Background: Radiofrequency catheter ablation in immature hearts has been associated with marked enlargement of lesions over time, with potential for related late adverse events. It remains unknown whether cryothermal ablation lesions display a similar pattern of growth.
Methods and results: Ablation lesions (n=384) were performed in 32 infant miniature swine in right and left atria, ventricles, and atrioventricular (AV) grooves preselected by a randomized factorial design devised to compare radiofrequency and cryothermal lesions produced by 7F 4-mm electrode-tip catheters. Animals were euthanized acutely or at 1, 6, or 12 months, according to the randomization scheme. The miniature swine weighed 8.8±1.2 kg and were 63±13 days of age at time of ablation. The minimum temperature during cryoablation was -79.8±3.4°C and the average temperature during radiofrequency ablation was 54.4±5.5°C. On morphometric analyses, no differences in the rate of growth of ablation lesions were noted between the 2 energy modalities in atria (P=0.44), ventricles (P=0.57), or AV grooves (P=0.69). Lesion volumes increased 3.3-fold in atria (95% confidence interval [CI], 2.3 to 4.3; P=0.001) and 2.2-fold in ventricles (95% CI, 1.4 to 3.0; P<0.0001), with the difference between chambers being nonsignificant (P=0.22). Whereas the depth of AV groove lesions increased over time (1.9-fold; 95% CI, 1.5 to 2.3; P<0.0001), lesion volumes did not enlarge significantly (1.5-fold; 95% CI, 0.4 to 2.6; P=0.45).
Conclusions: Ablation lesions produced by cryothermal energy in immature atrial and ventricular myocardium enlarge to a similar extent to radiofrequency ablation. In contrast, AV groove lesion volumes do not increase significantly with either energy modality.