[The validity of radiofrequency ablation for hepatocellular carcinoma]

Radiofrequency ablation therapy (RFA) has now become the mainstream percutaneous local treatment for hepatocellular carcinoma (HCC). RFA is superior to both percutaneous ethanol injection (PEI) and percutaneous microwave coagulation therapy (PMCT) because of the large coagulation area obtained by a single session of RF ablation. In addition, the local recurrence rate after RFA is lower than that after PEI. Recently, to improve tumor ablation efficacy, several devices have been reported. We also designed RFA with balloon occlusion of the hepatic artery (balloon-occluded RFA, BoRFA). The coagulation area obtained by BoRFA was significantly larger than that obtained by standard RFA. In Japan, the results for RFA remain insufficient because of the short follow-up periods after treatments. Within a few years, we expect to clarify the indications for RFA treatment for HCC and the choice between RFA and other local treatments.

Twenty years of percutaneous treatments for cystic echinococcosis: a preliminary assessment of their use and safety

Image-guided percutaneous treatments for echinococcal cysts were introduced in the mid-eighties. Today they represent a third therapeutic option, after surgery and benzimidazole derivatives. Two types of percutaneous treatments are available, based on the destruction of the germinal layer or the evacuation of the endocyst. To assess the extent of their use and their safety, a Medline search of the literature on this subject was performed. The number of cysts treated, their anatomical sites, the complications and, length of follow-up (when available), were all examined. The results show that percutaneous treatments for cystic echinococcosis are safe and efficacious in selected anatomical sites, provided basic safety issues are correctly addressed. However, before drawing final conclusions, a more detailed analysis of the literature is needed. Percutaneous treatments could be simplified and made more effective if a scolecidal agent could be found that melts the entire endocyst without causing harm to the biliary epithelium.

Lesion size estimator of cardiac radiofrequency ablation at different common locations with different tip temperatures

Finite element method (FEM) analysis has become a common method to analyze the lesion formation during temperature-controlled radiofrequency (RF) cardiac ablation. We present a process of FEM modeling a system including blood, myocardium, and an ablation catheter with a thermistor embedded at the tip. The simulation used a simple proportional-integral (PI) controller to control the entire process operated in temperature-controlled mode. Several factors affect the lesion size such as target temperature, blood flow rate, and application time. We simulated the time response of RF ablation at different locations by using different target temperatures. The applied sites were divided into two groups each with a different convective heat transfer coefficient. The first group was high-flow such as the atrioventricular (AV) node and the atrial aspect of the AV annulus, and the other was low-flow such as beneath the valve or inside the coronary sinus. Results showed the change of lesion depth and lesion width with time, under different conditions. We collected data for all conditions and used it to create a database. We implemented a user-interface, the lesion size estimator, where the user enters set temperature and location. Based on the database, the software estimated lesion dimensions during different applied durations. This software could be used as a first-step predictor to help the electrophysiologist choose treatment parameters.

A prospective, single-center clinical trial of a modified Cox maze procedure with bipolar radiofrequency ablation

OBJECTIVE

The Cox maze III procedure has excellent long-term efficacy in curing atrial fibrillation. It has not been widely practiced because it is technically challenging and requires prolonged cardiopulmonary bypass. The aim of this study was to examine a simplified Cox maze III procedure that uses bipolar radiofrequency energy as an ablative source.

METHODS

Beginning January 2002, a total of 40 consecutive patients underwent a modified Cox maze III procedure with bipolar radiofrequency energy. Nineteen had a lone maze procedure and 21 had a maze procedure plus a concomitant operation. One month after the operation, the first 8 patients were investigated with high-resolution magnetic resonance imaging. Patients were followed up monthly with clinical examination and electrocardiography.

RESULTS

There was no operative deaths. The crossclamp times were 47 +/- 26 minutes for the modified lone Cox maze III procedure and 92 +/- 37 minutes for the Cox maze III procedure plus concomitant procedures. These were significantly shorter than our previous times for the traditional Cox maze III procedure (93 +/- 34 minutes and 122 +/- 37 minutes, respectively, P <.05). Follow-up magnetic resonance imaging showed no evidence of pulmonary vein stenosis, and atrial contractility was preserved in all patients. There were no late strokes. At 6-month follow-up, 91% of patients (21/23) were in sinus rhythm.

CONCLUSIONS

Bipolar radiofrequency ablation can be used to replace the surgical incisions of the Cox maze procedure. This energy source did not result in pulmonary vein stenosis. The modification of the Cox maze III procedure to use bipolar radiofrequency ablation simplified and shortened this procedure without sacrificing short-term efficacy.

Experimental application of thermosensitive paramagnetic liposomes for monitoring magnetic resonance imaging guided thermal ablation

The use of a liposomal paramagnetic agent with a T(1)-relaxivity that increases markedly at temperatures above the phase transition temperature (T(m)) of the liposomal membrane was evaluated during magnetic resonance imaging (MRI) guided hyperthermia ablation. A neodymium-yttrium aluminum garnet (Nd-YAG) laser unit and a radiofrequency ablation system were used for tissue ablation in eight rabbit livers in vivo. One ablation was made in each animal prior to administration of the liposomal agent. Liposomes with a T(m) of 57 degrees C containing gadodiamide (GdDTPA-BMA) were injected iv, and two additional ablations were performed. T(1)-weighted scans were performed in heated tissue, after tissue temperature had normalized, and 15-20 min after normalization of tissue temperature. Increase in signal intensity (DeltaSI) for ablations prior to injection of the agent was 13.0% (SD = 5.7) for the laser group and 9.1% (SD = 7.9) for the radiofrequency group. Signal intensity after administration of the agent unrelated to heating was not statistically significant (DeltaSI = 1.4%, P = 0.35). For ablations made after injection of the agent, a significant increase was found in the laser (DeltaSI = 34.5%, SD = 11.9) and radiofrequency group (DeltaSI = 21.6%, SD = 22.7). The persistent signal enhancement found in areas exposed to a temperature above the threshold temperature above T(m) allows thermal monitoring of MRI guided thermal ablation.

Evaluation of temperature distributions in cadaveric lumbar spine during nucleoplasty

In this study, temperature maps were obtained throughout human cadaveric disc specimens (n = 6) during a simulated Nucleoplasty treatment. The procedure was performed using the Perc-DL SpineWand (ArthroCare, Sunnyvale, CA) inserted through a 17 gage needle into the human cadaveric disc. The device uses a dual mode heating technique which employs a high voltage radio frequency (RF) plasma field to vaporize tissue (Coblation), followed by bipolar RF current heating for thermal coagulation. The device, with a distal 's-curve', is manipulated manually to create a series of six channels at a 60 degrees angular spacing within a period of 3 min. A computer-controlled, motorized translational system was used to reproducibly mimic the insertion (Coblation) and retraction (rf-coagulation) performed during clinical implementation, with rotation performed manually between each Coblation/coagulation cycle. Transient temperature data were obtained using five multi-junction thermocouple probes (5-8 junctions spaced at either 2 or 5 mm intervals, with 0.33 or 0.56 mm probe diameter) spaced throughout the desired heating volume. Transient temperature curves were obtained from 26+ points throughout the disc, and the data used to calculate accumulated thermal doses. Transient peaks of 80-90 degrees C were recorded within the discs, with temperatures greater than 60-65 degrees C measured within a radial distance of 3-4 mm from the introducer (applicator centreline). Accumulated thermal doses of t43 > 250 min were produced at radial distances of up to 6 mm from the introducer. Gross inspection of the discs revealed a narrow region of coagulation along the insertion length. Given these radial thermal penetrations and the possibility for unpredictable positioning during current clinical implementation, high temperatures and lethal thermal doses in small regions outside of the nucleus, or within the bone endplates, may be possible in clinical implementation.

[Radiofrequency ablation (RFA) of lung metastases from colorectal cancer (CRC)-one-year follow-up]

Assess the safety and evidence of efficacy of RFA for colorectal (CRC) lung metastases with follow up to 1 year. Twenty-three patients had percutaneous RFA for 52 colorectal pulmonary metastases under fluoro-CT. Patients received IV conscious sedation and local analgesia with routine hospitalisation/monitoring for 24 h post RFA. Patients had CT scanning at 1 month and then 3 monthly with serum CEA assessment monthly and 3 monthly. All ablations were technically successful. Tumor diameter ranged from 0.3 to 4.2 cm. Pneumothorax occurred in 43% (10 of 23) of patients. Six patients required intercostal chest drain placement. Six patients had a second RFA, 4 for new lesions and 2 patients had a previously treated lesion retreated. Median admission was 2.0 days (range 1-9). Median follow-up is 428 days (range 173-829), with data reported to 1 year in this paper. Five patients died at 5, 6, 8, 8 and 12 months post RFA from extra-pulmonary (1) or widespread (4) disease. One patient developed malignant pleural effusion at 6 months after RFA. Cavitation was seen in nine treated lesions (17%), all resolved with scar tissue contraction by 12 months. Eighteen patients with CT scan follow-up at one year have 40 lesions classified as: disappeared (17), decreased (5), stable/same size (4), increased (14). Percutaneous imaging-guided RFA of multiple CRC pulmonary metastases is a minimally invasive treatment option with modest morbidity. A significant proportion of patients show good evidence of successful local control at one year.

Analysis of Catheter-Tip (8-mm) and Actual Tissue Temperatures Achieved During Radiofrequency Ablation at the Orifice of the Pulmonary Vein

Background— Many ablative approaches in or near the orifice of the pulmonary vein (PV) have demonstrated success in eliminating atrial fibrillation. Despite current practice, there are no data regarding the in vivo efficacy and safety of an 8-mm catheter tip for ablation at the PV orifice.

Methods and Results— Ten mongrel dogs were studied. Thermocouples were implanted in the atrial muscle of the PV orifice. Intracardiac echocardiography monitored catheter position, tip/tissue orientation, and microbubble formation. Ninety-four ablations were performed for 120 seconds. A temperature discrepancy >10°C between the catheter tip and tissue occurred during 47 (50%) of the ablations. Despite termination of energy delivery, the average tissue temperature remained within 1°C of the achieved steady state for 9 seconds. A temperature discrepancy >10°C was more common in the right superior PV, with oblique catheter positioning, when tissue temperatures were >60°C or 80°C, and with type 1 or type 2 microbubble formation. However, microbubbles were not present in 7 (13%, type 1) and 10 (40%, type 2) ablations with tissue temperatures >80°C. The maximum tissue temperature achieved with non–full-thickness lesions was 47.3±7.4°C vs 75.9±11.7°C ( P <0.0001) for full-thickness lesions.

Conclusions— Marked discrepancies between catheter-tip and tissue temperatures occurred with higher temperatures, prolonged ablation times, and unfavorable catheter thermistor–tissue contact. Also, these data suggest a conservative approach to atrial ablation, because full-thickness lesions were obtained when tissue temperatures reached 50°C to 60°C and the tissue retained high heat levels despite termination of radiofrequency energy. Finally, microbubbles are inconsistent markers of tissue overheating.

Transmembraneous irrigation of multipolar radiofrequency ablation catheters: induction of linear lesions encircling the pulmonary vein ostium without the risk of coagulum formation?

INTRODUCTION

Pulmonary vein (PV) isolation for the curative treatment of atrial fibrillation using conventional radiofrequency ablation (RF) catheters with the point by point technique is time consuming and carries a remaining risk for thrombembolic complications.

AIMS OF THE STUDY

Aim of the present in vivo study was to evaluate feasibility and safety of a novel multipolar irrigated ablation catheter designed to create contiguous lesions encircling the PV ostium in a single ablation position.

METHODS

The entire ablation section (tripolar, length of each electrode 22 mm, interelectrode distance 2 mm, helix radius: 9 and 10 mm) of the 7F RF catheter (Encirclr, Medtronic, MN, USA) was covered by a porous membrane (pore size 30 micron) providing continuous irrigation. The helical formed catheter was used in two different experimental settings. Initially, a thigh muscle preparation has been performed in 7 anesthetized sheep in order to evaluate the development of lesions at different power level (40-80 W) and RF duration (30-90 sec). The ablation catheter was placed at the surface of the thigh muscle in a perpendicular position (0.1 N contact pressure) and perfused with heparinized blood (250 ml/min, 37C degrees ). Irrigation was provided with a flow rate of 10 ml/min. The resulted lesion morphology was evaluated with regard to coagulum or crater formation and lesion depth and diameter. Subsequently in 9 anesthetized sheep intracardiac ablation has been achieved with 50 W and an irrigation flow of 10 ml/min. Transseptal puncture and RF ablations were guided using fluoroscopy and intracardiac echocardiography (ICE, Acuson, USA). Endpoint of the intracardiac RF applications was the reduction of local electrogram amplitude >50%. RF applications were achieved at both atrial appendages and in the orifices of the coronary sinus (CS), the vena cava inferior (VCI) and PV. Following RF ablation all animals were sacrificed and following in vivo staining (2% TTC) macroscopically and histologically investigations of the lesions were performed.

RESULTS

At the thigh muscle preparation 57 RF applications have been performed. The lesion depth was homogeneous without gaps between the ablation electrodes. There was a significant increase comparing 30 with 90 sec of RF duration for 40, 50 and 60 W applications respectively: 40 W: 1.1 +/- 0.4 vs. 3.6 +/- 0.5; 50 W: 1.2 +/- 0.3 vs. 4.6 +/- 0.4 mm and 60 W: 2.6 +/- 0.6 vs. 4.8 +/- 0.5 mm. All applications with 80 W (n = 3) had to be terminated due to immediate increase of impedance >150 omega. Late impedance rises (>60 sec) without occurrence of coagulum formation have been observed in 1 out of 4 RF applications with 60 W.A total of 85 RF applications could be achieved intracardiacally in the right atrium (right atrial appendage n = 18, ostium of the coronary sinus n = 12, ostium of the inferior caval vein: n = 12) and in the left atrium (left atrial appendage: n = 15, ostium of the PV: n = 28). ICE guided positioning of the catheter and showed during all applications no coagulum formation at the electrode or impedance rise (>150 Omega). Reduction of local electrograms (>50%) were observed following 48 out 85 (56%) RF applications. The lesions showed a homogeneous depth of 4 +/- 2 mm and a width 5 +/- 2 mm at the surface. No charring or crater formation could be observed in any of the lesions.

CONCLUSIONS

In the present in vivo studies it could be demonstrated that long irrigated ablation electrodes induce continuous lesions without the risk of thrombus formation at the electrode. Increase of RF duration from 30 to 90 seconds with power setting of 40-60 W, respectively, created deeper lesions without the risk of thrombus formation. Thus, the helical formed irrigated ablation catheter appears to be appropriate for simplified PV isolation.

Radiofrequency ablation of liver tumours: systematic review

Thermal ablation by use of radiofrequency energy can be used to achieve necrosis of liver tumours, and increased availability of this technique is leading to more widespread use. Much of the impetus for the use of radiofrequency ablation has come from cohort series that have provided an evidence base for this technique. Here, we give an overview of the current status of radiofrequency ablation for liver tumours, including its physical properties, to assess the characteristics that make this technique applicable in clinical practice. We review the technical development of probe design and summarise current indications and outcomes of reported clinical use. We also provide a profile of side-effects and information on the integration of this technique into the general management of patients with liver tumours. Current evidence suggests that radiofrequency ablation can be done with few side effects; however, although this technique seems to ablate tumours effectively, it should form part of multidisciplinary care for liver cancer. Crucially, the role of radiofrequency ablation in lengthening the survival of patients with liver tumours remains to be assessed.

A Prospective Multicenter Trial of Bipolar Radiofrequency Ablation for Atrial Fibrillation: Early Results

BACKGROUND

The Cox-Maze III remains the gold standard for the surgical treatment of atrial fibrillation. However, the "cut-and-sew" technique is time consuming and technically challenging. The pulmonary veins are the source of ectopy in the majority of patients with atrial fibrillation. The safety and efficacy of bipolar radiofrequency to electrically isolate the pulmonary veins was evaluated in a prospective multi-center trial.

METHODS

Beginning in January 2002, 30 patients at three medical centers underwent pulmonary vein isolation using bipolar radiofrequency and were followed for 6 months. Twenty-four of the patients also underwent a modified Cox-Maze III. Electrical isolation of the pulmonary veins was confirmed with intraoperative pacing. Pulmonary vein patency was assessed by magnetic resonance imaging or three-dimensional computed tomography in 15 patients at 1 month.

RESULTS

Mean age was 60.9 +/- 11.7 years. Nineteen patients had paroxysmal atrial fibrillation. All pulmonary veins were isolated in every patient. The left pulmonary veins underwent 3.0 +/- 1.4 applications for a total of 26.4 +/- 10.5 seconds. The right pulmonary veins underwent 2.8 +/- 1.1 applications for a total of 26.3 +/- 12.6 seconds. There was no operative mortality. At 1 month, imaging revealed no evidence of pulmonary vein stenosis. At 6 months, 96% of patients were in normal sinus rhythm.

CONCLUSIONS

The use of bipolar radiofrequency for electrical isolation of pulmonary veins and to replace other Cox-Maze III incisions is safe and effective at controlling atrial fibrillation. This emerging technology may shorten and simplify the surgical management of atrial fibrillation.

Successful Performance of Cox-Maze Procedure on Beating Heart Using Bipolar Radiofrequency Ablation: A Feasibility Study in Animals

BACKGROUND

The Cox-Maze procedure is the gold standard for the surgical treatment of atrial fibrillation with proven long-term efficacy. However, its application has been limited by its complexity and significant morbidity. The purpose of this study was to test the feasibility and safety of performing the Cox-Maze procedure using bipolar radiofrequency ablation on the beating heart without cardiopulmonary bypass.

METHODS

After median sternotomy, 6 Hanford mini-pigs underwent a modified Cox-Maze procedure using bipolar radiofrequency energy. The animals survived for 30 days. Atrial function, coronary artery, pulmonary vein anatomy, and valve function were assessed by magnetic resonance imaging. At reoperation, pacing documented electrical isolation of the pulmonary veins. Induction of atrial fibrillation was attempted by burst pacing with cholinergic stimulation. Histologic assessment was performed after sacrifice.

RESULTS

There were no perioperative mortalities or neurologic events. At 30 days, atrial fibrillation was unable to be induced, and pulmonary vein isolation was confirmed by pacing. Magnetic resonance imaging assessment revealed no coronary artery or pulmonary vein stenoses. Although atrial ejection fraction decreased slightly from 0.344 +/- 0.0114 to 0.300 +/- 0.055 (p = 0.18), atrial contractility was preserved in every animal. Histologic assessment showed all lesions to be transmural, and there were no significant stenoses of the coronary vessels or injuries to the valves.

CONCLUSIONS

Virtually all of the lesions of the Cox-Maze procedure can be performed without cardiopulmonary bypass using bipolar radiofrequency energy. There were no late stenoses of the pulmonary veins. Clinical trials of this new technology on the beating heart are warranted.

Thermal ablation for hepatocellular carcinoma

Thermal ablation, as a form of minimally invasive therapy for hepatocellular carcinoma (HCC), has become an important treatment modality. Because of the limitations of surgery, the techniques of thermal ablation have become standard therapies for HCC in some situations. This article reviews 4 thermal ablation techniques-radiofrequency (RF) ablation, microwave ablation, laser ablation, and cryoablation. Each of these techniques may have a role in treating HCC, and the mechanisms, equipment, patient selection, results, and complications of each are considered. Furthermore, combined therapies consisting of thermal ablation and adjuvant chemotherapy also show promise for enhancing these techniques. Important areas of research into thermal ablation remain, including improving the ability of ablation to treat larger tumors, determining the indications for each thermal ablation modality, optimizing image guidance, and obtaining good outcome data on the efficacy of these techniques.

The Vista System: A New Bipolar Resection Device for Endourological Procedures: Comparison with Conventional Resectoscope

OBJECTIVE

Conventional transurethral resection of the prostate (TURP) uses a monopolar electrocautery system in which the current passes from the active electrode through the patient's body towards the return plate and may cause distant negative effects. In this study a new developed resection device, the Vista system, using a bipolar electrocautery system and 0.9% sodium chloride solution for irrigation, was evaluated in an ex-vivo model.

METHODS

The modified model of the isolated blood perfused kidney was used to determine cutting qualities, ablation rate, blood loss and coagulation depth of the bipolar resectoscope. After ablating the renal tissue of a perfused kidney in a surface area, blood loss was semiquantitatively determined. Afterwards samples were taken and processed for histological evaluation of the coagulation depth. We compared the new bipolar resection device against a conventional monopolar resectoscope.

RESULTS

We found good cutting qualities of the bipolar resectoscope although it is more difficult to start a cut. The ablation rate is determined by the width of the electrode and is similar to the standard device (30 cm(2)/min). The bleeding is reduced with increasing output powers (26.13 +/- 6.15 g/min (level 5); 20.49 +/- 5,47 g/min (level 6); 13.16 +/- 5,47 g/min (level 7); 10.43 +/- 4.76 g/min (level 8) and lower compared to a conventional monopolar resectoscope (17.08 +/- 4.47 g/min). The coagulation depth increases with higher output powers but is reduced compared to the standard device (118 +/- 22 microm (level 5); 121 +/- 23 microm (level 6); 141 +/- 62 microm (level 7); 163 +/- 30 microm (level 8) versus 287 +/- 57 (monopolar resectoscope)).

CONCLUSION

Our results with the bipolar resection device for TURP suggest that it may offer an alternative to conventional TURP. As active and the return electrode are placed on the resectoscope, high current densities are achieved locally and complications caused by distant negative effects of the current are theoretically reduced in vivo. Furthermore the risk of TUR syndrome is theoretically eliminated by using physiological sodium chloride solution for irrigation. To prove the clinical significance of our ex-vivo findings, clinical studies including large numbers of patients have to be performed.

Noninvasive thermal ablation of hepatocellular carcinoma by using magnetic resonance imaging-guided focused ultrasound

A number of minimally invasive methods have been tested for the thermal ablation of liver tumors as an alternative to surgical resection. The use of focused ultrasound transducers to ablate deep tumors offers the first completely noninvasive alternative to these techniques. By increasing the flexibility of this technology with modern phased-array transducer design and by combining it with magnetic resonance imaging for targeting and online guidance, a powerful tool results with the potential to offer treatment to a larger population of patients, to reduce trauma to the patient, and to reduce the cost of treatment. In this article, we review previous work with focused ultrasound in the liver and recent experimental results with magnetic resonance imaging guidance.

Hepatic bipolar radiofrequency ablation using perfused-cooled electrodes: a comparative study in theex vivobovine liver

The purpose of this paper was to demonstrate the efficacy of the dual probe bipolar radiofrequency (RF) system with the perfused-cooled electrodes inducing coagulation necrosis in the ex vivo bovine liver. The perfused-cooled electrode that allows simultaneous internal cooling and interstitial hypertonic saline perfusion has been developed for RF ablation (RFA). RF was applied to excised bovine liver in a bipolar mode at 150 W using a 200 W generator with two perfused-cooled electrodes for 10 min. After placing the electrodes at 3 cm spacing in the explanted liver, 45 ablation zones were created with three different regimens: Group A, using both intraelectrode cooling and interstitial perfusion; group B, using only the intraelectrode cooling; and group C, using only interstitial perfusion. In groups A and C, RFA was performed with the infusion of 6% hypertonic saline at the rate of 2 ml min(-1). During RFA, we measured the tissue temperature at the midpoint between the two electrodes. The dimensions of the ablation zones and the changes in impedance, currents and liver temperature during RFA were compared in these three groups. The mean tissue impedance during RFA in group A (56.7+/-21.7 Omega) and group C (56.9+/-20.6 Omega) was significantly lower than group B (112+/-19.7 Omega) (p<0.001). The mean current was higher in group A (1765+/-128 mA) than groups B (760+/-321 mA) and C (1298+/-349 mA) (p<0.05). In addition, the shortest vertical diameter of coagulation necrosis was greater in groups A (4.9+/-0.5 cm) and C (4.6+/-0.7 cm) than in group B (3.5+/-0.4 cm) (p<0.05). The temperature at the mid-point between the two probes was higher in group A than other groups: 99 degrees C in group A, 88.9 degrees C in group B, and 94.3 degrees C in group C (p>0.05). The ratios of the diameter of the long-axis to the diameter of the vertical-axis of groups A, B and C were 1.1+/-0.1, 1.2+/-0.1, and 1.1+/-0.2, respectively (p<0.05). Bipolar RFA using intraelectrode cooling and the interstitial saline perfusion simultaneously produced ablation zones significantly larger than the area produced by only one measure.

Complete isolation of left atrium surrounding the pulmonary veins: new insights from the double-Lasso technique in paroxysmal atrial fibrillation

BACKGROUND

Paroxysmal atrial fibrillation (PAF) can be eliminated with continuous circular lesions (CCLs) around the pulmonary veins (PVs), but it is unclear whether all PVs are completely isolated.

METHODS AND RESULTS

Forty-one patients with symptomatic PAF underwent 3D mapping, and all PV ostia were marked on the 3D map based on venography. Irrigated radiofrequency energy was applied at a distance from the PV ostia guided by 2 Lasso catheters placed within the ipsilateral superior and inferior PVs. The mean radiofrequency duration was 1550+/-511 seconds for left-sided PVs and 1512+/-506 seconds for right-sided PVs. After isolation, automatic activity was observed in the right-sided PVs in 87.8% and in the left-sided PVs in 80.5%. During the procedure, a spontaneous or induced PV tachycardia (PVT) with a cycle length of 189+/-29 ms was observed in 19 patients. During a mean follow-up of 6 months, atrial tachyarrhythmias recurred in 10 patients. Nine patients underwent a repeat procedure. Conduction gaps in the left CCL in 9 patients and in the right CCL in 2 patients were closed during the second procedure. A spontaneous PVT with a cycle length of 212+/-44 ms was demonstrated in 7 of 9 patients, even though no PVT had been observed in 6 of these 7 patients during the first procedure. No AF recurred in 39 patients after PV isolation during follow-up.

CONCLUSIONS

Automatic activity and fast tachycardia within the PVs could reflect an arrhythmogenic substrate in patients with PAF, which could be eliminated by isolating all PVs with CCLs guided by 3D mapping and the double-Lasso technique in the majority of patients.

Laparoscopic radiofrequency ablation of hepatocellular carcinoma in the caudate lobe by using a new laparoscopic US probe with a forward-viewing convex-array transducer

BACKGROUND

The use of a new end-fire type laparoscopic US probe with a forward-viewing convex-array transducer allows the caudate lobe of the liver to be accessed. This study evaluated the preliminary results of treatment of hepatocellular carcinoma in the caudate lobe by using this new instrument.

METHODS

Three patients with hepatocellular carcinoma in the caudate lobe were selected. A laparoscopic US probe, with a forward-viewing convex-array transducer at the tip and a guide groove for puncture on the back, was used to monitor the position of the radiofrequency ablation needle during the treatment.

RESULTS

Ablation was performed without complication in all cases. Complete necrosis of the tumor was confirmed by postoperative CT. At a mean follow-up of 30.3 months, no local recurrence was observed in any patient.

CONCLUSIONS

Radiofrequency ablation of hepatocellular carcinoma in the caudate lobe of the liver by using a new laparoscopic US probe with a forward-viewing convex-array transducer at the tip was safe and effective.

Radiofrequency Ablation of Atrial Flutter Using Large-Tip Electrode Catheters

The use of large-tip ablation catheters in both animal and clinical studies has been documented in work conducted over the last 10 years. These studies have demonstrated the safety and efficacy of the use of 8- and 10-mm tip ablation catheters in the treatment of type I isthmus-dependent atrial flutter. Shorter procedure times are reported with the larger-tip ablation catheters compared to standard 4- or 5-mm tip ablation catheters, with comparable or greater efficacy, no significant increase in complications, and an improved quality of life. Larger-tip ablation electrodes do require the use of higher-power radiofrequency generators up to 100 W. The benefits of large-tip ablation catheters are thus well documented for the treatment of type I isthmus-dependent atrial flutter.

Ablation with an internally irrigated radiofrequency catheter: Learning how to avoid steam pops

OBJECTIVES

The aim of this study was to assess the feasibility of using electrode temperature, impedance, and power to predict and thereby potentially prevent steam pops during cooled radiofrequency (RF) ablation.

BACKGROUND

When myocardial temperature reaches 100 degrees C during RF catheter ablation, steam explosions are seen. Saline-cooled RF ablation reduces temperatures at the electrode-tissue interface, but excessive intramyocardial heating still may occur.

METHODS

In anesthetized swine, 26 cooled RF applications were made in the right and left atria while observing with intracardiac echocardiography (ICE). Power delivery was increased gradually until a steam explosion was seen or a maximum output of 50 W was reached.

RESULTS

ICE identified steam explosions in 21 RF applications. Steam explosions were associated with a large impedance increase, >25 Omega in only three cases, whereas small increases <10 Omega (mean 5.3 +/- 2.6 Omega) occurred in 18 cases. Mean electrode temperature at the time of steam explosion was 43.6 degrees C +/- 5.3; 18 of 21 explosions occurred when temperature reached >/=40 degrees C. Mean power and impedance drop were similar for applications with and without steam explosions. Five steam explosions were associated with a sudden drop in electrode temperature.

CONCLUSIONS

Steam explosions are common when cooled electrode temperature exceeds 40 degrees C and are not predictable from power or impedance drop. Small impedance rises and sudden drops in measured electrode temperature indicate possible steam formation. Maintaining cooled electrode temperature <40 degrees C during RF likely will reduce the risk of steam explosions.