Radiofrequency Ablation Delivery Research Articles

PO-664-06 PHRENIC RELOCATION BY ENDOSCOPY & INTENTIONAL PNEUMOTHORAX USING CARBON DIOXIDE (PHRENIC) TECHNIQUE FOR PERI-PHRENIC ATRIAL ARRHYTHMIAS

Strategies to prevent right phrenic nerve [PN] injury during ablation can be difficult to employ, including unsatisfactory complication rates with methods attempting to displace the PN by pericardial manipulation. Single lung ventilation and “intentional pneumothorax” by thoracic insufflation of carbon dioxide may optimize PN protection during delivery of radiofrequency ablation.

Abstract 12905: Left Atrial Appendage Arrhythmias in Patients With Epicardial or Endocardial Occlusive Devices

Background: The role of left atrial appendage (LAA) isolation in atrial fibrillation (AF) has been extensively studied. As this leads to loss of contractility, the risk for thromboembolism increases. Percutaneous occlusion of the left atrial appendage has been proven to prevent thromboembolisms, however, unlike epicardial ligation of the LAA, it does not provide electrical isolation. As such, the risk of recurrent atrial arrhythmias remains while an arrhythmia source originating around the occlusion device can be problematic. Objective: We present three patients with arrhythmias originating from the LAA after endocardial or epicardial occlusion. Utilizing ultra-high-density mapping a definition of arrhythmia circuit was delineated. Case Studies: Two patients with prior failed AF ablation prior to WATCHMAN TM implantation were referred for a second ablation. We created ultra-high-density maps processed the images with CARTO®3 Coherent mapping. CARTOSOUND® was used to delineate the WATCHMAN TM edges. Both patients were found to have arrhythmias originating from the LAA, proximal to the Watchman device. Delivery of radiofrequency ablation on the anterior aspect of the LAA stump in one patient and isolation of the LAA in the other patient terminated the arrhythmias. A third patient had a surgical closure of the LAA using an Atricure ® clamp as part of a conversion procedure. A recurrent arrhythmia was mapped inside the LAA, distal to the occluder. Ablation inside the LAA and through the Atricure® gap terminated the arrhythmia. Discussion: It is expected that the increasing prevalence of LAA occlusive devices will lead to an increase in atrial arrhythmias arising from the LAA post-occlusion. Conversely, electrical isolation of the LAA increases stroke risk. As the best staged approach for these patients remains unclear, a concomitant electrical isolation with ablation and LAA occlusion may be the optimal solution. Insufficient data and limiting healthcare economics prevent this approach from becoming a gold standard. Conclusion: Our cases confirm the LAA role in recurrent arrhythmias, highlight the difficult ablative management post LAA occlusion and support the use of high density mapping for a successful outcome.

Impedance fluctuation and steam pop occurrence during radiofrequency current ablation: An experimental in vitro model.

The radiofrequency impedance measurement is one of the basic parameters monitored during ablation procedures. An abrupt rise in impedance is often observed corresponding to a steam pop. The exact correlation between the occurrence of steam pop and subsequent rise in impedance has not been experimentally described so far. To evaluate the relationship between steam pop occurrence and impedance fluctuations observed during radiofrequency ablation (RFA). Porcine heart tissue specimens were appropriately prepared and placed in an experimental setup connected to electrophysiological equipment with 3D anatomical mapping facilities. The RFA lesions were performed in standardized conditions with the use of contact force measurement-enabled open irrigation ablation catheter (ThermoCool SmartTouch™, 3.5 mm tip, F-J curvature; Biosense Webster, Irvine, USA) in the power-control mode. The RFA delivery was stopped when the steam pop occurred. Time taken for the steam pop to occur and to the subsequent abrupt impedance rise was recorded, along with the impedance fluctuations during an application. In total, 25 experimental radiofrequency (RF) current deliveries ended up with steam pops, which occurred after 30-60 s. The time recorded from the beginning of the application up to the steam pop was shorter if increased power was applied (35 W compared to 30 W: 41.5 ±9.9 s compared to 49.9 ±8.2 s; p = 0.046). During all RF applications, impedance significantly but gradually decreased from 122.9 ±7.9 Ω to 87.5 ±3.6 Ω (p < 0.001) with a mean drop rate of 0.8 ±0.2 Ω/s. During all experiments, the abrupt and significant impedance increase (8.2 ±2.0 Ω, p < 0.001) was observed always after steam pop occurrence (207.4 ±155.9 ms). During RF current delivery which ended up with steam pop, an abrupt impedance increase was always registered after the occurrence of this phenomenon. Therefore, the impedance rise observed during steam popping cannot be used for its prediction. The time to steam pop was shorter for applications with increased power but not with greater contact force.

Evaluation of Radiofrequency AblationIrrigation Type: InVivo Comparison of Normal Versus Half-Normal SalineLesionCharacteristics.

This study investigated the impact of the type of catheter irrigant used during delivery of radiofrequency ablation. The use of half-normal saline (HNS) as an irrigant has been suggested as a method for increasing ablation lesion size but has not been rigorously studied in the beating heart or the use of a low-flow irrigation catheter. Sixteen swine underwent left ventricular mapping and ablation using either normal saline (NS) (group 1: n=9) or half-normal saline (HNS) (group 2: n=7). All lesions were delivered using identical parameters (40W with 10-second ramp, 30-second duration, 15ml/min flow, and 8- to14-g target contact force). An occurrence of steam pop, catheter char, or thrombus was assessed using intracardiac echocardiography and catheter inspection following each application. Lesion depth, width, and area were measured using electronic calibers. A total of 109 lesions were delivered in group 1 and 77 in group 2. There were significantly more steam pops in group 2 (32 of 77 [42%] vs. 24 of 109 [22%], respectively). The frequencies of catheter tip char were similar (group 1: 9 of 109 [8%] vs. group 2: 10 of 77 [13%]; p=0.29). Lesion depths, widths, and areas also were similar in both groups. The use of an HNS irrigant using a low-flow open irrigated ablation catheter platform results in more tissue heating due to higher radiofrequency current delivery directed to tissue, but this can lead to higher rate of steam pops. In this invivo porcine beating-heart model, the use of HNS does not appear to significantly increase lesion size innormal myocardium despite evidence of increased radiofrequency heating.

Intra-cardiac MR imaging &amp; MR-tracking catheter for improved MR-guided EP

Background Electrophysiology (EP) studies can diagnose & treat patients with arrhythmia. MR-guided EP is growing, driven by the ability of cardiac MRI to provide high-contrast images. For intra-procedural use, MRI provides images of the acute state of radio-frequency ablation (RFA) lesions, e.g. necrosis, edema and hemorrhage, that potentially reduce recurrences & complications [1,2]. Unfortunately, acquisition of these images using surface MRI coils, considering the high-spatial-resolution (~1×1×2mm) requirements, can be lengthy (scar~10 mins/scan, edema~12 mins/scan) [3], severely increasing the duration of MR-guided procedures. As demonstrated in other body regions, e.g. endorectal MRI, and with other imaging modalities (Intra-Cardiac Echo), intracavitary probes provide increased Signal-to-Noise-Ratio (SNR), due to their proximity to the area of interest. An Intra-cardiac MR imaging (ICMRI) coil may provide substantially higher SNR, but a complete application must also provide accurate heart motion compensation [4], in order to produce non-blurred images. We constructed an ICMRI catheter, with integrated imaging & positional-tracking elements, optimized for (1) cardiovascular introduction as a sheath “riding on” an EP ablation catheter & for (2) close-proximity imaging (~4 cm FOV) during RFA delivery.

Pre to Intraoperative Data Fusion Framework for Multimodal Characterization of Myocardial Scar Tissue.

Merging multimodal information about myocardial scar tissue can help electrophysiologists to find the most appropriate target during catheter ablation of ventricular arrhythmias. A framework is presented to analyze and combine information from delayed enhancement magnetic resonance imaging (DE-MRI) and electro-anatomical mapping data. Using this information, electrical, mechanical, and image-based characterization of the myocardium are performed. The presented framework allows the left ventricle to be segmented by DE-MRI and the scar to be characterized prior to the intervention based on image information. It allows the electro-anatomical maps obtained during the intervention from a navigation system to be merged together with the anatomy and scar information extracted from DE-MRI. It also allows for the estimation of endocardial motion and deformation to assess cardiac mechanics. Therefore, electrical, mechanical, and image-based characterization of the myocardium can be performed. The feasibility of this approach was demonstrated on three patients with ventricular tachycardia associated to ischemic cardiomyopathy by integrating images from DE-MRI and electro-anatomical maps data in a common framework for intraoperative myocardial tissue characterization. The proposed framework has the potential to guide and monitor delivery of radio frequency ablation of ventricular tachycardia. It is also helpful for research purposes, facilitating the study of the relationship between electrical and mechanical properties of the tissue, as well as with tissue viability from DE-MRI.

Lung Tumor Radiofrequency Ablation: Where Do We Stand?

Today, radiofrequency ablation (RFA) of primary and metastatic lung tumor is increasingly used. Because RFA is most often used with curative intent, preablation workup must be a preoperative workup. General anesthesia provides higher feasibility than conscious sedation. The electrode positioning must be performed under computed tomography for sake of accuracy. The delivery of RFA must be adapted to tumor location, with different impedances used when treating tumors with or without pleural contact. The estimated rate of incomplete local treatment at 18 months was 7% (95% confidence interval, 3-14) per tumor, with incomplete treatment depicted at 4 months (n = 1), 6 months (n = 2), 9 months (n = 2), and 12 months (n = 2). Overall survival and lung disease-free survival at 18 months were, respectively, 71 and 34%. Size is a key point for tumor selection because large size is predictive of incomplete local treatment and poor survival. The ratio of ablation volume relative to tumor volume is predictive of complete ablation. Follow-up computed tomography that relies on the size of the ablation zone demonstrates the presence of incomplete ablation. Positron emission tomography might be an interesting option. Chest tube placement for pneumothorax is reported in 8 to 12%. Alveolar hemorrhage and postprocedure hemoptysis occurred in approximately 10% of procedures and rarely required specific treatment. Death was mostly related to single-lung patients and hilar tumors. No modification of forced expiratory volume in the first second between pre- and post-RFA at 2 months was found. RFA in the lung provides a high local efficacy rate. The use of RFA as a palliative tool in combination with chemotherapy remains to be explored.

Clinical Application of Radiofrequency Ablation for Malignant Liver Tumor during Interruption of Hepatic Blood Flow

An experiment was conducted to investigate the changes in the thermocoagulation area induced by radiofrequency ablation (RFA) during interruption of the hepatic blood flow using the liver of a bovine. In a clinical case, the RFA was delivered percutaneously to hepatocellular carcinoma with a diameter of 25 mm during interruption of the hepatic blood flow. The RFA equipment used was 460-KHz Leveen needle electrode 26-207 (Boston Scientific, Tokyo, Japan). In the animal experiment, the radiofrequency electrode was introduced to a depth of 2 cm under the surface of the liver, and then eight umbrella-type needles were unfolded. Subsequently, RFA were of 40 W was delivered for 150 sec. The RFA delivery was carried out by the same procedure under the condition of hepatic blood flow interruption with a hemostatic tape. In the clinical application, a 6 F balloon catheter was inserted into the right hepatic vein, which was the dranage vein of the cancer-bearing area, and the artery was embolized with gel form the hepatic artery. Interruption of the portal blood flow in the cancer-bearing area was confirmed by CT scanning with portal venography. The animal experiment results showed that interruption of the hepatic arterial and portal blood flow provided more than twice the diameter of thermocoagulation by the non-interruption of the blood flow, and that the shape of the coagulation area was almost spherical. In conclusion, complete and spherical thermocoagulation was achieved by delivery of the RFA of 40 W, to hepatocellular carcinoma of 25 mm in diameter, for 4 minutes during interruption the hepatic blood flow.