Ablation Therapy for Arrhythmias

Radiofrequency ablation has an increasingly important role in the management of cardiac arrhythmias. Ablation involves the destruction of re-entry circuits, which are often caused by a myocardial scar or a developmental anomaly.

Supraventricular tachycardias

• Catheter ablation provides a safe and highly effective treatment for symptomatic patients with supraventricular tachycardia.¹ Ablation may be considered as first line in some situations, (e.g. symptomatic patient with Wolff-Parkinson-White syndrome). However, for patients with rhythm disturbances that are likely to spontaneously resolve (e.g. atrial tachycardia) or unlikely to recur (e.g. a first episode of atrial flutter), ablation would not be appropriate first-line therapy.²
• The common forms of SVT (e.g. atrioventricular nodal re-entrant tachycardia, SVT associated with WPW syndrome) are treatable with a success rate up to 95%. Cure rates for unifocal atrial tachycardia and common right atrial flutter are about 90%. Recurrent tachyarrhythmias can occur in the first few months after ablation but and these may be curable with a second procedure.
• Percutaneous radiofrequency ablation is a treatment option for symptomatic patients with atrial fibrillation refractory to anti-arrhythmic drug therapy or where medical therapy is contraindicated because of co-morbidity or intolerance.³ Radiofrequency ablation of the atria can be performed via a catheter introduced through a femoral vein or by surgical radiofrequency ablation in patients undergoing concomitant open-heart surgery.⁴
• Cryoablation or high-intensity focused ultrasound (HIFU) ablation may be used in the management of atrial fibrillation for patients undergoing concomitant open heart surgery, e.g. mitral valve replacement or repair.^5,6
• Microwave ablation of the atria for patients with atrial fibrillation can be performed via a catheter introduced through a femoral vein or by surgical microwave ablation in patients undergoing concomitant open-heart surgery.⁷
• In one major study, ablation success was particularly associated with ablation at the atrioventricular junction, atrioventricular nodal re-entrant tachycardia or left free wall accessory pathway.⁸ Recurrence was associated with ablation at the right free wall, postero-septal, septal, and multiple accessory pathways). Complications were more common with associated structural heart disease and the presence of multiple targets. Mortality was increased in the presence of heart disease, lower ejection fraction and with atrioventricular junction ablation.
• Catheter ablation of atrial flutter is usually effective, but there is a small risk of recurrent atrial flutter, and also a risk of atrial fibrillation during follow-up.⁹
• In experienced hands, paroxysmal atrial fibrillation can be eliminated in more than 85% of patients by ablation lasting less than 3 hours and with a risk of complications of 1 to 2%. Success rates are lower for patients with persistent atrial fibrillation.¹⁰

Ventricular arrhythmias

• Most ventricular arrhythmias result from myocardial scarring, most often caused by myocardial infarction. Ablation is not usually curative but may make the rhythm disturbance easier to control by means of anti-arrhythmic agents or an implantable cardioverter-defibrillator (ICD).
• Idiopathic VT is curable with a success rate of about 80%. Ablation is therefore an alternative to anti-arrhythmic drugs for controlling frequent episodes of ventricular tachycardia. Ablation of multiple ventricular tachycardias and unstable ventricular tachycardias is often possible, but is usually adjunctive therapy to an ICD in these patients.¹¹
• VTs associated with structural heart disease can be treated by catheter ablation but the success rate is much lower (about 50%).

• A cardiac catheter is introduced via the peripheral vascular system. A radiofrequency current is passed through an electrode on the end of the cardiac catheter.
• The lesions created are small, homogeneous, approximately 5-7 mm in diameter and 3-5 mm in depth.¹² This is has no effect on cardiac function.
• The procedure may take several hours or even longer. The patient may feel slight discomfort during the ablation.
• Patients appear to be particularly aware of their normal heartbeat after the procedure but this sensation disappears after a period of a few weeks. Patients do not require long-term follow up if the arrhythmia has been cured.

• Mortality rate is 0.1-0.2% of all procedures.
• Initially successful radiofrequency catheter ablation has a low, long-term recurrence rate (4%). Recurrence of accessory-pathway-mediated tachycardia is observed during the first month.¹³
• Cardiac complications: AV block, cardiac tamponade, coronary artery spasm or thrombosis, pericarditis.
• Vascular complications (2-4%): vascular injury, thromboembolism (less than 1%), hypotension, transient ischemic attack or stroke.
• Pulmonary complications: pulmonary hypertension, pneumothorax.
• Other complications: phrenic nerve paralysis, inappropriate sinus tachycardia.
• Radiation risk is low, but it may be greater than the risk from routine x-rays.
• Ablation of a pathway close to the AV node may require implantation of a pacemaker (less than 1% of cases).
• Cardiac wall perforation is rare and is usually due to catheter manipulation rather than the lesion created by ablation.