Elective Sacrifice Research Articles

Novel method of surgical preparation for transcatheter completion of Fontan circulation: Creation of an extracardiac pathway

The alliance between surgeons and interventionists has inspired creative techniques to surgically precondition the heart for subsequent transcatheter repair. The interest stems from the need to avoid repeated surgeries. Transcatheter Fontan completion of intracardiac pathway has been reported. To report a new surgical preparation for transcatheter completion of extracardiac Fontan circulation. The inferior vena cava (IVC) was cut and anastomosed end-to-end with the inferior end of a Gore-Tex conduit in 20 lambs. A ring was placed around the IVC near the anastomosis. The superior vena cava was cut and connected with the right atrium (RA) auricle. In group 1 (n=9), the Gore-Tex conduit was occluded at both ends by a polytetrafluoroethylene membrane. In group 2 (n=11), the upper segment of the Gore-Tex tube was opened and connected to the RA to allow free flow of IVC blood. Fontan completion was attempted 1-3 months following surgery. Animals were sacrificed just after or 3 months after completion. All lambs were successfully preconditioned. We failed to complete the pathway in all animals from group 1-autopsy showed occlusion of the pathway. In group 2, there was one postoperative death, one elective sacrifice after 2 months to assess pathway integrity, and nine successful completions. Autopsies showed widely patent pathway and well-deployed covered stents completely occluding the fenestrations. Circulating extracardiac conduit offers the best option to prepare for extracardiac Fontan completion. This surgical preparation opens new frontiers for transcatheter and hybrid techniques for extracardiac Fontan completion.

In vivo evaluation of the HeartWare MVAD Pump

The current design trend for left ventricular assist devices (LVADs) is miniaturization, which aims to increase the treatable patient population and enable new treatment indications by reducing surgical trauma and the complications associated with device implantation. The MVAD Pump (HeartWare Inc, Framingham, MA) is a small, axial VAD that uses magnetic and hydrodynamic impeller technology and incorporates wide helical flow channels to minimize shear stress. In this study, we implanted the MVAD Pump in an ovine model to evaluate device hemocomaptiblity, biocompatibility, performance, and safety. The MVAD Pump was implanted in an ovine model (n = 9) for 90 days. The pump was implanted through a thoracotomy and secured to the LV apex with a gimbaled sewing ring, which allowed for intraoperative adjustment of the insertion depth and angle of the inflow cannula. Serum analytes and coagulation parameters were analyzed at specific intervals throughout the study period. Pump flow, speed, and power were recorded daily to monitor device performance. Sheep were electively euthanized at 90 days for pathologic and histologic analysis. In this study, results demonstrated the safety, reliability, hemocompatability, and biocompatibility of the MVAD Pump. Nine animals were implanted for 90 ± 5 days. No complications occurred during surgical implantation. Seven of the 9 animals survived until elective sacrifice. Each sheep that survived to the scheduled explant appeared physically normal, with no signs of cardiovascular or other organ compromise. The 2 sheep that were euthanized early showed no evidence of device-related issues. The MVAD Pump was successfully implanted through a thoracotomy and demonstrated excellent hemodynamic support with no device malfunctions throughout the study period.

Plerixafor (AMD3100) induces prolonged mobilization of acute lymphoblastic leukemia cells and increases the proportion of cycling cells in the blood in mice

The CXCR4 antagonist Plerixafor (AMD3100) induces the rapid mobilization of hematopoietic stem and progenitor cells into the blood in mice and humans. AMD3100 similarly induces the mobilization of human acute lymphoblastic leukemia (ALL) cells into the blood in mice. In this study, the temporal response of pre-B ALL cells to AMD3100 was compared with that of normal hematopoietic progenitor cells (HPC) using an NOD/SCID xenograft model of ALL and BALB/c mice, respectively. ALL cells remained in the circulation up to 6 hours after AMD3100 administration, by which time normal HPCs were no longer detectable. AMD3100 also increased the proportion of actively cycling ALL cells in the peripheral blood. Together, these data suggest that ALL cells are more sensitive to the effects of bone marrow disruption than normal progenitors. Using the NOD/SCID xenograft model, we demonstrated that AMD3100 increased the efficacy of the cell cycle specific drug vincristine, resulting in reduced disease levels in the blood and spleens of animals over 3 weeks and extended the survival of NOD/SCID mice with ALL. These data demonstrate that mobilizing agents can increase the therapeutic effect of cell cycle dependent chemotherapeutic agents.

Bioengineered human and allogeneic pulmonary valve conduits chronically implanted orthotopically in baboons: Hemodynamic performance and immunologic consequences

This study assesses in a baboon model the hemodynamics and human leukocyte antigen immunogenicity of chronically implanted bioengineered (decellularized with collagen conditioning treatments) human and baboon heart valve scaffolds. Fourteen baboons underwent pulmonary valve replacement, 8 with decellularized and conditioned (bioengineered) pulmonary valves derived from allogeneic (N = 3) or xenogeneic (human) (N = 5) hearts; for comparison, 6 baboons received clinically relevant reference cryopreserved or porcine valved conduits. Panel-reactive serum antibodies (human leukocyte antigen class I and II), complement fixing antibodies (C1q binding), and C-reactive protein titers were measured serially until elective sacrifice at 10 or 26 weeks. Serial transesophageal echocardiograms measured valve function and geometry. Differences were analyzed with Kruskal-Wallis and Wilcoxon rank-sum tests. All animals survived and thrived, exhibiting excellent immediate implanted valve function by transesophageal echocardiograms. Over time, reference valves developed a smaller effective orifice area index (median, 0.84 cm(2)/m(2); range, 1.22 cm(2)/m(2)), whereas all bioengineered valves remained normal (effective orifice area index median, 2.45 cm(2)/m(2); range, 1.35 cm(2)/m(2); P = .005). None of the bioengineered valves developed elevated peak transvalvular gradients: 5.5 (6.0) mm Hg versus 12.5 (23.0) mm Hg (P = .003). Cryopreserved valves provoked the most intense antibody responses. Two of 5 human bioengineered and 2 of 3 baboon bioengineered valves did not provoke any class I antibodies. Bioengineered human (but not baboon) scaffolds provoked class II antibodies. C1q(+) antibodies developed in 4 recipients. Valve dysfunction correlated with markers for more intense inflammatory provocation. The tested bioengineering methods reduced antigenicity of both human and baboon valves. Bioengineered replacement valves from both species were hemodynamically equivalent to native valves.

Internal Aortic Annuloplasty: A Novel Technique

ABSTRACTBackground: The purpose of this study was to define an experimental model and a reproducible surgical technique for the preclinical assessment of safety and biocompatibility of a novel intra-annular internal aortic annulus repair device. Methods: Adult sheep were implanted with HAART Inc's 19 mm aortic annulus repair device via a transverse aortotomy using standard anesthetic, surgical, and cardiopulmonary bypass techniques. Animals were closely monitored throughout the study period until the time of elective sacrifice at 30 or 60 days. Results: Six adult sheep, mean age 63.2 weeks, mean weight 68.8 kg, underwent aortic annuloplasty with a 19 mm annuloplasty frame. Five of the sheep remained stable until scheduled sacrifice. The primary outcome of this study was animal mortality. Early mortality was seen in only one animal (16.7%), due to a surgical complication. Mild-to-moderate aortic insufficiency was observed in all animals upon echocardiographic examination at the time of elective sacrifice. Conclusions: Of the six animals that underwent aortic annuloplasty, there was one early death due to surgical complication. The remaining five subjects were clinically stable at the time of elective sacrifice. Any conclusions regarding the cause of the observed aortic insufficiency are beyond the scope of this feasibility study but would need to be fully evaluated in the preclinical assessment of any internal aortic annuloplasty device. We have shown that we have developed a reproducible surgical technique in a physiologically appropriate model for the preclinical assessment of internal aortic annulus repair devices.

Pediatric Cardiopulmonary Bypass Adaptations for Long-Term Survival of Baboons Undergoing Pulmonary Artery Replacement

Cardiopulmonary bypass (CPB) protocols of the baboon (Papio cynocephalus anubis) are limited to obtaining experimental data without concern for long-term survival. In the evaluation of pulmonary artery tissue engineered heart valves (TEHVs), pediatric CPB methods are adapted to accommodate the animals’ unique physiology enabling survival up to 6 months until elective sacrifice. Aortic access was by a 14F arterial cannula and atrial access by a single 24F venous cannula. The CPB circuit includes a 3.3 L/min flow rated oxygenator, ¼″ × ⅜″ arterial-venous loop, ⅜″ raceway, and bubble trap. The prime contains 700 mL Plasma-Lyte, 700 units heparin, 5 mL of 50% dextrose, and 20 mg amiodarone. Heparinization (200 u/kg) targets an activated clotting time of 350 seconds. Normothermic CPB was initiated at a 2.5 L/m2/min cardiac index with a mean arterial pressure of 55–80 mmHg. Weaning was monitored with transesophageal echocardiogram. Post-CPB circuit blood was re-infused. Chest tubes were removed with cessation of bleeding. Extubation was performed upon spontaneous breathing. The animals were conscious and upright 3 hours post-CPB. Bioprosthetic valves or TEHVs were implanted as pulmonary replacements in 20 baboons: weight = 27.5 ± 5.6 kg, height = 73 ± 7 cm, body surface area = 0.77 m2± 0.08, mean blood flow = 1.973 ± .254 L/min, core temperature = 37.1 ± .1°C, and CPB time = 60 ± 40 minutes. No acidosis accompanied CPB. Sixteen animals survived, four expired. Three died of right ventricular failure and one of an anaphylactoid reaction. Surviving animals had normally functioning replacement valves and ventricles. Baboon CPB requires modifications to include high systemic blood pressure for adequate perfusion into small coronary arteries, careful CPB weaning to prevent ventricular distention, and drug and fluid interventions to abate variable venous return related to a muscularized spleno-splanchnic venous capacity.

The mTOR Inhibitor RAD001 (Everolimus) Improves Survival in Preclinical Models of Primary Human ALL.

The Akt/mammalian target of rapamycin (mTOR) signaling pathway is a potential target in acute lymphoblastic leukemia (ALL) due to its constitutive expression and critical role in regulating leukemic cell growth and survival. In this study, we investigated whether RAD001 (Everolimus, Novartis), is effective as a therapeutic agent in a murine model of human ALL. Leukemic cells from 5 separate patient samples were injected into sub-lethally irradiated NOD/SCID mice and treatment was started after leukemia was clearly detectable in the blood (>5% peripheral blasts) and continued for 4 weeks. In 2 of 3 cases examined, animals treated with RAD001 as a single agent (5mg/kg, 3 times weekly) showed 2 to12-fold reduction in the number of circulating blasts and 2.5 to 30-fold decrease in splenomegaly after only 7 days of treatment (p<0.01). In 1 case, blasts completely disappeared by 14 days of treatment accompanied by recovery of normal hematopoiesis. In contrast vehicle treated mice showed progressive leukemia. In all 5 cases examined, decreased leukemic burden was associated with increased survival, with a median survival of 52 days in the RAD001 treated mice compared to 24 days in the control group (p<0.02 for all samples). Combination treatment with RAD001 and Vincristine (0.15–0.25 mg/kg, weekly) was more effective than either agent alone in reducing leukemic cell count and prolonging survival (p<0.02 compared to Vincristine alone). In one case, all mice treated with either RAD001 alone or RAD001 plus Vincristine survived for greater than 10 weeks following the completion of treatment and only one animal (RAD001 treated) showed signs of disease on elective sacrifice. Cell cycle analysis of cells recovered from the spleens of RAD001 treated animals revealed an arrest in the G0/G1 phase. Furthermore, electron microscopy demonstrated the predominant appearance of autophagy as well as limited apoptosis in cells within the sternums of treated animals. In conclusion, we have demonstrated the efficacy of RAD001 alone or with a subtherapeutic dose of Vincristine in an in vivo leukemia model. These preclinical results support further clinical development of mTOR inhibitors for the treatment of ALL patients. RAD001 may provide significant therapeutic benefit when used alone, or in combination with standard chemotherapy agents such as Vincristine.

Transcolonic ventral wall hernia mesh fixation in a porcine model

A natural orifice transluminal endoscopic surgery (NOTES) approach to ventral wall hernia repair may represent a potentially less invasive alternative to current transabdominal surgical techniques. We aimed to investigate the feasibility of using transcolonic NOTES to deliver hernia repair mesh into the peritoneal cavity, as well as the ability to manipulate composite mesh and secure it to the abdominal wall. Five pigs weighing 20 to 25 kg were used in this feasibility study involving two acute and three survival experiments. A prototype mesh delivery system was used to transfer 1.5 - 2-cm x 2.5 - 3-cm pieces of composite hernia mesh into the peritoneal cavity. Neodymium magnets on a prototype control arm were used to help position the mesh by magnetically engaging previously placed endoscopic clips. Transfascial fixation of the mesh with 3-0 monofilament sutures was achieved using a 19-gauge hollow needle, pusher wire, and a suture tag system. Composite hernia mesh was successfully transferred and secured in 5/5 attempts. All three survival animals thrived for 14 days prior to elective sacrifice. At necropsy, the mesh sites were found to be well peritonealized without adhesions. Suture placement through the posterior fascia was confirmed in 10/12 sutures. Of these, four sutures were within the abdominal musculature, and two sutures were through the anterior fascia (transfascial). Transcolonic delivery, transcutaneous magnetic manipulation, and fixation of composite hernia mesh are technically feasible in a porcine model with animal survival. An effective suturing method that allows consistent anchoring through the anterior fascia would be preferred and may require the development of novel devices.

Transcolonic Ventral Wall Hernia Mesh Fixation in a Porcine Model

BACKGROUND AND STUDY AIMS: A natural orifice transluminal endoscopic surgery (NOTES) approach to ventral wall hernia repair may represent a potentially less invasive alternative to current transabdominal surgical techniques. We aimed to investigate the feasibility of using transcolonic NOTES to deliver hernia repair mesh into the peritoneal cavity, as well as the ability to manipulate composite mesh and secure it to the abdominal wall. METHODS: Five pigs weighing 20 to 25 kg were used in this feasibility study involving two acute and three survival experiments. A prototype mesh delivery system was used to transfer 1.5 - 2-cm × 2.5 - 3-cm pieces of composite hernia mesh into the peritoneal cavity. Neodymium magnets on a prototype control arm were used to help position the mesh by magnetically engaging previously placed endoscopic clips. Transfascial fixation of the mesh with 3-0 monofilament sutures was achieved using a 19-gauge hollow needle, pusher wire, and a suture tag system. RESULTS: Composite hernia mesh was successfully transferred and secured in 5/5 attempts. All three survival animals thrived for 14 days prior to elective sacrifice. At necropsy, the mesh sites were found to be well peritonealized without adhesions. Suture placement through the posterior fascia was confirmed in 10/12 sutures. Of these, four sutures were within the abdominal musculature, and two sutures were through the anterior fascia (transfascial). CONCLUSIONS: Transcolonic delivery, transcutaneous magnetic manipulation, and fixation of composite hernia mesh are technically feasible in a porcine model with animal survival. An effective suturing method that allows consistent anchoring through the anterior fascia would be preferred and may require the development of novel devices.

Development of an ambulatory artificial lung in an ovine survival model.

We are developing an artificial lung (AL) as an eventual bridge to lung transplant or recovery. The device is rigidly housed, noncompliant, and has a very low resistance to blood flow. In eight sheep, arterial cannulae were anastomosed end-to-side to the proximal and distal main pulmonary artery, and attached to the AL. A pulmonary artery snare between anastomoses diverted full pulmonary blood flow through the AL. Eight of eight sheep survived the preparation. Mean pressure gradient across the AL was 8 mm Hg (3 Wood units; 8 mm Hg/2.8 L/min). Four of eight sheep tolerated immediate full diversion of blood flow and died at 24 and 40 hours (exsanguination) or 168 and 168 hours (elective sacrifice). Four of eight sheep were intolerant of full flow: two died of right heart failure at <8 hours with full flow through the device (full snare); the other two survived with partial device flow (partial snare), but the device clotted. These two then underwent successful closed-chest cannula thrombectomy and device change-out at 53 and 75 hours, and subsequently tolerated full flow. Long-term (up to 7 day) survival with complete diversion of pulmonary blood flow through a non-compliant, low-resistance AL is possible. Initial right heart failure in this model was 50% (4 of 8).

Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model.

To assess whether Cyclosporine A (CsA) or cycloheximide (CHX) can reduce ischemia-induced neurological damage by blocking apoptotic pathways, we assessed their effects on cerebral recovery in a chronic animal model of hypothermic circulatory arrest (HCA). Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In this blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), given intravenously before and subcutaneously for 7 days after HCA, or a single dose of 1 mg/kg CHX (n=8), given after weaning from cardiopulmonary bypass. Hemodynamics, intracranial pressure (ICP) and neurophysiological data (EEG, SSEP) were assessed for 3 h after HCA; early behavioral recovery was scored, and neurological/behavioral evaluation (9=normal) was carried out daily until elective sacrifice on postoperative day (POD) 7. Brains were selectively perfused and evaluated histopathologically for apoptosis. Basic hemodynamic data revealed no differences between CsA or CHX and control groups. ICP was significantly lower throughout rewarming (P=0.009) and reperfusion (P=0.05) in the CsA group. EEG recovery 3 h after HCA was observed in four of eight CsA animals but in only 1 of 12 controls (P=0.11) and one of eight CHX animals; cortical SSEP recovery also seemed faster in CsA animals, but failed to reach significance. Some early recovery scores were significantly better in the CsA group, and daily behavioral scores were consistently and significantly higher in the CsA-treated animals from POD1 through POD4. The data indicate that treatment with Cyclosporine A but not cycloheximide has a positive effect on cerebral recovery following HCA. Whether CsA results in inhibition of neuronal apoptosis, and/or inhibits release of cytokines and thereby reduces postischemic cerebral edema remains to be elucidated. The neuroprotective effect of CsA, if confirmed in further studies, would make its clinical application conceivable.

Biomembrane Mimicry Provides Improved Thromboresistance for Total Artificial Hearts

Thromboembolic events remain a significant issue in mechanical circulatory support. The aim of this study was to evaluate the potential benefit of surface modification in total artificial hearts (TAHs) using polymeric phospholipids (biomembrane mimicry). For this purpose, pneumatic TAHs (vacuum formed pellethane housing, hard double flap hinged inflow valves, soft trileaflet polyurethane outflow valves) had their blood-exposed surfaces either modified with polymeric phospholipids or unmodified before evaluation in bovine experiments. Orthotopic implantation of the TAHs was performed with cardiopulmonary bypass (CPB) using tip-to-tip heparin surface coated perfusion equipment and very low systemic heparinization (50 IU/kg bodyweight). After weaning from CPB and stabilizing hemodynamics, circulating heparin was neutralized with protamine (1:1). All animals were totally supported for 24 hours before elective sacrifice. No heparin was added at any time during support. Mean activated coagulation time (ACT) was 167+/-24 s at baseline before heparinization for CPB, 330+/-45 s at the end of CPB, 181+/-25 s after 1 hour of support, 180+/-31 s after 6 hours, and 185+/-28 s after 18 hours. After explantation, the TAHs perfused without anticoagulation were carefully analyzed. Atrial cuff coverage with red clot was 30+/-21% for artificial surfaces modified by biomembrane mimicry versus 100+/-0% for standard control surfaces (p<0.01). The number of macroscopic deposits found on the inflow valves was 1.33+/-0.47 for surfaces modified by biomembrane mimicry versus 3.83+/-1.86 for standard control surfaces (p<0.05). Likewise, on the outflow valves the number of macroscopic deposits was 0.00+/-0.00 for surfaces modified by biomembrane mimicry versus 1.00+/-0.81 for standard control surfaces (p<0.05). We conclude that presence and distribution of red clots and other macroscopic deposits are significantly different for artificial surfaces with biomembrane mimicry versus standard control surfaces. Application of the biomembrane mimicry concept has the potential to provide improved TAHs.

Retrograde cerebral perfusion enhances cerebral protection during prolonged hypothermic circulatory arrest: a study in a chronic porcine model

Background. This study was undertaken to confirm earlier findings that retrograde cerebral perfusion (RCP) can improve cerebral outcome after prolonged hypothermic circulatory arrest (HCA), and to determine whether RCP with inferior vena caval occlusion, which is more effective in removing particulate emboli, is superior to conventional RCP in enhancing cerebral protection. Methods. Sixty-two pigs (27 to 30 kg) were randomly assigned to undergo one of the following for 90 minutes at 20°C: antegrade cerebral perfusion (ACP); conventional RCP (RCP); RCP with occlusion of the inferior vena cava (RCP-O), or HCA with the head packed in ice. RCP flow was regulated to a sagittal sinus pressure of 20 mm Hg. Hemodynamic, electrophysiologic, and metabolic monitoring were carried out until 4 hours after rewarming, daily behavioral and neurologic assessments until elective sacrifice on day 7, and histologic analysis of the brain after death. Results. Complete behavioral recovery was seen in all surviving animals by day 5 after ACP or RCP, but in only 83% after RCP-O and 50% after HCA ( p = 0.001). A histopathologic score of 2 or more, indicating more than mild injury, was not found in any animal after ACP, in 27% after RCP, in 47% after HCA, and in 68% after RCP-O ( p = 0.002). The median oxygen consumption was 6.66 mL/min after ACP, 1.37 mL/min with RCP, and 1.02 mL/min with RCP-O ( p < 0.0001). The median amount of fluid sequestered was 2,450 mL after RCP-O, 760 mL after RCP, and −200 mL after ACP ( p < 0.0001). Conclusions. Conventional RCP without inferior vena caval occlusion results in a significantly better outcome than RCP-O after prolonged HCA, despite more efficient cerebral perfusion during RCP-O, and also provides cerebral protection superior to prolonged HCA alone, but care must be taken during its implementation to minimize cerebral edema and other possible causes of retroperfusion-related cerebral injury.

Long-Term Evaluation of Orthotopically Implanted Stentless Bioprosthetic Aortic Valves in Juvenile Sheep

The aim of this study was to develop a technically feasible and reproducible model for chronic evaluation of stentless bioprosthetic aortic valves implanted orthotopically using juvenile domestic sheep. This report summarizes the results of a study conducted to assess orthotopically placed 19-mm stentless aortic bioprosthetic valves. Twenty-seven juvenile sheep underwent aortic valve replacement. Standard cardiopulmonary bypass techniques were followed. The average cardiopulmonary bypass time was 73 min. No chronic anticoagulation was used. There were two deaths (7%) due to surgical complications. In the remaining 25 experiments, 11 animals (41%) died prior to the scheduled sacrifice on postoperative day 150. One early death occurred due to coccidiomycosis infection, one due to technical error, one due to pulmonary embolus, four due to prosthetic annular size disproportion, and four due to thrombi. The remaining 14 animals (52%) underwent left and right heart catheterization, angiography, echocardiography, and sacrifice after postoperative day 150. The average weight of the sheep at elective sacrifice was 60 kg (mean weight gain 12.5 kg). The average cardiac output for the sacrificed animals was 5.1 L/min. The mean velocity of blood across the aortic valve for the sacrificed animals was 317 cm/s and the mean pressure gradient was 26.2 mm Hg. Two features suggest that this model may have broad application. First, we have demonstrated that it is technically feasible to evaluate orthotopically placed stentless bioprosthetic aortic valves in growing sheep. Second, the aortic root size of the juvenile sheep allows for implantation and evaluation of a human size aortic valve (19 mm). We believe that this model is reproducible and can be used to study stentless valve designs.

Chronic Evaluation of Orthotopically Implanted Bileaflet Mechanical Aortic Valves in Adult Domestic Sheep

This study was intended to develop a technically feasible and reproducible model for chronic hemodynamic and mechanical evaluation of orthotopically implanted bileaflet mechanical aortic valves in adult domestic sheep. Three adult sheep (mean age 22 weeks, mean weight 76 kg) underwent aortic valve replacement using 19-mm bileaflet aortic valves. Standard cardiopulmonary bypass techniques were followed, including mild hemodilution, systemic hypothermia, and cardioplegic arrest. After performing a left fourth intercostal thoracotomy, the valves were placed using interrupted 3-0 Ticron (Davis + Geck) inverted mattress sutures through a transverse aortotomy. The averáge cardiopulmonary bypass time was 58 ± 1 min. No chronic anticoagulation was used. There were no surgical complications. All three animals (100%) remained clinically well until elective sacrifice after postoperative day 150. The average cardiac output for the animals at sacrifice was 3.8 ± 1.0 L/min. The mean aortic ejection velocity was 304.7 ± 47.3 cm/s and the mean pressure gradient was 24.6 ± 6.7 mm Hg. There was no clinically significant thrombus formation or paravalvular leaks. Thus, we have demonstrated that it is technically feasible to orthotopically implant mechanical aortic valves in sheep. There are several features that contribute to the success of this model, including use of a transverse aortotomy, adequate de-airing, and the use of mild hemodilution during bypass. We believe that this model is reproducible and can be used to study other valve designs. In addition, this model allows for site-specific preclinical assessment of new or modified mechanical heart valves.

Improved growth with bioabsorbable sutures in both high- and low-pressure zones

Compromised growth after operation remains a significant problem in the cardiovascular field. Some benefit of absorbable suture materials has been demonstrated for arterial anastomoses. However, for the low-pressure zone, few data are available. To assess growth in high- versus low-pressure zones we transected the abdominal aorta (high-pressure zone) as well as the inferior vena cava (low-pressure zone) in 10 young mongrel dogs using for reanastomosis 7-0 nonabsorbable versus absorbable running sutures in random order. All animals survived and were evaluated over 12 months including body weight (gain, 212% +/- 45% for nonabsorbable versus 218% +/- 8% for absorbable; not significant), angiography, and, after elective sacrifice, detailed studies of aorta and vena cava. Systematic complication of angiographic data at 12 months showed at the suture level an area of 13.8 mm2 for nonabsorbable versus 24.3 +/- 14.4 mm2 for absorbable sutures in the high-pressure zone as compared with 12.9 +/- 4.9 mm2 for nonabsorbable versus 25.3 +/- 15.4 mm2 for absorbable sutures in the low-pressure zone. Residual lumen, calculated as a function of the area above and below the suture, accounted for 35% +/- 10% for nonabsorbable versus 92% +/- 12% for absorbable sutures (p < 0.001) in the high-pressure zone as compared with 37% +/- 13% for nonabsorbable versus 75% +/- 15% for absorbable sutures (p < 0.003) in the low-pressure zone (high versus low, not significant). Poststenotic dilatation accounted for 199% +/- 22% for nonabsorbable versus 126% +/- 43% for absorbable sutures (p < 0.01) in the high-pressure zone. In the low-pressure zone, poststenotic dilatation remained below the inflow area, and the residual poststenotic lumen accounted for 52% +/- 14% for nonabsorbable versus 77% +/- 16% for absorbable sutures (p < 0.004). Macroscopic, light, and scanning electron microscopic studies confirmed different growth patterns in high- versus low-pressure zones. Aortic narrowing resulted in poststenotic dilatation and unrestricted outflow path (hourglass-type stenosis). Caval narrowing was followed by restriction of poststenotic outflow path (funnel-type stenosis). Absorbable suture material allows for superior growth in both high- and low-pressure zones.

The effects of prolonged treatment with citicoline in temporary experimental focal ischemia

Potential therapeutic effects of cytidine 5-diphosphocholine (citicoline), a key intermediary in the biosynthesis of the membrane phospholipid, phosphatidylcholine, are presumably related to enhanced phospholipid synthesis in the ischemic brain. We evaluated prolonged citicoline treatment in a temporary focal ischemia model. Using the suture occlusion model, we induced 2 hours of temporary ischemia in 30 Sprague-Dawley rats. The rats were randomly and blindly assigned to receive intraperitoneally 500 mg/kg citicoline (HD), 100 mg/kg citicoline (LD) or physiologic saline as the control group once daily for 7 days ( n = 10 per group) beginning at the time of reperfusion. Neurological scoring (0–5 scale) was performed daily. After elective sacrifice on day 7, or earlier if death occured prematurely, the brains underwent 2,3,5-triphenyltetrazolium chloride (TTC) staining for calculation of corrected infarct and edema volume. The mean corrected infarct volume in the HD group was 125 ± 45.2 mm 3 (mean ± SD), significantly smaller than controls, 243.5 ± 88.6 mm 3 ( p < 0.01, Scheffe's-test). The LD group infarct volume was 200.2 ± 62.8 mm 3 (N.S.). The mean amount of brain edema in the HD group was 46.4 ± 45.6 mm 3 was smaller than the controls, 92.3 ± 54.4 mm 3 and the LD group, 84.9 ± 71.7 mm 3 (N.S.). Mortality before day 7 in the HD was 30% while it was 50% in the two other groups. The neurologic score on day 7 was 2.5 ± 1.8 in the HD group, 3.3 ± 1.8 in the LD group and 3.4 ± 1.7 in controls (N.S.). These results demonstrate that extended high dose citicoline treatment significantly reduced infarct volume in this temporary focal ischemia model and that there was a trend toward reducing brain edema and mortality. These effects may be related to membrane stabilization and inhibition of free fatty acid release.

Effects of cardiomyoplasty on cardiac growth in rats.

Cardiomyoplasty (CMP) has been proposed as a treatment for pediatric patients, but restriction of cardiac growth by the muscle wrap is a potential source of concern. This possibility was investigated in an immature animal model. Six-week-old rats (body weight 203.8 +/- 5.4 g, mean +/- SEM) underwent either left thoracotomy with CMP (group I, n = 7), or thoracotomy without CMP (group II, n = 8). A third group (group III, n = 7) served as untreated controls. Final measurements were made 20 weeks later after body weights had reached a plateau. Preoperative body weights were not significantly different between the groups. At elective sacrifice, the body weights of animals that underwent surgery did not differ significantly (group I, 558.0 +/- 21.5 g and group II, 617.3 +/- 20.3 g), but were significantly less than those of control animals (727.6 +/- 13.3 g, p < 0.001 and p < 0.01, respectively). Cardiac ventricular weights in the CMP group were significantly less than those of control animals (group I, 1.21 +/- 0.06 g; group III 1.45 +/- 0.04 g; p < 0.01), but were not statistically different from those of the sham thoracotomy group (group II, 1.36 +/- 0.05 g). Mean left ventricular end-diastolic volumes were similar in all groups (group I, 0.67 +/- 0.07 mL; group II, 0.66 +/- 0.07 mL; and group III, 0.69 +/- 0.10 mL; p = ns). A major surgical procedure impairs growth in juvenile rats. no evidence emerged from this study for additional restriction of cardiac development due to cardiac wrapping. However, studies that include stimulated muscle wraps are needed before CMP should be considered for the pediatric age group.

Polymeric stenting in the porcine coronary artery model: Differential outcome of exogenous fibrin sleeves versus polyurethane-coated stents

Objectives. In a porcine coronary model, fibrin film soaked for 3 h in heparin was used as a circumferential coating on a tantalum stent to assess the effect of this naturally occurring biopolymer on arterial healing. The results were compared with those obtained with medical grade polyurethane-coated stainless steel stents.Background. Thrombus plays an important role in healing after arterial injury and may affect the development of neointimal hyperplasia. Manipulation of the initial thrombus may alter the healing response. To study this, we placed a template of fibrin in a porcine coronary artery restenosis model.Methods. Thirty-four fibrin film stents were delivered in 20 swine. Oversizing was avoided, to prevent deep arterial injury, by placement of optimally sized stents. Initial patency of the syented vessel was confirmed by angiography.Results. Three fibrin-stented swine died within 48 h; in each, the stent was occluded with a fibrin/red blood cell mass. In two of these three, a portion of the exogenous fibrin had become detached from the stent and partially occluded the lumen. Of the remaining 31 stents, all were patent at elective sacrifice at 28 days. Eightyfour percent had a diameter stenosis <50%, and the mean (± SD) diameter stenosis was 32.3 ± 13%. There was no evidence of significant foreign-body giant-cell reaction. These results contrasted with the medical grade polyurethane-coated stents placed according to the same protocol without oversizing. Twelve of these stents were placed; six swine died of thrombotic occlusion within the 1st 48 h. At elective sacrifice at 28 days, the remaining polyurethane-coated stents were occluded by marked neointimal hyperplasia.Conclusions. Fibrin film-coated stents seem promising as a template for modifying the local response to arterial injury and for potentially decreasing restenosis rates.

A Clinical Study of the Parameters and Effects of Temporary Arterial Occlusion in the Management of Intracranial Aneurysms

Temporary occlusion of intracranial arteries has emerged as a valuable technical adjunct in the management of intracranial aneurysms. The current study considered 121 patients (from a group of 234 consecutive aneurysm patients treated during a 2-yr period) who underwent elective temporary arterial occlusion. Twenty-one patients were excluded from further study because of an intraoperative rupture of an aneurysm, the elective sacrifice of afferent or efferent vessels, or the performance of an extracranial-intracranial arterial bypass graft; the remaining 100 patients underwent elective temporary occlusion under a standard neuroanesthetic regimen, including etomidate-induced burst suppression, normotension, normovolemia, and normothermia. In the postoperative period, radiographic evidence of ischemic brain injury in the distribution of the arteries occluded was selected as the end point for the failure of occlusion tolerance. The parameters evaluated with respect to this end point included the duration and nature of the temporary arterial occlusion, the number of the occlusive episodes, the specific vascular territory occluded, patient age, neurological status, presence of subarachnoid hemorrhage, vasospasm, and aneurysm size. Several parameters were found to be related to the postoperative development of ischemic injury. Patients more than 61 years of age and those in poor neurological condition (Hunt and Hess Grades III to IV) did not tolerate temporary occlusion as well as patients who were younger and in better condition. Patients occluded for less than 14 minutes routinely tolerated the iatrogenic ischemia; the 95% confidence level for the toleration of occlusion without the development of infarction occurred at 19 minutes. All patients occluded for more than 31 minutes had both clinical and radiographic evidence of cerebral infarction.(ABSTRACT TRUNCATED AT 250 WORDS)