Swine models in translational research and medicine.

Swine are increasingly studied as animal models of human disease. The anatomy, size, longevity, physiology, immune system, and metabolism of swine are more like humans than traditional rodent models. In addition, the size of swine is preferred for surgical placement and testing of medical devices destined for humans. These features make swine useful for biomedical, pharmacological, and toxicological research. With recent advances in gene-editing technologies, genetic modifications can readily and efficiently be made in swine to study genetic disorders. In addition, gene-edited swine tissues are necessary for studies testing and validating xenotransplantation into humans to meet the critical shortfall of viable organs versus need. Underlying all of these biomedical applications, the knowledge of husbandry, background diseases and lesions, and biosecurity needs are important for productive, efficient, and reproducible research when using swine as a human disease model for basic research, preclinical testing, and translational studies.

Safety and chronic lesion characterization of pulsed field ablation in a Porcine model.

BACKGROUND: Pulsed field ablation (PFA) has been identified as an alternative to thermal-based ablation systems for treatment of atrial fibrillation patients. The objective of this Good Laboratory Practice (GLP) study was to characterize the chronic effects and safety of overlapping lesions created by a PFA system at intracardiac locations in a porcine model. METHODS: A circular catheter with nine gold electrodes was used for overlapping low- or high-dose PFA deliveries in the superior vena cava (SVC), right atrial appendage (RAA), and right superior pulmonary vein (RSPV) in six pigs. Electrical isolation was evaluated acutely and chronic lesions were assessed via necropsy and histopathology after 4-week survival. Acute and chronic safety data were recorded peri- and post-procedurally. RESULTS: No animal experienced ventricular arrhythmia during PFA delivery, and there was no evidence of periprocedural PFA-related adverse events. Lesions created in all anatomies resulted in electrical isolation postprocedure. Lesions were circumferential, contiguous, and transmural, with all converting into consistent lines of chronic replacement fibrosis, regardless of trabeculated or smooth endocardial surface structure. Ablations were non-thermally generated with only minimal post-delivery temperature rises recorded at the electrodes. There was no evidence of extracardiac damage, stenosis, aneurysms, endocardial disruption, or thrombus. CONCLUSION: PFA deliveries to the SVC, RAA, and RSPV resulted in complete circumferential replacement fibrosis at 4-week postablation with an excellent chronic myocardial and collateral tissue safety profile. This GLP study evaluated the safety and efficacy of a dosage range in preparation for a clinical trial and characterized the non-thermal nature of PFA.

What Is "Preclinical Device Pathology": An Introduction of the Unfamiliar.

Medical device pathologists are involved in the preclinical evaluation of medical devices that will be temporarily inserted or permanently and often irreversibly implanted in the human body. The medical device industry is technology based, allowing for rapid device iterations; innovations occur at an accelerated rate compared to the innovations in the pharmaceutical industry. The device pathologist provides the pathology results and is, by training and experience, in an ideal position to help the medical engineer and innovator tackle biomedical problems and to comment on the possible and actual outcomes of preclinical studies. Device pathology expertise is typically a necessity in the prelude for regulatory submission. However, there is a lack of detailed guidelines for a comprehensive preclinical pathology evaluation of the final product after implantation in a test animal. What specifically unites device pathologists is the reliance on gross pathology as the basis for spatial context needed for appropriate histopathologic analyses, the knowledge of detailed protocol instructions, a good understanding of wound healing including the "implant trauma," and interaction with ambitious device innovators. In this article, it is my aim to amalgamate the following articles in this issue with pertinent background information intended to be informative, critical, and stimulating.

Two-year extractability of novel left ventricular, active fixation leads in the sheep model.

BACKGROUND: A cardiac lead with a side helix for active fixation to the coronary vein wall (Attain Stability® , Model 20066, Medtronic, Minneapolis, MN, USA) recently received CE Mark. The lead is designed to improve left ventricular (LV) placement and reduce dislodgement rates. The extractability of this active fixation LV lead has not been studied extensively. METHODS: Seventeen sheep were implanted with either an LV lead with a side helix (Model 20066, Model 20096, Medtronic) or a unipolar LV lead (Model 4193, Medtronic) as a control. Leads were extracted at approximately 26, 52, or 118 weeks. Standard extraction methodology was employed with quantitative traction up to 907 g (2 lbs.) using a locking stylet. Gross pathology and histology of the heart with particular attention to the lead tracts were performed. RESULTS: All leads were successfully removed in their entirety and required significantly less than 1 kg of traction force. The side helix disengaged from the vein as designed and resulted in no complications. No cardiac tissue was observed on any extracted lead. Gross pathology and histology were devoid of any helix-induced lesions in the vascular structures. The epicardium over the side helix was normal and the fibrotic reaction around the helix was not significantly different from that around the nonhelix portions of the study leads or the control lead. CONCLUSION: Extraction of the side helix, active fixation LV lead from the coronary veins in the sheep model is safe, without procedural complexity, and free of complications after long-term LV lead implant duration.

The Biophysics of Passive Convective Cooling During Catheter Ablation with Gold versus Platinum Electrodes and Multielectrode Phased Radiofrequency Energy Delivery.

INTRODUCTION: During radiofrequency (RF) catheter ablation, convective cooling of the ablated tissue by circulating blood allows higher power delivery and deeper penetration of volume heating without excess surface heating. The study aim was to characterize ablation lesions using electrode materials with differing thermal conductivities and magnitudes of passive convective cooling utilizing duty-cycled RF energy. METHODS AND RESULTS: RF ablations using a linear array of 4 3-mm platinum electrodes (n = 228) were compared to an array with gold electrodes (n = 244). RF was delivered using temperature feedback power control, in a blended bipolar:unipolar mode (2:1 and 4:1), to exposed porcine thigh muscle superfused with heparinized blood. For gold electrodes, lesion depths were 4.1 ± 0.8 mm in the 2:1 ablation mode and 3.7 ± 0.9 mm in the 4:1 ablation mode, versus 3.7 ± 1.0 mm and 3.3 ± 1.0 mm with platinum (P < 0.001 vs. gold, P = 0.004 platinum 2:1 vs. 4:1). More efficient passive cooling at all flow rates with gold versus platinum resulted in a lower mean electrode temperature and a higher proportion of ablations reaching maximum power before achieving target temperature. Therefore, the mean ablation power was higher with gold (6.5+2.1 vs. 5.5+2.3 W, P < 0.001), and lesion depth was greater (3.9+0.8 mm vs. 3.5+1.0 mm, P < 0.001) compared to platinum. CONCLUSIONS: Passive convective cooling during RF ablation is more efficient with gold compared to platinum electrodes, particularly when ablations are temperature limited. Using temperature feedback power control, deeper lesions can be reliably achieved with gold electrodes.

Effect of Steroid Elution on Electrical Performance and Tissue Responses in Quadripolar Left Ventricular Cardiac Vein Leads.

INTRODUCTION: The use of steroid elution (SE) electrode in a cardiac pacing lead is known to suppress myocardial inflammation to lower pacing thresholds (PTs). SE has been widely utilized on the distal electrode of left ventricular cardiac vein (LVCV) leads used in cardiac resynchronization therapy (CRT). However, no paired comparison in effect of SE has been studied in proximal electrodes of quadripolar LVCV leads. METHODS: We evaluated electrical performance and tissue responses of quadripolar LVCV lead electrodes with and without SE in two canine studies with a total of 14 canines. Extended bipolar PT and pacing impedance of the LVCV electrodes to right ventricle coil were collected via an implantable CRT device/programmer or a percutaneous threshold analyzer/pacing analyzer at weeks 0, 1, 2, 4, 6, 8, and 12. Gross and histopathological examinations of the canines were performed at the end of the studies. RESULTS: Our preclinical studies showed that SE had significant effects on the long-term pacing performance of quadripolar LVCV leads. The SE tip and ring electrodes reduced postimplant PT peak and chronic PT, P = 0.038. Histological examination of the perilead tissue capsules at 12 weeks showed a reduced thickness for the location of SE electrodes. CONCLUSION: SE electrodes in quadripolar LVCV leads lower the PTs, and therefore may potentially reduce long-term current drain of CRT systems, thus improving the device longevity. These preclinical data serve as rationale to include SE on proximal electrodes for the Attain Performa LVCV leads and future quadripolar LVCV leads development.

p53 family members in myogenic differentiation and rhabdomyosarcoma development.

The p53 family comprises the tumor suppressor p53 and the structural homologs p63 and p73. How the three family members cooperate in tumor suppression remains unclear. Here, we report different but complementary functions of the individual members for regulating retinoblastoma protein (RB) function during myogenic differentiation. Whereas p53 transactivates the retinoblastoma gene, p63 and p73 induce the cyclin-dependent kinase inhibitor p57 to maintain RB in an active, hypophosphorylated state. DeltaNp73 inhibits these functions of the p53 family in differentiation control, prevents myogenic differentiation, and enables cooperating oncogenes to transform myoblasts to tumorigenicity. DeltaNp73 is frequently overexpressed in rhabdomyosarcoma and essential for tumor progression in vivo. These findings establish differentiation control as a key tumor suppressor activity of the p53 family.

Effects of envelopes on cardiac implantable electronic device pocket healing: A head-to-head preclinical evaluation.

BACKGROUND: The healing response to cardiac implantable electronic device (CIED) implantation results in inflammation that can lead to fibrous pocket formation, which may disrupt pocket healing or complicate future interventions. OBJECTIVE: The purpose of this study was to assess CIED pocket healing with use of the second-generation TYRX absorbable antibacterial envelope (T2), the next-generation (NG) TYRX absorbable antibacterial envelope under development, and the CanGaroo® extracellular matrix envelope (ECM) compared to no envelope. METHODS: A total of 110 CIEDs were implanted in an ovine model, either with (T2, NG, or ECM) or without envelopes. Histopathologic and morphometric analyses were completed at several timepoints after implant (3 days, 7 days, 4 weeks, 12 weeks, 24 weeks). An independent pathologist completed a blinded histopathology assessment of the pockets. RESULTS: TYRX (T2/NG) pockets showed similar inflammatory and healing profiles to controls with more rapid provisional matrix formation compared to controls and ECM. ECM pockets exhibited increased acute (3 and 7 days) and chronic (24 weeks) inflammation. T2/NG had almost complete (T2) or complete (NG) absorption by week 12. ECM remained present at week 24 and was associated with significantly thicker capsules (ECM 0.80 ± 0.14 mm; NG 0.37 ± 0.10 mm; control 0.56 ± 0.17 mm). CONCLUSION: Compared to ECM, pockets with TYRX showed less inflammation, more rapid provisional matrix formation, faster absorption, and thinner capsules. TYRX pockets had low inflammation comparable to controls with accelerated provisional matrix deposition and tissue adhesion. The healing response to CIEDs used with TYRX fosters the formation of a well-healed pocket, which may bring patient benefit beyond its proven infection reduction.

Prolonged diabetes reversal after intraportal xenotransplantation of wild-type porcine islets in immunosuppressed nonhuman primates.

Cell-based diabetes therapy requires an abundant cell source. Here, we report reversal of diabetes for more than 100 d in cynomolgus macaques after intraportal transplantation of cultured islets from genetically unmodified pigs without Gal-specific antibody manipulation. Immunotherapy with CD25-specific and CD154-specific monoclonal antibodies, FTY720 (or tacrolimus), everolimus and leflunomide suppressed indirect activation of T cells, elicitation of non-Gal pig-specific IgG antibody, intragraft expression of proinflammatory cytokines and invasion of infiltrating mononuclear cells into islets.

Preclinical evaluation of a third-generation absorbable antibacterial envelope.

BACKGROUND: The TYRX (Medtronic) absorbable antibacterial envelope has been shown to stabilize implantable cardiac devices and reduce infection. A third-generation envelope was developed to reduce surface roughness with a redesigned multifilament mesh and enhanced form factor but identical polymer coating and antibiotic concentrations as the currently available second-generation envelope. OBJECTIVE: The purpose of this study was to compare drug elution, bacterial challenge efficacy, stabilization, and absorption of second- vs third-generation envelopes. METHODS: Antibiotic elution was assessed in vitro and in vivo. For efficacy against gram-positive/gram-negative bacteria, 40 rabbits underwent device insertions with or without third-generation envelopes. For stabilization (migration, rotation), 5 sheep were implanted with 6 devices each in second- or third-generation envelopes. Prespecified acceptance criteria were <83-mm migration and <90° rotation. Absorption was assessed via gross pathology. RESULTS: Elution curves were equivalent (similarity factors ≥50 per Food and Drug Administration guidance). Third-generation envelopes eluted antibiotics above minimal inhibitory concentration (MIC) in vivo at 2 hours postimplant through 7 days, consistent with second-generation envelopes. Bacterial challenge showed reductions (P <.05) in infection with second- and third-generation envelopes. Device migration was 5.5 ± 3.5 mm (third-generation) vs 9. 9 ±7.9 mm (second-generation) (P <.05). Device rotation was 18.9° ± 11.4° (third-generation) vs 17.6° ± 15.1° (second-generation) and did not differ (P = .79). Gross pathology confirmed the absence of luminal mesh remainders and no differences in peridevice fibrosis at 9 or 12 weeks. CONCLUSION: The third-generation TYRX absorbable antibacterial envelope demonstrated equivalent preclinical performance to the second-generation envelope. Antibiotic elution curves were similar, elution was above MIC for 7 days, infections were reduced compared to no envelope, and acceptance criteria for migration, rotation, and absorption were met.

Characterization of Phrenic Nerve Response to Pulsed Field Ablation.

BACKGROUND: Phrenic nerve palsy is a well-known complication of cardiac ablation, resulting from the application of direct thermal energy. Emerging pulsed field ablation (PFA) may reduce the risk of phrenic nerve injury but has not been well characterized. METHODS: Accelerometers and continuous pacing were used during PFA deliveries in a porcine model. Acute dose response was established in a first experimental phase with ascending PFA intensity delivered to the phrenic nerve (n=12). In a second phase, nerves were targeted with a single ablation level to observe the effect of repetitive ablations on nerve function (n=4). A third chronic phase characterized assessed histopathology of nerves adjacent to ablated cardiac tissue (n=6). RESULTS: Acutely, we observed a dose-dependent response in phrenic nerve function including reversible stunning (R2=0.965, P<0.001). Furthermore, acute results demonstrated that phrenic nerve function responded to varying levels of PFA and catheter proximity placements, resulting in either: no effect, effect, or stunning. In the chronic study phase, successful isolation of superior vena cava at a dose not predicted to cause phrenic nerve dysfunction was associated with normal phrenic nerve function and normal phrenic nerve histopathology at 4 weeks. CONCLUSIONS: Proximity of the catheter to the phrenic nerve and the PFA dose level were critical for phrenic nerve response. Gross and histopathologic evaluation of phrenic nerves and diaphragms at a chronic time point yielded no injury. These results provide a basis for understanding the susceptibility and recovery of phrenic nerves in response to PFA and a need for appropriate caution in moving beyond animal models.

Transmural atrial fibrosis after epicardial and endocardial argon-powered CryoMaze ablation.

BACKGROUND: The CryoMaze procedure is usually limited to endocardial ablation under cardio-pulmonary bypass. Epicardial ablation is considered inferior as endocardial islets of atrial tissue could theoretically remain viable, protected from cryoinjury by epicardial fat and endocardial circulating warm blood. Novel argon-powered cryoprobes with lower ablation temperatures have recently become available. It is unclear if these instruments can reliably induce transmural atrial fibrosis by epicardial cryoablation on the beating heart. METHODS: Ten sheep were divided into two equal groups. CryoMaze ablations were applied using an argon-powered cryoprobe with an ablation temperature of -185°C. In the control group, standardized ablations (n = 50) were applied endocardially under cardiopulmonary bypass. In the experimental group, corresponding ablations (n = 50) were applied epicardially on the beating heart. Postoperatively the animals were monitored for 30 days. At necropsy, the lesions were explanted and analyzed histologically for evidence of transmural fibrosis. RESULTS: Two animals in the control group and one animal in the experimental group died prematurely. Autopsy of the remaining animals showed that all lesions (n = 70) had retained their structural integrity. In the control group, histology demonstrated transmural fibrosis in 94% (28/30) of the endocardially applied lesions. In the experimental group, histology demonstrated transmural fibrosis in 95% (38/40) of the epicardially applied lesions. Statistical analysis revealed no significant difference between the two groups (p = 0.96). CONCLUSION: Argon-powered epicardial cryoablation on the beating heart is as efficient in inducing transmural fibrosis as the traditional technique of endocardial ablation under cardio-pulmonary bypass.

Reduction in Pulmonary Vein Stenosis and Collateral Damage With Pulsed Field Ablation Compared With Radiofrequency Ablation in a Canine Model.

BACKGROUND: Pulmonary vein (PV) stenosis is a highly morbid condition that can result after catheter ablation for PV isolation. We hypothesized that pulsed field ablation (PFA) would reduce PV stenosis risk and collateral injury compared with irrigated radiofrequency ablation (IRF). METHODS: IRF and PFA deliveries were randomized in 8 dogs with 2 superior PVs ablated using one technology and 2 inferior PVs ablated using the other technology. IRF energy (25-30 W) or PFA was delivered (16 pulse trains) at each PV in a proximal and in a distal site. Contrast computed tomography scans were collected at 0, 2, 4, 8, and 12-week (termination) time points to monitor PV cross-sectional area at each PV ablation site. RESULTS: Maximum average change in normalized cross-sectional area at 4-weeks was -46.1±45.1% post-IRF compared with -5.5±20.5% for PFA (P≤0.001). PFA-treated targets showed significantly fewer vessel restrictions compared with IRF (P≤0.023). Necropsy showed expansive PFA lesions without stenosis in the proximal PV sites, compared with more confined and often incomplete lesions after IRF. At the distal PV sites, only IRF ablations were grossly identified based on focal fibrosis. Mild chronic parenchymal hemorrhage was noted in 3 left superior PV lobes after IRF. Damage to vagus nerves as well as evidence of esophagus dilation occurred at sites associated with IRF. In contrast, no lung, vagal nerve, or esophageal injury was observed at PFA sites. CONCLUSIONS: PFA significantly reduced risk of PV stenosis compared with IRF postprocedure in a canine model. IRF also caused vagus nerve, esophageal, and lung injury while PFA did not.

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

BACKGROUND: 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. OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: Intracardiac PFA can be feasibly delivered from a circular catheter to create fibrotic lesions that have acute electrical effects, without injury to nontargeted tissue.

Dosing of the second-generation cryoballoon using acute time-to-pulmonary vein isolation as an indicator of durable ablation in a canine model.

BACKGROUND: Rigid time-based dosing protocol(s) currently used in the clinic for cryoballoon ablation of atrial fibrillation may be inadequate to guide the circumferential and transmural cryothermal energy transfer across the pulmonary vein (PV) and may result in injury to collateral tissues or electrical gaps between the PV and left atrium (LA). OBJECTIVE: A physiologic endpoint (e.g., acute time-to-PV isolation a.k.a. time-to-effect; TTE) may be effective in the determination of a transmural lesion formation and may allow for individualized ablation dosing across each PV. METHODS: Thirty PVs from 15 dogs were randomized into five dosing protocols, including (1) TTE + 60 s, (2) TTE + 90 s, (3) TTE + 120 s, (4) TTE + 150 s, and (5) 2 × 180 s. Ablations were conducted with a 23-mm second-generation cryoballoon, and TTE was assessed during a freeze by pacing from an inner balloon-lumen circular diagnostic catheter to a quadripolar diagnostic catheter in the coronary sinus. After ablation, animals were survived for 30 to 34 days, and repeat electrophysiology assessment of PV isolation was conducted after which animals were euthanized for gross anatomy and histological examination. RESULTS: At study termination, efficacy endpoint evaluations were based on maintenance of PV electrical isolation, gross anatomy assessment of PV lesions, and histological examination of PVs. Five efficacy endpoint failures were noted, including the following: 1 PV in the TTE + 90 sec group; 2 PVs in the TTE + 120 sec group; 1 PV in the TTE + 150 s group; and 1 PV in the 2 × 180 s group. Regarding safety, one phrenic nerve injury was observed in the 2 × 180 s cohort. No other complications were observed. CONCLUSIONS: In a canine model, effective PV isolation could be found even in the shortest duration dosing cohort (TTE + 60 s). One complication (phrenic nerve injury) was observed in the longest duration dosing group (2 × 180 s). Further studies will be required to correlate these results to a 28-mm cryoballoon (more commonly used in the cryoablation of a human LA); however, to date, this is the first reporting of a successful cryoablation using TTE + 60 s dosing (approximately 90 s total duration of freezing).

Comparison of a Saline-coupled Bipolar Sealer Versus Traditional Electrosurgery in a Porcine Model of Chronic Wound Healing.

OBJECTIVE: This study examines the healing dynamics of in vivo porcine muscle tissue wounds hemostatically treated with a saline-coupled bipolar tissue sealer (SCBS) compared with traditional electrosurgical (ES) coagulation. MATERIALS AND METHODS: Six cutaneous incisions were created on the dorsum of 28 adult male Yorkshire swine. The underlying muscle tissue was incised with a cold scalpel then treated with either SCBS (at 170 W) or traditional ES (at Coag 45 W). Time to hemostasis was recorded. Animals were humanely euthanized at day 2 and weeks 2, 3, or 8; treated tissue was harvested for histopathological evaluation. RESULTS: After 8 weeks, the extent of wound healing was similar between SCBS and ES. Both devices controlled bleeding effectively; however, SCBS-treated wounds exhibited a greater depth of thermal effect over the first 3 weeks despite a shorter treatment time. Wounds treated with SCBS demonstrated fewer inflammatory markers at early time points but healed more slowly, with scores that lagged behind ES for collagen deposition, fibrous tissue maturity, extracellular matrix, and stage of healing. Myofiber regeneration notably increased in SCBS-treated wounds at weeks 2, 3, and 8. By the end of the 8-week recovery period, there were no significant differences in healing parameters between the 2 groups. CONCLUSIONS: Overall, both devices elicited similar progression of healing by 8 weeks. The SCBS produced a deeper thermal effect in a shorter treatment time and improved myofiber regeneration compared with ES and had an equivalent overall course of healing.

Gene expression array analyses predict increased proto-oncogene expression in MMTV induced mammary tumors.

Exogenous infection by milk-borne mouse mammary tumor viruses (MMTV) typically induce mouse mammary tumors in genetically susceptible mice at a rate of 90-95% by 1 year of age. In contrast to other transforming retroviruses, MMTV acts as an insertional mutagen and under the influence of steroid hormones induces oncogenic transformation after insertion into the host genome. As these events correspond with increases in adjacent proto-oncogene transcription, we used expression array profiling to determine which commonly associated MMTV insertion site proto-oncogenes were transcriptionally active in MMTV induced mouse mammary tumors. To verify our gene expression array results we developed real-time quantitative RT-PCR assays for the common MMTV insertion site genes found in RIII/Sa mice (int-1/wnt-1, int-2/fgf-3, int-3/Notch 4, and fgf8/AIGF) as well as two genes that were consistently up regulated (CCND1, and MAT-8) and two genes that were consistently down regulated (FN1 and MAT-8) in the MMTV induced tumors as compared to normal mammary gland. Finally, each tumor was also examined histopathologically. Our expression array findings support a model whereby just one or a few common MMTV insertions into the host genome sets up a dominant cascade of events that leave a characteristic molecular signature.

Predictability of lesion durability for AF ablation using phased radiofrequency: Power, temperature, and duration impact creation of transmural lesions.

BACKGROUND: Long-term clinical outcomes for atrial fibrillation ablation depend on the creation of durable transmural lesions during pulmonary vein isolation and on substrate modification. Focal conventional radiofrequency (RF) ablation studies have demonstrated that tissue temperature and power are important factors for lesion formation. However, the impact and predictability of temperature and power on contiguous, transmural lesion formation with a phased RF system has not been described. OBJECTIVE: The purpose of this study was to determine the sensitivity, specificity, and predictability of power and temperature to create contiguous, transmural lesions with the temperature-controlled, multielectrode phased RF PVAC GOLD catheter. METHODS: Single ablations with the PVAC GOLD catheter were performed in the superior vena cava of 22 pigs. Ablations from 198 PVAC GOLD electrodes were evaluated by gross examination and histopathology for lesion transmurality and contiguity. Lesions were compared to temperature and power data from the phased RF GENius generator. Effective contact was defined as electrodes with a temperature of ≥50°C and a power of ≥3 W. RESULTS: Eighty-five percent (168 of 198) of the lesions were transmural and 79% (106 of 134) were contiguous. Electrode analysis showed that >30 seconds of effective contact identified transmural lesions with 85% sensitivity (95% confidence interval [CI] 78%-89%), 93% specificity (95% CI 76%-99%), and 99% positive predictive value (95% CI 94%-100%). Sensitivity for lesion contiguity was 95% (95% CI 89%-98%), with 62% specificity (95% CI 42%-78%) and 90% positive predictive value (95% CI 83%-95%). No char or coagulum was observed on the catheter or tissue. CONCLUSION: PVAC GOLD safely, effectively, and predictably creates transmural and contiguous lesions.

ABL-MYC retroviral infection elicits bone marrow plasma cell tumors in Bcl-X(L) transgenic mice.

Multiple myeloma is characterized by the accumulation of malignant plasma cells in the bone marrow. While there have been many attempts to genetically recapitulate this disease in animal models, few reports describe plasma cell tumors that exhibit bone marrow involvement. We recently described a Bcl-X(L) transgenic mouse that developed polyclonal non-malignant B-cell expansions in the bone marrow and lymphoid organs. In this report, we describe induction of plasma cell tumors in littermate control and Bcl-X(L) transgenic mice with a retrovirus expressing v-Abl and c-Myc. Nearly 100% of the ABL-MYC-infected littermate control and Bcl-X(L) mice developed plasma cell tumors. There was no difference in tumor latency in young mice infected; however, following ABL-MYC infection, aged Bcl-X(L) mice demonstrated a median survival of 9 weeks, while littermate control mice demonstrated a median survival of 19 weeks. Interestingly, while both littermate control and Bcl-X(L) mice infected with the ABL-MYC retrovirus developed extramedullary plasma cell tumors, only the ABL-MYC-infected Bcl-X(L) mice, but not the ABL-MYC-infected littermate control mice, developed bone marrow plasma cell tumors with characteristic radiolucent bone lesions. Tumor cell populations were clonally related, and analysis of tumor immunoglobulin genes demonstrated evidence consistent with somatic hypermutation. This report implicates an unidentified role of Bcl-X(L) in bone marrow plasma cell tumor formation, as ABL-MYC retroviral infection only elicits bone marrow plasma cell tumors in mice that ectopically express Bcl-X(L) in their B- and plasma cells.

Cyclosporine toxicity in immunosuppressed streptozotocin-diabetic nonhuman primates.

Streptozotocin (STZ) is widely applied in animal models of insulin-dependent diabetes mellitus. Adverse effects of STZ mainly concern liver and kidney. In nonhuman primates a single 100-150 mg/kg dose invariably induces diabetes with only rare adverse effects. We report one animal with renal failure necessitating sacrifice. Body weight (age) might be a confounding factor, i.e. older animals might be more vulnerable to STZ-related toxicity. We therefore recommended to administer STZ on a mg/m2 basis and not on a mg/kg basis. In our islet transplantation program nonhuman primates with STZ-induced diabetes received transplants under chronic immunosuppression including calcineurin inhibitors (cyclosporine, tacrolimus), drugs in the rapamycin class affecting growth factor-induced cell proliferation, and the sphingosine 1-phosphate receptor antagonist FTY720. Four animals developed renal failure and had to be sacrificed, most likely caused by cyclosporine. Kidney histology was typical for cyclosporine toxicity including thrombotic microangiopathy in glomeruli and fibrinoid necrosis of arteries, and for STZ toxicity including acute tubular necrosis and accumulations of erythroid precursors. This adverse effect was observed at a pharmacologically active cyclosporine exposure. Additionally, six diabetic animals without major adverse effects during cyclosporine or tacrolimus treatment are presented. We conclude that cyclosporine facilitates renal dysfunction in animals with STZ-induced diabetes, presumably related to an increased vulnerability to a toxic insult after STZ administration.