Catheter ablation to treat SVT

Catheter Ablation

Catheter ablation uses a narrow plastic tube, or catheter, to kill cells responsible for the heart rhythm problems caused by supraventricular tachycardia.

• Catheters: Narrow plastic tubes, usually 2-3 mm in diameter, inserted into the body and to the heart chambers.
• Ablation: Killing islands of cells, which are responsible for the heart rhythm problems

Using a fluoroscopy, the catheters are commonly inserted into the femoral artery or vein and advanced to the heart. A fluoroscopy is a weak form of X-ray, used to guide the catheters.

Once positioned in the heart, the catheter is used to record electrical signals. Measurements of the electrical conduction within the heart are made. The catheters positioned in the heart are used to send small electrical impulses to the heart. These impulses may be used to trigger or induce the supraventricular tachycardia.

In some cases, isoproterenol, a medication similar to adrenaline, is used to help create the tachycardia.

After the supraventricular tachycardia is produced, it is possible to determine the location from which the supraventricular tachycardia, a process called mapping. The location of the supraventricular tachycardia is determined by comparing the timing of the electrical signals recorded from the various catheter positions within the heart.

There are several technologies that may be used to assist in the mapping process.  These technologies use magnetic sensors or electrical impulse measurements in order to create a GPS-like map of the electrical activation of the heart. This electrical activation map helps to determine the site at which catheter ablation should be performed.

The location of the catheter ablation depends on the type of supraventricular tachycardia. In the most common type of supraventricular tachycardia, A-V nodal reentrant tachycardia, a region of heart cells outside the A-V node proper is targeted for ablation. For patients with accessory pathways, the ablation is performed at the region between the atrium and ventricles where conduction is not usually present.

Atrial tachycardias may be present in nearly all parts of the atria. In some cases atrial tachycardias and accessory pathways may exist on the left side of the heart. These cases may sometimes require a puncture of the wall separating the right atrium and the left atrium, a process called transseptal catheterization.

There are two energy sources that are commonly used for catheter ablation of supraventricular tachycardias.  These include catheter cryoablation and radiofrequency energy.  Catheter cryoablation may be selected when the location of the site to be ablated is close to the normal electrical system of the heart in order to minimize the risk of damage to it.

Success rate

In 90% or more patients, it is possible to produce the supraventricular tachycardia. However if it is not possible to produce the tachycardia, it usually is not possible to treat the patient with catheter ablation.

Sometimes there are indirect clues to the type and location of the site to be ablated even if it cannot be produced but this is not always the case. For most supraventricular tachycardias. catheter ablation is highly successful with initial success being 90% or more.

However, difficulty producing the supraventricular tachycardia prior to the ablation may make it more difficult to tell reliably that the supraventricular tachycardia has been successfully treated. Even if the supraventricular tachycardia is successfully treated, the supraventricular tachycardia may recur, sometimes up to 10-15% or more.  

The recurrence may be lower if the tachycardia was very easily produced prior to the ablation and may be higher if the structures are so close to the normal electrical system of the heart such as the A-V node that there were regions of the heart that were avoided to prevent damage to these structures.

Risks and complications

Generally there is a very low risk of damage to this system requiring a pacemaker, usually 1% or less. However, in some cases the location of the supraventricular tachycardia origin may be so close to the normal electrical conduction system that this risk may be much higher.

Overall, there is a 1% or less risk of serious or life-threatening complications with catheter ablation of supraventricular tachycardia, including:

• Stroke
• Heart attack
• Death
• Damage to the heart or lungs requiring surgery
• Puncture of the heart

For some arrhythmias that require treatment on the left side of the heart the risks are slightly higher but are still within this range.

Learn more about catheter ablation