AV nodal ablation
Atrial arrhythmias such as atrial tachycardia, flutter or fibrillation can usually be treated with antiarrhythmic drugs or cured with ablation. However in some patients this is not possible and other alternatives are sought. In these cases it acceptable to allow the atrial arrhythmia usually atrial fibrillation to occur but to use medications (digitalis, calcium or beta blockers) to slow ventricular response. In some patients, however, this strategy is either ineffective or the medications used cause side effects. Therefore an alternative strategy of destroying the AV node with ablation producing complete heart block and placing a pacemaker is a good one. Although this does not cure the atrial arrhythmia, it relieves most or all of the symptoms by slowing and regularizing the pulse. After this procedure, heart rhythm medications are stopped. Since the pacemaker senses patient motion and/or breathing rate, it will increase the heart rate to help the patient exercise. The chance of success of this ablation was 97% when RF energy was used in a large multicenter registry (1). The AV node can be ablated via the femoral vein in the right atrium in about 95% of patients. In the other 5%, the femoral artery is used to get to the left ventricle where the HIS bundle can be ablated. The risk of AV node ablation is less than 1%. The risks of the pacemaker are also about 1% and include death, stroke, damage to heart, lung, blood vessel or nerve, bleeding or infection. About 85% of patients feel much better after this procedure. About 10% of patients do not feel much better, and 5% feel worse. Unfortunately, there is no way to predict which patient will feel better and which will not. In nonresponders, sometimes upgrading the pacemaker to a biventricular device will help.
AV nodal ablation is better suited to older patients, patients who are in permanent AF, patients with a need for a PPM for another reason and patients who are not candidates for the other forms of therapy for their AF.
Cryoablation of the AV Node
Limited studies using cryoablation to destroy the AV node have been undertaken. In 2001 a series of 12 patients had attempted AV node cryoablation with success in all 12 (2). A larger series of patients with all kind of supraventricular arrhythmias included 12 patients who underwent attempted cryoablation of the AV node using a catheter with a very small tip electrode. In this trial, the procedure was successful in only 67%, explained in part by the small catheter tip (3). The most recent study (4) using a catheter with a larger tip showed permanent success in only 1 of 15 patients: results not nearly as good as what would be expected with RF energy. Therefore it appears that cryoablation plays a very limited role in AV nodal ablation.
- Scheinman M and Huang S. The 1998 NASPE prospective catheter ablation registry. PACE 2000; 23: 1020-1028
Results of a large multicenter registry of RF ablation including ablation of the AV node
- Dubuc M, Khairy P, Rodriguez-Santiago, etal. Catheter cryoablation of the atrioventricular node in patients with atrial fibrillation: a novel technology for ablation of cardiac arrhythmias. Journal of Cardiovascular Electrophysiology, 2001; 12: 439-444
8 of 12 people had a successful procedure using an early catheter prototype
- Friedman P, Dubuc M, Green M, etal. Catheter cryoablation of supraventricular tachycardia: results of the multicenter “frosty” trial. Heart Rhythm. 2004; 1: 129-138
Only 9 of 12 people had a successful procedure using the smallest cryocatheter (4mm tip) and a single-freeze strategy
- Perez-Castellano N, Villacastin J, Moreno J etal. High resistance of atrioventricular node to cryoablation: a great safety margin targeting perinodal arrhythmic substrates. Heart Rhythm. 2006; 3: 1189-1195
Only 1 of 15 patients had a successful procedure using the medium size cryocatheter and a single-freeze strategy