Scanning laser-induced endothelial injury: a standardized and reproducible thrombosis model for intravital microscopy.

Vascular injury models are indispensable for studying thrombotic processes in vivo. Amongst the available methods for inducing thrombosis, laser-induced endothelial injury (LIEI) has several unique advantages. However, a lack of methodological standardization and expensive instrumentation remain significant problems decreasing reproducibility and impeding the adoption of LIEI in the wider scientific community. In this, study, we developed a standardized protocol for scanning laser-induced endothelial injury (scanning-LIEI) of murine mesenteric veins using the intrinsic 405 nm laser of a conventional laser scanning confocal microscope. We show that our model produces thrombi with prominent core-shell architectures and minimal radiation-related fluorescence artefacts. In comparison with previous methods, the scanning-LIEI model exhibits reduced experimental variability, enabling the demonstration of dose-response effects for anti-thrombotic drugs using small animal cohorts. Scanning-LIEI using the intrinsic 405 nm laser of a confocal laser scanning microscope represents a new method to induce standardized vascular injury with improved reproducibility of thrombus formation. The reduced need for instrument customisation and user experience means that this model could be more readily adopted in the research community.

Inhibition of protease-activated receptor 4 impairs platelet procoagulant activity during thrombus formation in human blood.

UNLABELLED: Essentials The platelet thrombin receptor, PAR4, is an emerging anti-thrombotic drug target. We examined the anti-platelet & anti-thrombotic effects of PAR4 inhibition in human blood. PAR4 inhibition impaired platelet procoagulant activity in isolated cells and during thrombosis. Our study shows PAR4 is required for platelet procoagulant function & thrombosis in human blood. SUMMARY: Background Thrombin-induced platelet activation is important for arterial thrombosis. Thrombin activates human platelets predominantly via protease-activated receptor (PAR)1 and PAR4. PAR1 has higher affinity for thrombin, and the first PAR1 antagonist, vorapaxar, was recently approved for use as an antiplatelet agent. However, vorapaxar is contraindicated in a significant number of patients, owing to adverse bleeding events. Consequently, there is renewed interest in the role of platelet PAR4 in the setting of thrombus formation. Objectives To determine the specific antiplatelet effects of inhibiting PAR4 function during thrombus formation in human whole blood. Methods and Results We developed a rabbit polyclonal antibody against the thrombin cleavage site of PAR4, and showed it to be a highly specific inhibitor of PAR4-mediated platelet function. This function-blocking anti-PAR4 antibody was used to probe for PAR4-dependent platelet functions in human isolated platelets in the absence and presence of concomitant PAR1 inhibition. The anti-PAR4 antibody alone was sufficient to abolish the sustained elevation of cytosolic calcium level and consequent phosphatidylserine exposure induced by thrombin, but did not significantly inhibit integrin αII b ß3 activation, α-granule secretion, or aggregation. In accord with these in vitro experiments on isolated platelets, selective inhibition of PAR4, but not of PAR1, impaired thrombin activity (fluorescence resonance energy transfer-based thrombin sensor) and fibrin formation (anti-fibrin antibody) in an ex vivo whole blood flow thrombosis assay. Conclusions These findings demonstrate that PAR4 is required for platelet procoagulant function during thrombus formation in human blood, and suggest PAR4 inhibition as a potential target for the prevention of arterial thrombosis.

Safety and efficacy of targeting platelet proteinase-activated receptors in combination with existing anti-platelet drugs as antithrombotics in mice.

BACKGROUND AND PURPOSE: Developing novel anti-platelet strategies is fundamental to reducing the impact of thrombotic diseases. Thrombin activates platelets via proteinase-activated receptors (PARs), and PAR antagonists are being evaluated in clinical trials for prevention of arterial thrombosis. However, one such trial was recently suspended due to increased bleeding in patients receiving a PAR1 antagonist in addition to anti-platelet drugs that most often included both aspirin and clopidogrel. Therefore, it remains unclear how to best manipulate PARs for safe antithrombotic activity. To address this, we have examined potential interactions between existing anti-platelet drugs and strategies that target PARs. EXPERIMENTAL APPROACH: We used in vivo mouse models in which interactions between various anti-platelet strategies could be evaluated. We examined the effects on thrombosis and haemostasis in PAR4 -/- mice (platelets unresponsive to thrombin) treated with therapeutic doses of either aspirin or clopidogrel. KEY RESULTS: Using a model in which occlusive thrombosis occurred in PAR4 -/- mice or wild-type mice treated with aspirin or clopidogrel, PAR4 -/- mice treated with either anti-platelet agent showed marked protection against thrombosis. This antithrombotic effect occurred without any effect on haemostasis with aspirin, but not clopidogrel. Furthermore, specifically targeting thrombin-induced platelet activation (via PARs) improved the therapeutic window of non-specifically inhibiting thrombin functions (via anticoagulants). CONCLUSIONS AND IMPLICATIONS: Our results indicate that PAR antagonists used in combination with aspirin provide a potent yet safe antithrombotic strategy in mice and provide insights into the safety and efficacy of using PAR antagonists for the prevention of acute coronary syndromes in humans.

Mortality in infants with cardiovascular malformations.

UNLABELLED: Cardiovascular malformations are an important cause of infant death and the major cause of death due to malformation. Our aims were to analyse and categorise all deaths in infants with cardiovascular malformations, and to analyse trends in mortality over time and influences on mortality. We obtained details of infant deaths and cardiovascular malformations from the population of one health region for 1987-2006. We categorised deaths by cause and by presence of additional chromosomal or genetic abnormalities or non-cardiac malformations. In 676,927 live births the total infant mortality was 4,402 (6.5 per 1,000). A total of 4,437 infants had cardiovascular malformations (6.6 per 1000) of whom 458 (10.3%) died before 1 year of age. Of this number, 151 (33%) deaths had non-cardiac causes, 128 (28%) were cardiac without surgery and 179 (39%) occurred from cardiac causes after surgery. Death was unrelated to the cardiovascular malformation in 57% of infants with an additional chromosomal or genetic abnormality, in 76% of infants with a major non-cardiac malformation and in 16% of infants with an isolated cardiovascular malformation. Terminations of pregnancies affected by cardiovascular malformations increased from 20 per 100,000 registered births in the first 5 years to 78 per 100,000 in the last 5 years. A total of 2,067 infants (47%) underwent surgery and of these 216 (10%) died before 1 year of age. CONCLUSIONS: A total of 10.4% of infants who died had a cardiovascular malformation and two-thirds of deaths were due to the malformation or its treatment. Mortality declined due to increasing termination of pregnancy and improved survival after operation.

Transgenic, inducible RNAi in megakaryocytes and platelets in mice.

BACKGROUND: RNA interference (RNAi) is a powerful tool for suppressing gene function. The tetracycline (tet)-regulated expression system has recently been adapted to allow inducible RNAi in mice, however its efficiency in a particular cell type in vivo depends on a transgenic tet transactivator expression pattern and is often highly variable. OBJECTIVE: We aimed to establish a transgenic strategy that allows efficient and inducible gene knockdown in particular hematopoietic lineages in mice. METHODS AND RESULTS: Using a tet-regulated reporter gene strategy, we found that transgenic mice expressing the rtTA (tet-on) transactivator under control of the cytomegalovirus (CMV) promoter (CMV-rtTA mice) display inducible reporter gene expression with unusual and near-complete efficiency in megakaryocytes and platelets. To test whether the CMV-rtTA transgene can drive inducible and efficient gene knockdown within this lineage, we generated a novel mouse strain harboring a tet-regulated short hairpin RNA (shRNA) targeting Bcl-x(L) , a pro-survival Bcl-2 family member known to be essential for maintaining platelet survival. Doxycycline treatment of adult mice carrying both transgenes induces shRNA expression, depletes Bcl-x(L) in megakaryocytes and triggers severe thrombocytopenia, whereas doxycycline withdrawal shuts off shRNA expression, normalizes Bcl-x(L) levels and restores platelet numbers. These effects are akin to those observed with drugs that target Bcl-x(L) , clearly demonstrating that this transgenic system allows efficient and inducible inhibition of genes in megakaryocytes and platelets. CONCLUSIONS: We have established a novel transgenic strategy for inducible gene knockdown in megakaryocytes and platelets that will be useful for characterizing genes involved in platelet production and function in adult mice.

Cardiac transplantation in adults with congenital heart disease.

BACKGROUND: Due to increasing success with repair or palliation in childhood, there is a rapidly growing population of adult patients with complex congenital heart disease who may require transplantation. There remains little data on outcomes of cardiac transplantation in this group. METHODS: 38 orthotopic cardiac transplants were performed in 37 patients (18 men) > or =18 years of age with congenital heart disease (CHD) from 1988 to 2009 in our institution. Outcomes were reviewed using medical records and transplant databases. RESULTS: 15 patients (41%) had univentricular and 22 (59%) biventricular physiology. The biggest group was transposition of the great arteries following atrial switch in eight patients (22%). Six (16%) had no previous surgical intervention. Mean age at transplant was 33.5 years (range 19.1-59.9 years). 11 patients (30%) required additional surgical procedures at transplant. 16 (43%) died, 12 early and 4 late deaths (1.8, 2.4, 2.7 and 7 years). Survival was 70% at 30 days, 68% at 1 year, 58% at 5 years and 53% at 10 and 15 years. Outcome improved in later eras with reduction in 30-day mortality from 50% to 18% and increase in 5-year survival from 50% to 69%. Two patients developed post-transplant lymphoproliferative disease. None required long-term renal replacement therapy. One patient was re-transplanted for cardiac allograft vasculopathy. CONCLUSIONS: While operative mortality following cardiac transplantation for adult congenital heart disease is higher than for other diagnostic groups, long-term survival is good and comparable to patients without CHD. Disappointing early results are improved with increasing experience.

Atherosclerosis proceeds independently of thrombin-induced platelet activation in ApoE-/- mice.

Platelet activation has long been postulated to contribute to the development of atherosclerotic plaques, although the mechanism by which this might occur remains unknown. Thrombin is a potent platelet activator and transfusion of thrombin-activated platelets into mice increases plaque formation, suggesting that thrombin-induced platelet activation might contribute to platelet-dependent atherosclerosis. Platelets from protease-activated receptor 4-deficient (Par4-/-) mice fail to respond to thrombin. To determine whether thrombin-activated platelets play a necessary role in a model of atherogenesis, we compared plaque formation and progression in Par4+/+ and Par4-/- mice in the atherosclerosis-prone apolipoprotein E-deficient (ApoE-/-) background. Littermate Par4+/+ and Par4-/- mice, all ApoE-/-, were placed on a Western diet (21% fat, 0.15% cholesterol) for 5 or 10 weeks. The percent of aortic lumenal surface covered by plaques in Par4+/+ and Par4-/- mice was not different at either time point (2.2+/-0.3% vs. 2.5+/-0.2% and 5.1+/-0.4% vs. 5.6+/-0.4% after 5 and 10 weeks, respectively). Further, no differences were detected in the cross-sectional area of plaques measured at the aortic root (1.53+/-0.17 vs. 1.66+/-0.16x10(5)microm(2) and 12.56+/-1.23 vs. 13.03+/-0.55x10(5)microm(2) after 5 and 10 weeks, respectively). These findings indicate that thrombin-mediated platelet activation is not required for the early development of atherosclerotic plaques in the ApoE-/- mouse model and suggest that, if platelet activation is required for plaque formation under these experimental conditions, platelet activators other than thrombin suffice.

Towards an anatomically correct repair for anomalous left coronary artery arising from the pulmonary trunk.

BACKGROUND: Anomalous origin of the left coronary artery from the pulmonary trunk is rare, occurring at an incidence of 1 in 300,000. If not diagnosed and treated early, it is life-threatening. Children with the anomaly usually present in infancy with congestive cardiac failure, and are occasionally referred for cardiac transplant. We investigated the medium term outcome for patients following creation of a two-coronary arterial circulation. METHODS: Between 1992 and 2007, we diagnosed 15 patients seen at our Institution as having anomalous origin of the left coronary artery from the pulmonary trunk. Over a period of 13 years, aortic reimplantation was undertaken in 12 of these patients, who form the studied cohort. RESULTS: Direct reimplantation was performed in 5 patients. In 3 cases, a tension-free anastomosis was created using a caudally based flap. In another 3 cases, an extended flap was used, while a patch arterioplasty was fashioned in the final patient. There were no deaths. Left ventricular function recovered in all but one of the patients, and all patients had a reduction in the degree of mitral regurgitation. CONCLUSIONS: Among the variety of surgical techniques, transfer of the anomalous left coronary artery to the aorta is the ideal method for long-term patency and adequate blood supply. This can be achieved by creating flaps based on the walls of the pulmonary trunk and aorta, producing a dual coronary arterial supply with no mortality and low morbidity.

Clinical experience with assisted venous drainage cardiopulmonary bypass in elective cardiac reoperations.

Reoperative cardiac surgery is associated with substantial morbidity and mortality due to technical problems at sternal reentry, which can result in laceration of the right ventricle, innominate vein injury, or embolization from patent grafts. To minimize the risk associated with reentry, we adopted the method of assisted venous drainage in the cardiopulmonary bypass circuit with peripheral cannulation for cardiac reoperations. From March 1999 to May 2003, a series of 52 patients (38 males; mean age 48.7 years, range 4 months to 78 years) underwent cardiac reoperations performed with centrifugal pump venous-assisted cardiopulmonary bypass. EuroSCORE was 7.34 +/- 3.9 (range, 4-19). The reoperations were coronary artery bypass graft (25 patients), valve replacement/repair (18 patients), and complex pediatric procedures (11 patients). The studied adverse events were structural damage at reentry, mortality, blood loss, stroke, and hemolysis. Complications at sternotomy were damage to the innominate vein (1 patient) and aorta (1 patient) with blood loss of 625 and 225 mL, respectively. Four patients required intraaortic balloon pump or extracorporeal membrane oxygenation (n = 1) for hemodynamic support on weaning off cardiopulmonary bypass. Three patients died in the postoperative period. Our experience with centrifugal pump-assisted venous drainage in cardiac reoperations has shown excellent results, with reduced risk of damage to vital structures on sternal reentry. In cases in which structural damage did occur, blood loss was minimal.

Multicenter experience of ABO-incompatible pediatric cardiac transplantation.

Although ABO blood group incompatible cardiac transplantation in neonates and infants reduces waiting list mortality without compromising outcome, the technique has not been adopted by all centers, and to date Toronto remains the only center to have published results from a large case series. We present a review of ABO-incompatible heart transplantation in the United Kingdom (UK) where current recipient selection criteria differ somewhat from those used in the United States (US) and Canada. Between February 2000 and November 2006, 21 ABO-incompatible cardiac transplants were performed in children aged 2-40 months (median 10.0). Immunosuppression followed standard regimens. Pretransplant donor-specific isohemagglutinins of >1:4, (the UNOS cutoff), were present in five patients and reduced by plasma exchange. After transplantation, 19/21 recipients demonstrated persisting deficiency of donor-specific isohemagglutinins. Significant donor-specific isohemagglutinins levels were detected repeatedly in 2/21 recipients who have shown no clinical or biopsy evidence of rejection. All recipients survive without retransplantation and there have been no episodes of humoral rejection. We conclude it is possible for other centers to replicate the excellent results achieved in Toronto and that ABO-incompatible transplantation may be performed successfully in some patients beyond infancy with established isohemagglutinin production providing preoperative antibody removing strategies are used.

Accuracy of the aristotle basic complexity score for classifying the mortality and morbidity potential of congenital heart surgery operations.

BACKGROUND: The Aristotle Basic Complexity Score (ABC score) was derived by consensus of an international surgeon panel to facilitate assessment of surgical performance for quality improvement in congenital heart surgery. The utility of the ABC score depends on its ability to correctly classify procedures according to their potential for morbidity, mortality, and technical difficulty. This collaborative study combined two multiinstitution databases to assess how well the ABC score predicts the actual morbidity and mortality potential of 131 congenital heart surgery procedures. METHODS: Data from the European Association of Cardiothoracic Surgery (EACTS) congenital database (17,838 operations, 56 centers) and the Society of Thoracic Surgeons (STS) congenital database (18,024 operations, 32 centers) were analyzed. Discrimination of the ABC score for predicting in-hospital mortality and postoperative length of stay (PLOS) of more than 21 days was quantified by the C statistic. Procedure-specific rates of mortality and prolonged PLOS were compared with predictions from a logistic regression model, and an exact binomial test was used to identify procedures that were mortality and morbidity outliers. RESULTS: There was a significant positive correlation between the ABC score of a procedure and its observed procedure-specific risk of mortality (C = 0.70) and prolonged PLOS (C = 0.67). Several individual procedures were identifed as mortality and morbidity outliers. CONCLUSIONS: The ABC score generally discriminates between low-risk and high-risk congenital procedures making it a potentially useful covariate for case-mix adjustment in congenital heart surgery outcomes analysis. Planned revisions of the ABC score will incorporate empirical data and will benefit from the large sample sizes of the STS and EACTS databases.

Patient attitudes to sternotomy and thoracotomy scars.

BACKGROUND: There are no data comparing patient attitudes to sternotomy and thoracotomy scars following surgery for congenital heart disease (CHD). METHODS: Two hundred and one patients with a scar from CHD surgery (105 sternotomy, 36 thoracotomy, and 60 both scars) had a structured interview to explore attitudes to their scar. RESULTS: Comparable proportions of each group reported that they did not like or hated their scar (23/105 [22 %] sternotomy, 9/36 [25 %] thoracotomy, 17/60 [28 %] both scars). Significantly more patients stated that they where embarrassed by and/or their choice of clothing was affected by a thoracotomy scar (20/36, 56 %) than those with a sternotomy scar (36/105, 34 %), p = 0.04. This was also seen when comparing sternotomy alone with both scars (36/105 [34 %] vs. 34/60 [57 %], p = 0.008). CONCLUSIONS: Adults who have undergone surgery for CHD are more likely to have a negative attitude to a thoracotomy than a sternotomy scar. Before a change in surgical approach is considered based on patient preferences, the acceptability and psychological impact of the different scars following surgery needs formal study.

Effects of 'Bristol' on surgical practice in the United Kingdom.

In 1995 a child died following an arterial switch operation for complex transposition of the great arteries. There had been general concern regarding the outcomes for the arterial switch procedure in the unit in Bristol. A review, prompted by parents whose children had died, showed that 29 children had died and four others suffered from cerebral damage postoperatively. The General Medical Council (GMC) considered the conduct of three doctors from the unit. This hearing culminated in the suspension and subsequent removal from the Medical Register of the senior Cardiac Surgeon and the Chief Executive of the hospital. The second Cardiac Surgeon was banned from practising in the field of paediatric cardiac surgery for three years (his results in adult cardiac surgical practice were not called into question). Following this the Government set up a public Inquiry to investigate the causes behind the deaths. This Inquiry, which took three years, made recommendations that have affected the way all doctors in the UK practice.

Fatal hemorrhage from simple lacerations of the scalp.

Scalp lacerations are frequently seen in both living trauma victims and at post-mortem examination. In clinical circles, it is well known that even "trivial" lacerations of blood-rich areas such as the scalp may bleed profusely and persistently.It is less well known, however, that hemorrhage even from simple scalp lacerations may be fatal. We present seven cases in which hemorrhage from simple scalp lacerations was considered to be the principle cause of death.Chronic alcohol misuse, alcoholic liver disease, and the co-existence of other pathologies such as ischemic heart disease were frequently contributory factors.

Impaired hemostasis and protection against thrombosis in protease-activated receptor 4-deficient mice is due to lack of thrombin signaling in platelets.

Platelets from protease-activated receptor 4 (PAR4)-deficient mice are unresponsive to thrombin, and Par4-/- mice have prolonged bleeding times and are protected against thrombosis. However, in addition to its role in platelets, PAR4 contributes to thrombin signaling in cells in the blood vessel wall that might participate in hemostasis and thrombosis, such as endothelial cells. To determine whether the hemostatic and thrombotic phenotypes of Par4-/- mice were due to loss of PAR4 function in hematopoietic vs. other cell types, tail bleed times and thromboplastin-induced pulmonary embolism were examined in lethally irradiated mice reconstituted with Par4+/+ or Par4-/- bone marrow. In Par4+/+ and Par4-/- mice reconstituted with Par4+/+ marrow, the median tail bleed times were 2.0 and 1.7 min, respectively, vs. > 10 min for both Par4+/+ and Par4-/- mice reconstituted with Par4-/- marrow. In the pulmonary embolism model, Par4+/+ and Par4-/- mice reconstituted with Par4+/+ marrow survived a median of 3.7 and 2.8 min, respectively, after administration of thromboplastin, vs. > 20 min for both Par4+/+ and Par4-/- mice reconstituted with Par4-/- marrow. Further, the phenotype of mice reconstituted with Par4-/- marrow was almost as dramatic as that seen in Nf-e2-/- mice, which lack platelets. These data strongly suggest that increased tail bleed times and protection against thrombosis in Par4-/- mice are accounted for by lack of PAR4 function in platelets, emphasize the importance of thrombin signaling in platelets among the multiple pathways and cell types that govern hemostasis and thrombosis.

Life insurance and mortgage application in adults with congenital heart disease.

OBJECTIVE: To compare the outcome of life insurance and mortgage applications of adults with congenital heart disease (CHD) with controls and at different severities of CHD. METHODS: Two hundred and ninety-nine adult CHD patients underwent a questionnaire-based interview by a trained nurse. They were asked to give an identical questionnaire to a friend to act as a control. One hundred and seventy-seven controls replied. CHD patients were classified into three categories based on severity. Comparisons were made between matched controls and between different severities of CHD. RESULTS: Similar proportions of the CHD group (59%) had applied for life insurance as matched controls (56%). Compared to controls, significantly more of the adults with CHD who had applied for life insurance have been refused (34 vs 4%, P < 0.0001) or asked to pay extra (37 vs 6%, P = 0.0002). Mortgage application rate was also similar in both groups with more of the CHD patients refused than matched controls (20 vs 3%, P = 0.0004). These differences in both life insurance and mortgage remain significant when the cases and controls are matched by employment status and NYHA functional class. There was no significant difference in life insurance and mortgage application outcome between the groups of mild, significant and complex CHD. CONCLUSIONS: Adults with CHD are significantly more likely to have difficulty obtaining life insurance or a mortgage than controls. Refusal rates appear to be independent of the severity of CHD. This suggests that the label of CHD may have a negative impact despite the lesion being minor and that the outcome of an individual application is difficult to predict based on the severity of the CHD. The increasing numbers of adults with CHD suggest that this problem is likely to increase and needs to be addressed as it can have a major impact on the patient's quality of life.

Pulmonary malacoplakia in an immunocompetent girl: a case report.

Malacoplakia is an unusual inflammatory condition with distinctive histologic features. Involvement of the lung is quite uncommon and is rarely described in paediatrics. We report on a case of pulmonary malacoplakia in a teenage girl.