HISTOPATHOLOGY OF CANINE HEARTS SUBJECTED TO CATHETER ABLATION USING RADIOFREQUENCY ENERGY

To investigate the pathologic changes of the myocardium and the advers e effects of radiogrequency (RF) catheter ablation, we observed canine hearts that had been ablated by RF energy. Catheter ablation was admi nistered to three sites of the hearts of 46 dogs: endomyocardium, coro nary sinus, and atrioventricular junction. The dogs were sacrificed 0- 12 weeks after ablation and the lesions were stained with hematoxylin- eosin and Azan stain. Each ablated lesion was well demarcated from the adjacent normal tissue. The margin between the ablated lesion and nor mal tissue became clearer with time. The lesions were hemispherical an d measured about 2 to 10 mm in diameter and 1 to 6 mm in depth. Histol ogic examination in the acute phase demonstrated the presence of coagu lation necrosis of the myocardium, interstitial hemorrhage and edema, followed by infiltration of inflammatory cells. Granulation tissue rep laced the normal myocardium. In the chronic phase, the lesions became fibrotic and fatty. A mural thrombus was found in 30% of the cases of endomyocardial ablation and 50% of the right ventricular lesions were transmural. Ablated lesions in the coronary sinus extended to the left atrium and left ventricle. Obstruction of the coronary sinus was obse rved in 8% of the ablated dogs. Most of the lesions with complete atri oventricular block were ablated at the His penetrating region of the c onduction system. Thus, since the ablated lesions were clearly delinea ted, catheter ablation using RF energy appears to eliminate only the t arget area.