize atrial fibrillation and bradycardia, that is, low pulse rate, and give warnings in this direction. However, these recordings are very valuable for the doctor, because the answer to the question of whether there really is a rhythm disturbance at the time of the complaint, or if so, what type, may be hidden in that ECG. However, we must keep in mind that these ECGs do not give information about a heart attack.

Supraventricular Tachycardia ECG sample.
Supraventricular Tachycardia ECG sample.

What is SVT Treatment?

Treatment of supraventricular tachycardia is divided into stopping the palpitations during palpitations and preventing their recurrence in the long term. These treatments depend on the subtype of palpitations. You can do maneuvers such as coughing or straining to stop the palpitations. If it does not stop, it can be stopped in the emergency room with medication or various maneuvers. Electrophysiologic study and ablation are recommended as the first choice to prevent recurrence of palpitations in the long term and to eliminate the disease. The chance of success is very high. Drug treatments can also be applied according to patient preference.

What happens if supraventricular tachycardia is not treated?

If SVT is not treated, your symptoms will continue. Even if the medication prevents palpitations, it does not eliminate the disease. When you stop your medication, your palpitations will probably return. Another important issue is that SVTs can sometimes trigger other rhythm problems, such as atrial fibrillation. In fact, if a young patient has atrial fibrillation, electrophysiology procedures are performed to check if an SVT is causing it.

Is Supraventricular Tachycardia Dangerous?

Some SVTs are dangerous. If you have WPW (wolff parkinson white) syndrome, i.e. an extra conduction pathway in your heart, the moment of palpitations can be risky for you. This is because the rhythm disorder called atrial fibrillation that can develop with this syndrome can increase the ventricular rate too much.

Other SVTs are usually not life-threatening. However, if you have structural heart disease such as heart failure, valvular stenosis, coronary artery disease, narrowing of the arteries, enlargement of the heart, SVTs can lower your blood pressure too low or impair oxygenation of the heart tissue and pose a life risk.

How is SVT Ablation Performed?

Catheters are sent to the heart through veins in the groin for an electrophysiologic study. Measurements are made inside the heart. Palpitations are triggered and the mechanism is determined. Burning is applied from the safest place to disrupt the palpitation mechanism. Afterwards, the palpitations are tried to be triggered again. If the palpitations cannot be triggered and it is decided that sufficient ablation has been performed in the area causing palpitations, the procedure is terminated.

Electrophysiologic study image
Electrophysiologic study image

What is the success rate of SVT ablation?

SVT ablation is a treatment with a very high success rate. According to old data, the success rate is >95% in AVNRT and AVRT and 90-95% in atrial tachycardia and flutter (Reference-1). However, with the developing technology, this rate has increased even more. The success rate is 98-99% in AVNRT and AVRT and >95% in AT and flutter.

What should be considered after SVT ablation?

SVTs such as AVNRT and AVRT have a very low risk of recurrence after ablation. It is usually not necessary to continue palpitation medication. Normal life can be resumed after a few days. In atrial tachycardia or flutter, decisions are individualized based on the ablation strategy and associated conditions.

References: Reference-1

Share this post
Picture of Prof. Dr. Taylan Akgün
Prof. Dr. Taylan Akgün

He is a cardiologist specialised in the diagnosis and treatment of heart rhythm problems (ablation), pacemaker procedures.
He works in Istanbul province.

Related Articles