VAVD vacuum may cause bubble transgression in membrane oxygenators.

BACKGROUND:: Vacuum-assisted venous drainage (VAVD) is widely used to enhance venous blood return from patients undergoing cardiopulmonary bypass (CPB). This vacuum can accidentally reach the oxygenator of the heart-lung machine and draw gas bubbles into the blood. This is known as bubble transgression (BT) and may cause air emboli in the arterial blood line. In order to avoid BT and minimize the risk of patient injury, knowledge of oxygenator tolerance to vacuum load is critical. Thus, the main aim of this thesis was to investigate how much vacuum a membrane oxygenator can withstand before BT appears. METHODS:: We investigated four different adult oxygenators: Quadrox-i, Affinity Fusion, Capiox RX25 and Inspire 6M. They were tested in an in vitro setup where VAVD vacuum was allowed to reach the oxygenator through a non-occlusive roller pump. An ultrasonic clinical bubble counter, Gampt BCC 200, was used to count bubbles on the arterial line when the arterial pump was restarted. RESULTS:: We observed a significant increase in bubble count for two of the oxygenators, caused by -30 mmHg of VAVD vacuum in the blood reservoir (Affinity Fusion and Inspire 6M). Massive air ingress was shown in two of the oxygenators, caused by -30 mmHg of VAVD vacuum in the reservoir (Capiox RX25) and -40 mmHg of VAVD vacuum in the reservoir (Affinity Fusion). CONCLUSION:: VAVD vacuum may cause bubble transgression in an oxygenator. This was shown for all the oxygenators in this test. VAVD vacuum may cause visible massive air ingress in an oxygenator. This was shown for two of the oxygenators in this test (Capiox RX25 and Affinity Fusion). An alarm triggering on negative pressure in the oxygenator or a pressure relief valve might improve safety when using VAVD.

Heparin-coated cardiopulmonary bypass circuits selectively deplete the pattern recognition molecule ficolin-2 of the lectin complement pathway in vivo.

The complement system can be activated via the lectin pathway by the recognition molecules mannose-binding lectin (MBL) and the ficolins. Ficolin-2 exhibits binding against a broad range of ligands, including biomaterials in vitro, and low ficolin-2 levels are associated with increased risk of infections. Thus, we investigated the biocompatibility of the recognition molecules of the lectin pathway in two different types of cardiopulmonary bypass circuits. Bloods were drawn at five time-points before, during and postoperatively from 30 patients undergoing elective cardiac surgery. Patients were randomized into two groups using different coatings of cardiopulmonary bypass circuits, Phisio® (phosphorylcholine polymer coating) and Bioline® (albumin-heparin coating). Concentrations of MBL, ficolin-1, -2 and -3 and soluble C3a and terminal complement complex (TCC) in plasma samples were measured. Ficolin-3-mediated complement activation potential was evaluated with C4, C3 and TCC as output. There was no significant difference between the two circuit materials regarding MBL, ficolin-1 and -3. In the Bioline® group the ficolin-2 levels decreased significantly after initiation of surgery (P < 0.0001) and remained reduced throughout the sampling period. This was not seen for Phisio®-coated circuits. Ficolin-3-mediated complement activation potential was reduced significantly in both groups after start of operation (P < 0.0001), whereas soluble C3a and TCC in the samples were increased (P < 0.0001). Ficolin-2 was depleted from plasma during cardiac surgery when using heparin-coated bypass circuits and did not reach baseline level 24 h postoperation. These findings may have implications for the postoperative susceptibility to infections in patients undergoing extracorporeal circulation procedures.

High-intensity interval training improves peak oxygen uptake and muscular exercise capacity in heart transplant recipients.

Heart transplant (HTx) recipients usually have reduced exercise capacity with reported VO(2peak) levels of 50-70% predicted value. Our hypothesis was that high-intensity interval training (HIIT) is an applicable and safe form of exercise in HTx recipients and that it would markedly improve VO(2peak.) Secondarily, we wanted to evaluate central and peripheral mechanisms behind a potential VO(2peak) increase. Forty-eight clinically stable HTx recipients >18 years old and 1-8 years after HTx underwent maximal exercise testing on a treadmill and were randomized to either exercise group (a 1-year HIIT-program) or control group (usual care). The mean ± SD age was 51 ± 16 years, 71% were male and time from HTx was 4.1 ± 2.2 years. The mean VO(2peak) difference between groups at follow-up was 3.6 [2.0, 5.2] mL/kg/min (p < 0.001). The exercise group had 89.0 ± 17.5% of predicted VO(2peak) versus 82.5 ± 20.0 in the control group (p < 0.001). There were no changes in cardiac function measured by echocardiography. We have demonstrated that a long-term, partly supervised and community-based HIIT-program is an applicable, effective and safe way to improve VO(2peak) , muscular exercise capacity and general health in HTx recipients. The results indicate that HIIT should be more frequently used among stable HTx recipients in the future.

Proliferation signal inhibitors and post-transplant malignancies in heart transplantation: practical clinical management questions.

Although malignancy is a major threat to long-term survival of heart transplant (HT) recipients, clear strategies to manage immunosuppression in these patients are lacking. Several lines of evidences support the hypothesis of an anticancer effect of proliferation signal inhibitors (PSIs: mammalian target of rapamycin [mTOR] inhibitors) in HT recipients. This property may arise from PSI's ability to replace immunosuppressive therapies that promote cancer progression, such as calcineurin inhibitors or azathioprine, and/or through their direct biological actions in preventing tumor development and progression. Given the lack of randomized studies specifically exploring these issues in the transplant setting, a collaborative group reviewed current literature and personal clinical experience to reach a consensus aimed to provide practical guidance for the clinical conduct in HT recipients with malignancy, or at high risk of malignancy, with a special focus on advice relevant to potential role of PSIs.

Biocompatibility and pathways of initial complement pathway activation with Phisio- and PMEA-coated cardiopulmonary bypass circuits during open-heart surgery.

A randomized open-heart surgery study comprising 30 patients was undertaken to compare the biocompatibility of Phisio-(phosphorylcholine) and PMEA-(poly-2-methoxyethyl acrylate) coated cardiopulmonary bypass (CPB) circuits and to assess the initial complement pathway activation during open-heart surgery. Blood samples were obtained at five time points, from the start of surgery to 24 hours postoperatively. The following analyses were performed: haemoglobin, lactate dehydrogenase, leukocyte and platelet counts, myeloperoxidase and neutrophil-activating peptide-2, thrombin-anti-thrombin complexes, syndecan-1 and the complement activation products C1rs-C1-inhibitor complexes, C4bc, C3bc, C3bBbP and the terminal complement complex (TCC). No significant inter-group difference was found in any parameters, except for the concentration of TCC which was moderately lower in the PMEA group at termination of CPB. Complement activation during open-heart surgery was mainly mediated through the alternative pathway. In conclusion, PMEA- and Phisio-coated circuits displayed similar biocompatibility with respect to inflammatory and haemostatic responses during and after open-heart surgery.

In vitro and in vivo evaluation of Dideco's paediatric cardiopulmonary circuit for neonates weighing less than five kilograms.

The neonate cardiopulmonary bypass (CPB) circuit, including a KIDS D100 oxygenator (The Sorin Group, Mirandola, Italy) and a D130 arterial filter (The Sorin Group), was evaluated in vitro with respect to the removal of free micro gas bubbles. No gas bubbles > 40microm were measured after the arterial filter D130 upon manual introduction of 10 ml of air into the venous line or during the use of vacuum-assisted venous drainage (VAVD). The D130 arterial filter removed 88 % of gas bubbles < 40 microm during manual introduction of air into the venous line; however, only 50 % of gas bubbles < 40 microm were removed during the use of VAVD. The same CPB circuit was evaluated in vivo to compare with another CPB circuit, including a D901 oxygenator (The Sorin Group) and arterial filter D736 (The Sorin Group), in 155 neonates weighing < or =5 kg. The D100 circuit required significantly less priming volume than the D901 circuit. Postoperative haemoglobin was significantly higher, artificial ventilation time was significantly shorter and postoperative bleeding was significantly less in the D100 group. This neonate CPB circuit effectively removed the gas bubbles and required up to 37% less priming volume and, thus, decreased the need for blood transfusion.

Comparable biocompatibility of Phisio- and Bioline-coated cardiopulmonary bypass circuits indicated by the inflammatory response.

BACKGROUND: The biocompatibility of cardiopulmonary bypass surfaces has been improved by heparin and polymer surface modifications. The present study compared the effect of two such coatings on the inflammatory reactions after open heart surgery. METHODS: Thirty patients undergoing elective heart surgery were randomly assigned to receive one of two types of coated circuits: Bioline (n=15) or phosphorylcholine (Phisio, n=15). The platelet and leukocyte counts, neutrophil activation (myeloperoxidase), complement activation (C3a and TCC), concentrations of lactate dehydrogenase, 27 cytokines (including interleukins, chemokines and growth factors), thrombin-antithrombin complexes, and the endothelial cell marker syndecan-1 were analyzed at five predetermined time points until 24 hrs post operatively. RESULTS: Most measurements were comparable in both groups. However, myeloperoxidase was significantly higher in the Bioline group (p < 0.001). Postoperative lactate dehydrogenase concentrations were significantly higher in the Phisio group (p<0.01) and the maximal concentration of thrombin-antithrombin complexes 2 hours postoperatively tended to be higher in the Phisio group (p=0.08), consistent with a longer aortic cross-clamp and cardiopulmonary bypass time. CONCLUSIONS: The two circuits exhibited a comparable degree of in vivo biocompatibility.

Extracorporeal membrane oxygenation support for 59 days without changing the ECMO circuit: a case of Legionella pneumonia.

We report the successful use of veno-venous extracorporeal membrane oxygenation (ECMO) in a 53-year-old patient with Legionella pneumonia and acute respiratory distress syndrome (ARDS) with severe barotraumas. The patient was supported for 59 days without any changes in the ECMO circuit. This is probably the longest support ever reported using the same oxygenator.

Evaluation of oxygenators and centrifugal pumps for long-term pediatric extracorporeal membrane oxygenation.

OBJECTIVE: Two extracorporeal membrane oxygenation (ECMO) circuits for children under 10 kg were evaluated and compared for plasma leakage, hemolysis, blood transfusions, and durability. METHODS: Group A (n=20) was supported by ECMO circuits with the Minimax oxygenator and the Biomedicus centrifugal pump. Group B (n=10) was supported by ECMO circuits with the Lilliput 2 ECMO oxygenator and the Rotaflow centrifugal pump. RESULTS: ECMO circuit durability, as measured by oxygenator lifespan, was significantly better in Group B than in Group A (p = 0.04). There was significantly lower hemolysis, measured by plasma free hemoglobin, in Group B (p = 0.019), and patients in Group B had significantly less need for antithrombin III transfusion (p = 0.004). No plasma leakage was observed in Group B oxygenators, but plasma leakage was observed in all Group A oxygenators. CONCLUSION: The combination of a Rotaflow centrifugal pump and Lilliput 2 ECMO oxygenator in pediatric ECMO circuits improved durability and reduced circuit-induced hemolysis. This improvement may be due to the low priming volume, the oxygenator's plasma leakage resistance, the suspended rotor of the centrifugal pump, or a combination of these factors.

Role of complement in xenotransplantation.

The xenotransplantation research is driven by the increasing gap between the number of patients with end-stage organ failure on waiting lists for transplantation and the supply of allografts. The lack of success in developing suitable artificial organs for permanent treatment of organ failure has further strengthened the need for xenotransplantation research. Pigs are now generally accepted to be the source animal of choice. Transplantation of pig organs to humans faces several barriers which have to be overcome before it comes to clinical application: (1) anatomical and physiological conditions; (2) immunological rejection mechanisms; (3) molecular compatibility between signal molecules of the two species; (4) risk of transmission of microorganisms, particularly pig endogenous retroviruses; and (5) legal and ethical aspects both with respect to the animal and the recipient. Here we will focus on the role of the complement system in the rejection of immediately vascularized pig-to-primate xenografts. The hyperacute rejection occurring within minutes after transplantation is mediated by binding of natural antibodies to the Galalpha(l-3)Gal epitope on the endothelial cells with subsequent complement activation. Whereas inhibition of complement activation protects against hyperacute rejection, the role of complement in the later rejection phases is less clarified.

Human cytomegalovirus productively infects porcine endothelial cells in vitro.

BACKGROUND: The possibility that human cytomegalovirus (HCMV) may infect porcine endothelial cells (ECs) was investigated. This may be relevant during xenotransplantation of porcine cells or organs into human recipients. METHODS: HCMV was inoculated into low-passage porcine ECs. Replication of virus was detected by development of characteristic cytopathogenic effect. Appearance of immediate early, early, and late antigens was studied by immunocytochemical staining. Infectious virus was detected in human fibroblast cells. Presence of HCMV RNA was studied by Northern Blot and reverse transcriptase polymerase chain reaction. RESULTS: All parameters indicated that a fresh clinical HCMV isolate productively infects porcine ECs. The same cells do not fully support replication of the laboratory strain Ad 169. CONCLUSION: Our results may indicate the possibility of cross-species infectivity of HCMV to porcine cells.

Human serum-induced expression of E-selectin on porcine aortic endothelial cells in vitro is totally complement mediated.

BACKGROUND: Whereas complement is a key mediator of hyperacute xenograft rejection, its role in acute vascular rejection (AVR) is a matter of controversy. AVR is associated with de novo synthesis of endothelial cell-derived inflammatory mediators, including the leukocyte-recruiting adhesion molecule E-selectin. Here we investigate the role and mechanism of complement in human serum-induced porcine endothelial cell activation. METHODS: An in vitro xenotransplantation method was designed using porcine aortic endothelial cells stimulated with human serum in microculture wells. E-selectin expression was measured by cell-enzyme immunoassay. Complement inhibitors acting at different levels in the cascade were investigated for their effect on E-selectin expression. RESULTS: E-selectin was strongly induced by normal human serum but not by heat-inactivated serum. Compstatin, a synthetic C3 inhibitor, markedly reduced human serum-induced E-selectin expression. Purified C1-inhibitor suppressed E-selectin induction completely, indicating activation through the classical or lectin pathway. Furthermore, a monoclonal antibody (mAb) that inhibits cleavage of C5 or another mAb that blocks the function of C7, completely inhibited the expression of serum-induced E-selectin, consistent with the terminal C5b-9 complement complex being the mediator of the endothelial cell activation. Inhibition of the alternative pathway using a novel antifactor D mAb did not reduce E-selectin expression. CONCLUSION: Human serum-induced expression of porcine E-selectin is totally complement dependent, induced by a C1-inhibitor regulated pathway and mediated through the terminal complement complex. The data may have implications for therapeutic strategies, particularly of C1-inhibitor and anti-C5 mAb, to protect against endothelial cell activation and subsequent AVR of porcine xenografts.

Pig endogenous retrovirus--a threat to clinical xenotransplantation?

Transplantation shows good results for patients with end-stage disease, but there is an increasing lack of organs. Xenotransplantation, the transfer of live animal cells, tissues, or organs to another species, offers a potential solution to this shortfall. Pig is regarded as the animal of choice for this purpose. Meanwhile demonstration of pig endogenous retrovirus (PERV) in all porcine herds has caused serious concern with respect to a possible transmission of the virus to humans with a transplanted organ. Transmission to human cells has been documented under certain in vitro conditions. However, no such transmission has been demonstrated in vivo. The possible consequences of introducing PERV into immunocompromised human organisms are not known and it is necessary to collect more information. Novel and sensitive genomic assays to detect PERV infection are now available in addition to established virological, immunoserological and molecular methods. In order to minimise the risk of PERV transmission rigorous procedures should be established. International guidelines to reduce the risk should be followed. Although a number of immunological, physiological and virological questions need to be answered before the introduction of xenotransplantation as an alternative clinical treatment, some problems can only be solved by judicious clinical trials.

Inhibition of platelet aggregation by the GPIIb/IIIa antagonist reopro does not significantly prolong xenograft survival in an ex vivo model.

Effects on hyperacute rejection were studied in a discordant model with the platelet GPIIb/IIIa antagonist Reopro. Pig kidneys perfused with human blood survived median 118 min in the Reopro group and 103 min in the controls (P = 0.22). Platelet and leukocyte counts decreased, whereas plasma thrombospondin and soluble as well as platelet membrane P-selectin increased significantly in both groups without significant intergroup differences. beta-Thromboglobulin and myeloperoxidase increased significantly more in the control group than in the Reopro group (P = 0.009 and P = 0.02, respectively). The classical complement pathway was substantially and similarly activated in both groups. Light and electron microscopy revealed arterial thrombi and numerous glomerular platelet aggregates in the control group in contrast to the Reopro group. In conclusion, Reopro reduced platelet aggregation, and platelet and leukocyte activation to some extent, but had no effect on complement activation and did not significantly prolong xenograft survival, even though better preservation of morphology was shown.

Is atrial fibrillation caused by extracorporeal circulation?

BACKGROUND: Atrial fibrillation is the most common rhythm disturbance encountered after open heart operations, with a reported incidence up to 40%. Despite its high incidence and clinical relevance its etiology remains obscure. It has been hypothesized that atrial fibrillation might be related to extracorporeal circulation. We performed a retrospective study (January 1, 1997 to December 31, 1997) comparing the incidence of atrial fibrillation in 3 groups of patients revascularized with and without extracorporeal circulation. METHODS: The first group comprised patients with coronary artery disease operated on with standard revascularization technique with cardiopulmonary bypass (n = 685). The second group included patients who had minimally invasive coronary artery bypass grafting without the use of extracorporeal circulation (n = 19). Patients in the third group had off-pump transmyocardial laser revascularization (n = 19). RESULTS: There was no significant difference in the incidence of atrial fibrillation in the group that had conventional coronary artery bypass and the group that had minimally invasive coronary artery bypass without cardiopulmonary bypass. The incidence of atrial fibrillation was significantly lower in the transmyocardial laser group compared with the other two groups. CONCLUSIONS: The present study found that postoperative atrial fibrillation is not caused solely by extracorporeal circulation, but patients who had transmyocardial laser revascularization had a significantly lower incidence of atrial fibrillation.

Compstatin, a peptide inhibitor of C3, prolongs survival of ex vivo perfused pig xenografts.

Compstatin, a newly described C3-binding peptide, inhibits complement activation by blocking C3 convertase-mediated cleavage of C3. As the complement activation is an essential part of the rejection reaction, we evaluated the ability of Compstatin to delay or prevent hyperacute rejection in an ex vivo xenograft model. Pig kidneys were perfused with fresh human blood containing either Compstatin (n=6) or a control agent (n=6). Graft survival and activation of complement, leukocytes and platelets both in the fluid-phase and in the tissue were examined. The survival of the Compstatin-perfused kidneys (median, 380 min) was significantly (P=0.0036) longer than that of the controls (median, 90 min). The classical complement pathway (C1rs-C1inhibitor and C4bc) was significantly and equally activated in both groups during the first 60 min. C3 activation products increased fivefold and terminal complement complex eightfold in the control group, but no increase occurred in the Compstatin group during this period. Immunohistochemistry showed less C3 and fibrin deposition and immune electron microscopy showed less terminal SC5b-9 complement complex deposition in the Compstatin group. A significant change in total white cells, neutrophils, myeloperoxidase, and expression of the surface activation markers CD11b (CR3) and CD35 (CR1) and CD62L (L-selectin) was observed in both groups. Leukocyte activation was lower in the Compstatin group but the difference was not statistically significant. There were no differences in platelet counts, thrombospondin, soluble P-selectin or beta-thromboglobulin between the groups. We conclude that Compstatin prolongs graft survival and suggest that it may be a useful agent for attenuating hyperacute rejection by inhibiting C3 and thus terminal complement pathway activation.