A total of 154 patients underwent cryoablation for AVNRT during the study period. () Most patients had a normal heart structure, with AVNRT as the only arrhythmia substrate. A total of ten patients (6.5%) had congenital heart disease, consisting of atrial septal defects (3), aortic valve abnormalities (3), Ebstein’s anomaly (1), patent ductus arteriosus (1), unbalanced AV canal defect (1), L-transposition of the great arteries (1). Nineteen patients had additional arrhythmias either documented previously or identified during this electrophysiology study. The additional arrhythmias included Wolff-Parkinson-White syndrome (7), concealed accessory pathway (1), ectopic atrial tachycardia (6), atrial fibrillation (4), and junctional ectopic tachycardia (1). Ten patients underwent previous electrophysiology studies, 5 of whom had successful RF ablations for an accessory pathway. Two patients had prior RF ablations for AVNRT at other institutions. Three patients had prior studies but no ablation was performed secondary to small patient size at the initial electrophysiology study. One patient had had a prior pacemaker placed for cardioinhibitory syncope. Two of our patients had RF ablation of an accessory pathway during the same procedure as the cryoablation for AVNRT.
Comparison of cryoablation procedures for AVNRT with the 4 mm versus 6 mm cryoablation catheter tips
During the electrophysiology study and ablation, sustained AVNRT was identified in 123 (79%) patients and nonsustained in 21 (14%). Ten (7%) had presumed AVNRT. Of the 144 patients with identified AVNRT, these tachycardias were typical in 128 (89%) and atypical in 14 (10%). Two patients had typical and atypical AVNRT.
The 4 mm tip cryoablation catheter was utilized in 98 (64%) patients and the 6 mm tip in 56 (36%) patients. Patients undergoing cryoablation with the 4 mm tip catheter were younger (p=0.002) and smaller (p=0.004) than those with the 6 mm tip catheter. ()
Initial success of cryoablation for AVNRT was documented in 146/154 (95%). () In comparing the 4 mm cryoablation catheter tip to the 6 mm tip, there was no difference in initial success rates (93% versus 98%, respectively, p=0.15). Patients undergoing cryoablation with the 4 mm tip cryoablation catheter had a significantly longer procedural time but had fewer cryoablations lasting ≥ 240 seconds compared to patients with the 6 mm tip. Interestingly, both populations had the same median number of 4 lesions, but distributions that were different enough to result in a statistically significant difference when evaluated by the Mann-Whitney ranks sum test. Furthermore, the mean number of cryoablations for each population were significantly different (the mean number of lesions lasting ≥ 240 seconds for the population treated with the 4 mm tip was 3.9; for the 6 mm tip it was 4.6 lesions). ()
Outcomes of patients presenting for cryoablation of atrioventricular nodal reentrant tachycardia (AVNRT)
Six patients had procedural failures for cryoablation secondary to the following: 1 patient developed transient 3rd
degree AV block with mechanical contact from a 4 mm tip cryoablation catheter and no lesions were delivered (reported in a previous series) 8
and 5 (four with the 4 mm tip, one with the 6 mm tip) patients had persistent AVNRT and crossed over to RF. Two patients (both 4 mm tip) were listed as indeterminate. After the initial series of cryoablation lesions, these two patients continued to have inducible AVNRT. Several additional cryoablation lesions were then placed. On the final cryoablation lesion, transient 1st
(1 patient) or 2nd
(1 patient) degree AV block occurred and the procedure was concluded without repeat atrial extrastimulus testing.
For patients with successful procedures, AV nodal echo beats continued to be present in 34/139 (24%) patients. The vast majority of these patients (32/34) had single echo beats, and 2 patients had two AV nodal echo beats. Dual AV nodal physiology was present in 68/134 (51%) pre-ablation and this was reduced to 32/119 (27%) post-cryoablation (p< 0.001). The finding of PR ≥ RR was documented in 71/125 (57%) pre-ablation and this was reduced to 8/110 (7%) post-ablation (p< 0.001). There was no difference between the 4 mm and 6 mm tip with regards to these parameters.
Transient 3rd degree AV block developed in 9/154 (6%) patients. The AV block occurred with catheter contact (5) or during cryoablation (4). The AV block was generally only a few beats and recovered with moving the catheter away from the AV nodal area or on rewarming of the cryoablation catheter. One patient developed third degree heart block 39 seconds after the onset of cryoablation with a 6 mm tip, at which point cryoablation was terminated. After recovery of atrioventricular conduction without any intervention, no further lesions were placed, and on further extrastimulus testing, no evidence of AVNRT remained. This patient has not recurred. Another patient required temporary pacing for ten minutes after mechanical contact prior to the delivery of any lesions, and then went on to have a successful ablation.
Follow-up was available for all 146 patients at a median duration of 12 months (6–31). The overall AVNRT recurrence rate for patients after an initially successful cryoablation was 21/146 (14%). The recurrence rate for the 4 mm tip cryoablation catheter (18%) was higher than for the 6 mm tip (9%), but did not reach statistical significance (p=0.16). The median time to recurrence was 2.5 months (range 0.25 – 20 months). Patients who underwent cryoablation with the 4 mm tip cryoablation catheter had a longer duration of follow-up compared to the 6 mm tip. ( & ).
Kaplan-Meier freedom from arrhythmia recurrence following an initially successful cryoablation for atrioventricular nodal reentrant tachycardia (AVNRT). Patients are grouped based on cryoablation catheter tip size. Log-rank P= 0.2729
Of the 19 patients with additional arrhythmias, only one had a recurrence. This patient had atrial fibrillation/flutter during the initial procedure. His arrhythmia recurrence was identified as AVNRT during a followup electrophysiology study.
Predictors of AVNRT recurrence
With univariate analysis, a longer fluoroscopy time was the only significant factor associated with AVNRT recurrence. () The presence of AV nodal echo beats after an ablation was not associated with a recurrence. Furthermore, neither of the two patients with 2 AV nodal echo beats had a recurrence. The presence of dual AV node physiology post-ablation trended towards a significant association with a recurrence (p = 0.08). However, only 51% (68/134) of our population had dual AV nodal physiology pre-ablation.
Comparison of patients with and without AVNRT recurrence following an initially successful cryoablation.
Multivariate analysis using logistic regression failed to identify any significant predictor of AVNRT recurrence. This multivariate analysis was performed with a number of different models incorporating age, weight, additional arrhythmias, congenital heart disease, fluoroscopy time, procedural time, PR ≥ RR (before and after ablation), dual AV node physiology (before and after ablation), cryoablation catheter tip size, number and duration of cryoablation lesions, presence of AV block, and follow-up time.