Effect of radiofrequency energy delivery in proximity to metallic medical device components

Abstract

Radiofrequency (RF) ablation of cardiac arrhythmias is often performed in the presence of metallic materials in the heart. We hypothesize that metal objects in proximity to an RF ablation source can lead to ohmic heating of surrounding tissue. Furthermore, we hypothesize that insulation of the metal can mitigate this RF effect. A model consisting of viable bovine myocardium or thermochromic liquid crystal medium, a circulating saline bath at 37°C, and a load cell was used. A 4-mm RF ablation catheter was positioned with 10 g of force over bovine myocardium and placed in proximity to a copper wire, a defibrillator lead, and a circular mapping catheter. RF was applied at 30 W, and tissue temperatures were measured. Ablation near insulated and noninsulated esophageal temperature probes was also performed. Ablation in proximity to metal resulted in higher temperatures. Average maximum distances for observed thermal changes to >45°C for the ± lead were 5.2 ± 0.3 mm and 5.7 ± 0.4 mm when metal was interposed between the catheter and the ground electrode. Presence of an esophageal temperature probe increased temperatures in tissues adjacent to the probe and caused lesions remote to the ablation site. Esophageal probe insulation prevented these tissue temperature increases and injury to nontargeted tissues. Effects of RF ablation are potentiated near metallic components of medical devices, leading to significant tissue heating. Further research is needed to assess the safety impact of RF in the myocardium near metallic objects, particularly esophageal temperature probes.