Cooled-tip Electrode Research Articles

Intraoperative Radiofrequency Ablation Using a Loop Internally Cooled-Perfusion Electrode: In Vitro and In Vivo Experiments

We sought to validate the efficiency of intraoperative radiofrequency ablation (RFA) using a prototype loop internally cooled-perfusion (LICP) electrode to induce coagulation in the subcapsular portion of the liver. In in vitro experiments, 30 ablation regions were created using a 200-W generator and a LICP electrode featured simultaneous intraelectrode cooling and continuous flow of hypertonic saline along the shaft in explanted bovine liver. In the in vivo experiments, 26 ablation zones were created according to one of the five protocols in 10 dogs: group A, RFA using a cooled-tip electrode (n = 6); group B, RFA using a LICP electrode with 2 cm loop tip (n = 6); group C, RFA using a LICP electrode with a 3-cm loop tip (n = 6); group D, RFA using a cooled-tip electrode and Pringle maneuver (n = 4); and group E, RFA using a LICP electrode with 2 cm loop tip and Pringle maneuver (n = 4). The dimensions of the coagulation parameters were compared between the groups. In the in vitro experiments, RFA using a 2- or 3-cm diameter LICP electrode (3.6 +/- 0.3 cm, 3.4 +/- 0.5 cm, respectively) created deeper dimensions of coagulation than did a 4-cm electrode (2.3 +/- 0.2 cm; P < 0.05). In the in vivo experiments, the RFA using the LICP electrodes in porcine liver with normal perfusion induced wider but superficial ablation regions when compared to standard RFA using an internally cooled electrode (P < 0.05). However, using a Pringle maneuver, RFA with a LICP electrode created a larger volume of ablation area when compared to RFA using an internally cooled electrode with a similar range of axial diameter along the electrode axis: 30.0 +/- 6.1 cm3 (group D) versus 68.5 +/- 14.0 cm3 (group E; P < 0.05) Intraoperative RFA using the LICP electrode induced a well-defined semicircular coagulation with a 3.5-cm axial diameter in the subcapsular region of the liver. This device appears to be promising for the treatment of superficial tumors during intraoperative RFA.

Evaluation of liver parenchymal pressure and portal endothelium damage during radio frequency ablation in an in vivo porcine model

We previously developed a multi-step, incremental expansion method (multi-step method) for radio frequency ablation (RFA) in vitro, which prevented increases in pressure and reduced the ablation time as compared with other methods. In this study, we evaluated liver parenchymal pressure and portal endothelium damage during RFA with different devices and protocols in an in vivo porcine model. Nine healthy female pigs were anaesthetized. RFA was performed with two different devices and protocols; one involved the use of a LeVeen needle with a single-step full expansion method or a multi-step method, and the other used a cool-tip needle with 40 or 60 W power. We measured the pressure in the liver parenchyma and the gallbladder during RFA. We also evaluated portal endothelium damage by NADH staining. The multi-step method with the LeVeen electrode resulted in the lowest parenchymal and intra-gallbladder pressures (multi-step method<single-step method <cool-tip 40 W <cool-tip 60 W). In contrast, the ablation time was shortest with the cool-tip needle at 60 W (cool-tip 60 W <cool-tip 40 W=multi-step method <single-step method). NADH staining revealed severe endothelium damage after ablation with the cool-tip needle, but only slight damage with the LeVeen needle. Ablation with the LeVeen needle, especially when used with a multi-step protocol, produced less of an increase in liver parenchymal and intra-gallbladder pressures and less damage to portal endothelial cells than did the cool-tip electrode.

Tumoral response factors after radiofrequency ablation of hepatocellular carcinoma in cirrhotic liver

Hepatocellular carcinoma (HCC) ablation by radiofrequency (RFA) is a novel technique with a great variety of methods whose efficacy and predictive factors have not been completely studied. Some of the main predictive factors in this type of treatment are analyzed in the present study. Ninety-three patients with hepatocellular carcinoma over cirrhosis, and with no indication for surgical resection were treated by RFA. Two different types of electrodes were used for RFA (refrigerated-"Cool-Tip" and perfusion with saline solution, the approach was percutaneous, by laparoscopy or laparotomy. Overall survival at 1, 2 and 3 years was 88, 81, and 76%, with a free-disease survival (FDS) of 66, 31 and 17%, respectively. For tumors less than 3 cm, FDS at 1,2 and 3 years was 74, 44 and 30%, while for more than 3 cm in size FDS was 55, 12 and 0% (p = 0.02). FDS for HCC with one nodule was 70, 36 and 22%, and for more than one nodule it decreased to 50, 17 and 0% at 1, 2 and 3 years, respectively (p = 0.07). Surprisingly, the method employed for RFA has a main influence in FDS, with 0% at 3 years for perfusion electrodes and 26% for cool-tip electrodes at the same period. In this series, overall survival at three years was relatively high; however, tumoral size, number of nodules and RFS method were independent variables associated with disease-free survival.

Radiofrequency Thermal Ablation in Canine Femur: Evaluation of Coagulation Necrosis Reproducibility and MRI-Histopathologic Correlation

Our purposes were to determine whether a single application of radiofrequency energy to normal bone can create coagulation necrosis reproducibly and to assess the accuracy of MRI at revealing the extent of radiofrequency-induced thermal bone injury. Using a 200-W generator and a 17-gauge cooled-tip electrode, a total of 11 radiofrequency ablations were performed under fluoroscopic guidance in the distal femurs of seven dogs. Radiofrequency was applied in standard monopolar mode at 100 W for 10 min. During radiofrequency ablation, the changes in impedance and currents were recorded. MRI, including unenhanced T1- and T2-weighted images and contrast-enhanced fat-suppressed T1-weighted images, was performed to evaluate ablation regions. Six dogs were killed on day 4 after MRI and one dog on day 7. In all animals, radiofrequency ablation created a well-defined coagulation necrosis and no significant complications were noted. The mean long-axis diameter and the mean short-axis diameter of the coagulation zones produced were 45.9 +/- 5.5 mm and 17.7 +/- 2.7 mm, respectively. At gross examination, thermal ablation regions appeared as a central, light-brown area with a dark-brown peripheral hemorrhagic zone, which was surrounded by a pale-yellow rim. On MRI, the ablated areas showed multilayered zones with signal intensities that differed from normal marrow on unenhanced images and a perfusion defect on contrast-enhanced T1-weighted images. The maximum difference between lesion sizes on MR images, established by measuring macroscopic coagulation necrosis, was 3 mm. The correlation between the diameter of coagulation necrosis and lesion size at MRI was strong, with correlation coefficients ranging from 0.89 for unenhanced T1-weighted images and 0.97 for unenhanced T2-weighted images to 0.98 for contrast-enhanced T1-weighted images (p < 0.05). Radiofrequency ablation created well-defined coagulation necrosis in a reproducible manner, and MRI accurately determined the extent of the radiofrequency-induced thermal bone injury.

Laparoscopic liver resection using radio frequency ablation in a porcine model

The aim of this study was to assess the feasibility, efficacy, and safety of laparoscopic left lateral lobe resection, using radiofrequency ablation (RFA) with internally cooled tip electrodes, in a porcine model. Eight domestic pigs underwent left lateral hepatic lobectomy. RFA was the sole hemostatic method applied throughout the entire operation. After 0, 7, 30, or 120 days the animals were killed in order to study the macroscopic and microscopic findings on the liver edge. An average of 90 min was enough for the entire operation. No signs of blood loss or infection were observed up to 4 months postoperatively. There was no mortality either during or after surgery. The pathology of the liver revealed the three zone lesions. Our study demonstrates that laparoscopic left lateral lobectomy using RFA is technically feasible hi the porcine model and is proved to be highly effective and safe hemostatic method.

The End of Cryotherapy for the Treatment of Nonresectable Hepatic Tumors?

Liver resection is generally accepted as the standard of care for patients with hepatic metastases from colorectal tumors in the absence of extrahepatic disease and for selected patients with primary hepatocellular carcinoma. However, in any given cohort of patients with hepatic tumors, most will be unsuitable for resection because of the extent of hepatic tumor burden, extrahepatic disease, or comorbidity. Treatment options in this setting include systemic modalities such as chemotherapy, regional interventions such as intra-arterial chemotherapy, and direct tumor ablation. Direct ablative treatments include intratumoral ethanol, laser, cryotherapy, and, more recently, radiofrequency ablation. Until the advent of radiofrequency, direct intratumoral ethanol and cryotherapy were perhaps the most widely used ablative approaches. Ethanol can be injected percutaneously and does not rely on costly equipment for delivery, and treatments can be repeated. Cryotherapy uses liquid nitrogen at )196 C delivered through a closed triplelumen probe and relies on cooling of liver tumors to at least )35 C. Tumor cell death occurs as a consequence of the formation of intracellular crystals during rapid freezing. Although widely used over the past decade, cryotherapy for liver tumors is not without problems. Freezing can lead to cracking or shearing of the liver parenchyma, andmajor hemorrhage results if these shearing injuries extend into major vessels. Late hemorrhage and intrahepatic abscesses related to biliary injury are also recognized complications. In addition to these local effects of cryotherapy, there are systemic side effects: the cytokine-mediated systemic illness associated with cryotherapy is characterized by fever, tachycardia, and tachypnea. This is known as the cryoshock syndrome and, in particular, can be associated with pleural effusion, diffuse lung injury, and acute renal tubular necrosis. The role of cryotherapy has become increasingly challenged since the advent of radiofrequency thermal ablation. This technique involves the passage of alternating high-frequency current (typically 10 kHz) through tissue. The molecular agitation caused by high-frequency energy leads to an increase in temperature in the tissue through which the current passes without causing muscle contraction or pain. If the field is applied between two equal-sized electrodes, the current flow per unit area of the electrode (current density) is similar in both electrodes. However, if one electrode is smaller, then, because the same total amount of current still has to flow, the current density is much higher at the smaller electrode, with a correspondingly higher temperature. Commercial availability of cooled-tip multiprobe electrodes equipped with probe-tip thermal sensors now permits the creation of a precise hepatic parenchymal ablation. In an important study, Scudamore et al. performed radiofrequency ablation of resectable liver tumors in 10 patients (7 patients with colorectal liver metastases) and then undertook liver resection in 9 of these individuals within 6 weeks of the ablation. On histological examination of the resected specimen by using nicotinamide adenine dinucleotide (NADH; a histochemical technique for demonstration of tissue oxidative enzyme activity), ablated tissue was recognized in all nine cases. The Received October 15, 2004; accepted December 2, 2004; published online March 3, 2005. Address correspondence and reprint requests to: Ajith K. Siriwardena, MD, FRCS; E-mail: ajith.siriwardena@cmmc.nhs.uk.

Comparison of Renal Ablation with Monopolar Radiofrequency and Hypertonic-Saline-Augmented Bipolar Radiofrequency: In Vitro and In Vivo Experimental Studies

We sought to determine whether hypertonic-saline (HS)-augmented bipolar radiofrequency ablation has advantages over monopolar radiofrequency ablation for creating larger areas of coagulation necrosis in the kidney. Using a 200-W generator and bipolar perfused-cooled electrodes or a monopolar cooled-tip electrode, we performed 14 radiofrequency ablations in explanted bovine kidneys. Radiofrequency was applied in standard monopolar (n = 7) or bipolar (n = 7) modes at 100 W for 10 min. In the bipolar mode, the perfused-cooled electrodes were placed at interelectrode distances of 3 cm, and a 6% sodium chloride solution was instilled into tissue at a rate of 2 mL/min through the electrodes. For in vivo experiments, either monopolar (n = 7) or HS-augmented bipolar (n = 7) radiofrequency ablation was performed in the lower pole of canine kidneys. Three days after the procedure, contrast-enhanced CT scans were obtained to evaluate the volumes of the ablation regions, and the kidneys were harvested for gross measurements. Technical parameters such as changes in impedance and current during radiofrequency ablation and dimensions of the thermal ablation zones were compared between the two groups. In ex vivo and in vivo experiments, the frequency of the pulsed radiofrequency application caused by rises in impedance was higher in the monopolar mode than in the bipolar mode during the application of radiofrequency energy. The in vivo study showed that the bipolar radiofrequency ablation allowed larger mean current flows than the monopolar radiofrequency ablation (i.e., mean +/- SD, 1,654 +/- 144 mA vs 967 +/- 597 mA) (p < 0.05). Ex vivo studies revealed that the volumes of bipolar radiofrequency-induced ablation regions were substantially larger than those of monopolar radiofrequency-induced ablation regions (26.1 +/- 10.5 cm(3) vs 10.2 +/- 4.2 cm(3)). In vivo studies showed bipolar radiofrequency ablation achieved larger coagulation necrosis than monopolar radiofrequency (3.2 +/- 0.3 cm vs 2.4 +/-0.4 cm) (p < 0.05). This was confirmed by the measured volume of nonenhancing area on contrast-enhanced CT (20.4 +/- 6.4 cm(3) vs 13.5 +/- 6.0 cm(3)). HS-augmented bipolar radiofrequency ablation using perfused-cooled electrodes shows better performance in creating coagulation necrosis than monopolar radiofrequency ablation in the kidney of an animal model.

Percutaneous radiofrequency ablation for hepatocellular carcinoma

Radiofrequency ablation (RFA) was introduced recently as a therapeutic modality for hepatocellular carcinoma (HCC), an alternative to percutaneous ethanol injection therapy (PEIT), which is coming into use worldwide. Previously reported treatment efficacy and complication rates have varied considerably. Between February 1999 and February 2003, the authors performed 1000 treatments of RFA to 2140 HCC nodules in 664 patients with a cooled-tip electrode at the University of Tokyo Hospital (Tokyo, Japan). Short-term and long-term complications were analyzed by treatment and session basis. Cumulative survival was also assessed in 319 patients who received RFA as primary treatment (naive patients) and 345 patients who received RFA for recurrent tumor after previous treatment including resection, PEIT, microwave coagulation therapy, and transarterial embolization (nonnaive patients). A total of 40 major complications (4.0% per treatment, 1.9% per session) and 17 minor complications (1.7% per treatment, 0.82% per session) were observed during the observation period until March 31, 2004. There were no treatment-related deaths. Surgical intervention was required in one case each of bile peritonitis and duodenal perforation. The cumulative survival rates at 1, 2, 3, 4, and 5 years were 94.7%, 86.1%, 77.7%, 67.4%, and 54.3% for naive patients, whereas the cumulative survival rates were 91.8%, 75.6%, 62.4%, 53.7%, and 38.2% for nonnaive patients, respectively. The authors confirmed the safety and efficacy of RFA for HCC in a large-scale series and long-term prognosis was satisfactory.

Lung Radiofrequency Ablation with and without Bronchial Occlusion: Experimental Study in Porcine Lungs

This study was undertaken to compare the thermal lesion volumes in normal pig lungs when radiofrequency (RF) ablation is performed with and without airway occlusion. RF ablation was performed in six pigs. A straight 17-gauge internally cooled-tip electrode with a 2-cm exposed tip was inserted into the center of the lower lobe of the lung under biplane fluoroscopic guidance. In each animal, RF ablation was performed for 12 minutes with balloon occlusion of the main bronchus in one lung and without balloon occlusion in the contralateral lung. The tissue temperature around the electrode tip was measured immediately after RF application. The volumes of the thermal lesions were compared by histologic examination of the groups of lungs ablated with and without airway occlusion. Tissue temperature was significantly higher in the bronchial occlusion group than in the group with normal ventilation (51 degrees C +/- 7 vs. 44 degrees C +/- 2; P < .05). RF ablation with bronchial occlusion resulted in the creation of a significantly greater thermal lesion volume compared with RF ablation with normal ventilation (6,535 mm(3) +/- 1,114 vs 3,368 mm(3) +/- 676; P < .03). Prevention of ventilation in the normal swine lung via bronchial balloon occlusion during RF ablation increases the thermal ablation lesion volume, suggesting that active ventilation is a significant cause of in vivo heat loss.

Radio-Frequency Tissue Ablation in Liver Trauma: An Experimental Study

The liver is the most frequently injured intra-abdominal organ. Radio-frequency tissue ablation (RFA) with cooled tip electrodes is here experimentally used for the treatment of liver trauma. A grade III and a grade III to IV trauma each were produced in the livers of 10 domestic pigs. RFA was applied around the sites of injury until hemostasis was achieved. The animals were sacrificed at 0, 3, 7, 14, and 21 days and examined. The livers were subjected to histologic and radiologic examination. Two similar traumas were created in the livers of two more animals and were left surgically untreated as a control group. The two untreated animals died immediately postoperatively, proving the severity of the injuries. Hemostasis was achieved in all treated animals. Mortality and morbidity were zero. No blood, pus, bile, or other fluid was found in the abdomen at sacrifice. A three-zone pattern of lesion was recognized around the electrode placement at histology. RFA is an efficient and safe hemostatic method for grade III and grade III to IV hepatic trauma. Further studies are required for its use in humans.

Radiofrequency ablation of 40 lung neoplasms: preliminary results.

Radiofrequency thermal ablation is a minimally invasive treatment widely used for treatment of liver neoplasms and has also been tested on other types of tumor. Few studies have been published regarding the use of radiofrequency thermal ablation in the treatment of lung neoplasms. This study was performed to evaluate the technical feasibility, the safety, and the efficacy of lung radiofrequency thermal ablation. Between February 2002 and March 2003, 18 subjects with unresectable lung neoplasms, four of whom had primary neoplasms and 14 of whom had metastatic neoplasms, underwent lung radiofrequency ablation. The technique was performed percutaneously using a monopolar cooled-tip electrode needle under CT guidance with the patient under general anesthesia. Patients had no more than three nodules with a total diameter of 10 cm and no evidence of extrathoracic disease. A total of 40 nodules were treated in 24 therapeutic sessions. After treatment, patients underwent follow-up every 3 months by CT and nuclear MRI with gadolinium for a median time of 8 months (range, 2-14 months). No evidence of local relapse was discovered in 94.4% of subjects. The treatment was safe and well tolerated. Complications encountered included massive pneumothorax, which occurred in one subject, requiring pleural drainage. Other complications were moderate pneumothorax (also requiring pleural drainage), cough, fever, slight dyspnea, and pain, but these complications were short in duration and successfully treated. Radiofrequency thermal ablation is a promising technique in the treatment of patients with lung neoplasms and has been found to be both safe and technically feasible.

Effectiveness of radiofrequency ablation for hepatocellular carcinomas larger than 3 cm in diameter.

Radiofrequency ablation is a safe and effective treatment for hepatocellular carcinomas 3.1 to 8.0 cm in diameter. Case series with prospective data collection. Tertiary referral center. Eighty-six patients with hepatocellular carcinoma treated with radiofrequency ablation from May 1, 2001, to December 31, 2002, were placed into categories of those with tumors 3 cm or smaller (group 1, n = 51) and those with tumors 3.1 to 8.0 cm (group 2, n = 35) in diameter. Radiofrequency ablation was performed with a single or cluster cool-tip electrode. The choice of treatment route was based on tumor size and position. Complication, treatment mortality, and complete ablation rates. Radiofrequency ablation was performed percutaneously in 26 patients in group 1 and 9 patients in group 2, with laparoscopy in 2 patients in group 1 and 1 patient in group 2, and with open operation in 23 patients in group 1 and 25 patients in group 2. The complication rates were 12% and 17% in group 1 and group 2, respectively (P =.48); treatment mortality rates were 0% and 3%, respectively (P =.41). Complete ablation rates after a single session of ablation assessed by means of computed tomography 1 month after treatment were 94% and 91% in group 1 and group 2, respectively (P =.68). Radiofrequency ablation is a safe and effective treatment for patients with hepatocellular carcinomas 3.1 to 8.0 cm in diameter.

Delayed portal vein thrombosis after experimental radiofrequency ablation near the main portal vein

Portal venous blood flow may protect adjacent tumour cells from thermal destruction with radiofrequency ablation (RFA). This study aimed to investigate the local effect of RFA on the main portal vein branch, and the completeness of cellular ablation in its vicinity, with or without a Pringle manoeuvre using a porcine model. This was an in vivo study on 23 domestic pigs. RFA using a cooled-tip electrode was performed 5 mm from the left main portal vein branch under ultrasonographic guidance for 12 min with (n = 10) or without (n = 10) a Pringle manoeuvre. Ten pigs were killed 4 h after the procedure to study the early effects of RFA and ten others were killed 1 week later to determine any delayed effect. As a control, sham operations with a Pringle manoeuvre for 12 min were performed on three pigs. The flow velocity changes of portal vein and hepatic artery were measured using Doppler ultrasonography, and the completeness of cellular ablation around the portal vein was assessed qualitatively by histochemical staining and quantitatively by measuring intracellular levels of adenosine 5'-triphosphate (ATP). In the absence of the Pringle manoeuvre, there was no significant change in mean(s.d.) portal vein flow velocity before RFA (20.0(3.5) cm/s) and at 4 h (18.5(2.5) cm/s) (P = 0.210) and 1 week (19.5(2.2) cm/s) (P = 0.500) after the procedure. Gross and histological examination of the portal vein branches showed no damage without the Pringle manoeuvre. In all pigs that underwent RFA with a Pringle manoeuvre, the portal vein was occluded 1 week after the operation; histological examination of the affected portal vein showed severe thermal injury and associated venous thrombosis. The local effect of RFA on the hepatic artery was similar. With intact portal blood flow during RFA, complete ablation of liver tissue around the pedicle was demonstrated by histochemical staining and measurement of the intracellular ATP concentration. RFA was safe when applied close to the main portal vein branch without a Pringle manoeuvre, with complete cellular destruction. Use of the Pringle manoeuvre resulted in delayed portal vein and hepatic artery thrombosis and injury to the hepatic artery and bile duct.

Percutaneous radiofrequency ablation for inoperable non-small cell lung cancer and metastases: preliminary report.

To assess technical feasibility, efficacy, and complications of percutaneous computed tomography (CT)-guided transthoracic radiofrequency (RF) ablation for treating inoperable non-small cell lung cancer (NSCLC) and lung metastases. Twenty-six patients with 27 NSCLCs and four patients with five lung metastases underwent RF ablation with cooled-tip electrodes with CT guidance. Patients were not candidates for surgery because of either advanced-stage disease (n = 20) and/or comorbid processes (n = 4) or refusal to undergo surgery (n = 6). The procedure was performed with the intent to cure in 10 (33%) patients with stage I tumors and as palliative therapy in 20 (67%) patients. Contrast material-enhanced CT was performed immediately, 1 month, and then every 3 months after RF ablation to evaluate the response to therapy. Time to death for each patient was calculated with Kaplan-Meier analysis, and the effect of tumor size and the extent of coagulation necrosis on time to death were determined. Complete necrosis was attained in 12 (38%) of 32 lesions; partial (>50%) necrosis, in the remaining 20 (62%) lesions. Tumor size was a major discriminator in achieving complete necrosis. Complete necrosis was attained in all six (100%) tumors smaller than 3 cm but only in six (23%) of 26 larger tumors (P <.05). Mean survival of patients with complete necrosis (19.7 months) was significantly better than that of patients with partial necrosis (8.7 months) (P <.01). There were three (in 30 patients, 10%) major complications, which included acute respiratory distress syndrome, and two pneumothoraces that required thoracostomy. RF ablation appears to be a safe and promising procedure for the treatment of inoperable NSCLC and metastases.

Radio-frequency thermal ablation with hypertonic saline solution injection of the lung: ex vivo and in vivo feasibility studies.

The aim of this study was to assess the effects of simultaneous instillation of NaCl solutions during radio-frequency ablation (RFA) on the dimension of the ablated lesion in ex vivo bovine lung tissue and in vivo rabbit lung tissue. The RFA was induced in ex vivo bovine lung tissue which was inflated with room air and in vivo rabbit lung tissue by a 500-kHz RF generator and a 17-G cooled-tip electrode. In in vivo experiments, RFA was performed using CT guidance. The RF energy was applied for 5 min with or without instillation of 0.9 or 36% NaCl solutions. The changes in tissue impedance, current, power output, and temperature of the electrode tip were automatically measured. The maximum diameter of all thermal lesions was measured perpendicular to the electrode axis by two observers. In an ex vivo study, the mean lesion diameters using 36 and 0.9% NaCl solutions were larger than those of the control group: 51+/-8, 34+/-6, and 5+/-2 mm ( p<0. 05). In in vivo rabbit lung tissue, the mean lesion diameter with NaCl solution (15.3+/-3.1 mm) was larger than that of the lesion without NaCl solution (8.5+/-1.4 mm; p<0.05). With instillation of NaCl solutions, a marked decrease of tissue impedance (>100 Omega) and corresponding increase of current flow occurred in both ex vivo and in vivo studies. This experimental study demonstrates that RF ablation with simultaneous NaCl solution infusion of the lung is more effective in achieving coagulation necrosis than conventional RFA procedure.

Percutaneous Radiofrequency Thermal Ablation of Lung VX2 Tumors in a Rabbit Model Using a Cooled Tip-Electrode

To evaluate the feasibility, safety, and effectiveness of percutaneous CT-guided transthoracic radiofrequency ablation (RFA) of lung VX2 tumors implanted in rabbits. Thirty-five rabbits with implanted lung VX2 tumors were divided into two groups, an RFA group (n = 28) and a control group (n = 7). In the RFA group, RFA was performed on VX2 tumors using a 17-gauge internally cooled-tip electrode. Contrast-enhanced CT was performed before the RFA and on the same day, day 3, weeks 1, 2, 3, and months 1, 2, 6, and 9, after the RFA. The therapeutic efficacy was evaluated by CT and pathologic findings. RFA of lung tumors was technically successful in each instance. Complete tumor ablation was achieved in 19 of the 28 rabbits (67.9%) in the RFA group. Nine rabbits (32.1%) showed local tumor relapse and mediastinal lymph nodal or pleural metastasis. The animals in the control group died of end-stage malignancies with diffuse tumor spread and malignant pleural effusion (mean 26 +/- 2.7 days). There were 17 (60.7%) complications related to the procedure, ie, pneumothorax (n = 12), obstructive pneumonia (n = 3), hemothorax (n = 1), and burn (n = 1). RFA of centrally located VX2 tumors (in inner 2/3 of the lung) was more frequently associated with complications than RFA of peripherally located VX2 tumors ( P= 0.02). This experimental study demonstrates the feasibility of RFA therapy for treating lung VX2 tumors in rabbits, although RFA for central tumors carries the potential for major complications, including large pneumothorax or obstructive pneumonia.

Open radio-frequency thermal ablation of renal VX2 tumors in a rabbit model using a cooled-tip electrode: feasibility, safety, and effectiveness.

The purpose of this study was to evaluate the feasibility, safety, and effectiveness of radio-frequency (RF) ablation using an internally cooled-tip electrode on renal VX2 tumors implanted in rabbits. Thirty-three rabbits with implanted renal VX2 tumors were divided into two groups: an RF ablation (RFA) group ( n=27) and a control group ( n=6). In the RFA group, RFA was performed on 27 implanted VX2 tumors using a cooled RF electrode and they were divided into three subgroups according to the follow-up period: acute (1-3 days, n=12); subacute (1-4 weeks, n=9); and chronic (2-7 months, n=6). Contrast-enhanced spiral CT was performed before the RFA and at the day, day 3, weeks 1, 2, 4, and months 2 and 7, after the RFA. The therapeutic efficacy was evaluated by the survival rate, CT, and pathologic findings. The RFA of renal tumors was technically successful in each instance. Complete tumor ablation was achieved in 22 of the 27 rabbits (81.5%) in the RFA group: 5 rabbits survived longer than 8 weeks without any evidence of viable tumor (18.5%) and 17 rabbits were found free of viable tumors when killed (63.0%). Five rabbits showed local tumor relapse and/or hematogenous lung metastasis after ablation (a recurrence rate of 18.5%). There were 11 (40.7%) complications related to the procedure. This experimental study demonstrates the feasibility of RFA therapy to treat renal VX2 tumors in rabbits, although RFA for central tumors carries some major potential complications, including renal arterial injury.

Role of catheter and surgical ablation in congenital heart disease

The role of surgery and radiofrequency current ablation for the treatment of tachycardias in patients with congenital heart disease The use of radiofrequency current application as a treatment strategy has stimulated a revolution in our understanding of tachycardia mechanisms. The extension of its use to patients with congenital heart defects and tachyarrhythmias has opened the door to new treatments with known success rates and known risks for mortality and morbidity. Antiarrhythmic surgery aims to dissect or excavate a responsible substrate and is especially worth considering if cardiac surgery is being undertaken for other reasons. With suitable surgical skill and interest, and with strong electrophysiologic support, high success rates have been documented. Antiarrhythmic surgical incisions have the advantage of being visually controllable regarding the extent and location of damage to myocardial tissue. In other situations, radiofrequency current ablation is preferred because of its less-invasive character, its use of local anesthesia, and the avoidance of surgical trauma. Both surgery and catheter ablation require precise clarification of the tachycardia mechanism and precise localization of the underlying substrate. The importation of such techniques into the realm of open chest surgery would be difficult in light of the need for multiple intracardiac catheters and repeated fluoroscopically guided catheter positioning. Electrophysiologic studies performed during the antiarrhythmic surgical procedure cannot provide complete information, and their use is thus restricted to the arrhythmogenic myocardial target only [32,45]. In contrast, catheter-mediated electrophysiologic studies offer the option of exact diagnosis, precise substrate localization, and interventional treatment in a single session. Moreover, validation of the linear lesion's completeness has become a reliable predictor for mid- and long-term success in avoiding recurrences. As a result, the application of catheter-mediated ablation has exploded within the past 15 years. Antiarrhythmic surgery has survived as a discipline in a decreasing number of experienced hands [43,44]. As a result of recent experiences and modern technology, success rates above 90% [74-76, 81,88] for the interventional treatment of congenital tachycardias have become comparable to those reported in patients with "normal" hearts. For acquired tachycardias, acute success rates today range about 80% at the atrial level. The rate of recurrence is still relatively high at about 10-25% [73,76,77,79,91,96,102]. Further improvements are being pursued. Data on the treatment of acquired tachycardias at the ventricular level is largely anecdotal. Good early success rates are combined with a tendency to recurrence in longer-term follow-up [50,76,103-108]. Some of the late VT ablation recurrences may be explained by the fact that fibrotic, scarred, and hypertrophic myocardial tissue at the targeted site often prevents effective radiofrequency current application and lesion generation. In order to improve RF lesion depth and continuity, newly designed technologies for radiofrequency current ("cooled tip electrode", Cordis Webster, Baldwin Park, CA), and alternative energy sources (cryo-ablation, micro-wave, or ultrasound) are being readied for introduction in the very near future. For patients suffering from recurrent tachycardias and having other reasons for open-heart surgery, a hybrid concept can be created, utilizing modern 3-D electro-anatomical reconstruction as a basis for an electrophysiologically informed surgical procedure. Following such a concept, a hemodynamic catheterization can be combined with an electrophysiologic study to define critical myocardial zones for induced macro-re-entry tachycardias, or of those zones expected to play an arrhythmogenic role in the future. With such information, surgical incisions for cardiac access and repair can be planned and performed. The role of surgery in antiarrhythmic treatment can become preventive. Myocardial tissue is incised for cannulation and repair in a way that can reduce the chance of later scar-associated tachycardias [109]. The extension of surgical cuts to physiologic barriers of electrical conduction is a major strategy for the primary prevention of postsurgical or incisional arrhythmias. In addition, the simultaneous treatment at heart surgery of already existing tachycardias can be offered within the same session as a secondary preventive concept. Despite the immense growth of knowledge and experience in recent years, there is still a need for more knowledge about the factors causing arrhythmogenesis and their interactions. Prospective and randomized studies are needed to show the most effective strategies to prevent arrhythmia-mediated death. The future of antiarrhythmic treatment will less be directed by the limitations of current interventional tools, which will be improved, and more by an evolutionary process in philosophy regarding the understanding of arrhythmogenesis in these patients as the basis for new concepts of arrhythmia prevention and treatment.

Ultrasound-Guided Radiofrequency Thermal Ablation of Normal Kidney in a Rabbit Model: Correlation with CT and Histopathology

Purpose: To assess the feasibility and safety of using a cooled-tip electrode to perform percutaneous radiofrequency ablation of kidney tissue in rabbits, and to evaluate the ability of CT to reveal the appearance and extent of tissue necrosis during follow-up after ablation. Materials and Methods: Using ultrasound guidance, a 17-G, cooled-tip electrode was inserted into the right lower portion of the kidney in 26 New Zealand White rabbits. Radiofrequency was applied for 2 mins, and biphasic helical CT scanning was used to assess tissue destruction and the presence or absence of complications immediately after the procedure and at 24 hrs, 2 and 3 days, and 1, 2, 3, 4, 5, 6 and 7 weeks. The study had three phases: acute [immediately killed : N=10]; subacute [killed at 24 hrs (n=3), 2 days (n=3), 3 days (n=1) : N=7]; chronic [killed at 1 week (n=4), 2 weeks (n=2), 4 weeks (n=1), 7 weeks (n=1) : N=8]. After the animals were killed, their kidneys were histopathologically examined and the radiologic and pathologic findings of lesion size and configuration were correlated. Results: In each instance, ultrasound-guided radiofrequency ablations of the lower pole of the kidney were technically successful. Contrast-enhanced biphasic helical CT revealed regions of hypoattenuation devoid of parenchymal enhancement, and these correlated closely with true pathologic lesion size (r=0.884; p>0.05). In subacute and chronic models, CT scanning revealed gradual spontaneous resorption of the ablated lesion and the presence of perilesional calcification. Histopathologically, in the acute phase the ablated lesions showed coagulative necrosis and infiltration of inflammatory cells, and in the chronic phase there was clear cut necrosis of glomeruli, tubules and renal interstitium, with diminishing inflammatory response and peripheral fibrotic tissue formation. Conclusion: Ultrasound-guided renal radiofrequency ablation is technically feasible and safe. In addition, the avascular lesion measured at contrast-enhanced helical CT closely correlated with the size of ablated tissue. Contrast-enhanced CT may therefore be used for serially monitoring the effect of radiofrequency ablation. In the future, RF ablation may offer an alternative treatment option for renal cancer.

Radiofrequency Ablation for Eradication of Renal Tumor in a Rabbit Model by Using a Cooled-tip Electrode Technique

Radiofrequency Ablation for Eradication of Renal Tumor in a Rabbit Model by Using a Cooled-tip Electrode Technique