Multiple-Electrode Radiofrequency Ablation Creates Confluent Areas of Necrosis: In Vivo Porcine Liver Results

Abstract

PURPOSE-To prospectively evaluate an impedance-based multiple-electrode RF ablation system for creation of confluent areas of hepatic coagulation in an in vivo porcine model. MATERIALS & METHODS-Pre-approval was obtained from our institutional research animal care and use committee. A prototype multiple-electrode RF system was created allowing switching between three electrically-independent electrodes at impedance spikes (30 Ω increase). Forty-two coagulation zones [single=18, cluster=12, multiple-electrode (three singles spaced 2 cm apart)=12] were created at laparotomy in fifteen ~90 kg female pigs. Half of the ablations were performed for 12 minutes and half for 16 minutes. Coagulation zones were excised and sliced (~3 mm) for measurements. ANOVA and two sample t-tests (Bonferroni's correction, α=.0033) were used to test for differences between groups.RESULTS-At 12 minutes, mean (±SD) multiple-electrode coagulation was significantly larger than single (minimum diameter: 2.8±0.6 vs. 1.6±0.6 cm; maximum diameter: 4.2±0.7 vs. 2.0± 0.5 cm; volume: 22.1±10.7 vs. 6.7±3.7 cm 3 ; P<.0033, all comparisons). Multiple-electrode maximum diameter was significantly larger than cluster at 12 minutes (4.2±0.7 vs. 2.9±0.3 cm, P=.02). At 16 minutes, multiple-electrode coagulation zones (minimum diameter: 3.2±0.6 cm; maximum diameter: 4.2±0.6 cm; volume: 29.1±8.3 cm 3 ) were significantly greater than single (minimum diameter: 1.7±0.5 cm; maximum diameter: 2.2±0.6 cm; volume: 7.1±3.5 cm 3 ; P<.0033, all comparisons) and cluster controls (minimum diameter: 2.3±0.3 cm, P=.007; maximum diameter: 3.2±0.4 cm, P=.005; volume: 13.1±3.0 cm 3 , P<.0033).

Distant Infusion of Saline May Enlarge Coagulation Volume During Radiofrequency Ablation of Liver Tissue Using Cool-tip Electrodes Without Impairing Predictability

“…It is known that internal cooling causes a "heat sink effect," which removes heat from the tissue next to the electrode, preventing tissue charring, increasing power deposition into the tissue, and thus producing larger coagulation zones than noncooled techniques [26]. With internal cooling, previous studies have obtained coagulation volumes of 6.7 cm 3 [27] and 5.76 cm 3 [28]. On the other hand, when internal cooling was combined with saline perfusion, the results showed even better efficiency in energy deposition [9,10], creating greater coagulation volumes.…”

“…However, the minimum transverse diameter was significantly higher in group 2 than in group 1. This parameter is a limiting factor when determining the effectiveness of a particular ablation procedure [27] to ensure that the whole target volume is completely destroyed. Our results therefore suggest that the hybrid applicator could also create coagulations with a greater minimum transverse diameter.…”

“…These applicators were initially designed to increase coagulation volume by expanding prongs in all directions and to generate heat around the prongs. However, it has been suggested that this arrangement can increase coagulation shape irregularity [27]. Tungjitkusolmun et al [32] obtained mushroomlike coagulations zones using theoretic modeling to study the thermal performance of a multitined applicator.…”

Switching bipolar hepatic radiofrequency ablation using internally cooled wet electrodes: comparison with consecutive monopolar and switching monopolar modes

“…[17][18][19] Recently, multiple-electrode RFA approaches, including the switching monopolar (SM) mode, bipolar mode and multipolar mode, have been attempted with each demonstrating efficiency in creating a larger ablation zone in liver tissue than in the standard monopolar RF technique. 2,[20][21][22][23][24][25][26] Theoretically, RFA in switching bipolar (SB) mode using multiple electrodes should further improve the thermal and electronic efficiency of RFA devices compared to conventional monopolar modes. However, until now, the efficacy of SB-RFA with internally cooled wet (ICW) electrodes, which allow simultaneous internal cooling and saline infusion, in creating 3-to 5-cm coagulation areas, have not been tested in previous in vivo studies.…”

Bipolar radiofrequency ablation with 2 × 2 electrodes as a building block for matrix radiofrequency ablation:Ex vivoliver experiments and finite element method modelling

“…Thirdly, in vivo animal studies will have to be confirmed by a human clinical trial treating primary or secondary tumours in healthy and cirrhotic liver [15]. Unfortunately, a large-animal tumour model is not yet available [112]. Nevertheless ex vivo studies in explanted animal livers remain a good starting point for the pilot investigation and development of novel radiofrequency ablation techniques [113].…”