BAD NAUHEIM, GERMANY. In 1998 Professor Michel Haissaguerre at the Hopital Cardiologique du Haut Leveque in Bordeaux reported that paroxysmal atrial fibrillation was mainly triggered by "rogue" cell clusters in the pulmonary veins. Early ablation techniques aimed at isolating the pulmonary veins from the left atrium by using radiofrequency (RF) energy to "burn" a ring of lesions just inside the vein. Unfortunately, this led to several cases of pulmonary veins stenosis (narrowing of the diameter of a vein by 50% or more). Thus, newer RF ablation techniques place the lesion ring in the left atrium itself rather than inside the veins, thus avoiding the danger of stenosis.
Nevertheless, placing a complete lesion ring just inside the vein is still theoretically at least, the best way of ensuring a complete electrical barrier between the potentials originating in the veins and the left atrium itself. The search for a technique that could achieve this without the danger of stenosis eventually led to the development of cryoablation in which a catheter or inflated balloon (cryo-balloon) cooled with liquid nitrogen is used to create the lesion ring. Early experiments showed that lesions created with cryoablation did not cause pulmonary vein stenosis.
German electrophysiologists now report on the evaluation of a new cryo-balloon device (Artic Front, Cryocath, Quebec, Canada) and an 8-mm cryo-catheter (Freezor Max) also developed by Cryocath. Their clinical trial involved 293 patients with paroxysmal afib and 53 with persistent afib. The average age of the patients was 59 years (62% male). They had suffered from symptomatic afib for an average of 7 years and had tried at least two antiarrhythmic drugs with no success. Forty-five percent of the study participants had hypertension and another 17% had mild heart disease, but none had advanced structural heart disease.
The patients all underwent pulmonary vein isolation using either a 23-mm or a 28-mm diameter balloon (when inflated) and the 8-mm catheter as required to reach spots missed by the balloons. The procedure was performed under conscious sedation using electrophysiological mapping with Lasso catheters and fluoroscopy as needed. Total average procedure time was about 3 hours (170 minutes), fluoroscopy time averaged 40 minutes, and total cryo application averaged 46 minutes. Each vein, on average, received 2.8 cryo-balloon applications lasting about 5 minutes each. All patients remained on warfarin and antiarrhythmic medication for the first 3 months following the procedure (blanking period).
After the blanking period patients were scheduled for quarterly follow-up visits, which included 7-day Holter ECG recordings. After an average 12-month follow-up, 74% of paroxysmal afibbers had experienced no recurrence of AF without the use of antiarrhythmics. NOTE: A total of 79 paroxysmal afibbers were lost to follow-up for one reason or another; thus, the success rate based on the total number of patients undergoing the initial ablation is probably somewhere between 54% and 74%. The success rate among persistent afibbers was only 42%. The main adverse event during the trial was phrenic nerve palsy (PNP), which was observed in 26 patients (11%) during ablation of the right superior vein. Most (90%) of PNPs occurred during the use of the 23-mm balloon. All cases of PNP were fully resolved in less than a year. No cases of stenosis, atrioesophageal fistula, stroke or death occurred, but 2 patients (0.8%) did develop left atrial flutter during the blanking period. No other atrial tachycardia or flutter developed during follow-up.
The German researchers conclude that cryoablation is safe and effective for paroxysmal afibbers, but not recommended for those with persistent AF. NOTE: Five of the 16 authors of this paper had received financial support from Cryocath.
Neumann, T, et al. Circumferential pulmonary vein isolation with the cryoballoon technique. Journal of the American College of Cardiology, Vol. 52, July 22, 2008, pp. 273-78
Editor's comment: This large-scale trial of ablation using the cryo-balloon technique confirms that the procedure is safe and reasonably effective for paroxysmal afibbers, but much less so for persistent afibbers. This is not really too surprising since the cryo-balloon technique only addresses isolation of the pulmonary veins, but does not involve linear ablations and other substrate modifications necessary to adequately deal with persistent AF. It is, unfortunately, not clear from the article why only 214 of the original 293 paroxysmal afibbers were followed up in arriving at the 74% success rate. Thus, the quoted success rate would seem to be a bit uncertain and could, presumably, be as low as 55%.