Don't forget to gather the evidence: myocardial effects of cryoablation in the immature heart.

In this issue of The Journal, Khairy et al1 present the results of an impeccably performed study comparing the effects of cryothermal (CRYO) and radiofrequency (RF) ablation on the developing swine heart. Despite the earlier report from my group in 1994 that RF lesions appear to grow when placed in the atria and ventricles of developing hearts,2 until now no parallel study has been published to assess the late effects of CRYO in the atria, ventricles, and AV groove of the immature heart. This lack of data may have come from a combination of limited funding sources and a form of complacency, perhaps based on early animal and human data demonstrating the relative safety of CYRO over RF techniques,3–7 all factors that may have led to acceptance of this new technology as preferable to RF for the developing heart. In fact, Khairy et al initially speculated that CRYO lesions would act differently than RF lesions at late follow-up, based on the different mechanisms of cell injury, and the distinct acute histological features of the lesions from the two techniques.4 When the data were in, they actually demonstrated that there were no differences between the late effects of CRYO and RF on developing myocardium, and both techniques led to longterm lesion growth and invasion of scar tissue into surrounding myocardium.1