Estimation of Temperature During Radiofrequency Catheter Ablation Using Impedance Measurements

Abstract

Temperature monitoring during radiofrequency catheter ablation is useful but requires specialized equipment that is not generally available. Previous studies have shown that impedance characteristically decreases as the result of heating at the electrode-tissue interface. The purpose of the current study was to determine if impedance changes during radiofrequency current application could be used to estimate endocardial temperature in patients undergoing catheter ablation. Data from 43 patients treated with a thermistor ablation catheter were retrospectively analyzed. The slope of the initial 2 seconds of the impedance curve and subsequent changes in impedance were incorporated into an equation for estimation of temperature in real-time. The accuracy of this equation was assessed by prospectively comparing the calculated and measured temperatures in 19 patients. Of the 88% of energy applications that were suitable for analysis, the average difference between calculated and measured temperatures was 5.2 +/- 5.6 degrees C. The average error was < 10 degrees C in 89% of applications. The results of this study suggest that impedance measurements can be used to quantify tissue temperature in real-time during radiofrequency catheter ablation. This method is sufficiently accurate to allow titration of power output to produce temperatures in the useful range (50-80 degrees C) while avoiding excessive heating (> 90 degrees C).

Observations on Attenuation of Local Electrogram Amplitude and Circuit Impedance During Atrial Radiofrequency Ablation: An In vivo Investigation Using a Novel Direct Endocardial Visualization Catheter

“…The usefulness of impedance decrement in predicting tissue heating has been studied extensively. It is an accepted marker for catheter tissue contact . Twenty percent decrement was chosen as significant, as many of the previous studies indicated that 5–20% decrement was suggestive of effective ablation .…”

Remote magnetic versus manual catheters: evaluation of ablation effect in atrial fibrillation by myocardial marker levels

“…The short application time was employed to reduce the risk of char formation [21]. Efficiency is lower during the first few seconds of RFA delivery, until the output reaches a plateau and the lesions might be enlarged up to 180 s of energy delivery [22, 23]. A longer time to the plateau phase and longer ablation time at each site in the RMI group may have led to a lower TnTc.…”

Impedance and Temperature Monitoring Improve the Safety of Closed‐Loop Irrigated‐Tip Radiofrequency Ablation

“…The impedance fall that occurs during RF ablation has been postulated to be caused by an increase in tissue temperature, 7,8,10,12 but some authors have detected irreversible changes in components of the impedance 11 . Data recorded during repeated ablations at the same site suggested that the impedance drop occurring during radiofrequency ablation in cardiac tissue appeared to be due to reversible factors (e.g., temperature) rather than irreversible changes.…”