Chronic Porcine Model Research Articles

ID: 344721 Removal Procedure of a Helical Wire Structure Electrode from Benchtop and Chronic Porcine Models

ID: 344721 Removal Procedure of a Helical Wire Structure Electrode from Benchtop and Chronic Porcine Models

Novel Image-Guided Percutaneous Lung Tissue Excision Device With Integrated Sealing of Blood Vessels and Airways: An In Vivo Preclinical Study.

This study evaluated the efficacy of the Minimally Invasive Targeted Resection (MiTR) device, a novel electrosurgical instrument that allows for targeted excision of a lung abnormality while using bipolar radiofrequency (RF) energy to seal blood vessels and airways. The MiTR system was evaluated in 7 acute and 2 chronic porcine (7-day) models to evaluate the efficacy of tissue excision with bipolar RF sealing of blood vessels and airways and application of an autologous blood patch into the excised tissue cavity. Air leak was recorded for all evaluations. The study was approved by the institutional ethical board. Nineteen lung tissue samples, measuring 2.5 cm long × 1.2 cm diameter, were excised. In 8 of 9 animals (89%), hemostasis and pneumostasis were observed visually at the completion of the procedure. In 2 of 2 chronic animals (100%), hemostasis and pneumostasis persisted for the 7-day observation period. Histologic examination of the excised samples showed preservation of the core parenchymal architecture without evident tissue damage of the samples that would impair pathologic analysis. Percutaneous resection of targeted lung tissue with the MiTR system demonstrated hemostasis and pneumostasis while obtaining a histologically intact sample. After regulatory approval, the use of this device could offer more tissue for analysis than a transthoracic needle biopsy or bronchoscopy and a far less invasive alternative to video-assisted thoracic surgery or thoracotomy. This may also expand patient and physician options for the early diagnosis and treatment of lung cancer.

Evaluation of a New Cystoscopic Cryocatheter and Method for the In Situ Destruction of Bladder Cancer: Preliminary In Vivo Study.

Purpose: To assess the ability to deliver full-thickness bladder wall cryoablation through a cystoscopic approach using a new closed-loop 6F cryocatheter and thermal dose-controlled protocol. Materials and Methods: Evaluations were conducted using a chronic porcine model wherein 10 lesions/animal were created throughout the bladder (bladder wall, trigone region, ureteral orifice, and distal ureter). A 6F cryocatheter was passed through the working channel of a flexible cystoscope. Single 1- and 1.5-minute freeze protocols in a saline environment were evaluated and resultant lesion size was determined. A laparoscopic approach was utilized to observe the transmural extension of the ice propagation. Results: Studies demonstrated the generation of transmural lesions characterized by full-thickness histologic necrosis after freezing for 1.5 minutes regardless of tissue thickness (range 2-12 mm). All animals were found to have good overall health (maintained weight, appetite, mobility, and energy levels) throughout the recovery period. No significant deviations were noted in complete blood count and serum chemistry bloodwork except for elevated creatine kinase levels. Importantly, no fistulas or perforations were noted. Conclusions: The cryocatheter was able to rapidly and effectively freeze the bladder wall through a cystoscopic approach. The results showed the ability to consistently ablate an ∼1 cm diameter and up to 1.2 cm deep using a single 1.5-minute freeze protocol. Analysis of the ablation efficacy revealed ∼80% destruction within the frozen mass. Although further testing and refinement are needed, these studies demonstrate the potential of this new approach to provide a next-generation strategy for the treatment of bladder cancer.

Ischemia-induced ventricular proarrhythmia and cardiovascular autonomic dysreflexia after cardioneuroablation

Cardioneuroablation (CNA) is an attractive treatment of vasovagal syncope. Its long-term efficacy and safety remain unknown. The purpose of this study was to develop a chronic porcine model of CNA to examine the susceptibility to ventricular tachyarrhythmia (ventricular tachycardia/ventricular fibrillation [VT/VF]) and cardiac autonomic function after CNA. A percutaneous CNA model was developed by ablation of left- and right-sided ganglionated plexi (n = 5), confirmed by histology. Reproducible bilateral vagal denervation was confirmed after CNA by extracardiac vagal nerve stimulation (VNS) and histology. Chronic studies included 16 pigs randomized to CNA (n= 8) and sham ablation (n = 8, Control). After 6 weeks, animals underwent hemodynamic studies, assessment of cardiac sympathetic and parasympathetic function using sympathetic chain stimulation and direct VNS, respectively, and proarrhythmic potential after left anterior descending(LAD) coronary artery ligation. After CNA, extracardiac VNS responses remained abolished for 6 weeks despite ganglia remaining in ablated ganglionated plexi. In the CNA group, direct VNS resulted in paradoxical increases in blood pressure, but not in sham-ablated animals (CNA group vs sham group: 8.36% ± 7.0% vs -4.83% ± 8.7%, respectively; P = .009). Left sympathetic chain stimulation (8 Hz) induced significant corrected QT interval prolongation in the CNA group vs the sham group (11.23% ± 4.0% vs 1.49% ± 4.0%, respectively; P < .001). VT/VF after LAD ligation was more prevalent and occurred earlier in the CNA group than in the control group (61.44 ± 73.7 seconds vs 245.11 ± 104.0 seconds, respectively; P = .002). Cardiac vagal denervation is maintained long-term after CNA in a porcine model. However, chronic CNA was associated with cardiovascular dysreflexia, diminished cardioprotective effects of cardiac vagal tone, and increased susceptibility to VT/VF in ischemia. These potential long-term negative effects of CNA suggest the need for rigorous clinical studies on CNA.

TCT-321 Performance, Long-Term Safety and Biocompatibility of a Novel PFO Closure Device in a Chronic Porcine Model

TCT-321 Performance, Long-Term Safety and Biocompatibility of a Novel PFO Closure Device in a Chronic Porcine Model

Abstract 14327: Intramyocardial Delivery of an Imageable Theranostic Hydrogel Post Myocardial Infarction Alters Regional Strain and Reduces Remodeling in Chronic Porcine Model

Introduction: Myocardial infarction (MI) causes acute regional changes in stiffness and strain, resulting in pathological remodeling in the left ventricle (LV). Intramyocardial injection of hydrogel (HG) into the MI region may alter deformation and improve LV remodeling. Using high resolution cineCT (CCT) we evaluated changes in regional strain, global function, and geometry in chronic porcine MI model. Methods: Yorkshire pigs (n=12) subjected to 90 min balloon occlusion and reperfusion were randomized 5 days post MI to intramyocardial delivery of MI+HG (n=6) or MI only (n=6). Imageable HG was delivered in a 3x3 grid after assessing MI region with hybrid 201 Tl SPECT/CT. Contrast CCT was performed at baseline, day 5 (post MI before HG delivery), and day 12 (7 days post HG delivery) to assess end diastolic volume (EDV) and ejection fraction (EF). Custom software was used to calculate 3D myocardial Lagrangian strains on 6 HG animals and 3 MI only animals in remote, border (&gt;50% normal) and MI regions (&lt;50% normal). Results: At day 5 in both groups, EDV increased by 13.2% (p=0.016), LVEF decreased by 15.7% (p=0.008), and radial strain (E rr ) decreased in MI region by -0.11 (p=0.007). On day 12, EDV decreased by 8.3% in the MI+HG group but increased by 10.4% in the MI only group (p=0.003). LVEF increased significantly in the MI+HG group by 8.96% and was significantly greater than in MI only group (p=0.027) which had no significant changes. Average change in E rr between baseline and day 12 was not different between groups within the MI (p=0.13) or border region (p=0.67). However, average E rr did not decline in the MI+HG group (+0.029) but significantly declined in MI only group (-0.14, p=0.017) (MI+HG vs MI only; p=0.003), mirroring EDV changes. Conclusions: Intramyocardial delivery of HG 5 days post-MI resulted in greater improvement in E rr in remote region and global LVEF and a decrease in EDV suggesting reduced LV remodeling compared to MI only controls.

Comparison of Two Percutaneous Atrial Septal Defect Occluders for Device Healing and Nickel Release in a Chronic Porcine Model

Aims To investigate the healing process and nickel release of the Hyperion occluder (Comed BV, Netherlands), as compared to the Amplatzer septal occluder (ASO) (St. Jude Medical Inc., St. Paul, MN, USA) in a chronic swine model. Background Some long-term complications occurring after percutaneous atrial septal defect (ASD) closure may be partially associated with an inappropriate healing of the device and increased nickel release. There is no direct comparative study of different occluders for healing and nickel release. Methods After percutaneous ASD creation, 12 pigs were implanted with 15 mm Hyperion (n = 6) and 15 mm ASO (n = 6) devices. After 1 month (n = 3 for each device) and 3 months (n = 3 for each device) of follow-up, device explantation was performed and healing was assessed using histopathological workup. Systemic and tissular nickel release was performed. Results Implantation was successful in 100% without complications. Device coverage was observed as early as 1 month after implantation and was almost complete after 3 months. A granulation tissue with a predominantly mononuclear inflammatory reaction was observed in contact with nitinol wires while an inflammatory reaction was seen in contact with textile fibers. We found no statistically significant difference between the 2 devices whether for histological grading scores or systemic nickel release, regardless to follow-up duration. Conclusions In this preclinical study, we demonstrated that Amplatzer septal occluder and Hyperion occluder were not significantly different for device healing and nickel release processes.

Remote Ischemic Preconditioning in Spinal Cord Protection: A Surviving Porcine Study

Surgical repair of thoracic aorta can compromise blood flow of the spinal cord. To mitigate spinal cord ischemia (SCI) additional protection methods are needed. In experimental studies remote ischemic preconditioning (RIPC) has proven to be an effective method of protecting organs from ischemia. The aim of the study was to assess efficacy of RIPC in spinal cord protection in a chronic porcine model. Sixteen piglets were assigned into the RIPC group (8) and the control group (8). RIPC was performed using blood pressure cuff in a 5-minute ischemia followed by a 5-minute reperfusion repeating cycles 4 times. The left subclavian artery and all segmental arteries above diaphragm were ligated at 5-minute intervals to accomplish SCI. The follow-up comprised a 4-hour intensive monitoring and a 7-day recovery phase. Blood samples were obtained, motor-evoked potentials and near-infrared spectroscopy (NIRS) of longitudinal back muscles were measured. Paraplegia was assessed every day postoperatively. Histopathological analysis of the spinal cord was performed after 7 days. NIRS values 4 hours after SCI were higher in the RIPC group, 45.5 (44.5-47.0), than in the control group, 41.5 (40.5-44.0) (P = 0.042). Nadir value of NIRS was 43.4 (39.3-46.0) in the RIPC group and 38.9 (38.-40.0) in the control group (P = 0.014). On the first postoperative day the RIPC group reached modified Tarlov score of 3 (2-3) vs 2 (1-2) in the control group (P = 0.024). RIPC hastens the recovery from SCI during the first postoperative day.

Optimal occlusion pattern for minimally invasive staged segmental artery coil embolization in a chronic porcine model.

Minimally invasive staged segmental artery coil- and plug embolization (MIS2ACE) has been introduced for spinal cord injury prevention prior to open or endovascular thoraco-abdominal aortic aneurysm repair. To date, no optimal pattern has been developed. The aim of this study was to identify the optimal MIS2ACE occlusion pattern. Twenty-five juvenile pigs were randomly assigned to 3 MIS2ACE occlusion patterns (2 stages) and a control group [single-stage segmental artery (SA) occlusion, N = 7]. The first pattern started with occlusion of all lumbar segmental arteries in the first stage and the remaining thoracic arteries in the second stage (regional pattern, N = 6). In group 2, an alternating approach with occlusion of every other SA in the first stage and the remainder in the second stage was used (alternating pattern, N = 6). The third pattern started with occluding the watershed area between thoracic level 12 and lumbar level 2 in the first stage and the remaining arteries in the second stage (watershed pattern, N = 6). Neurological assessment at 6-h intervals and spinal cord tissue perfusion measurements via microspheres at 6 time points were performed. At the end of the experiments, the spinal cord was histopathologically examined. An average of 6 ± 2 coils were used per SA. In the control group a total of 57% (N = 4) of animals experienced permanent paraplegia, 1 animal (16%) of the alternating and watershed intervention group suffered from permanent paraplegia. Animals from the staged regional pattern did not experience permanent paraplegia. Furthermore, no evidence of significant tissue damage was observed (P < 0.05 vs control). Tissue perfusion of the lumbar spinal cord in the regional pattern group recovered within 3 days after the second stage to 89.2 ± 47 percent-of-baseline (P = 0.393), whereas mean perfusion of the other 2 intervention groups and the control remained significantly lower compared to the baseline (35.7 ± 16%, 30.2 ± 11% and 63.2 ± 19, P < 0.05). This study provides evidence that MIS2ACE (minimally invasive staging) may result in less ischaemic spinal cord injury and favourable neurological outcomes compared to complete (1 stage) SA occlusion. A regional-based occlusion pattern (starting with the lumbar segmental arteries) seems to be the best 2-stage approach.

Evaluation of collateral network near-infrared spectroscopy during and after segmental artery occlusion in a chronic large animal model

ObjectiveIschemic spinal cord injury remains the most devastating complication after open and endovascular aortic repair. Collateral network near-infrared spectroscopy has been introduced to noninvasively monitor real-time spinal cord oxygenation. In view of recent advancements in endovascular treatment and minimally invasive staged preconditioning before aortic repair, this study sought to evaluate collateral network near-infrared spectroscopy during and after segmental artery occlusion in a chronic porcine model. MethodsSurgery for segmental artery occlusion was performed in 12 juvenile pigs, and bilateral lumbar collateral network near-infrared spectroscopy was recorded. Two intervention groups were designed: Group 1 received subtotal segmental artery occlusion (mimicking reimplantation of crucial segmental arteries with patent T12/T13, N = 5), and group 2 received total occlusion (T4-L5, N = 7). Pigs were monitored over 3 days. ResultsAll animals were paraplegic during the first 24 hours. The subtotal occlusion group completely recovered, whereas 57% of the total occlusion group remained paraplegic (N = 4/7). After segmental artery occlusion, collateral network near-infrared spectroscopy decreased from 92.3% ± 8% of baseline to 69.3% ± 18% after 10 minutes in the subtotal group (P = .003-.017) and from 90.1% ± 4% to 58.2% ± 9% in the total group (P < .001-.008). Throughout the postoperative period, collateral network near-infrared spectroscopy in the total occlusion group remained lower compared with the subtotal group (<30% baseline threshold, P < .05). Lumbar collateral network near-infrared spectroscopy and neurologic outcome were significantly correlated (R = 0.7, P < .001). ConclusionsLumbar collateral network near-infrared spectroscopy reacts to occlusion of segmental arteries and correlates with neurologic outcome. The preliminary data suggest that collateral network near-infrared spectroscopy may be a valuable noninvasive tool for detecting imminent spinal cord ischemia during and after aortic procedures involving segmental artery occlusion.

Intracardiac pulsed field ablation: Proof of feasibility in a chronic porcine model

Radiofrequency (RF) has become an accepted energy source for myocardial ablation but may result in discontinuous lesions and nontargeted tissue injury. We examined the feasibility and safety of lesion formation using high-amplitude, bipolar pulsed electric fields delivered from a multielectrode array catheter. The purpose of this study was to compare duty-cycled radiofrequency ablation (RFA) to pulsed field ablation (PFA) in terms of acute electrical effects, 2-week lesion formation, and injury to nontargeted tissues. Intracardiac ablations were performed in 6 pigs using a circular pulmonary vein ablation catheter. The energy source for ablation delivery was randomized to deliver either PFA or RFA to 3 atrial endocardial sites. Bipolar pace capture and electrogram amplitude measurements were recorded at each site. Histopathology and necropsies were performed after 2 weeks. The circular pulmonary vein ablation catheter was used to deliver pulsed electric fields to produce cardiac lesions without skeletal muscle stimulation. Evaluating all ablations in each site, electrogram amplitudes were reduced to <0.5 mV in 67.5% of PFA vs 27.0% of RFA deliveries (P <.001). Bipolar cardiac capture was lost after 100% vs 92.0% of PFA vs RFA (P = .005). At 2 weeks, PFA resulted in consistent transmural and homogeneous replacement fibrosis devoid of lingering myocyte "sequesters." RFA lesions showed a stronger inflammatory response extending to the epicardial fat, arterial injury, and thrombosis. Neither PFA nor RFA lesions showed endocardial thrombus. Intracardiac PFA can be feasibly delivered from a circular catheter to create fibrotic lesions that have acute electrical effects, without injury to nontargeted tissue.

Matrix Signaling Subsequent to a Myocardial Infarction: A Proteomic Profile of Tissue Factor Microparticles

This study investigated the release and proteomic profile of tissue factor microparticles (TFMPs) prospectively (up to 6 months) following a myocardial infarction (MI) in a chronic porcine model to establish their utility in tracking cellular level activities that predict physiologic outcomes. Our animal groups (n= 6 to 8 each) consisted of control, noninfarcted (negative control); infarcted only (positive control); and infarcted animals treated with cardiac resynchronization therapy (CRT) and a β-blocker (BB) (metoprolol succinate). The authors found different protein profiles in TFMPs between the control, infarcted only group, and the CRT+ BB treated group with predictive impact on the outward phenotype of pathological remodeling after an MI within and between groups. This novel approach of monitoring cellular level activities by profiling the content of TFMPshas the potential of addressing a shortfall of the current crop of cardiac biomarkers, which is the inability to capture composite molecular changes associated with chronic maladaptive signaling in a spatial and temporal manner.

P612Feasibility and safety of a wireless pulmonary artery pressure monitoring system in chronic porcine models of pulmonary hypertension

P612Feasibility and safety of a wireless pulmonary artery pressure monitoring system in chronic porcine models of pulmonary hypertension

Unexpected Internalization of a Pulmonary Artery Band in a Porcine Model of Tetralogy of Fallot.

We report our experience of an unexpected complication of internalization of a pulmonary artery (PA) band in the vascular lumen, which occurred in a chronic porcine model of repaired tetralogy of Fallot (TOF). Twelve piglets were divided into 3 groups: (1) TOF model animals (PA band plus pulmonary valvotomy, n = 4), (2) pulmonary insufficiency (PI) animals (pulmonary valvotomy, n = 4), and (3) control animals (n = 4). A nonabsorbable, coated braided polyester tape was used to perform the main pulmonary artery banding. Echocardiography was performed 4 months postoperatively. After each animal was euthanized, PA histological analysis was performed in animals with band internalization. Significant postsurgical pulmonary regurgitation and right ventricular enlargement were present in the TOF and PI, compared with control animals, whereas no significant pulmonary stenosis was observed in TOF animals when compared with PI group. Postmortem examination of all TOF animals revealed the constricting band to be intact but partially internalized into the PA lumen, allowing blood flow around the stenosis. Histological sections of the banded PA in the area of internalization showed a significant disorganization of the medial layer, with significant scarring and fibrotic reaction surrounding the outside of the band and the presence of inflammatory cells suggesting a significant inflammatory response during band internalization. Band internalization may occur after PA banding using a nonabsorbable, coated braided polyester tape in a chronic porcine model of repaired TOF. This unusual complication was likely due to the type of material used for banding.

Robot-assisted Fallopian tube transection and anastomosis using the new REVO-I robotic surgical system: feasibility in a chronic porcine model.

To evaluate the feasibility and safety of the new REVO-I robotic platform by performing Fallopian tube transection and anastomosis in live porcine models. A prospective chronic animal study was carried out in four crossbred female pigs. The primary outcome was assessment of the pigs' 2-week survival. The secondary outcomes were measurements of intra-operative variables and the complications or difficulties arising when using the REVO-I. Fallopian tube anastomosis was successfully performed in four porcine models. The mean (range) operating time was 66 (46-104 min), docking time 22.25 (14-53) min and console time 18 (13-20) min. The REVO-I robotic system functioned appropriately, with no technical problems or difficulties noted during the procedures. Both the surgeon and the bedside assistants reported ease of use and better performance with subsequent procedures. All pigs were alive 2 weeks after surgery, with no peri-operative complications related to the use of the robot. This preclinical chronic porcine study showed that the REVO-I robotic surgical system is a feasible and safe robotic instrument that can be used by surgeons to perform skillful robotic procedures in porcine models. Our next objective will be to demonstrate its safety in humans.

Robot-assisted ureteral reconstruction using a tubularized peritoneal flap: a novel technique in a chronic porcine model.

To evaluate the feasibility and functional outcomes in porcine models of a novel robotic surgical technique for the treatment of complex ureteral injuries and strictures. Six pigs underwent robotic ureteral reconstruction using a long tabularized peritoneal flap and followed for 6-9weeks after the surgery. Ureteral flap vascularity, intra-renal pressure, patency of the conduct, endoscopic aspect of the flap, renal function and histopathology were evaluated. All animals successfully underwent ureteral reconstruction using a tubularized peritoneal flap. Median operative time was 223min (162-360). Flap tubularization suture took 31min (19-47), and proximal anastomosis took 20min (15-38). Bladder mobilization with psoas hitch and distal anastomosis took 9min (7-12) and 23min (13-46), respectively. On follow-up, significant shrinkage of the ureteral flap in both length and width was observed. Antegrade pyelograms confirmed dilation and tortuosity of the proximal ureter, dilation of the renal pelvis, and major and minor calyxes without any definitive strictures. Microscopically, focal urothelial lining was seen in the neoureter. Creatinine level was significantly higher at the end of the follow-up period (p=0.003). Robot-assisted ureteral reconstruction using a tubularized peritoneum flap is technically feasible and reproducible. The flap sustained abundant vascular supply after different intervals of follow-up and the peritoneal mesenchymal cells differentiated into urothelium and myofibroblasts. Further studies are needed to address the issue of functional obstruction to improve long-term renal function outcomes.

The Effect of Contact Force in Atrial Radiofrequency Ablation: Electroanatomical, Cardiovascular Magnetic Resonance, and Histological Assessment in a Chronic Porcine Model

ObjectivesThis study sought to determine the effect of contact force (CF) on atrial lesion size, quality, and transmurality by using a chronic porcine model of radiofrequency ablation. BackgroundCF is a major determinant of ventricular lesion formation, but uncertainty exists regarding the most appropriate CF parameters to safely achieve permanent, transmural lesions in the atria. MethodsIntercaval linear ablation (30 W, 42°C, 17 ml/min irrigation) was performed in 8 Göttingen minipigs by using a force-sensing catheter with CF >20 g (high force) or <10 g (low force) at alternate ends of the line, separated by an intentional gap. Voltage mapping and cardiovascular magnetic resonance (CMR) imaging were performed pre-ablation, immediately after ablation, and at 2 months’ post-procedure. Lesions were sectioned orthogonal to the axis of ablation to assess transmurality. ResultsMean CF was 22.6 ± 11.4 g and 7.8 ± 4.0 g in the high and low CF regions. Acute tissue edema was greater with high CF, both caudally (7.0 mm vs. 4.6 mm; p = 0.016) and cranially (6.9 mm vs. 4.6 mm; p = 0.038). There was no difference in chronic lesion size (voltage mapping) or volume (late gadolinium enhancement CMR) between high and low CF regions. There was no difference in scar density (assessed by low-voltage criteria and late gadolinium enhancement signal intensity) or histological transmurality between high and low CF regions. ConclusionsAlthough high CF (>20 g) resulted in more acute tissue edema than low CF (<10 g), chronically there was no difference in lesion size, quality, or transmurality. Appropriate CF targets for atrial ablation may be lower than previously thought.

1CMR characterization of linear ablation lesions with varyng contact force – a chronic porcine model

Introduction: Catheter-myocardium contact force (CF) is a major determinant of ablation lesion generation, with higher CF associated with greater energy transfer. The effect of contact force on atrial lesion formation has not been characterized in an in vivo model. Acute and chronic atrial injury can be visualized with T2-weighted (T2W) and late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) and in combination with voltage mapping, histology and ex vivo MR provides the necessary tools for detailed ablation lesion characterization. We investigated the effect of contact force on lesion characteristics, including transmurality, acutely and 2 months after atrial ablation. Methods: Under general anaesthesia, femoral venous access was obtained in eight Gottingen minipigs. In two animals, pre-ablation CMR imaging was performed. Using an electro-anatomical mapping system (Carto3, Biosense Webster) the geometry of the right atrium was obtained with a 20-pole circular mapping catheter (Lasso Nav, D curve, Biosense Webster). An intercaval linear ablation lesion was created using a CF-sensing catheter (SmartTouch, Biosense Webster, 30W, 48C, 20ml/min irrigation). Target contact forces of >20g (high force) or <10g (low force) were used alternately at the cranial and caudal ends of the ablation line. After ablation, repeat CMR imaging of the ablation lesion was performed. CMR was repeated at 2 months before the animals were sacrificed. Ablation lesions were dissected en bloc and mounted in frames before ex vivo MR was performed. Finally, lesions were sectioned orthogonal to the axis of the ablation line to complete the assessment of transmurality. Result: Applied CF was 9.1±3.5g and 34.6±18.6g in the low and high CF regions. Qualitative analysis of chronic voltage mapping illustrated resolution of normal voltage in the low force ablation regions. Acute wall thickness (measured on T2W images) was significantly greater in the high CF region, for both the caudal (7.0mm vs. 4.6mm; p=0.016) and cranial (6.9mm vs. 4.6mm; p=0.038) ends of the ablation line (Fig. A). There were no significant differences between the mean T2W or LGE SI according to force in either the acute or chronic scans. Chronic lesion volume (LGE) was greater in high CF regions for the cranial, but not caudal, ends of the ablation line (Fig. B). Ex vivo MR and macroscopic sectioning confirmed full-thickness lesions were created in both low and high CF regions. Conclusion: Acute T2 CMR displays the extent of atrial wall injury following RF ablation and is proportional to CF, supporting a role for contact force monitoring during ablation. T2 and LGE CMR SI of ablation lesions at both acute and chronic timescales are similar regardless of the CF used during ablation, and lesion volume is only increased with high CF in certain regions of ablation. These findings suggest other ablation-related parameters including catheter stability may play a larger role in predicting chronic lesion formation. ![Graphic][1] [1]: /embed/inline-graphic-1.gif

Preliminary application of in vivo cardiac diffusion weighted MRI in chronic myocardial infarction porcine model

Background Cardiac diffusion-weighted MRI is a non-contrast technique that has the potential to identify changes in tissue microstructure in acute myocardial infarction (MI) in humans and rats [1,2]. The trace apparent diffusion coefficient (trADC) was found to be significantly increased in the infarcted region relative to remote regions. The increased trADC is attributed to an increase in extracellular space following cell death, where restriction in water diffusion is less. The aim of this study was to perform in vivo cardiac diffusionweighted MRI in a chronic MI porcine model to see if this increased trADC chronically persists and correlate it with scar tissue delineated by late gadolinium enhancement (LGE) imaging. Methods Four chronic MI (8 weeks post MI induced by completely occluded proximal LAD) mini pigs were scanned on a 3T MR system (Siemens Verio). Before contrast was administered, M1M2 motion compensated [3] diffusionprepared 2D segmented TSE was performed to derive trADC maps (TR/TE = 3RR/8.4 ms, a = 180°, 2.1 × 2.1 ×8m m 3 , 3 slices, diffusion TEprep = 105 ms, b = 400 s/ mm 2 ,G diff = 43 mT/m, three orthogonal DW directions). Diffusion preparation was applied in the most quiescent phase identified by CINE imaging (35 phases). Contrast LGE GRE imaging was performed roughly 15 min post contrast injection (TR/TE/TI = 326/1.47/300 ms, a =2 0°, 1.3 ×1 .3 ×8m m 3 , 12 slices). The lateral wall of the most basal slice (furthest from the LAD occlusion) was designated as the remote region. The region of infarction was determined by elevated trADC and signal intensity in LGE (both required μinfarct >μremote +5 sremote). For each pig, the mean trADC’s calculated for the infarct and remote regions. The infarct area determined by elevated trADC was compared to the LGE infarct area. Differences in means were tested for significance with a two tailed paired t-test. Cardiac phase mismatch between trADC maps and LGE images was corrected using a nonlinear B-spline registration, whose transform was derived from two phases of CINE closest to the trADC map and LGE. Results M1M2 diffusion-prepared TSE scans resulted in mean infarct trADC values of 2.4 ± 0.2 × 10 -3 mm 2 /s and mean remote trADC values of 1.4 ± 0.4 × 10 -3 mm 2 /s (p < 0.05). The location of elevated trADC infarct region agreed well with the LGE infarct area. The mean trADC and mean LGE infarct area was 0.9 ± 0.1 cm 2 and 0.8 ± 0.1 cm 2 , respectively (p = 1). In the infarct regions, wall motion was akinetic. Conclusions In this preliminary study, infarct regions delineated by elevated trADC correlated well with infarct regions defined by protocol matched LGE in area size and location. The roughly 50% increase in trADC values found in the infarct region relative to the remote region was statistically significant. Further histological studies and larger sample size are needed to confirm the origin of the increase in trADC and its relationship with infarcted tissue.

Evaluation of a novel cryoablation system: in vivo testing in a chronic porcine model.

Cryoablation is commonly used at present in the surgical treatment of atrial fibrillation (AF). However, there have been few studies examining the efficacy of the commonly used ablation devices. This report compares the efficacy of two cryoprobes in creating transmural endocardial lesions on the beating heart in a porcine model for chronic AF. In six Hanford miniature swine, the right atrial appendage and the inferior vena cava were isolated using a bipolar radiofrequency clamp to create areas of known conduction block. A connecting ablation line was performed endocardially via a purse string with the novel malleable 10-cm Cryo1 probe for 2 minutes at -40°C. Additional ablation lines were created with the Cryo1 and the 3.5-cm 3011 Maze Linear probe on the right and the left atrial wall. Epicardial activation mapping was performed before and immediately after ablation as well as 14 days postoperatively. Histologic examination was performed 14 days postoperatively. Transmural lesions were confirmed in 83/84 cross-sections (99%) for the Cryo1 probe and in 40/41 cross-sections (98%) for the 3011 Maze Linear probe. There was no difference between the devices in lesion width (mean ± SD, Cryo1, 10.7 ± 3.5 mm; 3011, 10.0 ± 3.9 mm; P = 0.31), lesion depth (Cryo1, 4.5 ± 1.7 mm; 3011, 4.6 ± 1.5 mm; P = 0.74), or atrial wall thickness (Cryo1, 4.5 ± 1.8 mm; 3011, 4.7 ± 1.7 mm; P = 0.74). There was a conduction delay across the right atrial ablation line (20 ± 2 milliseconds vs 51 ± 8 milliseconds, P < 0.001) that remained unchanged at 14 days (51 ± 8 milliseconds vs 52 ± 10 milliseconds, P = 0.88). The Cryo1 probe created transmural lesions on the beating heart, resulting in sustained conduction delay. Both probes had a similar performance in lesion geometry in this chronic animal model.