Ablation therapy for arrhythmias

Patients with cardiac arrhythmias may be asymptomatic, have serious symptoms and a poor quality of life, or present with sudden cardiac death.¹ 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. Although the incidence of complications is low, serious complications can occur and include valvular disruption, coronary occlusion, cerebrovascular accident and death.²

Method

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 and have 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.

Contra-indications³

Bleeding diatheses and coagulopathy are the main contraindication for catheter ablation. There are otherwise no absolute contraindications. Relative contraindications may include:

• Vascular access contraindication:

  • Deep vein thrombosis for femoral vein access.

  • Peripheral arterial disease and aortic dissection in case of retrograde aortic approach.

• Intracardiac thrombi (risk of embolisation).

Indications

The main indications for catheter ablation are:

• Symptomatic supraventricular tachycardia (SVT) due to atrioventricular nodal re-entrant tachycardia (AVNRT), Wolff-Parkinson-White syndrome, unifocal atrial tachycardia, and atrial flutter (especially common right atrial forms).

• Atrial fibrillation with lifestyle-impairing symptoms, after inefficacy or intolerance of at least one antiarrhythmic agent.

• Symptomatic ventricular tachycardia (VT), especially idiopathic VT.⁴

Other indications for catheter ablation include:

• Symptomatic drug-refractory idiopathic sinus tachycardia.

• Lifestyle-impairing ectopic beats.

• Symptomatic junctional ectopic tachycardia.

Atrial fibrillation

• Although antiarrhythmic drugs are useful, ablation therapy has become a primary therapeutic strategy for atrial fibrillation.⁵

• The success rate of catheter ablation for atrial fibrillation is superior to the efficacy of antiarrhythmic drugs. Sinus rhythm is restored in approximately 85% of cases at one year and 52% at five years. Longer duration of atrial fibrillation and increased size of the left atrium increase the risk of recurrence.⁶

• Ablation is also associated with a complication rate of 2-3%.⁷
  
  Indications for catheter ablation of atrial fibrillation:⁸
  

  • Symptomatic atrial fibrillation refractory or intolerant to at least one antiarrhythmic medication: recommended for paroxysmal atrial fibrillation, reasonable for persistent atrial fibrillation and may be considered for long-standing persistent atrial fibrillation.

  • Symptomatic atrial fibrillation prior to initiation of antiarrhythmic drug therapy with an antiarrhythmic agent: reasonable for paroxysmal atrial fibrillation and may be considered for persistent and for long-standing persistent atrial fibrillation.

• Ablation may be more successful in patients with paroxysmal atrial fibrillation rather than persistent atrial fibrillation.⁹

• Radiofrequency catheter ablation seems to be more effective than medical therapy as first-line treatment of paroxysmal atrial fibrillation in relatively young and otherwise healthy patients but may also cause more severe adverse effects.¹⁰

• Percutaneous radiofrequency ablation is a treatment option for symptomatic patients with atrial fibrillation refractory to antiarrhythmic drug therapy or where medical therapy is contra-indicated because of comorbidity or intolerance.¹¹

• 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.¹²

• Cryoablation or high-intensity focused ultrasound (HIFU) ablation may be used in the management of atrial fibrillation for patients undergoing concomitant open heart surgery - eg, mitral valve replacement or repair.^{13 14}

• 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.¹⁵

• In experienced hands, paroxysmal atrial fibrillation can be eliminated in more than 85% of patients by ablation lasting less than three hours and with a risk of complications of 1-2%. Success rates are lower for patients with persistent atrial fibrillation.¹⁶

• However, there are only limited long-term data on the safety and efficacy of ablation therapy for atrial fibrillation ablation.⁹

The National Institute for Health and Care Excellence (NICE) does not currently recommend percutaneous (non-thoracoscopic) epicardial catheter radiofrequency ablation for atrial fibrillation.¹⁷

SVTs and atrial flutter

• Catheter ablation has been extensively employed as a well-tolerated, often curative therapy for SVT.¹⁸

• Studies of radiofrequency ablation for the treatment of patients with typical atrial flutter and atrioventricular node-dependent SVT report high efficacy rates and low rates of complications.¹⁹

• Ablation may be considered as first-line in some situations (eg, a symptomatic patient with Wolff-Parkinson-White syndrome). Selective radiofrequency catheter ablation of the slow pathway is an ideal method to treat most patients with AVNRT.²⁰ However, for patients with rhythm disturbances that are likely to resolve spontaneously (eg, atrial tachycardia) or unlikely to recur (eg, a first episode of atrial flutter), ablation would not be appropriate first-line therapy.²

• The common forms of SVT (eg, AVNRT, SVT associated with Wolff-Parkinson-White 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 these may be curable with a second procedure.

• 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.²¹ However, radiofrequency catheter ablation is considered to be a relatively safe and effective procedure for the therapeutic treatment of typical atrial flutter.²²

Ventricular arrhythmias^{23 24}

• 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 antiarrhythmic agents or an implantable cardioverter defibrillator (ICD).

• Ablation can often be used as an alternative to antiarrhythmic drug therapy for controlling frequent episodes of VT.

• Idiopathic VT is curable with a success rate of about 80%. Ablation is therefore an alternative to antiarrhythmic drugs for controlling frequent VT episodes. Ablation of multiple VTs and unstable VTs is often possible but is usually adjunctive therapy to an ICD in these patients.

• VTs associated with structural heart disease can be treated by catheter ablation but the success rate is much lower (about 50%).

Complications^{8 25 26}

Ablation is associated with a significant risk of complications, some of which might result in life-long disability and/or death. Available data has indicated an overall incidence of complications of 6.29%, with in-hospital mortality of 0.46%.

• Cardiac complications - eg, high-grade atrioventricular block, cardiac tamponade, coronary artery spasm or thrombosis, pericarditis, valve trauma.

• Vascular complications - eg, retroperitoneal bleeding, haematoma, vascular Injury, transient ischaemic attack or stroke, hypotension, thromboembolism, air embolism.

• Pulmonary complications - eg, pulmonary hypertension (secondary to pulmonary vein stenosis), pneumothorax.

• Other potential complications include left atrial-oesophageal fistula, acute pyloric spasm or gastric hypomotility, phrenic nerve paralysis, radiation or electrically induced skin damage, infection at access site, inappropriate sinus tachycardia and pro-arrhythmia.

• Radiation risk (low).

• Ablation of a pathway close to the atrioventricular node may require implantation of a pacemaker.

• Cardiac wall perforation is rare.