SUBENDOCARDIAL AND INTRAMURAL TEMPERATURE RESPONSE DURING RADIOFREQUENCY CATHETER ABLATION IN CHRONIC MYOCARDIAL-INFARCTION AND NORMAL MYOCARDIUM

Background The ability of radiofrequency energy to extend across scar tissue is unknown. We investigated the effects of radiofrequency cathe ter ablation on intramural temperature in experimental chronic myocard ial infarction. Methods and Results Myocardial infarction was induced in eight dogs by a transcatheter coronary artery occlusion-reperfusion technique. The dogs were reanesthetized after 15 to 24 days. Four add itional dogs served as controls. The freshly excised preparations were cut and placed in a saline bath at 37 degrees C. Temperature-guided e nergy applications with a preselected catheter tip temperature of 80 d egrees C were performed for 60 seconds with a 7F ablation catheter. Th ermoelements were inserted into the ventricular muscle at depths of 2. 5 to 3.0 mm (''subendocardial'') and 5.5 to 6.0 mm (''intramural''). S urviving muscle fibers were interspersed among the transmural scar tis sue. The maximal temperatures did not differ significantly between nor mal hearts and chronic infarctions at the subendocardial (64.5+/-6.4 d egrees C versus 66.7+/-6.6 degrees C) or intramural thermo-element (51 .9+/-5.7 degrees C versus 52.3+/-5.7 degrees C). The myocardial temper ature rise was slow, and steady-state temperatures had not been reache d after 60 seconds. The intramural temperatures in chronic infarctions measured 49.0+/-4.3 degrees C after 40 seconds of energy delivery and were still below the critical tissue temperature of 50 degrees C that is necessary to induce permanent myocardial damage. Conclusions Tempe rature-guided radiofrequency ablation in a dog model of chronic myocar dial infarction may induce tissue temperatures >50 degrees C at a dept h of 5.5 to 6.0 mm. The intramural temperature rise was slow, indicati ng that long energy applications might be necessary if the arrhythmoge nic substrate is subepicardial.