Monopolar Radiofrequency Ablation Research Articles

Time Course of Nicotinamide Adenine Dinucleotide Diaphorase Staining after Renal Radiofrequency Ablation Influences Viability Assessment

Nicotinamide adenine dinucleotide (NADH) diaphorase staining has been used to confirm cell viability or death after radiofrequency ablation (RFA) of renal tissue. The time course over which NADH staining status converts from viable to non-viable after a lethal insult has not been defined for renal RFA, but the change may not be immediate. Our objective was to assess porcine renal tissue for viability using NADH diaphorase staining at various times after RFA. Seven pigs underwent monopolar RFA of both kidneys followed by needle biopsy of the ablation zone before and immediately after ablation and at 15-minute intervals thereafter. Initially, a single kidney was treated, and the contralateral kidney was treated 2 weeks later. Biopsies were taken from untreated renal parenchyma in a similar time course after nephrectomy to examine the effect of ischemia. All biopsy specimens, as well as representative sections of the ablation zone, were subjected to NADH staining and reviewed by a pathologist who was blinded to the tissue treatment. Most of the post-RFA biopsy specimens (86%) showed non-viable tissue. However, 14% of the specimens revealed viable tissue as late as 150 minutes after RFA. Therefore, none were positive. In the nephrectomy parenchyma, 92% of the biopsy specimens showed viable tissue as late as 4 hours after the onset of ischemia. Staining for NADH can establish tissue non-viability after RFA, but the timing of staining after treatment must be considered when interpreting results to avoid false positive tests. Tissue that is apparently viable by NADH staining within 2.5 hours of RFA may in fact have been ablated.

Investigation of the influence of blood flow rate on large vessel cooling in hepatic radiofrequency ablation / Untersuchung des Einflusses der Blutflussgeschwindigkeit auf die Gefäßkühlung bei der Radiofrequenzablation von Lebertumoren

Radiofrequency (RF) ablation using high-frequency current has become an important treatment method for patients with non-resectable liver tumors. Tumor recurrence is associated with tissue cooling in the proximity of large blood vessels. This study investigated the influence of blood flow rate on tissue temperature and lesion size during monopolar RF ablation at a distance of 10 mm from single 4- and 6-mm vessels using two different approaches: 1) an ex vivo blood perfusion circuit including an artificial vessel inserted into porcine liver tissue was developed; and 2) a finite element method (FEM) model was created using a novel simplified modeling technique for large blood vessels. Blood temperatures at the inflow/outflow of the vessel and tissue temperatures at 10 and 20 mm from the electrode tip were measured in the ex vivo set-up. Tissue temperature, blood temperature and lesion size were analyzed under physiological, increased and reduced blood-flow conditions. The results show that changes in blood flow rate in large vessels do not significantly affect tissue temperature and lesion size far away from the vessel. Monopolar ablation could not produce lesions surrounding the vessel due to the strong heat-sink effect. Simulated tissue temperatures correlated well with ex vivo measurements, supporting the FEM model.

Surgery for atrial fibrillation with radiofrequency ablation: four years experience

Atrial fibrillation (AF) is very common in patients undergoing open heart surgery. AF ablation with different sources of energy, enables the surgeon to create linear lesions rapidly and safely. However, results of these technologies need examination. We report the clinical results obtained in a 4-year experience using mono- and bipolar radiofrequency (RF) ablation of AF in a heterogeneous group of 183 patients. From May 2001 until December 2005 a total of 183 patients underwent pulmonary vein isolation using RF energy. In 73 cases, monopolar RF was used. Energy was applied in the endocardium in 40 cases (Group A) and in the epicardium in 33 cases (Group B). From May 2003, bipolar RF was used in a total of 110 patients (Group C). Duration of AF, left atrial dimensions, age or reoperations, were not considered contraindications to ablation. Ablation procedure for AF ablation was associated with a variety of cardiac procedures, from isolated mitral valve procedure to complex ascending aorta operations. In-hospital mortality was 3.8% in the whole group (range 2.7-6.1%). Mortality and morbidity were not related with the ablation procedure. At the follow-up time of 50.9+/-3.3, 48.2+/-3.1, 32.7+/-0.9 months (Group A, B and C, respectively), sinus rhythm (SR) is present in a percentage of 75%, 67.7%, 79.4% of patients. Higher incidence of AF recurrence occurred in the first six months after surgery in all three groups. Late recurrence was higher in the epicardial group and overall freedom of AF was 64% in Group A, 46% in Group B and 71.1% in Group C (P=0.01). Our results demonstrate that the epicardial monopolar RF ablation obtains worse results than the endocardial monopolar RF and the bipolar RF ablation. Bipolar RF theoretically grants transmurality and is easy and safe, and a complete ablation setting lines can be achieved. Bipolar RF enables extension of ablation to every patient on AF undergoing a cardiac operation.

Radiofrequency Ablation of Osteoid Osteoma: Initial Results with a Bipolar Ablation Device

To report the initial results with percutaneous radiofrequency (RF) ablation of osteoid osteomas with a bipolar ablation device. Twelve patients (seven male patients and five female patients; mean age, 17.3 years; age range, 6-36 y) with clinically and radiologically suspected osteoid osteoma were treated with computed tomography-guided percutaneous bipolar RF ablation. The procedure was performed with the patients under general anesthesia. After localization of the nidus, an 11-gauge hollow drill was introduced into the nidus through a 9-F introducer sheath. A bipolar 18-gauge RF probe with a 9-mm active tip was inserted through the introducer sheath and connected to the RF generator. Energy application was started at 2 W and subsequently increased to a maximum of 5 W. The procedure was terminated if a resistance of 900 Omega was reached. Mean duration of energy deposition was 8.3 +/- 4.0 minutes, with a mean energy application of 1.8 +/- 2.9 kJ (range, 0.3 - 7 kJ). In one patient, the intervention had to be repeated twice to achieve total pain relief. Eleven of 12 patients (92%) remained free of symptoms at a follow-up time of 15.1 +/- 9.5 months (range, 5 - 31 months). One patient had recurrence of pain 16 months after the procedure and was treated surgically. No complications occurred. Patients resumed normal activity within 24 hours. Percutaneous bipolar RF ablation is an efficient and safe treatment of osteoid osteoma. Short-term efficacy of bipolar RF ablation may rival the results of monopolar RF ablation. Further studies are needed to address the long-term efficacy of this technique.

Experimental Radiofrequency Ablation Near the Portal and the Hepatic Veins in Pigs: Differences in Efficacy of a Monopolar Ablation System

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. 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. 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 <or= 0.05) of the zones of ablation near the hepatic veins were larger than that near the portal vein (7.5 +/- 4.1 mL, 3.2 +/- 0.7 cm, 2.6 +/- 0.7 cm, 2.4 +/- 0.6 cm). Energy deposition needed to ablate liver tissue was higher (P = 0.003) for radiofrequency ablation near the portal vein (3.16 +/- 1.58 kJ/mL) than for radiofrequency ablation near the hepatic veins (1.65 +/- 1.14 kJ/mL). Higher energy deposition is needed to ablate liver tissue near the portal vein than near the hepatic veins. As a result, the zone of ablation is larger near the hepatic vein than near the portal vein.

Permanent Atrial Fibrillation Ablation Surgery in CABG and Aortic Valve Patients is at Least as Effective as in Mitral Valve Disease

Data on combined permanent atrial fibrillation (pAF) surgery and coronary artery bypass grafting (CABG) and/or aortic valve replacement (AVR) are scarce, and the mid- and long-term effects on survival and cardiac rhythm are unknown. In a prospective analysis 125 patients (Group I: CABG and/or AVR, n = 50; Group II: mitral valve [MV] surgery, n = 75) with pAF (> or = 6 months) underwent either concomitant monopolar (Group I: n = 20; Group II: n = 75) or bipolar (Group I: n = 30) radiofrequency (RF) ablation procedures. Group I patients had a significantly smaller left atrial (LA) size than Group II patients (LA-diameter: 47.7 +/- 4.6 vs. 58.2 +/- 6.1 mm; p < 0.01). Regular follow-up was performed from 3 to 36 months after surgery to assess survival, NYHA-class, and conversion rate to stable sinus rhythm (SR). Early mortality (< 30 days) of Group I patients was 0% (Group II: 2.7%), cumulative survival at long-term follow-up was 0.95 vs. 0.82 (p = 0.31) and NYHA-class improved significantly in both groups, particularly in cases with stable SR. At follow-up 80% of Group I patients had SR (Group II: 70%). In Group I patients the bipolar approach was associated with significantly shorter ablation procedure times compared to the monopolar procedure (12.1 +/- 3.4 vs. 18.9 +/- 1.6 min; p < 0.05). Concomitant pAF ablation surgery in CABG and/or AVR is safe and at least as effective as in MV surgery, presumably because severe LA enlargement is exceptionally rare in this group.

93 Radiofrequency ablation of prostate using bipolar technology

Introduction: Monopolar radiofrequency ablation has become an accepted modality within minimally invasive treatments for benign prostatic obstruction (BPO). Lesions created by bipolar technology are greater in size than those produced by monopolar devices. Recently, a bipolar system has been developed. This pilot study aims to determine if there is sufficient efficacy of this bipolar system to justify further clinical studies.Patients and Methods: Fourteen patients with BPO were identified for this pilot study of radiofrequency interstitial thermotherapy (RFITT) using the CelonUroTM bipolar probe and generator (OLYMPUS Winter and Ibe GmbH). Inclusion criteria included IPSS&gt;12, QL&gt;2 and Qmax&lt;12 ml/s. The mean age was 62 years (range 53–77) and the mean TRUS prostate size was 33.7 cc(range 15–66). The majority treated on a day case basis.Results: The mean number of radiofrequency lesions per prostate was 6.2 (range 3–12). The mean operating time was 19.8 min (12–34). Baseline IPSS, QL, Qmax and PVR were respectively 23, 4.8, 7.1 ml/s and 168 ml. Ten patients have 6–12 data and nine patients have 12‐month follow up data. At 6–12 weeks and at one year followup, there are highly statistically significant (P &lt; 0.01) and clinical significant improvements in IPPS, QL, Qmax and PVR. These were respectively, 12.8, 2.1, 14 ml/s, 75 ml and 10.3, 1.7, 12.5 ml/s and 77 ml. Two patients developed urinary retention; both were catheter free by 4 weeks but one was salvaged with TURP by request of the patient. No retrograde ejaculation was reported amongst those who were sexually active. No other complications were reported.Conclusions: RFITT represents a further development in radiofrequency technology for the minimally invasive treatment of BPO. These early results indicate potential efficacy of bipolar radiofrequency ablation to treat BPO. Randomised studies using bipolar RFITT are necessary to determine its positioning between drug therapy and cavitating surgical procedures in terms of efficacy and morbidity profile.

Multiple-electrode Radiofrequency Ablation: Simultaneous Production of Separate Zones of Coagulation in an In Vivo Porcine Liver Model

A multiple-electrode radiofrequency (RF) system was developed based on switching between electrodes that allows for the simultaneous use of as many as three electrically independent electrodes. The purpose of this study was to determine if each multiple-electrode ablation zone is identical to an ablation zone created with conventional single-electrode mode. Nine female domestic pigs (mean weight, 90 kg) were used for this study. A prototype monopolar multiple-electrode RF ablation system was created with use of an RF generator and an electronic switching algorithm. A maximum of three electrodes can be used simultaneously by switching between electrodes at each impedance spike (30 omega greater than baseline levels). A total of 39 zones of ablation were created at open laparotomy in pig livers with use of a conventional single electrode (n = 9), two single electrodes simultaneously (n = 6 ablations; 12 ablation zones), or three single electrodes simultaneously (n = 6 ablations; 18 ablation zones). RF electrodes were spaced in separate lobes of the liver when multiple zones of coagulation were created simultaneously. Animals were euthanized after RF ablation, livers were removed, and ablation zones were sectioned and measured. Zones of coagulation created simultaneously with two or three electrodes were equivalent to ablation zones created with use of conventional single-electrode ablation. No significant differences were observed among control animals treated with a single electrode, those with two separate zones of ablation created simultaneously, and those with three simultaneously created ablation zones in terms of mean (+/-SD) minimum diameter (1.6 cm +/- 0.6, 1.6 cm +/- 0.5, and 1.7 cm +/- 0.4, respectively), maximum diameter (2.0 cm +/- 0.5, 2.3 cm +/- 0.5, 2.2 cm +/- 0.5, respectively), and volume (6.7 cm3 +/- 3.7, 7.4 cm3 +/- 3.8, and 7.8 cm3 +/- 3.9; P > .30, analysis of variance, pairwise t-test comparisons). A rapid-switching multiple-electrode RF system was able to simultaneously create as many as three separate ablation zones of equivalent size compared with single-electrode controls. This system would allow physicians to simultaneously treat multiple tumors, substantially reducing procedure time and anesthesia risk.

A cooled intraesophageal balloon to prevent thermal injury during endocardial surgical radiofrequency ablation of the left atrium: a finite element study

Recent clinical studies on intraoperative monopolar radiofrequency ablation of atrial fibrillation have reported some cases of injury to the esophagus. The aim of this study was to perform computer simulations using three-dimensional finite element models in order to investigate the feasibility of a cooled intraesophageal balloon appropriately placed to prevent injury. The models included atrial tissue and a fragment of esophagus and lung linked by connective tissue. The lesion depth in the esophagus was assessed using a 50 °C isotherm and expressed as a percentage of thickness of the esophageal wall. The results are as follows: (1) chilling the esophagus by means of a cooled balloon placed in the lumen minimizes the lesion in the esophageal wall compared to the cases in which no balloon is used (a collapsed esophagus) and with a non-cooled balloon; (2) the temperature of the cooling fluid has a more significant effect on the minimization of the lesion than the rate of cooling (the thermal transfer coefficient for forced convection); and (3) pre-cooling periods previous to RF ablation do not represent a significant improvement. Finally, the results also suggest that the use of a cooled balloon could affect the transmurality of the atrial lesion, especially in the cases where the atrium is of considerable thickness.

Excessive Hyperthermic Necrosis of a Pulmonary Lobe after Hypertonic Saline-Enhanced Monopolar Radiofrequency Ablation

Although there has been a feasibility study of saline-enhanced radiofrequency ablation of the lung in rabbits, there has been no report on hypertonic saline-enhanced radiofrequency ablation of human pulmonary tumors or its complication. We report a case in which a large necrotic cavity was produced in the lung after hypertonic saline-enhanced radiofrequency ablation of recurrent metastatic tumor from hepatocellular carcinoma. Although hypertonic saline-enhanced radiofrequency ablation is powerful and efficient in local ablation, it is difficult to predict the exact extent of ablation, especially in the lungs. This can be dangerous, as there is a high chance of producing an ablation area much larger than expected and, hence, major complications. Special attention is required not to overablate while using this technique.

Radiofrequency Ablation for the Treatment of Liver Tumors in the Caudate Lobe

To evaluate the effectiveness of radiofrequency (RF) ablation for liver tumors located in the caudate lobe. Ten patients (46-79 years of age; median, 70 y), eight with hepatocellular carcinoma (HCC) and cirrhosis and two with colorectal metastases in the caudate lobe, were treated with 5.8% NaCl tissue-perfused monopolar (n=7) or bipolar (n=3) RF ablation. The median tumor diameter was 41 mm (range, 25-70 mm). Procedures were performed under ultrasound and computed tomography (CT) guidance in eight and two patients, respectively. One month later, the treatment response was assessed by CT. Transhepatic right intercostal and transomental anterior epigastric routes were used for tumor puncture in eight and two patients, respectively. The entire RF ablation treatment required one or two procedures (median, 1.5), including two to 15 electrode repositionings (median, 6). After RF ablation procedure, one patient experienced jaundice that resolved spontaneously. In one patient, CT follow-up showed asymptomatic segmental biliary duct dilations. Median total hospital stay was 3 days (range, 2-9 d). Complete ablation was achieved in nine of 10 tumors. In one patient, ethanol ablation was necessary to complete RF ablation treatment. After a median follow up of 9.5 months (range, 5-25 mo), three patients remained tumor-free and seven had tumor relapse: two local, four distant, and one mixed. Repeat RF ablation was successfully performed in four cases. RF ablation of liver tumors located in the caudate lobe is effective despite the deep location of tumors and the vicinity of major vessels.

Ex Vivo Experiment of Saline-Enhanced Hepatic Bipolar Radiofrequency Ablation with a Perfused Needle Electrode: Comparison with Conventional Monopolar and Simultaneous Monopolar Modes

The purpose of this study was to validate the saline-enhanced bipolar radiofrequency ablation (RFA) technique using a perfused electrode to increase RF-created coagulation necrosis, to compare that technique with monopolar RFAs and to find appropriate concentrations and volumes of perfused NaCl solution for the bipolar RFA. A total of 90 ablations were performed in explanted bovine livers. In the initial experiments to determine appropriate conditions for bipolar RFA, we created five thermal ablation zones in each condition, with instillations of varied concentrations (0.9-36%) or injection rates (30 mL/hr-120 mL/hr) of NaCl solution. After placement of one or two 16-gauge open-perfused electrodes into bovine livers, the NaCl solution was instilled into the tissue through the electrode. In the second part of the study, 10 ablation zones were created using one or two perfused electrodes for each of five groups under different conditions: a conventional monopolar mode with 0.9% NaCl solution (group A) or with 6% NaCl solution (group B), a simultaneous monopolar mode with 6% NaCl solution (group C) and a bipolar mode with 6% NaCl solution (groups D and E). RF was applied to each electrode for 20 min in groups A, B, C, and E, or for 10 min in group D. During RFA, we measured the tissue temperature 15 mm from the electrode. The temperature changes during the RFA and the dimensions of the ablation zones were compared among the groups. Bipolar RFA created larger short-axis diameters of coagulation necrosis with 6% NaCl solution (35.8 +/- 15 mm) than with 0.9% NaCl solution (17 +/- 9.7 mm) (P < 0.05). However, concentrations of NaCl solution above 6% did not further increase the extent of coagulation necrosis. In addition, bipolar RFA with 6% NaCl solution instillation at a rate of 1.0 mL/min (37.9 +/- 5.4 mm) or 2.0 mL/min (35.6 +/- 9.3 mm) produced larger diameters at the mid-point between the electrodes of the ablated lesion than did 0.5 mL/min (25.8 +/- 9.3 mm) (P < 0.05). The bipolar mode showed a more rapid increase in temperature at the mid-point between the two probes, up to 60 degrees C, than did the monopolar modes (P < 0.05). In addition, the bipolar RFA (group E) treated for 20 min showed a larger value of the short-axis diameter than did the conventional or simultaneous monopolar modes (P < 0.05), and bipolar RFA (group D) treated for 10 min, showed similar results with conventional monopolar modes treated for 20 min (P > 0.05): 31.0 +/- 5.4 mm (group A); 28.8 +/- 3.8 mm (group B); 25.5 +/- 6.4 mm (group C); 32.6 +/- 4.2 mm (group D); 49.4 +/- 5.0 mm (group E). Bipolar RFA with instillation of 6% NaCl solution through an open perfusion system demonstrates better efficacy in creating a larger ablation zone than does conventional or simultaneous monopolar modes at the various times examined. Therefore, hypertonic saline-enhanced bipolar RFA seems to be a promising approach for treating larger liver tumors.

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.

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

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. 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. 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). 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.

Bipolar Radiofrequency Ablation Using Wet-Cooled Electrodes: An In Vitro Experimental Study in Bovine Liver

Our aim was to evaluate the performance of hypertonic saline (HS)-enhanced bipolar radiofrequency ablation using wet-cooled electrodes versus monopolar radiofrequency ablation to create coagulation necrosis in explanted bovine liver. HS-enhanced bipolar radiofrequency ablation using the wet-cooled electrodes shows better performance in creating coagulation necrosis than the monopolar mode.

Monopolar and Bipolar Radiofrequency Ablation Surgery: 3-Year Experience in 90 Patients with Permanent Atrial Fibrillation

In our population, permanent atrial fibrillation (pAF) is a serious concomitant problem in patients scheduled for open heart surgery. The high incidence necessitates reliable methods of treating pAF efficiently. We report our 3-year experience with a safe concept of using monopolar and bipolar radiofrequency (RF) ablation procedures. Ninety patients (mitral, n = 56; aortic, n = 22; aortic and mitral, n = 1; coronary artery bypass grafting, n = 11) underwent either monopolar (n = 77) or, recently, bipolar (n = 13) RF ablation procedures that produced encircling isolation lesions around the left and the right pulmonary veins (PVs) and a connection line between the two. Amiodarone was given for 3 months after surgery. Hospital mortality was 2.2%. At follow-up, 75% of the patients were in stable sinus rhythm (SR). Preoperative pAF duration, etiology of heart disease, and type of RF energy application were not predictive of the risk of persisting pAF after surgery. Whereas patients (50 of 90) with small preoperative left atrial (LA) diameters (<56 mm) had SR in almost 90% of cases, large preoperative LA diameters (>or=56 mm; 40 of 90 patients) were associated with a significant risk of persisting pAF (P < .05). Particularly in cases of small preoperative LA diameters, isolation of the PVs using either monopolar or bipolar RF ablation procedures in combination with amiodarone therapy represents a safe and efficient option for curing pAF in patients undergoing open heart surgery.

Optimization of Wet Radiofrequency Ablation Using a Perfused-Cooled Electrode: A Comparative Study in Ex Vivo Bovine Livers

ObjectiveTo determine the optimized protocol for wet monopolar radiofrequency ablation (RFA) using a perfused-cooled electrode to induce coagulation necrosis in the ex vivo bovine liver.Materials and MethodsRadiofrequency was applied to excised bovine livers in a monopolar mode using a 200W generator with an internally cooled electrode (groups A and B) or a perfused-cooled electrode (groups C, D, E, and F) at maximum power (150-200 W) for 10 minutes. A total of 60 ablation zones were created with six different regimens: group A - dry RFA using intra-electrode cooling; group B - dry RFA using intra-electrode cooling and a pulsing algorithm; group C - wet RFA using only interstitial hypertonic saline (HS) infusion; group D - wet RFA using interstitial HS infusion and a pulsing algorithm; group E - wet RFA using interstitial HS infusion and intra-electrode cooling; and group F - wet RFA using interstitial HS infusion, intra-electrode cooling and a pulsing algorithm. In groups C, D, E, and F, RFA was performed with the infusion of 6% HS through the perfused cooled electrode at a rate of 2 mL/minute. During RFA, we measured the tissue temperature at a distance of 15 mm from the electrode. The dimensions of the ablation zones and the changes in impedance, currents, and liver temperature during RFA were compared between these six groups.ResultsDuring RFA, the mean tissue impedances in groups A (243 ± 88 Ω) and C (252.5 ± 108 Ω) were significantly higher than those in groups B (85 ± 18.7 Ω), D (108.2 ± 85 Ω), E (70.0 ± 16.3 Ω), and F (66.5 ± 7 Ω) (p < 0.05). The mean currents in groups E and F were significantly higher than those in groups B and D, which were significantly higher than those in groups A and C (p < 0.05): 520 ± 425 mA in group A, 1163 ± 34 mA in group B, 652.5 ± 418 mA in group C, 842.5 ± 773 mA in group D, 1665 ± 295 mA in group E, and 1830 ± 109 mA in group F. The mean volumes of the ablation regions in groups E and F were significantly larger than those in the other groups (p < 0.05): 17.7 ± 5.6 cm3 in group A, 34.5 ± 3.0 cm3 in group B, 20.2 ± 15.6 cm3 in group C, 36.1 ± 19.5 cm3 in group D, 68.1 ± 12.4 cm3 in group E, and 79.5 ± 31 cm3 in group F. The final tissue temperatures at a distance of 15 mm from the electrode were higher in groups E and F than those in groups A, C, and D (p < 0.05): 50 ± 7.5℃ in group A, 66 ± 13.6℃ in group B, 60 ± 13.4℃ in group C, 61 ±12.7℃ in group D, 78 ± 14.2℃ in group E, and 79 ± 12.0℃ in group F.ConclusionWet monopolar RFA, using intra-electrode cooling and interstitial saline infusion, showed better performance in creating a large ablation zone than either dry RFA or wet RFA without intra-electrode cooling.

Bipolar Radiofrequency Ablation of the Kidney: Comparison with Monopolar Radiofrequency Ablation

We report initial ex vivo and in vivo studies using bipolar radiofrequency (RF) ablation of porcine kidneys. An internal ground electrode is positioned in the kidney opposite the RF electrode, resulting in ablation of all the intervening renal tissue. Ex vivo preparations of 10 porcine kidneys were perfused continuously with Ringer's solution and treated with either standard external grounded RF (N = 3) or bipolar RF ablation with 1 (N = 2), 2 (N = 3), or 3 (N = 2) cm of separation between the ground probe and the RF probe using a Model 30 RITA generator (RITA, Mountain View, CA). Target temperatures were 90 degrees C for 8 minutes. Gross and histologic assessments were made acutely. Four domestic pigs were treated with monopolar RF ablation of the lower pole of one kidney and bipolar RF with a 12-mm separation between the probes of the contralateral lower pole. Animals were harvested 48 hours later to maximize tissue damage for gross measurements and histologic evaluation. Ex vivo studies revealed grossly monopolar lesions 1.5 cm in maximum diameter and 1.75 cm(3) in volume. In comparison, bipolar lesions were 2.8 cm in maximum diameter and 10.3 cm(3) in volume using 3 cm of electrode separation. There was histologic evidence of cell death in all specimens. In vivo studies showed two distinct gross lesions with RF: one blanched and one hemorrhagic. Using bipolar RF, larger blanched lesions were achievable than with monopolar RF (2.80 cm(3) v 1.63 cm(3)). Overall, the combinations of blanched and hemorrhagic lesions were similar with monopolar and bipolar RF (5.01 v 5.31 cm(3)). Histologic evaluation verified cell death in the blanched lesions and rare areas of normal tissue in the hemorrhagic lesions. As shown by ex vivo data, bipolar RF can create larger lesions than does monopolar RF. In vivo, at 48 hours, both blanched and hemorrhagic gross lesions were seen using RF. In this model, blanched lesions predominated when performing bipolar RF.

Hepatic bipolar radiofrequency ablation creates coagulation zones close to blood vessels: a finite element study.

Radiofrequency (RF) ablation has become an important means of treatment of non-resectable primary and metastatic liver tumours. Recurrence of treated tumours is associated with cancer cell survival next to blood vessels. The paper examines the performance of classical monopolar, and two configurations of bipolar, RF ablation using a LeVeen ten-prong catheter. Finite element method models of monopolar and bipolar configurations were created at 5 mm distance from a vessel of the size of a typical portal vein (10 mm diameter). In one bipolar configuration, the probes were oriented in the same axial direction (asymmetric configuration); in the second bipolar configuration, the two probes were facing each other (symmetric configuration). The distribution of temperature and current density was analysed for three different flow conditions: normal flow, reduced flow due to portal hypertension and high flow. For normal flow, the distance between the formed coagulation zone and the blood vessel was 1.8 mm for monopolar, 1 mm for asymmetric bipolar, and 0.2 mm for symmetric bipolar, configurations. Symmetric bipolar RF ablation creates coagulation zones significantly closer to blood vessels compared with monopolar RF ablation. This may reduce tumour cell survival next to blood vessels and reduce recurrence rates.

Radiofrequency ablation of primary and metastatic hepatic malignancies.

The majority of patients with primary of metastatic hepatic tumors are not candidates for resection, because of tumor size, location near major intrahepatic blood vessels precluding a margin-negative resection, multifocality, or inadequate hepatic function related to coexistent cirrhosis. Radiofrequency ablation (RFA) is an evolving technology being used to treat patients with unresectable primary and metastatic hepatic cancers. RFA produces coagulative necrosis of the tumor through local tissue heating. Liver tumors are treated percutaneously, laparoscopically, or during laparotomy, using ultrasonography to identify tumors and to guide placement of the RFA needle electrode. For tumors smaller than 2.0 cm in diameter, one or two deployments of the monopolar multiple-array needle electrode are sufficient to produce complete coagulative necrosis of the tumor. However, with increasing size of the tumor, there is a concomitant increase in the number of deployments of the needle electrode and the overall time necessary to produce complete coagulative necrosis of the tumor. In general, RFA is a safe, well-tolerated, effective treatment for unresectable hepatic malignancies less than 6.0 cm in diameter. Effective treatment of larger tumors awaits the development of more powerful, larger array monopolar and bipolar RFA technologies.