Investigation and Treatment of Supraventricular Tachycardia
Supraventricular tachycardia (or SVT) is a relatively common fast heart rhythm disturbance that can affect people of any age from young children to the elderly. Many people suffer from these attacks of fast heart rhythms for many years before seeking help or treatment. It is unusual for patients to come to direct harm as a consequence of SVT but they can have a major impact on patientsí quality of life and activities. Many patients will be offered medication to prevent attacks of SVT and often this approach can be very successful. These can include beta-blockers (atenolol, bisoprolol), calcium antagonists (verapamil and diltiazem), stronger drugs such as flecainide or sotalol and in some cases amiodarone. However, many patients do not want to take medication for the rest of their live, or suffer side effects, or the medications prove to partially or completely ineffective. In these situations, patients may be referred for consideration of electrophysiolgical studies with a view to radiofrequency ablation.
Types of SVT
How is the procedure performed?
The procedure is performed as a day case procedure under local anaesthetic and light sedation. Two or three plastic tubes are inserted into a vein in the leg and through these, fine catheters are passed up the vein until they enter the right atrium (one of the upper heart chambers). These special catheters have the ability to detect the normal electrical signals within the heart which are then displayed on a computer screen. It is possible to send weak electrical impulses down the catheters which stimulate the heart and allow us to pace the heart and introduce extra heart beats which often trigger an attack of SVT. During the fast rhythm we are able to define the electrical circuit responsible for the fast rhythm and identify a target for treatment that will eliminate the circuit and prevent further attacks of SVT. It is very usually very easy for us to start and stop the SVT, and we do not usually need to leave the SVT running for more than a minute.
The target area is treated with a technique known as radiofrequency ablation.One of the catheters has the ability to deliver high frequency electrical energy to the surface of the heart which results in a spot burn approximately 4mm in diameter which eliminates the ability of that spot to conduct the electrical signals needed to maintain the fast rhythm.
The success rate of this procedure ranges from 80-95% depending on the exact nature and location of the circuit. Recurrences are rare but repeat procedures can be performed and are often quicker than the intial procedure. The procedure lasts between one and two hours in total but the actual treatment with ablation is often only 60 seconds although treatment at more than one site may be needed to get rid of the SVT.
What are the risks?
Ablation procedures are very safe and the risk of life threatening complications is extremely low. However, some patients will suffer bruising or bleeding at the top of the leg where the tubes were inserted into the vein. This is generally minor and does not require any specific treatment other than some light pressure if bleeding is occurring. In approximately 0.5% of patients there can be bleeding around the outside of the heart. If this occurs, it can be necessary to insert a needle under the ribs to drain any collection of blood. This procedure is performed under local anaesthetic and the bleeding almost always stops spontaneously. There is also a very small risk of damage to the normal conduction system in the heart and in extreme cases this can result in a slow heart rhythm and the need for a permanent pacemaker. This probably happens in less than 1 in 200 cases and depends on the site of the circuit for the SVT. If your doctor thinks that there is a higher than average risk f ending up with a pacemaker he will let you know before doing the treatment.
What will happen after the procedure?
It is not uncommon to experience short episodes of palpitations or extra heart beats in the first few weeks after the procedure. This is often just a reflection of the minor irritation caused to your heart and generally settles down. The DVLA regulations state that patients must not drive a car or any other vehicle for 7 days after the procedure.
Patients who take warfarin may be able to stop it one month after the procedure. Before this, it is usually necessary to confirm that the heart is still in a normal rhythm by performing an ECG. Your heart rhythm specialist will probably want to see you in an outpatient clinic at some point after the ablation to ensure that the procedure has been a success and make any necessary changes to your medication.