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  • Mark A. Capeless, MD, FACC
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AV node ablation/modification –

Historically the most common catheter ablation procedure performed in patients with atrial fibrillation has been AV nodal ablation with implantation of an electronic pacemaker. This procedure is indicated for patients with high ventricular rates who cannot tolerate the levels of medication required to achieve adequate heart rate control (average heart rate between 60-100, and adequate heart rate response to exercise).  RFCA of the AV junction results in excellent rate control, relieves palpitations, and improves functional capacity.  However, it requires permanent pacemaker implantation to manage the resulting AV block and requires anticoagulants to prevent stroke because the atrial fibrillation itself is not suppressed by this procedure.

A related procedure is AV nodal modification without pacemaker implantation.  In this procedure the slow pathway inputs to the AV node are ablated similarly to the ablation procedure performed in patients with AVNRT described above.  Occasionally this causes sufficient AV nodal conduction delay without causing heart block. This type of ablation is not commonly performed because it is felt to be less effective than AV nodal ablation.

Pulmonary vein isolation and catheter-based maze procedure –

Catheter ablation of atrial tissue to cure atrial fibrillation is evolving rapidly. The procedure is technically demanding, more risky, and may not apply to all patients with atrial fibrillation.  Recently it has been observed that >90% of patients with the paroxysmal form of atrial fibrillation (i.e. AF that starts and stops on its own) results from high frequency firing from atrial tissue connections that extend into the proximal portion of pulmonary veins.  It is possible to ablate these connections making it impossible for the high frequency pulses to exit the pulmonary veins thereby eliminating episodes of paroxysmal atrial fibrillation.   This requires delivery of catheters into the left atrium and carries with it a 1-3% risk of causing stroke and/or pulmonary vein stenosis.  Pulmonary vein stenosis is constriction of the pulmonary vein orifice in response to the radiofrequency energy.  The efficacy of the procedure as it is currently being performed is between 70-80%, and may be higher when patients included are those undergoing repeat procedures and/or further antiarrhythmic drug therapy. 

Improving the efficacy of pulmonary vein isolation is the subject of intense research efforts. In addition, novel catheter based approaches to treat more persistent forms of atrial fibrillation are being developed.  It is anticipated that technical advances will allow performance of a catheter-based maze procedure similar to a procedure now performed with surgery.  In the latter a series of incisional scars are created during open-heart surgery.  These scars compartmentalize the atria such that atrial fibrillation cannot occur.  In most instances this procedure can be performed while maintaining atrial mechanical function.  Although the cure rate is high – even for patients with chronic atrial fibrillation – extensive surgery is required.  It may be that the creation of similar lines of block with catheter-based RF energy, in addition to pulmonary vein isolation, may achieve the same result.  This is a subject of active research in our laboratory.