Kay D Parker

Impact of Freezing Time and Balloon Size on the Thermodynamics and Isolation Efficacy During Pulmonary Vein Isolation Using the Second Generation Cryoballoon

Background—The differences in ablation characteristics of freezing time and balloon size using second generation cryoballoon are still unknown. Methods and Results—Twenty-six dogs underwent pulmonary vein (PV) isolation. Balloon and tissue temperatures (left atrial–PV junction, phrenic nerve, and internal esophagus) were monitored. The ablation duration was randomized to either 3 or 4 minutes, which did not show significant differences in temperature profiles, PV isolation success rate, complications, or histological changes. Twenty dogs underwent cryoablation using 28-mm cryoballoon, 6 dogs were done using the 23-mm cryoballoon. Positioning of the 23-mm cryoballoon was more distal in the PV, which resulted in better PV occlusion. Temperature profiles showed lower temperatures in the 23-mm cryoballoon than in the 28-mm cryoballoon (inner balloon, median [range]: −51.5 [−66.0 to −31.0] versus −43.0 [−64.0 to −26.0]°C, P<0.001; balloon surface: −43.0 [−60.0 to −15.8] versus −6.5 [−46.2 to 28.9]°C, P<0.001; left atrial–PV junction: −6.7 [−20.0 to 21.4] versus 15.8 [−14.4 to 35.1]°C, P<0.001), and trended toward a higher PV isolation success rate in the 23-mm cryoballoon. Histologically, deeper extensions of ablative lesions into the PV were seen with 23-mm cryoballoon, and larger ablative lesions were seen in the left atrial antrum using 28-mm cryoballoon. Conclusions—The efficacy of 3-minute ablation was not significantly different from 4-minute ablation in dogs. The 23-mm cryoballoon had a greater cooling effect than the 28-mm cryoballoon for small PVs, but showed narrower ablative lesions in the left atrial antrum.

Spatial and Time-Course Thermodynamics During Pulmonary Vein Isolation Using the Second-Generation Cryoballoon in a Canine In Vivo Model

Background—Thermodynamics in the left atrium–pulmonary vein (PV) junction, phrenic nerve, and esophagus during PV isolation (PVI) using the second-generation cryoballoon are not known. Methods and Results—Twenty dogs underwent PVI using second-generation cryoballoon. Ablations were performed for ⩽2 deliveries based on PVI without a bonus freeze. Inner balloon, balloon surface, and tissue temperatures were monitored during cryoablation. The tissue thermocouples were placed on the epicardial surface of the left atrium–PV junction, as well as on the phrenic nerve and within the esophagus. A total of 259 cryoballoon and 229 tissue tissue thermocouples profiles during 53 cryoablations of 40 PVs were analyzed. Acutely, PVI was achieved in 36 of 40 PVs (90%). Conductive tissue cooling spread radially from the balloon–left atrium–PV contact point. The lowest tissue temperatures were dependent on the distance of the tissue thermocouples to the balloon surface (r=0.85; P<0.001). In addition, blood flow leaks around the balloon had a warming effect on the balloon and tissue temperature profiles. Chronic isolation (mean, 48±16 days) was achieved in 27 of 36 PVs (75%). In 8 of 9 acutely isolated but with chronic reconnection PVs, the blood flow leak location was concordant with chronic reconnection gap. Although only 1 esophageal ulcerated lesion was observed, neither phrenic nerve palsy nor severe PV stenosis was seen in any dogs. Conclusions—Variance in tissue thermodynamics during cryothermal ablation depends on the distance from balloon and peri-balloon blood flow leaks. This information may be useful for successful PVI without severe complications.

Effect of Left Atrial Ablation Process and Strategy on Microemboli Formation During Irrigated Radiofrequency Catheter Ablation in an In Vivo Model

Background—Formation of microemboli during catheter ablation has been suggested as a cause for asymptomatic cerebral emboli. However, it is unknown which part of the process and ablation setting/strategy is most strongly related to this occurrence. Methods and Results—A total of 27 pigs were used. Catheter/sheath manipulations in left atrium were performed in 25 of 27 pigs outfitted with microemboli monitoring systems. Ablations using open-irrigated radiofrequency catheters were performed in 18 of 25 pigs. Two of 27 pigs did not undergo left atrial procedures and were injected with microembolic materials in the carotid artery to serve as positive controls. In total, 334 sheath/catheter manipulations (transseptal puncture, sheath flushing, catheter insertion, pulmonary vein venography, and sheath exchange) and 333 radiofrequency applications (power setting, 30/50 W; point-by-point/drag ablations) were analyzed. High microbubble volume in the extracorporeal circulation loop and a high number of microembolic signals in carotid artery were observed during sheath/catheter manipulations especially in saline/contrast injections at fast speed and ablations with steam pop. Fast sheath flushing produced significantly higher microbubble volume than slow sheath flushing (median, 12 200 versus 121 nL; P<0.0001). A total of 44 of 126 (35%) blood filters in the circulation loop showed microparticles (thrombus/coagulum and tissue). Most of them were seen after radiofrequency application especially in 50-W ablations, drag ablations, and steam pop. Brain magnetic resonance imaging showed positive-embolic lesions in control pigs. Conclusions—Formation of microbubbles was the greatest during fast saline/contrast injections and steam pops, whereas high-power radiofrequency applications, drag ablations, and steam pops produced most of the microparticles.

External Arrhythmia Ablation Using Photon Beams

Background— This study sought to investigate external photon beam radiation for catheter-free ablation of the atrioventricular junction in intact pigs. Methods and Results— Ten pigs were randomized to either sham irradiation or irradiation of the atrioventricular junction (55, 50, 40, and 25 Gy). Animals underwent baseline electrophysiological evaluation, cardiac gated multi-row computed tomographic imaging for beam delivery planning, and intensity-modulated radiation therapy. Doses to the coronary arteries were optimized. Invasive follow-up was conducted ⩽4 months after the irradiation. A mean volume of 2.5±0.5 mL was irradiated with target dose. The mean follow-up length after irradiation was 124.8±30.8 days. Out of 7 irradiated animals, complete atrioventricular block was achieved in 6 animals of all 4 dose groups (86%). Using the same targeting margins, ablation lesion size notably increased with the delivered dose because of volumetric effects of isodose lines around the target volume. The mean macroscopically calculated atrial lesion volume for all 4 dose groups was 3.8±1.1 mL, lesions extended anteriorly into the interventricular septum. No short-term side effects were observed. No damage was observed in the tissues of the esophagus, phrenic nerves, or trachea. However, histology revealed in-field beam effects outside of the target volume. Conclusions— Single-fraction doses as low as 25 Gy caused a lesion with interruption of cardiac impulse propagation using this respective target volume. With doses of ⩽55 Gy, maximal point-doses to coronary arteries could be kept <7Gy, but target conformity of lesions was not fully achieved using this approach.

Integration of myocardial scar identified by preoperative delayed contrast-enhanced MRI into a high-resolution mapping system for planning and guidance of VT ablation procedures

Myocardial scarring creates a substrate for reentrant circuits which can lead to ventricular tachycardia. In ventricular catheter ablation therapy, regions of myocardial scarring are targeted to interrupt arrhythmic electrical pathways. Low voltage regions are a surrogate for myocardial scar and are identified by generating an electro anatomic map at the start of the procedure. Recent efforts have focussed on integration of preoperative scar information generated from delayed contrast-enhanced MR imaging to augment intraprocedural information. In this work, we describe an initial feasibility study of integration of a preoperative MRI derived scar maps into a high-resolution mapping system to improve planning and guidance of VT ablation procedures.

WE-EF-BRA-03: Catheter- Free Ablation with External Photon Radiation: Treatment Planning, Delivery Considerations, and Correlation of Effects with Delivered Dose

Purpose: To plan, target, and calculate delivered dose in atrioventricular node (AVN) ablation with volume-modulated arc therapy (VMAT) in an intact porcine model. Methods: Seven pigs underwent AVN irradiation, with prescription doses ranging between 25 and 55Gy in a single fraction. Cardiac CT scans were acquired at expiration. Two physicians contoured AVN targets on 10 phases, providing estimates of target motion and inter-physician variability. Treatment planning was conducted on a static phase-averaged CT. The volume designated to receive prescription dose covered the full extent of AVN cardiac motion, expanded by 4mm for setup uncertainty. Optimization limited doses to risk structures according to single-fraction tumor treatment protocols. Orthogonal kV images were used to align bony anatomy at time of treatment. Localization was further refined with respiratory-gated cone-beam CT, and range of cardiac motion was verified under fluoroscopy. Beam delivery was respiratory-gated for expiration with a mean efficiency of 60%. Deformable registration of the 10 cardiac CT phases was used to calculate actual delivered dose for comparison to electro-anatomical and visually evident lesions. Results: The mean [minimum,maximum] amplitude of AVN cardiac motion was LR 2.9 [1.7,3.9]mm, AP 6.6 [4.4,10.4]mm, and SI 5.6 [2.0,9.9]mm. Incorporating cardiac motion into the dose calculation showed the volume receiving full dose was 40–80% of the volume indicated on the static planning image, although the contoured AVN target received full dose in all animals. Initial results suggest the dimensions of the electro-anatomical lesion are correlated with the 40Gy isodose volume. Conclusion: Image-guidance techniques allow for accurate and precise delivery of VMAT for catheter-free arrhythmia ablation. An arsenal of advanced radiation planning, dose optimization, and image-guided delivery techniques was employed to assess and mitigate effects of cardiac and respiratory motion. Feasibility of delivery to the pulmonary veins and left ventricular myocardium will be investigated in future studies. D. Packer Disclosures: Abiomed, Biosense Webster, Inc., Boston Scientific Corp., CardioFocus, Inc., Johnson and Johnson, Excerpta Medica, Ortho-McNeil-Jannsen, Sanofi Aventis, CardioInsight Technologies, InfoBionic, SIEMENS, Medtronic, Inc., CardioDx, Inc., CardioInsight Technologies, FoxP2 Medica, Mediasphere Medical, Wiley-Blackwell, St. Jude Medical, Endosense, Thermedical, EP Advocate LLC, Hansen Medical, American Heart Association, EpiEP, NIH

SU‐E‐T‐253: Treatment Planning and Dose Delivery of Photon Radiation Therapy of Cardiac Arrhythmias for Isolated Perfused Porcine Hearts

Purpose: To develop treatment plans and delivery techniques for ex situ isolated perfused (Langendorff) porcine hearts in order to explore the feasibility of using photon radiation to create cardiac lesions as a treatment for cardiac arrhythmias. Methods: Six domestic swines were used for the creation of Langendorff preparation, of which three received radiation and three served as a control group. For the study group, treatment planning was performed on their CT images. Two stainless‐steel clips in the CS ostium and in the pulmonary artery and the beaker were contoured and assigned to the proper CT numbers. Treatment couch attenuation and clip scattering were also taken into account. The AV node was contoured and was positioned at the isocenter of the accelerator. MLC were used to provide conformal shaping of the photon beam and a 1 cm margin was added around the AV node to accommodate cardiac motion. 3D conformal planning technique was chosen. Two orthogonal KV images were acquired before the radiation delivery for accurate positioning of the heart. Results: 200 Gy was successfully delivered to the AV node of the heart in the service mode of the machine. The field size was about 3 × 3 cm^2. The dose distribution was not uniform in the target due to the one or three fixed beam arrangement. The averaged delivery time was about 40 minutes with an averaged dose rate of 600 MU/min. Complete heart block was observed during treatment and notable cellular damages were presented in the histological specimen. Conclusion: Simple and efficient treatment plan and delivery technique are required to deliver high dose to the ex situ isolated hearts in a short time window. Flattening‐Filter‐Free mode of the Linac will dramatically decrease the delivery time and therefore allow the development of more complicated treatment plans, for example, the IMRT. Dr. DL Packer in the past 12 months has provided consulting services for Abiomed, Biosense Webster, Inc., Boston Scientific, CardioFocus, CardioInsight, Excerpta Medica, FoxP2 Medica LLC, InfoBionic, Inc., Johnson & Johnson Healthcare Systems, Johnson & Johnson, MediaSphere Medical, LLC, Medtronic CryoCath, OrthoMcNeill, Sanofi‐aventis, Siemens, St. Jude Medical, and Siemens AG. Dr. Packer received no personal compensation for these consulting activities. [PLEASE NOTE: any web or printed program must include this statement of noncompensation] Dr. DL Packer receives research funding from the Biosense Webster, Boston Scientific/EPT, Endosense, EpiEP, EP Advocate, Medtronic CryoCath LP, Minnesota Partnership for Biotechnology and Medical Genomics/ University of Minnesota, NIH, CardioFocus, Hansen Medical, Siemens P4D, St. Jude Medical, Siemens AcuNav, and Thermedical (EP Limited). Dr. Packer received Royalties from Blackwell Publishing and St. Jude Medical. Dr. HI Lehmann receives a research fellowship from the German Heart Foundation/Deutsche Herzstiftung e.V. Mit Foerdermitteln der Deutschen Herzstiftung e.V.