RADIOFREQUENCY CATHETER ABLATION OF ATRIAL ARRHYTHMIAS - RESULTS AND MECHANISMS

Background Radio frequency catheter ablation is accepted therapy for p atients with paroxysmal supraventricular tachycardia and has a low rat e of complications. For patients with atrial arrhythmias, catheter abl ation of the His bundle has been an option when drugs fail or produce untoward side effects. Although preventing rapid ventricular response, this procedure requires a permanent pacemaker and does not restore th e atrium to normal rhythm. Therefore, we evaluated the safety and effi cacy of radiofrequency ablation directed at the atrial substrate. Meth ods and Results Thirty-seven patients with 42 atrial arrhythmias (mean +/-SD age, 41+/-24 years) who had failed a median of three drugs were enrolled. Diagnoses were automatic atrial tachycardia in 12, atypical atrial flutter in 1, typical atrial flutter in Is, reentrant atrial ta chycardia in 8, and sinus node reentry in 3 patients. Sites for atrial flutter ablation were based on anatomic barriers in the floor of the right atrium. For automatic atrial tachycardia, the site of earliest a ctivation before the P wave was sought. All with reentrant atrial tach ycardia had previous surgery for congenital heart disease and reentry around a surgical scar, anatomic defect, or atriotomy incision and our goal was to identify a site of early activation in a zone of slow con duction. At target sites, 20 to 50 W of radiofrequency energy was deli vered during tachycardia between the 4- or 5-mm catheter tip and a ski n patch, except in 4 patients with atrial flutter, in whom a catheter with a 10-mm thermistor-embedded tip was used. Procedure end point was inability to reinduce tachycardia. Acute success was achieved in 11 o f 12 (92%) with automatic atrial tachycardia, 17 of 18 (94%) with typi cal atrial flutter, 7 of 8 (88%) with reentrant atrial tachycardia, an d 3 of 3 (100%) with sinus node reentry but not in the patient with at ypical atrial flutter. For tachycardia involving reentry (reentrant at rial tachycardia and atrial flutter), successful ablation required sev ering an isthmus of slow conduction. For those with atrial flutter, th is was between the tricuspid annulus and the coronary sinus os (10) or posterior (4) or posterolateral (3) between the inferior vena cava (2 ) or an atriotomy scar (1) and the tricuspid annulus. Deep venous thro mbosis occurred in 1 patient. At mean follow-up of 290+/-40 days, the ablated arrhythmia recurred in 1 (9%) with automatic atrial tachycardi a, 5 (29%) with atrial flutter, and 1 (14%) with reentrant atrial tach ycardia, all of whom had successful repeat ablation. Previously undete cted arrhythmias occurred in 2 patients who are either asymptomatic or controlled with medication. Conclusions Ablation of automatic and ree ntrant atrial tachycardia and atrial flutter had a high success rate a nd caused no complications from energy application. Repeat procedures may be required for long-term success, especially in patients with atr ial flutter. The mechanism by which ablation is successful is similar for atrial flutter and other forms of atrial reentry and involves seve ring a critical isthmus of slow conduction bounded by anatomic or stru ctural obstacles. Automatic arrhythmias are abolished by directing les ions at the focus of abnormal impulse formation.