Ablation for Cardiac Arrhythmia
The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic drugs, cardioversion-defibrillation,implantable cardioverter-defibrillators (ICDs), pacemakers (and a special form of pacing, cardiac resynchronization therapy), catheter ablation, surgery, or a combination, is used.
If a tachyarrhythmia depends on a specific pathway or ectopic site of automaticity, the site can be purposefully destroyed (ablated) to effect cure. There are several methods of ablation:
Ablation is usually accomplished using transvenous catheter supplied low-voltage, high-frequency (300 to 750 MHz) electrical radiofrequency (RF) energy. This energy heats and necroses an area < 1 cm in diameter and up to 1 cm deep.
Cryoablation uses tissue freezing (to -70° C) to effect tissue destruction. Other delivery systems have been developed for intraoperative use.
Before energy can be applied, the target site or sites must be identified during an electrophysiologic study.
Success rate is > 90% for reentrant supraventricular tachycardias (via the atrioventricular [AV] node or an accessory pathway), focal atrial tachycardia and atrial flutter, and focal idiopathic ventricular tachycardia (VT—right ventricular outflow tract, left septal, or bundle branch reentrant VT). Because atrial fibrillation (AF) often originates in or is maintained by an arrhythmogenic site in the pulmonary veins, this source can be electrically isolated by ablations at the pulmonary vein–left atrial junction or in the left atrium. Alternatively, in patients with refractory AF and rapid ventricular rates, the AV node may be ablated after permanent pacemaker implantation. Ablation is sometimes successful in patients with VT refractory to drugs particularly when ischemic heart disease is present.
Transcatheter ablation is safe; mortality risk is higher in complex procedures. Mortality is < 1/2000 for noncomplex ablation procedures but may be as high as 1/500 for pulmonary vein isolation procedures for atrial fibrillation or ventricular tachycardia substrate ablation procedures.
Complications include valvular damage, pulmonary vein stenosis or occlusion (if used to treat atrial fibrillation), stroke or other embolism, cardiac perforation, tamponade (1%), and unintended AV node ablation.