FACTORS INFLUENCING IMPEDANCE DURING RADIOFREQUENCY ABLATION IN HUMANS

Impedance during radiofrequency (RF) catheter ablation procedures is d ependent on a variety of parameters related to the catheter, cabling, reference patch, body size, and temperature. To examine the influence of body size, impedance was measured during clinical ablation procedur es in 93 patients (Group I) with a wide range of body sizes. In 14 oth er patients (Group II), impedance was measured during variations in ca theter tip size (5, 6 and 7 Fr), reference patch size (120 and 60 cm(2 )), patch location (chest vs. thigh), and catheter tip tissue contact. The average impedance was also compared to average tip temperature in Group II patients. Impedance decreased with increasing catheter tip s ize, reference patch size and proximity of the patch to the heart. How ever, the effects of body geometry were complex. For example, using a chest patch, impedance increased with body surface area, but using a t high patch it decreased, suggesting that lung volume may increase impe dance, but body width may actually decrease it. An increase in tip tis sue contact, relative to blood contact, increased the impedance, sugge sting that impedance may be a useful measure of tip tissue contact. Fi nally impedance decreased with increasing tip temperature, suggesting that impedance may he useful as a real time measure of tissue and bloo d heating. The results are interpreted in terms of an electrical analo g which suggests further that despite the lower total power when the s ame voltage is applied to a higher impedance, less voltage should be a pplied to achieve the same tissue effect when the measured impedance i s higher.