Transvenous cryo-ablation of the slow pathway for the treatment of atrioventricular nodal re-entrant tachycardia: a single-centre initial experience study.

AIMS Within the last several years, transvenous cryo-ablation has become an alternative method to perform ablation of the slow-pathway. This study evaluated the acute and long-term safety and effectiveness of atrio-ventricular nodal re-entrant tachycardia (AVNRT) cryo-ablation. METHODS AND RESULTS The first 69 consecutive patients with AVNRT (60 slow-fast, 4 fast-slow, and 5 slow-slow) who underwent slow-pathway cryo-ablation were included. Mean age was 37 +/- 15, body weight 68 +/- 14 kg, symptom duration 125 +/- 104 months, and number of ineffective antiarrhythmic (AA) drugs 1.8 +/- 1.4. A 7 Fr cryo-catheter (Cryocath(A)) was used, with initially 4-mm-tip and later with 6-mm-tip electrode. Cryo-mapping (n = 7.9 +/- 8.4 per pt) was performed at the temperature of -30 degrees C to test the effect on the target ablation site. Successful cryo-mapping was defined as abolition of nodal conduction jump or AV nodal refractory period prolongation. Cryo-ablation (n = 5.1 +/- 4.9 per pt) was then applied by freezing to -75 degrees C for 4 min in duration if no AV-block occurred. Acute procedural success (defined as AVNRT non-inducibility) after the first cryo-ablation attempt was achieved in 60/69 patients (87%). During cryo-ablation, inadvertent transient AV-block was encountered in 14 patients (five I AV-block and nine II-III AV-block). A mid-septal target site was the only variable correlated with inadvertent AV-block occurrence during cryo-ablation (P < 0.02). Long-term clinical success after cryo-ablation was globally achieved in 56/66 (85%) with a mean follow-up of 18 +/- 9 months (3 pts dropped-out). After the first procedure, 41/66 (62%) had no relapse, eight had a dramatic reduction in AVNRT duration-frequency and considered themselves cured, and five needed previously ineffective AA (with no relapse in three, drastic reduction in AVNRT duration-frequency in two). The five last patients needed one or more procedures, after which one had no recurrence and one had reduction in duration-frequency. Absence of recurrence after the first procedure was positively correlated with 6-mm-tip cryo-catheter use (<0.001) and negatively with acute procedural success (<0.001). At multivariate analysis, both were independently significant (<0.04 and <0.008, respectively). Long-term clinical success was correlated only with 6-mm-tip cryo-catheter use (<0.001). CONCLUSIONS Slow pathway cryo-ablation is associated with an acute success but a higher recurrence rate. A 6-mm-tip cryo-catheter seems to assure during cryo-ablation a large acute and long-term success. AV-block seems non-guaranteed by a negative cryo-mapping, stressing on need of a careful surveillance. Nevertheless, the theoretical advantage of avoiding the risk of permanent AV-block when compared with radiofrequency needs larger series to be demonstrated.