PATHOLOGY OF THE CARDIAC LESIONS INDUCED BY RADIOFREQUENCY ABLATION IN AN EXPERIMENTAL-MODEL

Radiofrequency catheter ablation is increasingly being used for the tr eatment of several tachyarrhythmias. The main aim of this paper is to describe the lesional pathology produced by this type of current. Four teen Wistar rats (mean weight 300 g) were subjected to discharges of a 700 KHz, pure, unmodulated, sine-wave radiofrequency generator. Three rats, through open chests, received epicardial shocks and were immedi ately sacrificed (''acute'' lesions). The remaining 11 rats received s hocks through percutaneously plunged tungsten wires, and were sacrific ed 1 to 4 weeks after the procedure (''chronic'' lesions). Hearts were fixed in buffered (pH7) 10% formalin solution. Selected slices were s tained with hematoxilin-eosin and Mallory trichrome. Other slices were fixed in 3% glutaraldehyde and post-fixed in osmium tetroxyde, dehydr ated and included in Polybed 812. Ultrathin slices were stained with u ranil acetate and lead citrate and examined in a JEOL JEM-100 C electr onic microscope. ''Acute'' specimens showed small coagulation necrosis areas, well delimited by carbonization and hemorrhages. Neighbouring myocardium showed one o two rows of moderate cell lesions which consis ted of cytoplasmic homogeneization and increased contracture bands. '' Chronic'' lesions showed granulation tissue with mononuclear infiltrat es and neoformation vessels surrounding a central necrosis area. The o lder the lesion, the larger the number of fibroblasts and mature colla gen tissue. Ultrastructural studies showed irreversible myocardial cha nges in the lesional borders, with cytosolic and myofibrillar edema, c ontracture bands and rupture of mitochondrial crests. Radiofrequency l esions are limited, shallow and with net borders, which makes them alm ost ideal for subendocardial ablation of small arrhythmogenic areas.