Effect of Environmental Impedance Surrounding a Radiofrequency Ablation Catheter Electrode on Lesion Characteristics

Abstract

Environmental Impedance and Ablation Lesions Introduction The electrical conductivity of the environment surrounding a catheter electrode may affect radiofrequency (RF) current. A higher impedance environment enveloping a catheter tip can be insulating and thus direct RF preferentially into targeted cardiac tissue. We sought to evaluate whether different environmental impedances will affect RF lesions. Methods An ex vivo model using bovine myocardium, load cell, and 4 mm ablation catheter was tested using a circulating bath of normal (0.9%; NS) and half normal (0.45%; HNS) saline. Ablations were performed at 50 W. In addition, using a porcine thigh prep model, warmed heparinized blood was circulated at 350 mL/min. Prior to ablation, circulating bath impedance was altered with NS and HNS. RF was applied at 30 W with a force‐sensing, open irrigated catheter. Results Ex vivo RF with a 4 mm catheter using an HNS bath led to larger lesions, 286.7 ± 64 mm³ versus 198.9 ± 61 mm³ (P < 0.001), compared to an NS bath. In the porcine thigh prep, for RF in the high impedance (HNS) bath, initial and final impedances were higher, and the measured impedance reductions during ablation were larger, compared to RF in the low impedance (NS) bath. In vivo ablation within a higher impedance bath created larger lesion sizes, compared to a lower impedance bath, 222.4 ± 63.4 mm3 versus 135.4 ± 61.7 mm3 (P < 0.001). Conclusions A higher impedance surrounding an RF catheter can facilitate more effective RF and thereby increase lesion size. This may have implications for RF safety and efficacy, especially in the epicardium where pericardial fluid can be altered with infusion of ionic solutions.

Nonionic irrigated radiofrequency ablation of refractory incessant ventricular tachycardia via great cardiac vein

“…Nguyen and colleagues1, 2, 3 have compared RF lesion size with NS, half NS, and D5W irrigation in preclinical animal models. D5W was found with the largest lesions as compared to the former 2 fluids, which has been attributed to decreased dispersion or shunting of energy that may result with an ionic charged solution, decreasing the local impedance field.…”

“…The potential complication of D5W irrigation is higher incidence of steam pops (50/80 applications) when using high power (50 W) and a perpendicular position 1 ; we applied lower power and parallel touch in this case, which may help avoid the risk. Meanwhile, for achieving deeper lesions, we increased the impedance cutoff to improve the efficacy of RF energy delivery 3 . Whether increasing to high power may have been equally as effective as changing the irrigant, our clinical experience has shown rapid increases in temperature that impair continued RF when ablating within the coronary venous system.…”

Patient Selection for Epicardial Ablation—Part II: The Epicardial Approach and Current Challenges Associated with Epicardial Ablation

“…Additional ex vivo and in vivo studies have confirmed that increased fluid in the pericardial space leads to smaller lesion formation and that a higher impedance fluid in this same space can facilitate effective delivery of RF ablation to the myocardium. 25…”

“…Decreasing the ionic concentration of the irrigant by using a fluid such as half-normal saline can increase the surrounding impedance and thus decrease the loss of RF to the surrounding environment, allowing for greater RF delivery ( Figure 1B). 25,34 With regard to environmental impedance, this may be of greater importance in the epicardium, given the presence of intrapericardial fluid and epicardial fat.…”

Forging ahead: Update on radiofrequency ablation technology and techniques

“…Results show a high rate of acute success among those treated, although steam pops were noted in 12 cases . Effect of environmental impedance can also alter lesion size with higher impedance surrounding RF catheters facilitating more effective RF energy delivery . This may have implication on use of high impedance supported ablation in the epicardium.…”