Supraventricular tachycardia and ablation
What is Supraventricular tachycardia (SVT)
This is an abnormal heart rhythm originating from the top chambers of the heart (atria). When this occurs, the heart will suddenly start racing. This can start with a trigger or without any apparent reason. Triggers include alcohol, caffeine, stress, anxiety or exercise. The heart rate can increase to over 150 beats per minute and sometimes above 200 beats per minute. This compares with a normal heart rate which is between 60 and 100 beats per minute.
Supraventricular tachycardia from Khan Academy.
Patients will usually feel palpitations and sometimes dizzy. Blackout is unusual. After the episode, some patients may feel exhausted.
SVT is benign in the majority of situations. It is unlikely to damage your heart or cause life-threatening problems. There are some rare exceptions and your doctor will discuss this with you if relevant.
How do you treat an episode of SVT?
Many SVT episodes will respond to so-called "vagal" manoeuvres, which you may be taught how to do by your doctor. These actions increase the effect of the vagus nerve on the heart, which transiently blocks the AV Node. The AV Node is the normal electrical connection between the top heart chambers (atria) and bottom heart chambers (ventricles).
Examples of vagal manoeuvres include:
- Blowing into a syringe
- Bearing down while holding your breath
- Rubbing on your neck artery
If you attend hospital during your SVT, the hospital doctors will be able to record your heart rhythm with an ECG during the vagal manoeuvre. This recording can be very helpful for your Electrophysiologist, even if it failed to stop the SVT.
If the vagal manoeuvre fails to work, medications can be injected into your bloodstream that have a more profound effect on the AV Node.
How does SVT occur?
There are three main types of SVT. Your ECG may indicate which type you have, although it is not always obvious before the electrophysiology study (EPS).
AVNRT (Atrioventricular Nodal Reentry Tachycardia). This is the commonest type of SVT. An extra connection is present in about one third of people within the AV Node, which is considered a normal variant, but can lead to a short circuit rhythm (AVNRT) in a minority.
AVRT (Atrioventricular Reentry Tachycardia) and WPW (Wolff-Parkinson-White Syndrome). Some patients are born with a second abnormal conduction channel between atria and ventricles, separate from the AV node, called accessory pathways or bypass tracts. These accessory pathways, together with the AV Node, can cause a short circuit rhythm (AVRT). Sometimes, these accessory pathways can be identified on the ECG during normal heart rhythm. People who experience palpitations with evidence of an accessory pathway on ECG are termed to have Wolff-Parkinson-White syndrome.
Atrial tachycardia. This is the least common type of SVT. This occurs when a cluster of cells within your atrium abnormally give rise to an electrical impulse instead of the natural pacemaker of your heart (the sinus node).
What are the treatment options for SVT?
There are generally three options to treat SVT.
No treatment. As SVT is not usually dangerous, you may simply chose to live with it if your symptoms are infrequent or non-troubling. Intermittent vagal manoeuvres can be used as required to stop SVT episodes each time they occur if you have been taught how to do this safely by your doctor.
Medications. You may wish to reduce yours symptoms by taking medications. Depending on the frequency of your symptoms, you might take tablets on a daily basis or on an as required basis at the time of symptoms. All medications come with side effects and your doctor will discuss these with you.
Radiofrequency Ablation. This is a procedure performed by an Electrophysiologist to provide a cure for the SVT and is considered the first-line treatment for most SVT. Ablation is explained in detail below.
How do I prepare for SVT ablation?
Please refer to the section on EPS.
How is Radiofrequency Ablation performed for SVT?
Please refer to the section on EPS on how EPS is performed.
Radiofrequency ablation is usually carried out during the same session following your EPS as the necessary catheters within the heart are already in place. Radiofrequency ablation can be performed when your Electrophyiologist has determined a diagnosis for your SVT following the EPS. You will have the option of having the ablation performed on a separate day if you wish to consider other options.
Radiofrequency ablation can be performed under local anaesthetic with sedative medications or occasionally under general anaesthesia. This will be discussed with you.
Radiofrequency energy is applied to the unnecessary connection within your AV node (for AVNRT) or at the accessory pathway (for WPW or AVRT). If your diagnosis is Atrial Tachycardia, radiofrequency energy is applied to the abnormal cells from which the impulse originates. Patients may feel a transient warm discomfort in the chest during the delivery of radiofrequency ablation energy.
The ablation procedure including EPS will take between 1 and 3 hours.
What is the success rate for ablation for SVT?
The success rate of ablation completely curing your SVT depends on which type of SVT you have but is usually approximately 95%. There is a 5% chance of the SVT recurring after an apparently successful procedure.
What are the risks of SVT ablation?
Ablation for SVT is commonly performed and is a low-risk procedure. The worldwide complication rate for ablation procedures is less than 0.5%. Although most patients who undergo ablation for SVT do not experience any complications, you should be aware of the following risks:
- Blood vessel problems: bleeding, bruising, damage to the vessel wall, abnormal connections and blood clots can form in the blood vessel in your groin or higher up near the heart. Usually these settle by themselves, but sometimes medications, injections or small operations are required to fix them.
- Abnormal heart rhythms: these are deliberately provoked during the procedure, but can become unstable requiring an electric “shock” to restore a normal heart rhythm. There is a very small risk of requiring a pacemaker if the normal and necessary electrical system of the heart is damaged.
- Perforation: there is a very small chance of causing a leak of blood around your heart. This usually settles without treatment but can also be dealt with by inserting a drain from the chest wall.
- Life-threatening complications like stroke or heart attack are exceedingly rare (less than 0.1%). There is no risk of stroke if the ablation takes place entirely on the right side of the heart.
What happens after the SVT ablation?
You will be required to lie flat for 2-4 hours. During this time, your nurse will check on you to see if there is bleeding or swelling at the groin site. Most people can start eating and drinking water within 4-6 hours after the procedure. Most patients stay in the hospital overnight and their heart rhythm may be monitored. Your Electrophysiologist may stop, switch or commence you on new medications after the procedure.
You should avoid strenuous physical activity and sports for 2 weeks after the procedure. Most people take approximately 1 week off work. Some patients may experience minor chest discomfort and brief palpitations several days after the procedure. This may be due to the irritation caused by the ablation and will usually settle. If this persists, please consult your Electrophysiologist. You should not drive for at least 48 hours although we usually recommend that you do not drive for a week.
Your groin site might be sore for several days. A small bruise at the groin site is normal but if it starts to bleed, you can contact your local doctor or the Electrophysiologist.