Needle-based ablation of renal parenchyma using microwave, cryoablation, impedance- and temperature-based monopolar and bipolar radiofrequency, and liquid and gel chemoablation: laboratory studies and review of the literature

BACKGROUND AND PURPOSE: Small renal tumors are often serendipitously detected during the screening of patients for renal or other disease entities. Rather than perform a radical or partial nephrectomy for these diminutive lesions, several centers have begun to explore a variety of ablative energy sources that could be applied directly via a percutaneously placed needle-like probe. To evaluate the utility of such treatment for small renal tumors/masses, we compared the feasibility, regularity (consistency in size and shape), and reproducibility of necrosis produced in normal porcine kidneys by different modes of tissue ablation: microwaves, cold impedance-based and temperature-based radiofrequency (RF) energy (monopolar and bipolar), and chemical. Chemoablation was accomplished using ethanol gel, hypertonic saline gel, and acetic acid gel either alone or with simultaneous application of monopolar or bipolar RF energy. MATERIALS AND METHODS: A total of 107 renal lesions were created laparoscopically in 33 domestic pigs. Microwave thermoablation (N=12) was done using a Targis T3 (Urologix) 10F antenna. Cryoablation (N=16) was done using a single 1.5-mm probe or three 17F microprobes (17F SeedNet system; Galil Medical) (N=10 single probe and N=6 three probes); a double freeze cycle with a passive thaw was employed under ultrasound guidance. Dry RF lesions were created using custom-made 18-gauge single-needle monopolar probe with two or three exposed metal tips (GelTx) (N=12) or a single-needle bipolar probe (N=6) at 50 W of 510 kHz RF energy for 5 minutes. In addition, a multitine RF probe (RITA Medical Systems) was used in one set of studies (N=6). Both impedance- and temperature-based RF were evaluated. Chemoablation was performed with 95% ethanol (4 mL), 24% hypertonic saline (4 mL), and 50% acetic acid (4 mL) as single injections. In addition, chemoablation was tested with monopolar and bipolar RF (wet RF). Tissues were harvested 1 week after ablation for light microscopy. RESULTS: In 11 of the 15 ablation techniques, there was complete necrosis in all lesions; however, three ethanol gel lesions had skip areas, three hypertonic saline gel lesions showed no necrosis or injury, and one monopolar RF and one bipolar RF lesion showed skip areas. In contrast to impedance-based RF, heat-based RF (RITA) caused complete necrosis without skip areas. All cryolesions resulted in complete tissue necrosis, and cryotherapy was the only modality for which lesion size could be effectively monitored using ultrasound imaging. CONCLUSIONS: Cryoablation and thermotherapy produce well-delineated, completely necrotic renal lesions. The single-probe monopolar and bipolar RF produce limited areas of tissue necrosis; however, both are enhanced by using hypertonic saline, acetic acid, or ethanol gel. Hypertonic saline gel with RF consistently provided the largest lesions. Ethanol and hypertonic saline gels tested alone failed to produce consistent cellular necrosis at 1 week. In contrast, RITA using the Starburst XL probe produced consistent necrosis, while impedance-based RF left skip areas of viable tissue. Renal cryotherapy under ultrasound surveillance produced hypoechoic lesions, which could be reasonably monitored, while all other modalities yielded hyperechoic lesions the margins of which could not be properly monitored with ultrasound imaging.     

Biliary lesions during radiofrequency ablation in liver. Study on the pig

BACKGROUND: Radiofrequency (RF) is a method of in situ destruction of liver tumor. Biliary complications are bile ducts stenosis or biliary abcess. The aim of this work was to study consequences of liver RF on bile ducts. METHODS: A porcine model of biliary lesions was created using radiofrequency ablation liver. Twenty-two pigs were used for the study. The RF RITA 1500 generator (RITA Medical Systems, Mountain View, Calif., USA) was used for all experiments. The needle was positioned under sonographic control in liver parenchyma beside bile ducts. Two lesions were performed in left liver. Four groups of 5 pigs were treated. The pigs were sacrificed 1 or 3 weeks after the procedure. Pringle maneuver was utilized in half of the RF procedures. An ex vivo cholangiogram was obtained by direct injection into the main bile duct. Samples of RF lesions of liver parenchyma near and at a distance from the RF lesions were taken for pathological studies. RESULTS: Radiological lesions were biliary stenosis, with or without upstream bile duct dilatation, or complete interruption of the bile duct, or extravasation of the radiological contrast agent. Histological lesions of bile ducts were observed near RF lesions and at distance of the RF lesions when a Pringle maneuver was used or when the liver was removed after 3 weeks. CONCLUSIONS: RF ablation in contact of the intrahepatic bile duct induced biliary lesions. Therefore, it is required to stay away from the bile duct or to protect it when performing RF ablation.     

Transperineal radiofrequency interstitial tumor ablation of the prostate: Correlation of magnetic resonance imaging with histopathologic examination

Objectives

Radiofrequency (RF) energy has recently been employed to destroy human tissue in vivo. The purpose of this study was to investigate the safety of this approach in localized carcinoma of the prostate (CaP) and specifically, the predictability of lesions obtained with radiofrequency interstitial tumor ablation (RITA).

Methods

Using RITA, a total of 21 lesions were induced in 10 patients with localized CaP (mean age 70.4 years). RF was delivered transperineally under transrectal ultrasound (TRUS) guidance. All patients underwent endorectal magnetic resonance imaging (MRI) before and after treatment. Radical prostatectomy was performed in all patients 1 to 7 days after RITA. Three of the patients were treated with local anesthesia only. The predictability of the thermal lesion was assessed by correlating the findings of intraoperative TRUS, preand post-RITA endorectal MRI, and the histologic examination of the specimen.

Results

Postoperatively, patients were catheterized for an average of 1.8 days (1 to 3 days). Lesions of 2 × 2 × 2 cm were targeted. Average lesion diameters obtained on MRI were 2.08 ± 0.23 × 2.09 ± 0.36 × 2.28 ± 0.21 cm. Average lesion diameters defined by coagulative necrosis at histologic examination were 2.20 ± 0.23 × 2.10 ± 0.31 × 2.38 ± 0.14 cm. There were no statistically significant differences (P = 0.377) between average lesion volume on MRI (5.37 ± 1.83 cm³) and average lesion volume at histology (5.86 .63 cm³). No complications or adverse events were noted.

Conclusions

In this Phase I study, RITA was shown to be safe and feasible, and to result in lesions that were predictable in size and location. MRI accurately visualized and verified the area of coagulative necrosis as documented at histology. The procedure is technically simple and can even be performed under local anesthesia.     

Magnetic resonance imaging for assessment of radiofrequency lesions in kidney tissue immediately after ablation: an experimental study

BACKGROUND AND PURPOSE: Radiofrequency ablation (RFA) is an attractive minimally invasive treatment option for small renal masses. The purpose of this study was to investigate the morphologic imaging appearance of RF lesions immediately after the ablation of kidney tissue using standard clinical MR sequences, as well as to investigate the correlation between MR and gross lesion size. MATERIALS AND METHODS: Ablations were performed 17 times in a standardized model of ex-vivo perfused porcine kidneys using a resistance-controlled RF device (250 W, 470 kHz) and a nonexpandable bipolar applicator inserted into the center of healthy renal parenchyma. The RF current was applied for 9 minutes at 20 W. Imaging was performed after ablation using standard clinical MR sequences: morphologic T(1)/T(2)- weighted images and an isotropic post-contrast T(1) high-resolution measurement (VIBE). Maximum lesion diameters were measured in three directions and were compared with the measurements of the gross lesions. Histologic (hematoxylin + eosin and nicotinamide adenine dinucleotide staining) and statistical analyses were performed. RESULTS: The gross pathologic examination showed a firm, white-yellow ablation zone sharply demarcated from the untreated tissue. The histologic examination confirmed cellular viability outside but not in the treatment zone. The RF lesions were hyperintense on T(1)-weighted images and hypointense on T(2)-weighted images. The lesion size measured in the VIBE images correlated best with the macroscopic lesion size (N = 16). CONCLUSIONS: Morphologic MR T(1) and T(2) sequences of RF lesions immediately after ablation produce reliable and consistent imaging characteristics. The post-contrast, high-resolution sequence (VIBE) enables the extent of the lesion to be determined accurately. The potential uses of this imaging strategy in clinical practise warrant further investigation on human renal-cell carcinoma.     

Minimally invasive treatment of renal cell carcinoma: comparison of 4 different monopolar radiofrequency devices

OBJECTIVES: Radiofrequency Ablation is an investigational treatment option for RCC. The aim of our study was to test the ablation algorithms of four different RF systems in a standardized ex vivo perfused porcine kidney model. MATERIALS AND METHODS: A multiline monopolar dry electrode (impedance-based system), a multiline monopolar dry electrode (temperature-based system), a single monopolar wet electrode (impedance-based system) and a single monopolar dry, internally-cooled electrode (impedance-based system) were selected. RF energy was applied at different treatment parameters (power with and without control, tissue temperature, saline enhancement) for 1, 3, 5 and 9 minutes in healthy perfused ex vivo porcine tissue. Each treatment parameter was repeated 5 times. Maximum vertical, long-axis and short-axis diameters of the macroscopic lesion were measured and lesion volumes/ shapes were calculated. RESULTS: Lesion volumes increased significantly with the pre-selected tissue temperature and saline enhancement. Saline enhancement created larger, but irregular shaped lesions. The impedance-based system created lesion volumes that were predictable by treatment time and generator power. Lesions were unpredictable when uncontrolled generator power was applied. The created lesion shape was dependent on the selected electrode configuration. CONCLUSIONS: The currently available monopolar RFA systems offer different specific technical features to control tissue ablation. Detailed knowledge of the specific characteristics of each RF system is necessary to provide a higher chance of successful clinical outcome by complete and reliable ablation.     

Thin-layer ablation of human esophageal epithelium using a bipolar radiofrequency balloon device

BACKGROUND: The goal of this study was to determine the optimal treatment parameters for the ablation of human esophageal epithelium using a balloon-based bipolar radiofrequency (RF) energy electrode. METHODS: Immediately prior to esophagectomy, subjects underwent esophagoscopy and ablation of two separate, 3-cm long, circumferential segments of non-tumor-bearing esophageal epithelium using a balloon-based bipolar RF energy electrode (BARRX Medical, Inc., Sunnyvale, CA, USA). Subjects were randomized to one of three energy density groups: 8, 10, or 12 J/cm2. RF energy was applied one time (1x) proximally and two times (2x) distally. Following resection, sections from each ablation zone were evaluated using H&E and diaphorase. Histological endpoints were complete epithelial ablation (yes/no), maximum ablation depth, and residual ablation thickness after tissue slough. Outcomes were compared according to energy density group and 1x vs 2x treatment. RESULTS: Thirteen male subjects (age, 49-85 years) with esophageal adenocarcinoma underwent the ablation procedure followed by total esophagectomy. Complete epithelial removal occurred in the following zones: 10 J/cm2 (2x) and 12 J/cm2 (1x and 2x). The maximum depth of injury was the muscularis mucosae: 10 and 12 J/cm2 (both 2x). A second treatment (2x) did not significantly increase the depth of injury. Maximum thickness of residual ablation after tissue slough was only 35 microm. CONCLUSIONS: Complete removal of the esophageal epithelium without injury to the submucosa or muscularis propria is possible using this balloon-based RF electrode at 10 J/cm2 (2x) or 12 J/cm2 (1x or 2x). A second application (2x) does not significantly increase ablation depth. These data have been used to select the appropriate settings for treating intestinal metaplasia in trials currently under way.     

Prevention of biliary lesions that may occur during radiofrequency ablation of the liver: study on the pig

OBJECTIVE: To prevent bile duct injury by using a cold 5% glucose isotonic solution cooling in the bile ducts when radiofrequency (RF) is performed in a porcine model. SUMMARY BACKGROUND DATA: Complications that may arise during liver RF ablation include biliary stenosis and abscesses. METHODS: The RITA 1500 generator was used for the experiments. Two lesions were performed in the left liver. The pigs were killed 1 or 3 weeks after the procedure. An ex vivo cholangiogram was obtained by direct injection into the main bile duct. Samples of RF lesions, of liver parenchyma near and at a distance from the RF lesions, underwent pathologic studies. Two groups of 20 pigs each were treated: one without perfusion of the bile ducts and the other with perfusion of cold 5% glucose isotonic solution into the bile ducts. The Pringle maneuver was used in 50% of the RF procedures. Radiologic lesions were classified as biliary stenosis, complete interruption of the bile duct, or extravasation of the radiologic contrast liquid. RESULTS: Histologic lesions of the bile ducts were observed near the ablated RF lesion site and at a distance from the RF lesions when a Pringle maneuver was performed. Radiologic and histologic lesions of the bile ducts were significantly reduced (P < 0.0001) when the bile ducts were cooled. CONCLUSIONS: Cooling of the bile ducts with a cold 5% glucose isotonic solution significantly protects the intrahepatic bile ducts from damages caused by the heat generated by RF when performed close to the bile ducts.     

Haemostatic partial nephrectomy using bipolar radiofrequency ablation

OBJECTIVE: To determine whether an electrode array with a bipolar radiofrequency ablation (RFA) energy source can be used to perform a haemostatic partial nephrectomy by simultaneously ablating and coagulating renal tissue. MATERIALS AND METHODS: Lower-pole partial nephrectomy was performed in 12 porcine kidneys using a bipolar RFA system. Intraoperative ultrasonography was used to identify and avoid the collecting system. Tissues were positioned between opposing electrodes and tissue impedance monitored using a proprietary feedback and control algorithm. Ablation time and power, lesion width and length, and tissue thickness were recorded. The kidneys were assessed in vivo to show haemostasis of the remaining renal unit. Collecting system integrity was assessed with methylene blue injection, and the resected tissue analysed histologically. RESULTS: Partial nephrectomies were successful in all 12 porcine kidneys; the mean nephrectomy specimen was 3.2 x 2.6 cm. The total ablation time (sem) per lesion was 211 (15) s and the mean power was 23 W. Methylene blue injection showed an intact collecting system in 11 of the 12 kidneys, and haematoxylin and eosin staining showed a mean zone of necrosis of 9 mm at the resection margin. Ultrasonography revealed flow to the remaining kidneys after RFA and the in vivo assessment of haemostasis revealed no abnormal bleeding or haemorrhage from the kidneys. CONCLUSIONS: Applying bipolar RF energy to an electrode array can enable transmural excision of renal parenchyma in vivo in a bloodless fashion without collecting system injury.     

Geometry and temperature distribution during radiofrequency tissue ablation: an experimental ex vivo model

PURPOSE: To investigate the temperature distribution and geometry of lesions created by radiofrequency (RF) tissue ablation. MATERIALS AND METHODS: We developed an ex-vivo thermal model based on the ability of egg whites to coagulate at 62 degrees to 65 degrees C. This property allows us to observe and record the formation of "lesions" created by different commercially available RF generators and probes. RESULTS: The lesions created by the Radionics Cool-Tip RF system were mostly cylindrical or barrel-shaped, while RITA StarBurst XL and StarBurst XLi electrodes produced cone-like or mushroom-shaped lesions. The time required to achieve maximum lesion size was between 3 and 5 minutes in most trials. The formation of lesions stopped when thermodynamic equilibrium was achieved. CONCLUSIONS: The geometry of lesions does not correlate precisely with manufacturer reports, which describe spherical lesions for both RF systems. The 12-minute treatment cycle recommended by company's algorithm may not be necessary because lesion formation was completed and thermodynamic equilibrium was reached significantly earlier. We believe the results of our study may be useful in better understanding the RF ablation process, better planning, and improvement of clinical outcome.     

B型超声引导经皮经肝穿刺射频治疗肝癌的近期疗效

目的 评估集束电极射频（radiofrequency,RF)治疗肝癌的临床疗效及适应证。方法 回顾分析我院245例肝癌患者经集束电极射频治疗的临床资料,比较治疗前后癌体内血液供应状况,癌灶体积,胎甲球蛋白（AFP）的变化,及患者自觉症状的改善情况。结果 AFP术后1周内下降者占50％,患者自觉症状明显改善。癌灶直径小于5cm的肝癌,术后1至6个月内70％－90％癌灶血液供应消失,癌灶缩小,甚至消失。个别癌灶复发经再次射频治疗得到控制。直径大于5cm的肝癌,配合介入栓塞治疗,60％癌灶缩小。继发性肝癌,就癌灶而言,射频治疗术后癌灶缩小,症状得到控制。结论 B型超声引导下集束电极射频治疗肝癌近期疗效确切。直径小于5cm的癌灶疗效理想,直径大于5cm的肝癌,采用多点射频治疗,再配合介入栓塞治疗,也取得了比较理想的疗效。     

Comparison of radiofrequency ablation, cryoablation, and nephrectomy in treating implanted VX-2 carcinoma in rabbit kidneys

PURPOSE: To compare the efficacy of radiofrequency (RF) ablation, cryoablation, and radical nephrectomy in the treatment of implanted VX-2 carcinoma in rabbit kidneys. MATERIALS AND METHODS: Sixty-eight New Zealand White rabbits were implanted with 1-mm3 segments of VX-2 carcinoma in the left kidney. Seven days after implantation, the tumors were treated with one of the following: (1) RF ablation using a 12-gauge electrode (RITA Medical Systems, Mountain View, CA) at 90 degrees C for 8 minutes with a 5-mm tumor margin target temperature of 60 degrees C (N = 20); (2) cryoablation using a 15 minute double-freeze technique with 2.4-mm cryoprobes and the Cryocare system (Endocare Inc., Irvine, CA) with a 5-mm tumor margin target temperature of -20 degrees C (N = 20); (3) open radical nephrectomy (N = 20); or (4) no treatment (controls; N = 8). Rabbits were allowed to survive for a total of 22 days and sacrificed; and the kidneys, lungs, liver, spleen, urinary bladder, and ureter were removed and examined grossly and histologically for tumor. RESULTS: Findings in animals sacrificed at 15 days post-treatment showed significant differences between all treatment groups and untreated controls (P < 0.002) Using a 3 x 2 chi-square comparison, no differences in disease-free survival were observed between the RF ablation group, the cryoablation group, and the open nephrectomy group (P = 0.72) CONCLUSION: Radiofrequency ablation, cryoablation, and radical nephrectomy were all efficacious in the treatment of implanted VX-2 renal tumors compared with untreated controls (P = 0.002). No statistically significant difference was found between any of the three treatments.     

Laparoscopic radiofrequency thermal ablation of hepatocarcinoma: preliminary experience

The objective was to evaluate the feasibility, safety, and effectiveness of radiofrequency thermal ablation (RFT), performed during laparoscopy with a cooled-tip electrode needle, in the treatment of neoplastic hepatic focal lesions. Seven patients with hepatocarcinoma (10 hepatic lesions) were treated during laparoscopy with RFT using a 100-watt RF generator and 17-gauge, dual-lumen, cooled-tip electrode needles with a 3-cm exposed tip. The mean exposure time was 12 minutes for each needle insertion. Spiral computed tomography scanning detected complete tumor necrosis in nine lesions; in one lesion, peripheral neoplastic tissue was detected, and percutaneous RFT was performed. Two patients during follow-up developed two new neoplastic lesions, treated with percutaneous ethanol injection. No recurrences of the treated lesions were seen after 6 months of follow up. Intraoperative RFT with a cooled-tip electrode needle is a safe and effective local treatment of hepatic focal lesions during laparoscopic surgery. Possible indications are large hepatocarcinoma (>5 cm), superficial lesions, multiple lesions, or tumor located near vascular or biliary structures.     

Safety and efficacy of radiofrequency ablation of brain: a potentially minimally invasive treatment for brain tumours.

INTRODUCTION: Cerebral metastases are associated with a very poor prognosis. The best survival results are seen after surgical resection. However this involves a relatively invasive procedure and many patients are not suitable for surgical resection. We have evaluated the safety and efficacy of radiofrequency ablation of the brain in a sheep model. METHODS: We produced ablations of 1 - 3 cm diameter in the brain of sheep using the RITA starburst XL probe and RITA 1500 generator. We varied the time of RF application between 1 minute and 5 minutes and observed the animals for between 24 hours and 3 weeks for short-term and long-term effects and measured the intracranial pressure (ICP) in 2 animals following RFA. RESULTS: A total of 8 ablations were produced in 8 sheep. There was no change in the ICP measurements and there were no neurological complications in the 5 sheep with superficial ablation of up to 2 cm. Three sheep failed to regain consciousness due to large ablations near the brain stem and cerebellum. The sizes of the ablations were confirmed on necropsy and there was no other evidence of damage to the surrounding brain. Satisfactory ablation of brain was achieved at 70 degrees C and an ablation time as short as 3 minutes produced a 1.5 - 2.0 cm diameter of ablation. CONCLUSION: Cerebral RFA is a relatively safe and effective technique capable of producing a predictable ablation with no damage to surrounding brain. The potential of this technique requires further evaluation but likely advantages include the ability to treat multiple tumours and perform repeated treatment with a minimally invasive approach.     

Treatment of renal tumors with radiofrequency ablation

BACKGROUND: Radiofrequency (RF) energy has been investigated as a minimally invasive modality for ablating small renal tumors. Recent advances in the application of this technology have improved its safety and effectiveness. MATERIALS AND METHODS: We describe the technology of RF application and review the current delivery systems as applied to renal tumor ablation. We also review relevant animal studies, which have revealed the natural history of ablated renal tissue. Finally, we examine recent human trials with an emphasis on longer-term follow-up, imaging, complications, and successful ablation according to tumor location within the kidney; i.e., central v peripheral. RESULTS: Radiofrequency ablation can be performed safely in a minimally invasive fashion either percutaneously or laparoscopically. Energy delivery varies, and available systems include dry, wet, cooled-tip, and bipolar electrodes. Heat rise and subsequent charring in the tissue adjacent to the electrode is limited by temperature or impedance-based feedback systems. In animal studies, ablation results in complete cell kill, as judged by nicotinamide adenine dinucleotide diaphorase staining. Clinical trials with intermediate follow-up show excellent success rates. Tumors >3 cm and central tumors have a higher recurrence rate after RFA than smaller, more peripheral tumors. CONCLUSIONS: The current literature suggests that RFA is a promising minimally invasive method of treating small renal tumors. Nevertheless, long-term follow-up is still required, and questions remain regarding the optimal delivery system, duration of ablation, and method of surveillance.     

Radiofrequency ablation lesions in a pig liver model.

BACKGROUND: Radiofrequency (RF) ablation has been reported as a means of liver tumor destruction. This study evaluates the use of ultrasound monitoring of radiofrequency lesion creation and describes the morphology, histologic characteristics, and vascular effects of radiofrequency ablations in a pig liver model. MATERIALS AND METHODS: Hemodynamic monitoring was established and laparotomies were performed in 50-kg pigs. Under ultrasound guidance, radiofrequency needle probes were placed in the liver at predetermined locations. Radiofrequency energy was applied over 15 min to generate lesions 3 cm in diameter. Eighty lesions were generated in 10 animals. At the completion of the experiment, the lesions were examined with ultrasound and then excised for CT, gross, and histologic examination. RESULTS: There were no adverse systemic effects. Ultrasound imaging demonstrated the size, shape, and position of the lesions. Gross examination demonstrated a core of ablated tissue with a surrounding 1- to 2-mm hemorrhagic perimeter. Lesion volumes averaged 12.8 cc(3) (range 5-34 cc(3)). Final lesion shape and size were frequently altered by the cooling effect of local blood flow. Histologic stains demonstrated microvascular thrombosis and coagulative necrosis within the lesions. There appeared to be 100% cellular destruction within the lesion by cytochemical staining. CONCLUSIONS: We demonstrated that RF ablation is capable of killing large volumes of normal liver tissue; however, local vasculature plays a significant a role in defining the ultimate size and shape of the lesion created. This may interfere with the utility of radiofrequency ablation as a modality for local tumor control.     

Experimental radiofrequency ablation near the portal and the hepatic veins in pigs: differences in efficacy of a monopolar ablation system

BACKGROUND: We sought to compare the efficacy of a monopolar radiofrequency ablation system in vivo near the portal vein and the hepatic veins in porcine liver. MATERIALS AND METHODS: Radiofrequency ablation of healthy livers near the portal vein and the hepatic veins was performed in 10 pigs with a multitined expandable electrode. Volumes and diameters of zones of ablation were assessed by magnetic resonance imaging. RESULTS: Volumes (16.0 +/- 5.5 mL, P = 0.001) and diameters (4.0 +/- 0.7 cm, 3.3 +/- 0.7 cm, 3.0 +/- 0.6 cm, P 相似文献   

Biparietal bidirectional bipolar radiofrequency in hybrid cardiac ablation: an in vitro evaluation

 Open in a separate windowOBJECTIVESThe aim of this study was to evaluate the lesion size and depth of radiofrequency (RF) ablation in a simultaneous biparietal bidirectional bipolar (SBB) approach, compared to a simultaneous and staged unipolar and uniparietal bipolar setup [simultaneous uniparietal bipolar (SiUB) and staged uniparietal bipolar (StUB), respectively]. METHODSFresh left atrial porcine tissue was mounted into the ABLA-BOX simulator. Different ablation approaches were tested: (i) SBB: a concept consisting of SBB endo-epicardial ablation, (ii) SiUB: simultaneous epicardial uniparietal bipolar and endocardial unipolar ablation and (iii) StUB: staged epicardial uniparietal bipolar and endocardial unipolar ablation. In the StUB setup, a 1-h interval between the epi-endo ablation was respected.RESULTSTransmural lesions were present in 90% of the bipolar biparietal ablations, yet no full transmurality was observed in the simultaneous nor in the staged unipolar with uniparietal bipolar ablation group. In SBB, the area and volume of the ablation lesions were smaller (523.33 mm²/mm and 52.33 mm³/mm, respectively) than in SiUB (588.17 mm²/mm and 58.81 mm³/mm, respectively) and StUB (583.76 mm²/mm and 58.37 mm³/mm, P = 0.044). Also, in SBB, the overall, epicardial and endocardial maximum diameters of the lesions (1.59, 1.57 and 1.52 mm; respectively) were smaller than in SiUB (2.38, 2.26 and 2.33 mm; respectively) and in StUB (2.36, 2.28 and 2.14 mm; respectively, all P < 0.001).CONCLUSIONSAlthough bipolar biparietal bidirectional RF ablation results in smaller lesions than uniparietal bipolar and unipolar ablation, their capacity to penetrate the tissue is much higher. Moreover, in uniparietal RF applications, the energy spreads in the superficial layers of the tissue but fails to penetrate. Therefore, the degree of transmurality is much higher when using such a ‘truly bipolar’ ablation approach.     

In-vivo evaluation of a novel bipolar radiofrequency device for interstitial thermotherapy of liver tumors during normal and interrupted hepatic perfusion

BACKGROUND: Only monopolar systems have thus far been available for radiofrequency ablation of liver tumors, whose application is restricted because of the incalculable energy flow, reduction of electrical tissue conduction, and limited lesion size. The aim of this study was to evaluate a novel internally cooled bipolar radiofrequency application device under in vivo conditions and to compare the effect of this system on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion. MATERIALS AND METHODS: In a porcine liver model, RFA (60 W, 12 min) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). RFA parameters (impedance, power output, temperature, applied energy) were determined continuously during therapy. RFA lesions were macroscopically assessed after liver dissection. RESULTS: Bipolar RFA induced clinical relevant ellipsoid thermal lesions without complications. Hepatic inflow occlusion led to a 4.3-fold increase in lesion volume after arterial microembolization and a 5.8-fold increase after complete interruption (7.4 cm(3)versus 31.9 cm(3)versus 42.6 cm(3), P < 0.01). CONCLUSIONS: The novel bipolar RFA device is a safe and effective alternative to monopolar RFA-systems. Interrupting hepatic perfusion significantly increases lesion volumes in bipolar RFA. This beneficial effect can also be achieved in the percutaneous application mode by RFA combined with arterial microembolization via a hepatic artery catheter.     

Large hepatic ablation with bipolar saline-enhanced radiofrequency: an experimental study in in vivo porcine liver with a novel approach

SUMMARY BACKGROUND DATA: Radiofrequency ablation (RFA) is a relatively new technology for the local destruction of liver tumors. Development of recent devices has enabled the creation of larger lesions. Nevertheless, treating liver tumors larger than 2.5 cm in diameter often requires multiple overlapping ablations to encompass the tumor and the surrounding healthy tissue rim with an increasing risk of local recurrence. MATERIAL AND METHODS: RFA (480 kHz) of the liver using our method was undertaken on a total number of 15 healthy farm pigs with (Group B, n = 8) or without (Group A, n = 5) the Pringle maneuver via laparotomy. The pigs were followed and euthanized on the seventh day of the experiment. Livers were removed for histological assessment. Time of the procedure, impedance, current, power output, energy output, temperatures in the liver, central temperature of the animal, volume size of the lesion, and delivered energy per lesion volume were determined and compared among groups. Additionally a regularity ratio (RR) was determined by gross examination of the specimen and scored (0-3) taking into account regularity and predictability of the ablation with pathologic assessment. RESULTS: With both methods, ellipsoid lesions were created between the two probes. In both groups tissue impedance fell with time (r = -0.47, P < 0.01 and r = -0.34, P < 0.05, in Groups A and B, respectively). The mean lesion size achieved with the Pringle maneuver was the largest lesion size described in the literature for any RFA method in vivo and was greater in Group B than in Group A (123.22 cm(3) +/- 49.62 and 52.40 cm(3) +/- 23.59, respectively, P < 0.05). A better regularity and predictability evaluated by RR was observed in Group B compared to Group A (1.88 +/- 1.35 and 0.40 +/- 0.55, respectively, P < 0.05). Five major complications were described and attributed primarily to failure in isolation from hypertermic lesions. CONCLUSIONS: Our new bipolar saline-enhanced electrode with Pringle maneuver achieves large hepatic ablations in in vivo pig liver. These large lesions are well-tolerated by the animal when thermal injuries to adjacent structures are avoided.     

Three years experience with monopolar and bipolar radiofrequency ablation surgery in patients with permanent atrial fibrillation.

OBJECTIVE: In our population permanent atrial fibrillation (pAF) is a frequent concomitant problem in patients undergoing open heart surgery. A 3-year experience with a treatment strategy using mono- and bipolar radiofrequency (RF) ablation procedures in a heterogeneous group of patients is reported. METHODS: In a prospective analysis the incidence of pAF among all patients undergoing open heart surgery in our department between February 2001 and July 2004 was evaluated. In a second step a selective group of 106 patients with pAF (primary mitral: n=63; aortic: n=24; CABG: n=16; aortic+mitral: n=3) underwent either monopolar (n=86) or bipolar (n=20) RF ablation procedures creating two encircling isolation lesions around the left and the right pulmonary veins (PVs) and a connection line between both. In addition amiodarone was given for 3 months after surgery. Regular follow-ups were performed 3, 6, 9, 12, 18, 24 and 36 months after surgery. RESULTS: The incidence of pAF in the total group of 4.110 patients was 3.6%. While the rate was low in cases without severe heart valve disease (1.1%), a significantly higher presence of pAF in patients scheduled for heart valve surgery (10.3%) was observed (P<0.0001). The incidence was 30-39% in patients with degenerative and rheumatic mitral valve (MV) disease, and further particularly high in the older aged compared to younger patients (4.2-8.3% at 70-99 years; P<0.001). Hospital mortality after combined open heart and RF ablation surgery was 1.9%. Whereas patients with small left atrial size (LA-diameters <56 mm; n=59) had SR in almost 90% at follow-up, LA enlargement (LA-diameter > or =56 mm; n=47) was associated with a significant risk of persisting pAF after surgery (P=0.033, 0.002 and 0.006 at 3, 6 and 9 months follow-up). CONCLUSION: The use of RF ablation procedures in combination with amiodarone therapy represents a safe and efficient option to cure pAF during open heart surgery in a selective group of patients. The preoperative LA size was of significant importance for the outcome in this investigation.