A Novel Temperature Controlled Bipolar Radiofrequency Ablation: An Ex Vivo Study for Optimizing Efficacy and Safety Parameters
Authors: Inaba Osamu , Inamura Yukihiro , Takagi Takamitsu , Meguro Shin , Nakata Kentaro , Michishita Toshiki , Isonaga Yuhei , Tachibana Shinichi , Ohya Hiroaki , Sato Akira , Miyazaki Shinsuke , Yamauchi Yasuteru , Goya Masahiko , Nitta Junichi , Sasano Tetsuo 
Published: November 2024

Background

Bipolar radiofrequency catheter ablation (BRFA) is a potential treatment for refractory ventricular arrhythmias from deep myocardial tissue. However, clear indicators of efficacy and safety remain undefined.

Methods

In an ex vivo model, BRFA was performed using either the QDOT Micro™ (QDT) or Thermocool SmartTouch SF™ as the active catheter, with the DiamondTemp Ablation™ (DTA) as the return catheter. Predictors of transmural lesion formation and steam-pop occurrence were assessed.

Results

A total of 391 BRFA applications were performed with variations in the interelectrode distance between the active and return catheter tips, ranging from 6 to 27 mm, under various catheter tip and tissue contact configurations. The ablation index (AI) adjusted for inter-electrode distance effectively predicted transmural lesion formation. Logistic regression analysis revealed a coefficient for AI of −0.040 (SE: 0.0067; 95% CI: [−0.053, −0.027]; p < 0.0001) and for inter-electrode distance of 2.2 (SE: 0.35; 95% CI: [1.5, 2.9]; p < 0.0001). The decision boundary for transmural lesion formation was AI = 54 × inter-electrode distance – 260. When AI exceeded this value, sensitivity, specificity, and positive and negative predictive values for predicting transmural lesions were 89%, 92%, 91%, and 90%, respectively. When the AI was further increased by 50, the specificity reached 100%.

Steam-pops on the active catheter side occurred only during power-controlled BRFA and were absent in temperature-controlled BRFA with a 45°C cutoff. On the return side, steam-pops occurred when DTA temperature exceeded 55°C, with deeper cracks observed above 60°C.

Conclusions

An AI adjusted for inter-electrode distance strongly predicted transmural lesions. Temperature-controlled BRFA with a 45°C cutoff for QDT as the active catheter and 55°C for DTA as the return catheter may prevent steam-pops. Additionally, steam-pops occurring at higher catheter tip temperatures were associated with deeper tissue cracks.

Clinical Perspective

What is known?

Bipolar radiofrequency ablation has shown promise as an effective treatment option for ventricular arrhythmias originating from deep regions of the ventricular myocardium.

The indicators for successful transmural lesion formation and the predictors for steam-pop are not yet well understood, and the accuracy of conventional metrics remains limited.

What the study adds

The ablation index (AI) necessary for achieving successful transmural lesion formation during bipolar radiofrequency ablation, using a QDOT micro™ (QDT) as the active catheter and a DiamondTemp Ablation™ (DTA) the return catheter, can be determined using the formula: AI = 54 × inter-electrode distance – 260, where the inter-electrode distance denotes the distance between the active and return electrodes.

During bipolar radiofrequency ablation, performing temperature-controlled ablation with a temperature cutoff of 45°C for the QDT and 55°C for the DTA may help prevent steam-pop.

Furthermore, the higher the DTA temperature at the time of steam-pop, the deeper the cracks that are formed.