Impedance-decline-guide power control long application time bipolar radiofrequency catheter ablation

Computer simulation of low-power and long-duration bipolar radiofrequency ablation under various baseline impedances

Compared to traditional unipolar radiofrequency ablation (RFA), bipolar RFA offers advantages such as more precise heat transfer and higher ablation efficiency. Clinically, myocardial baseline impedance (BI) is one of the important factors affecting the effectiveness of ablation. We aim at finding suitable ablation protocols and coping strategies by analyzing the ablation effects and myocardial impedance changes of bipolar RFA under different BIs. In this research, a three-dimensional local myocardial computer model was constructed for bipolar RFA simulation, and in vitro experimental data were used to validate accuracy. Four fixed low-power levels (20 W, 25 W, 30 W, and 35 W) and six myocardial BIs (91.02 Ω, 99.83 Ω, 111.03 Ω, 119.77 Ω, 130.03 Ω, and 135.45 Ω) were set as initial conditions, with an ablation duration of 120-s. In the context of low-power and long-duration (LPLD) ablation, the maximum TID (TIDM) decreased by 21-32 Ω, depending on the BI. In cases where steam pop did not occur, TIDM increased with the increase in power. For the same power, there was no significant difference in TIDM for the range of BIs. In cases where steam pop occurred, for every 1 Ω increase in BI, TIDM increased by 0.34-0.41 Ω. The simulation results also showed that using a higher power resulted in a smaller decrease in TIDM. This study provided appropriate ablation times and impedance decrease ranges for bipolar LPLD RFA. The combination of 25 W for 120-s offered optimal performance when considering effectiveness and safety simultaneously.

Symmetrical recovery time course between impedance and intramyocardial temperature after bipolar radiofrequency ablation; Role of impedance monitoring to estimate temperature rise

INTRODUCTION

During radiofrequency (RF) ablation, impedance monitoring has been used to avoid steam-pop caused by excessive intramyocardial temperature (IMT) rise. However, it is uncertain why the impedance decline is related to steam-pop and whether the impedance decline is correlated to IMT.

METHODS

Twenty-one bipolar ablations (40 W, 30-g contact, 120 s) were attempted for seven perfused porcine myocardium. Immediately after ablation, a temperature electrode was inserted into the mid-myocardial portion, and the recovery process of impedance and its correlation to IMT were assessed.

RESULTS

Transmural lesion was created in all 21 applications but steam-pop occurred in 5/21 applications with large impedance decline. In the 16 applications without steam-pop, impedance and IMT soon after ablation were 97.2 ± 4.0 Ω and 66.1 ± 4.8 °C, respectively. Reasonably high linear correlation was demonstrated between the maximum IMT after ablation and impedance differences before and after ablation. Recovery processes of the decreased impedance and the elevated IMT fit well to each equation of the single exponential decay function and showed symmetric shapes with no statistical difference of time constant (100.1 ± 34.5 s in impedance vs. 108.7 ± 27.3 s in IMT) and half-time of recovery (144.5 ± 49.8 s in impedance vs. 156.9 ± 39.4 s in IMT). Recovered impedance after ablation (104.8 ± 3.9 Ω) was 5.1 ± 2.0 Ω smaller than that before ablation (109.9 ± 2.7 Ω), suggesting several factors other than IMT rise participate in impedance decline in RF ablation.

CONCLUSIONS

Recovery of impedance and IMT after ablation well correlated, which supports the usefulness of impedance monitoring for safe RF ablation.

Bipolar ablation of ventricular arrhythmias: Step-by-step

Radiofrequency (RF) ablation of intramural ventricular arrhythmias (VAs) may require advanced ablation techniques to achieve effective energy transfer to the targeted tissue. As an alternative to standard RF ablation, catheter ablation can also be conducted in bipolar configuration when two ablation catheters participate in the RF circuit. This strategy has proved to result in deeper lesion formation and may be effective for eliminating arrhythmias that have been refractory to standard ablation. In this article, we provide a step-by-step guide on when and how to perform bipolar ablation of VAs.

Distribution of excitation recoverable myocardium after radiofrequency ablation and its relation to energy application time and irrigation

INTRODUCTION

Radiofrequency (RF) catheter ablation induces excitation recoverable myocardium around durable core lesions, and its distribution may be different depending on energy delivery methods.

METHODS AND RESULTS

In coronary perfusing porcine hearts, pacing threshold through the ventricle was measured using eight-pole (1-mm distance) needle electrodes vertically inserted into myocardium before, within 3 min after and 40 min after 40 W ablation with 10-g catheter contact (Group 1: irrigation catheter for 15 s, Group 2: irrigation catheter for 40 s, Group 3: nonirrigation catheter for 15 s, Group 4: nonirrigation catheter for 40 s). Ablation was accomplished in all 12 ablations in Groups 1-3 whereas in 8/12 ablations in Group 4 because of high-temperature rise. Within 3 min after ablation, 10.0 V pacing uncaptured electrodes were distributed from the surface to inside the myocardium, and its depth was deeper in 40 s than in 15 s ablation. 40 min after ablation, excitation recovery at one or more electrodes below the durable lesion was observed in all Groups. Excitation recovery electrodes were also observed on the surface in Group 1 but not the other Groups. Accordingly, the number of excitation-recovered electrodes were larger in Group 1 than the other Groups.

CONCLUSIONS

Regardless of the ablation methods, excitation recoverable myocardium was present around 1.0 mm below the durable lesions. Lesions created by short application time using an irrigation catheter may have included large excitation recoverable myocardium soon after ablation because of the presence of reversible myocardium on well-irrigated myocardial surfaces.