SVT and WPW
What is SVT?
Supraventricular tachycardia (SVT) refers to a group of abnormal fast heart rhythms that arise because of a problem involving the upper chambers of the heart.
WPW is short for Wolf-Parkinson White syndrome which is a special form of SVT.
How does SVT occur?
In some hearts, an abnormal heart rhythm may arise from the heart’s upper chambers when an electrical impulse either starts from a different location other than the SA node, or follows a route (or pathway) that is not normally present. When this occurs the heart will suddenly start racing.
During SVT, the heart rate is usually over 150 beats per minute and often over 200 beats per minute. In some individuals, certain things will trigger episodes. These include caffeine, alcohol, anxiety, exercise, or sudden movements such as bending over. In others, episodes can occur at any time without a trigger.
During episodes, you will usually be aware of the rapid beating of your heart. Other symptoms might include dizziness (blacking out may occur but is unusual), breathlessness, sweating, chest pain, and anxiety. After an episode it is usual to feel very tired.
Is SVT dangerous?
In the overwhelming of cases, SVT is a benign condition. This means that it will not cause sudden death, will not damage the heart or cause a heart attack, and will not shorten life span. There are some rare exceptions that your doctor will discuss with you if relevant.
What tests do I need if I have SVT?
You may require the following initial tests:
- Blood tests – To determine if there is an underlying condition that has provoked your arrhythmia, such as thyroid or electrolyte disturbances and to check the condition of your liver and kidneys.
- ECG – An ECG may provide clues about the cause of your arrhythmia by evaluating your heart rhythm.
- Holter monitor – To evaluate your heart rhythm over a 24 h period, and record periods of arrhythmia for analysis.
- Echocardiogram – To confirm that the structure and function of your heart is sound.
What type of SVT do I have?
There are 3 main types of SVT. Although an ECG can provide helpful clues, an electrophysiology (EP) study is normally required to properly diagnose your SVT.
AV Nodal Re-entry Tachycardia (AVNRT)
This is the most common form of SVT and involves an abnormal short circuit occurring at the AV node. Instead of a single AV node connection between the top and bottom chambers, there is a second connection that is abnormal. The normal and abnormal connections are termed “fast” and “slow” pathways respectively, describing their electrical conduction properties. The slow pathway is present from birth. A single extra beat arising from anywhere in the heart may result in electrical conduction through this abnormal connection. The electrical signal then gets caught up in a short circuit around the AV node resulting in an abnormally fast heart rhythm.
Atrioventricular Re-entry Tachycardia (AVRT) and Wolff Parkinson White (WPW) Syndrome
AVRT is an abnormal electrical circuit involving the AV node and an “accessory pathway” connecting the upper and lower chambers. An accessory pathway is a small abnormal electrical connection that has been present since birth and is not directly connected to the AV node. Most often, it occurs on the left side of the heart. A single extra beat arising from anywhere in the heart may result in electrical conduction through this extra pathway.
The electrical signal then gets caught up in a short circuit involving the pathway and the AV node, resulting in an abnormally fast heart rhythm accompanied by palpitations. The short circuit may occur in a clockwise or anticlockwise fashion. In some individuals, evidence of the accessory pathway can be seen on an ECG performed while in normal rhythm – here, the condition is called WPW syndrome.
Focal Atrial Tachycardia
This is the least common form of SVT. There is an extra abnormal origin of the electrical impulse from a small area in the atria other than the SA node. It is not known when or why such an extra focus develops.
How is SVT treated?
There are 3 main options for people with SVT:
- No specific treatment. SVT is almost always harmless. For those people having infrequent and short-lived episodes that are not troublesome, one option is to simply live with it. Episodes of SVT can often be terminated using the Valsalva manoeuvre: (1) take a deep breath in and hold it, (2) hold your abdomen rigid, (3) use your hands to press against your abdomen as hard and long as you can. This may result in brief dizziness and is best performed while lying down or seated in an armchair.
- Medication. For people who do not wish to continue having episodes, a second option is to take regular daily medication. There are a variety of different possible medications. Medications reduce the frequency and severity of episodes but do not cure the problem. There is also the possibility of developing side effects from these drugs, which at times may be worse than the SVT symptoms themselves.
- Catheter ablation. This is a minimally invasive procedure that cures the condition by using a keyhole instrument called a “catheter” to deliver radiofrequency energy to ablate (destroy) the abnormal tissue responsible for the SVT. This is a safe and minimally invasive procedure that cures SVT. It is highly effective with an overall success rate of over 95%. A catheter is used to deliver radiofrequency energy to ablate the critical piece of tissue that either supports the arrhythmia circuit or that is generating the abnormal electrical impulses. Depending on certain factors, the procedure may be performed under moderate intravenous sedation, or under a full general anaesthetic.