Inflammatory response to cardiopulmonary bypass

Inflammation in cardiac surgical patients is produced by complex humoral and cellular interactions with numerous pathways including activation, generation, or expression of thrombin, complement, cytokines, neutrophils, adhesion molecules, mast cells, and multiple inflammatory mediators. Because of the redundancy of the inflammatory cascades, profound amplification occurs to produce multiorgan system dysfunction that can manifest as coagulopathy, respiratory failure, myocardial dysfunction, renal insufficiency, and neurocognitive defects. Coagulation and inflammation are also closely linked through networks of both humoral and cellular components including proteases of the clotting and fibrinolytic cascades, including tissue factor. Vascular endothelial cells also mediate inflammation and the cross talk between coagulation and inflammation. Novel antiinflammatory agents inhibit these processes by several mechanisms such as preventing proteolysis of the protease-activated receptor (aprotinin), inhibiting complement-mediated injury (pexelizumab), or inhibiting contact activation (kallikrein inhibitors). Surgery alone also activates specific hemostatic responses, activation of immune mechanisms, and inflammatory response mediated by the release of various cytokines and chemokines. Novel agents are under investigation to further improve outcomes in cardiac surgical patients.

The effects of fibrinogen levels on thromboelastometric variables in the presence of thrombocytopenia

BACKGROUND

The binding of fibrinogen and fibrin to platelets is important in normal hemostasis. The extent of platelet-fibrin interaction can be measured as the viscoelastic strength of clot by rotational thromboelastometry (ROTEM). In this study, we investigated the effect of fibrinogen concentration and its relative contribution to overall clot strength using ROTEM.

METHODS

Blood samples were collected from healthy volunteers. The effects of platelet count on clot strength, determined by maximum clot elasticity (MCE), were evaluated on ROTEM using platelet-rich plasma (PRP) adjusted with autologous plasma to generate a range of platelet counts. PRPs were adjusted to 10 x 10(3) mm(-3), 50 x 10(3) mm(-3), and 100 x 10(3) mm(-3) and spiked with fibrinogen concentrates at 550 and 780 mg/dL. The effect of fibrin polymerization on clot strength, independent of platelet attachment, was analyzed by the cytochalasin D-modified thromboelastometry (FIBTEM) method. Additional retrospective analysis of clot strength (MCE) in two groups of thrombocytopenic patients was conducted.

RESULTS

Clot strength (MCE) decreased at a platelet count below 100 x 10(3) mm(-3), whereas increases in MCE peaked and reached a plateau at platelet counts from 400 x 10(3) mm(-3). Increasing fibrinogen concentrations in PRP increased clot strength in a concentration-dependent manner, even at low platelet counts (10 x 10(3) mm(-3)). The positive correlation between clot strength and plasma fibrinogen level was also confirmed in the analysis of the data obtained from 904 thrombocytopenic patients.

CONCLUSIONS

These in vitro and clinical data indicate that the clot strength increases in a fibrinogen concentration-dependent manner independent of platelet count, when analyzed by ROTEM. The maintenance of fibrinogen concentration is critical in the presence of thrombocytopenia. EXTEM (extrinsic activation) and FIBTEM may be useful in guiding fibrinogen repletion therapy.

Blood coagulation: hemostasis and thrombin regulation

Perioperative bleeding is a major challenge particularly because of increasing clinical use of potent antithrombotic drugs. Understanding current concepts of coagulation is important in determining the preoperative bleeding risk of patients, and in managing hemostatic therapy perioperatively. The serine protease thrombin plays pivotal roles in the activation of additional serine protease zymogens (inactive enzymatic precursors), cofactors, and cell-surface receptors. Thrombin generation is closely regulated to locally achieve rapid hemostasis after injury without causing uncontrolled systemic thrombosis. During surgery, there are major disturbances in coagulation and inflammatory systems because of hemorrhage/hemodilution, blood transfusion, and surgical stresses. Postoperative bleeding often requires allogeneic blood transfusions, which support thrombin generation and hemostasis. However, procoagulant activity and inflammation are increased postoperatively; thus, antithrombotic therapy may be required to prevent perioperative thrombotic complications. There have been significant advances in the management of perioperative hemostasis and thrombosis because of the introduction of novel hemostatic and antithrombotic drugs. However, a limitation of current treatment is that conventional clotting tests do not reflect the entire physiological processes of coagulation making optimal pharmacologic therapy difficult. Understanding the in vivo regulatory mechanisms and pharmacologic modulation of thrombin generation may help control bleeding without potentially increasing prothrombotic risks. In this review, we focus on the regulatory mechanisms of hemostasis and thrombin generation using multiple, simplified models of coagulation.

Fast heating of ultrahigh-density plasma as a step towards laser fusion ignition

Modern high-power lasers can generate extreme states of matter that are relevant to astrophysics, equation-of-state studies and fusion energy research. Laser-driven implosions of spherical polymer shells have, for example, achieved an increase in density of 1,000 times relative to the solid state. These densities are large enough to enable controlled fusion, but to achieve energy gain a small volume of compressed fuel (known as the 'spark') must be heated to temperatures of about 108 K (corresponding to thermal energies in excess of 10 keV). In the conventional approach to controlled fusion, the spark is both produced and heated by accurately timed shock waves, but this process requires both precise implosion symmetry and a very large drive energy. In principle, these requirements can be significantly relaxed by performing the compression and fast heating separately; however, this 'fast ignitor' approach also suffers drawbacks, such as propagation losses and deflection of the ultra-intense laser pulse by the plasma surrounding the compressed fuel. Here we employ a new compression geometry that eliminates these problems; we combine production of compressed matter in a laser-driven implosion with picosecond-fast heating by a laser pulse timed to coincide with the peak compression. Our approach therefore permits efficient compression and heating to be carried out simultaneously, providing a route to efficient fusion energy production.

Bleeding management with fibrinogen concentrate targeting a high-normal plasma fibrinogen level: a pilot study

BACKGROUND

Bleeding diathesis after aortic valve operation and ascending aorta replacement (AV-AA) is managed with fresh-frozen plasma (FFP) and platelet concentrates. The aim was to compare haemostatic effects of conventional transfusion management and FIBTEM (thromboelastometry test)-guided fibrinogen concentrate administration.

METHODS

A blood products transfusion algorithm was developed using retrospective data from 42 elective patients (Group A). Two units of platelet concentrate were transfused after cardiopulmonary bypass, followed by 4 u of FFP if bleeding persisted, if platelet count was < or =100 x 10(3) microl(-1) when removing the aortic clamp, and vice versa if platelet count was >100 x 10(3) microl(-1). The trigger for each therapy step was > or =60 g blood absorbed from the mediastinal wound area by dry swabs in 5 min. Assignment to two prospective groups was neither randomized nor blinded; Group B (n=5) was treated according to the algorithm, Group C (n=10) received fibrinogen concentrate (Haemocomplettan P/Riastap, CSL Behring, Marburg, Germany) before the algorithm-based therapy.

RESULTS

A mean of 5.7 (0.7) g fibrinogen concentrate decreased blood loss to below the transfusion trigger level in all Group C patients. Group C had reduced transfusion [mean 0.7 (range 0-4) u vs 8.5 (5.3) in Group A and 8.2 (2.3) in Group B] and reduced postoperative bleeding [366 (199) ml vs 793 (560) in Group A and 716 (219) in Group B].

CONCLUSIONS

In this pilot study, FIBTEM-guided fibrinogen concentrate administration was associated with reduced transfusion requirements and 24 h postoperative bleeding in patients undergoing AV-AA.

Finding the optimal concentration range for fibrinogen replacement after severe haemodilution: an in vitro model

BACKGROUND

Replacement of fibrinogen is presumably the key step in managing dilutional coagulopathy. We performed an in vitro study hypothesizing that there is a minimal fibrinogen concentration in diluted whole blood above which the rate of clot formation approaches normal.

METHODS

Blood samples from six healthy volunteers were diluted 1:5 v/v with saline keeping haematocrit at 24% using red cell concentrates. We measured coagulation factors and thrombin generation in plasma at baseline and after dilution. Thromboelastometry was used to evaluate (i) speed and quality of clot formation in diluted samples supplemented with fibrinogen 50-300 mg dl(-1) and (ii) clot resistance to fibrinolysis. Diluted and undiluted samples with no added fibrinogen served as controls.

RESULTS

Coagulation parameters and platelets were reduced by 74-85% after dilution. Peak thrombin generation was reduced by 56%. Adding fibrinogen led to a concentration-dependent improvement of all thromboelastometric parameters. The half maximal effective concentration (EC50) for fibrinogen replacement in haemodiluted blood was calculated to be 125 mg dl(-1). Adding tissue plasminogen activator, 0.15 microg ml(-1), led to a decrease of clot firmness and lysis time.

CONCLUSIONS

The target plasma concentration for fibrinogen replacement was predicted by these in vitro results to be greater than 200 mg dl(-1) as only these concentrations optimized the rate of clot formation. This concentration is twice the level suggested by the current transfusion guidelines. Although improved, clots were prone to fibrinolysis indicating that the efficacy of fibrinogen therapy may be influenced by co-existing fibrinolytic tendency occurring during dilutional coagulopathy.

Plasma devices to guide and collimate a high density of MeV electrons

The development of ultra-intense lasers has facilitated new studies in laboratory astrophysics and high-density nuclear science, including laser fusion. Such research relies on the efficient generation of enormous numbers of high-energy charged particles. For example, laser-matter interactions at petawatt (10(15) W) power levels can create pulses of MeV electrons with current densities as large as 10(12) A cm(-2). However, the divergence of these particle beams usually reduces the current density to a few times 10(6) A cm(-2) at distances of the order of centimetres from the source. The invention of devices that can direct such intense, pulsed energetic beams will revolutionize their applications. Here we report high-conductivity devices consisting of transient plasmas that increase the energy density of MeV electrons generated in laser-matter interactions by more than one order of magnitude. A plasma fibre created on a hollow-cone target guides and collimates electrons in a manner akin to the control of light by an optical fibre and collimator. Such plasma devices hold promise for applications using high energy-density particles and should trigger growth in charged particle optics.

Usefulness of standard plasma coagulation tests in the management of perioperative coagulopathic bleeding: is there any evidence?

Standard laboratory coagulation tests (SLTs) such as prothrombin time/international normalized ratio or partial thromboplastin time are frequently used to assess coagulopathy and to guide haemostatic interventions. However, this has been challenged by numerous reports, including the current European guidelines for perioperative bleeding management, which question the utility and reliability of SLTs in this setting. Furthermore, the arbitrary definition of coagulopathy (i.e. SLTs are prolonged by more than 1.5-fold) has been questioned. The present study aims to review the evidence for the usefulness of SLTs to assess coagulopathy and to guide bleeding management in the perioperative and massive bleeding setting. Medline was searched for investigations using results of SLTs as a means to determine coagulopathy or to guide bleeding management, and the outcomes (i.e. blood loss, transfusion requirements, mortality) were reported. A total of 11 guidelines for management of massive bleeding or perioperative bleeding and 64 studies investigating the usefulness of SLTs in this setting were identified and were included for final data synthesis. Referenced evidence for the usefulness of SLTs was found in only three prospective trials, investigating a total of 108 patients (whereby microvascular bleeding was a rare finding). Furthermore, no data from randomized controlled trials support the use of SLTs. In contrast, numerous investigations have challenged the reliability of SLTs to assess coagulopathy or guide bleeding management. There is actually no sound evidence from well-designed studies that confirm the usefulness of SLTs for diagnosis of coagulopathy or to guide haemostatic therapy.

A comparative evaluation of rotation thromboelastometry and standard coagulation tests in hemodilution-induced coagulation changes after cardiac surgery

BACKGROUND

Coagulopathy after cardiopulmonary bypass (CPB) is caused by multiple perturbations in cellular and humoral elements of coagulation. A timely and comprehensive method to evaluate hemostasis would be helpful in the management of bleeding patients after CPB. The assessment of whole blood coagulation using rotation thromboelastometry (ROTEM) was compared to coagulation tests routinely performed during cardiac surgery.

STUDY DESIGN AND METHODS

Blood was obtained from 26 patients undergoing CPB surgery at baseline, at 60 minutes on CPB, at the end of CPB, and on admission to intensive care unit. ROTEM tests (extrinsically activated [EXTEM], intrinsically activated [INTEM], specific clot formation [FIBTEM]), prothrombin time, activated partial thromboplastin time, platelet (PLT) count, fibrinogen, prothrombin level, antithrombin level, and thrombin generation (TG) measurement were performed.

RESULTS

We observed strong correlations between FIBTEM-amplitude at 10 minutes (A10) and fibrinogen level (r=0.87; p<0.001) and between EXTEM/ INTEM-A10 variables and PLT count (r=0.72 and 0.67, respectively; p<0.001). Receiver operating characteristic analysis demonstrated that EXTEM-A10 and INTEM-A10 are predictive of thrombocytopenia below 80×10(9)/L (area under the curve [AUC], 0.83 and 0.82, respectively), and FIBTEM-A10 was highly predictive of fibrinogen level below 200 mg/dL (AUC, 0.96). There were only weak correlations found between TG peak and clot formation time of EXTEM or INTEM (r=0.30 and 0.29, respectively; p<0.05).

CONCLUSION

ROTEM variables demonstrated clinically relevant correlations with PLT counts and fibrinogen levels. In particular, decreasing levels of fibrinogen can be quickly determined (<15-20 min) using FIBTEM.

A novel automated microchip flow-chamber system to quantitatively evaluate thrombus formation and antithrombotic agents under blood flow conditions

BACKGROUND AND AIMS

In the present study, we describe a newly developed microchip-based analytical system to evaluate white thrombus formation (WTF). Efficacies of various antithrombotic agents were compared under different flow conditions.

METHODS

Whole blood containing corn trypsin inhibitor was perfused over a microchip coated with collagen and tissue thromboplastin at the lower and higher shear rates of 240 and 600 s(-1) , and WTF process inside the microchip was quantified by monitoring a flow pressure. Parameters of T(10) (time to 10 kPa), T(10-80) (time from 10 to 80 kPa) and OT (occlusion time; time to 80 kPa) were used to evaluate the onset and the growth rate of WTF, and the capillary occlusion, respectively.

RESULTS

After perfusion was started, white thrombus composed of activated platelets and fibrin was formed on the coated surface. Thrombus gradually increased in size and eventually occluded the capillary. Among anticoagulants, heparin (0.5-1.0 U mL(-1)) potently prolonged T(10) at both shear rates, whereas low molecular weight heparin (1.0-2.0 IU mL(-1)) inhibited the growth of WTF at the lower shear rate. Among antiplatelet agents, abciximab (1-2 μg mL(-1)) significantly reduced the size and number of thrombi, which was additively enhanced in the presence of heparin (0.5 U mL(-1) ). OS-1 (specific GPIbα-antagonist) prevented the complete capillary occlusion.

CONCLUSION

The novel monitoring system of WTF may be useful in preclinical and clinical evaluations of different types of antithrombotic strategies, and their effects in combination.

Management of hemorrhage in cardiothoracic surgery

Bleeding is an important issue in cardiothoracic surgery, and about 20% of all blood products are transfused in this clinical setting worldwide. Transfusion practices, however, are highly variable among different hospitals and more than 25% of allogeneic blood transfusions have been considered inappropriate. Furthermore, both bleeding and allogeneic blood transfusion are associated with increased morbidity, mortality, and hospital costs. In the past decades, several attempts have been made to find a universal hemostatic agent to ensure hemostasis during and after cardiothoracic surgery. Most drugs studied in this context have either failed to reduce bleeding and transfusion requirements or were associated with severe adverse events, such as acute renal failure or thrombotic/thromboembolic events and, in some cases, increased mortality. Therefore, an individualized goal-directed hemostatic therapy ("theranostic" approach) seems to be more appropriate to stop bleeding in this complex clinical setting. The use of point-of-care (POC) transfusion and coagulation management algorithms guided by viscoelastic tests such as thromboelastometry/thromboelastography in combination with POC platelet function tests such as whole blood impedance aggregometry, and based on first-line therapy with fibrinogen and prothrombin complex concentrate have been associated with reduced allogeneic blood transfusion requirements, reduced incidence of thrombotic/thromboembolic and transfusion-related adverse events, and improved outcomes in cardiac surgery. This article reviews the current literature dealing with the management of hemorrhage in cardiothoracic surgery based on POC diagnostics and with specific coagulation factor concentrates and its impact on transfusion requirements and patients' outcomes.

Haemodilution-induced profibrinolytic state is mitigated by fresh-frozen plasma: implications for early haemostatic intervention in massive haemorrhage

BACKGROUND

Fibrinolysis contributes to coagulopathy after major trauma and surgery. We hypothesized that progressive haemodilution is responsible, at least in part, for increased fibrinolytic tendency of blood clot.

METHODS

The study was performed in two parts. First, whole blood (WB) samples collected from six healthy, consented volunteers were diluted in vitro with either saline or fresh-frozen plasma (FFP) to 40% and 15% of baseline. We quantified factor levels related to coagulation and fibrinolysis, and measured endogenous thrombin generation in undiluted control plasma samples and in samples diluted with saline or FFP. Additionally, thromboelastometry was used to assess susceptibility to fibrinolysis after adding tissue plasminogen activator in undiluted WB samples and in samples diluted with saline before and after substitution of fibrinogen or FFP. Secondly, as a model of in vivo haemodilution, we evaluated the same parameters before and after operation in nine consented patients undergoing off-pump coronary artery bypass surgery.

RESULTS

The dilution with saline caused dose-dependent decreases in plasma levels of coagulation and antifibrinolytic factors, and in thrombin generation. In FFP-supplemented samples, factor levels and thrombin generation were maintained within normal ranges. Fibrinolytic tendency was significantly higher after haemodilution with saline independent of fibrinogen substitution compared with FFP. Similarly, increased tendency for fibrinolysis was also observed in the in vivo haemodilution.

CONCLUSIONS

We demonstrated in vitro and in vivo that progressive haemodilution decreases endogenous antifibrinolytic proteins including alpha(2)-antiplasmin and thrombin-activatable fibrinolysis inhibitor, resulting in increased fibrinolytic tendency. Therefore, early fluid replacement therapy with FFP might be advantageous after massive haemorrhage.

The effects of platelet count on clot retraction and tissue plasminogen activator-induced fibrinolysis on thrombelastography

Clot retraction and fibrinolysis may present as a decrease in amplitude on thrombelastography (TEG). The former represents normal or hyperactive platelet function, and the latter represents a fibrinolytic state. It is important to distinguish clot retraction from fibrinolysis because the treatment of each condition is different. To distinguish between these phenomena, we performed TEG with platelet-poor plasma (PPP) and platelet-rich plasma (PRP) with an increasing platelet count (range, 50-1200 x 10(9)/L) with or without abciximab. Maximum amplitude (MA) and the percentage decrease of amplitude at 30 and 60 min after MA were examined for each sample. Blood samples to which tissue plasminogen activator (tPA) was added served as positive controls for fibrinolysis. Morphological changes of clots and D-dimer levels were also examined. With higher platelet counts, the percentage decrease of amplitude after MA increased significantly at 30 and 60 min, but not in the abciximab samples. Morphological changes of clots have shown clot retraction in PRP, but not in PPP or PRP pretreated with abciximab. D-dimer levels increased only in samples to which tPA was added, but not in native PPP or PRP samples. In conclusion, we have shown that the decrease in amplitude at 30 and 60 min can be due to platelet-mediated clot retraction and can be attenuated by sample pretreatment with abciximab, which interrupts platelet-fibrin(ogen) binding.

Roles of thrombelastography and thromboelastometry for patient blood management in cardiac surgery

The value of thrombelastography (TEG) and thromboelastometry (ROTEM) to improve perioperative hemostasis is under debate. We aimed to assess the effects of TEG- or ROTEM-guided therapy in patients undergoing cardiac surgery on the use of allogeneic blood products. We analyzed 12 trials including 6835 patients, 749 of them included in 7 randomized controlled trials (RCTs). We collected data on the amount of transfused allogeneic blood products and on the proportion of patients who received allogeneic blood products or coagulation factor concentrates. Including all trials, the odds ratios (ORs) for transfusion of red blood cell (RBC) concentrates, fresh-frozen plasma (FFP), and platelets were 0.62 (95% confidence interval [CI], 0.56-0.69; P<.001), 0.28 (95% CI, 0.24-0.33; P<.001), and 0.55 (95% CI, 0.49-0.62; P<.001), respectively. However, more than 50% of the patients in this analysis were derived from one retrospective study. Including RCTs only, the ORs for transfusion of RBC, FFP, and platelets were 0.54 (95% CI, 0.38-0.77; P<.001), 0.36 (95% CI, 0.25-0.53; P<.001), and 0.57 (95% CI, 0.39-0.81; P=.002), respectively. The use of coagulation factor concentrates was reported in 6 studies, 2 of them were RCTs. The ORs for the infusion of fibrinogen and prothrombin complex concentrate were 1.56 (95% CI, 1.29-1.87; P<.001) and 1.74 (95% CI, 1.40-2.18; P<.001), respectively. However, frequencies and amounts were similar in the intervention and control group in the 2 RCTs. It is presumed that TEG- or ROTEM-guided hemostatic management reduces the proportion of patients undergoing cardiac surgery transfused with RBC, FFP, and platelets. This presumption is strongly supported by similar ORs found in the analysis including RCTs only. Patient blood management based on the transfusion triggers by TEG or ROTEM appears to be more restrictive than the one based on conventional laboratory testing. However, evidence for improved clinical outcome is limited at this time.

Pulmonary thromboembolism during adult liver transplantation: incidence, clinical presentation, outcome, risk factors, and diagnostic predictors

BACKGROUND

Intraoperative pulmonary thromboembolism (PTE) is an often overlooked cause of mortality during adult liver transplantation (LT) with diagnostic challenge. The goals of this study were to investigate the incidence, clinical presentation, and outcome of PTE and to identify risk factors or diagnostic predictors for PTE.

METHODS

Four hundred and ninety-five consecutive, isolated, deceased donor LTs performed in an institution for a 3 yr period (2004-6) were analysed. The standard technique was a piggyback method with veno-venous bypass without prophylactic anti-fibrinolytics. The clinical diagnosis of PTE was made with (i) acute cor pulmonale, and (ii) identification of blood clots in the pulmonary artery or observation of acute right heart pressure overload with or without intracardiac clots with transoesophageal echocardiography.

RESULTS

The incidence of PTE was 4.0% (20 cases); cardiac arrest preceded the diagnosis of PTE [75% (15)] and PTE occurred during the neo-hepatic phase [85% (17)], especially within 30 min after graft reperfusion [70% (14)]. Operative and 60 day mortalities of patients with PTE were higher (P<0.001) than those without PTE (30% vs 0.8% and 45% vs 6.5%). Comparison of perioperative data between the PTE group (n=20) and the non-PTE group (n=475) revealed cardiac arrest and flat-line thromboelastography in three channels (natural, amicar, and protamine) at 5 min after graft reperfusion as the most significant risk factors or diagnostic predictors for PTE with an odds ratio of 154.32 [95% confidence interval (CI): 44.82-531.4] and 49.44 (CI: 15.6-156.57), respectively.

CONCLUSIONS

These findings confirmed clinical significance of PTE during adult LT and suggested the possibility of predicting this devastating complication.

A microchip flow-chamber system for quantitative assessment of the platelet thrombus formation process

As the pathogenesis of arterial thrombosis often includes platelet thrombus formation (PTF), antiplatelet agents are commonly used for the prevention of thromboembolic events. Here, using a novel microchip flow-chamber system we developed to quantitatively analyze the PTF process, we evaluated the pharmacological efficacies of antiplatelet agents under different arterial shear rates. Hirudin-anticoagulated whole blood was perfused over a collagen-coated microchip at shear rates of 1000, 1500, and 2000s(-1), and PTF in the absence and presence of various antiplatelet agents was observed microscopically and quantified by measuring flow-pressure changes. The onset of PTF was measured as T(10) (time to reach 10 kPa), and AUC(10) (area under the flow pressure curve for the first 10 min) was calculated to quantify the overall stability of the formed thrombus. Aspirin and AR-C66096 (P2Y(12)-antagonist) at high concentrations (50 μM and 1000 nM, respectively) prolonged T(10) only modestly (AR-C66096>aspirin), but effectively decreased AUC(10), resulting in unstable PTF at all examined shear rates. With dual inhibition using both aspirin (25 μM) and ARC-66096 (250 nM), AUC(10) was drastically reduced. Nearly complete suppression of AUC(10) was also observed with abciximab (2 μg ml(-1)) and beraprost (PGI(2)-analog; 4 nM). Although OS-1 (GPIbα-antagonist; 100 nM) prevented complete capillary occlusion, significant amounts of microscopic thrombi were observed on the collagen surface. In contrast to abciximab and beraprost, OS-1 differentially affected PTF under higher shear conditions. Our novel analytical system is capable of distinguishing the pharmacological effects of various antiplatelet agents under physiological shear rates, suggesting that this system may aid in the determination of the appropriate type and dose of antiplatelet agent in the clinical setting.

Myocardial infarction and cerebrovascular accident following non-cardiac surgery: differences in postoperative temporal distribution and risk factors

BACKGROUND

Myocardial infarction and stroke after non-cardiac surgery are two ominous cardiovascular complications believed to share similar pathophysiological processes. However, the differences in the temporal distribution between them have not been adequately investigated in a large cohort of patients.

METHODS AND RESULTS

The preoperative clinical features and daily occurrence of myocardial infarction and stroke were routinely recorded in 36 634 consecutive patients following elective non-cardiac, non-carotid surgery. The preoperative characteristics and postoperative daily distribution of postoperative myocardial infarction and stroke were compared using exponential and linear regressions models. Myocardial infarction and stroke occurred in 122 (0.33%) and 126 (0.34%) patients, respectively, during the first 30 days after surgery. More patients with myocardial infarction had diabetes mellitus and cardiac disease (P = 0.041 and <0.0001, respectively) whereas more patients with stroke were older and female (P = 0.003 and 0.038, respectively). The peak incidence of myocardial infarction was on the day of surgery (43%) and declined exponentially thereafter (F = 725.4, P < 0.0001). However, postoperative stroke best fitted a linear regression with almost even daily distribution (F = 15.9, P = 0.0004). The median time to myocardial infarction was one day [95% confidence interval (95% CI) = 0-2 days] compared with nine days (95% CI = 7-11 days) for stroke.

CONCLUSIONS

The peak incidence of postoperative myocardial infarction is early after non-cardiac surgery and declines exponentially thereafter, as opposed to stroke, which occurs at a constant rate during the postoperative period. Myocardial infarction and cerebrovascular accident following non-cardiac surgery differ in their preoperative risk factors, and in the postoperative time-line of their occurrence.

Electron Microscopic Evaluations of Clot Morphology During Thrombelastography??

In this study, we characterized clot morphology with a scanning electron microscope (SEM) at time points corresponding to the commonly used thrombelastography (TEG) variables, illustrating the correlation of the physical clot formation with TEG(R) tracings. The first channel of the TEG analyzer was used to obtain the tracings of clot formation, while the sub-samples for the SEM were obtained from the second TEG channel. Different types of samples were examined, including whole blood, abciximab-treated whole blood, platelet-rich plasma (PRP), and abciximab-treated PRP. The SEM images were obtained at reaction time, different amplitudes (5-30 mm), maximum amplitude (MA), and at amplitude 60 min after MA. In the whole blood, coarse fibrin and activated platelets were observed at reaction time and fibrin strands progressively became more solid and intertwined at amplitude 10 mm and thereafter. Red blood cells were surrounded with fibrin strands at amplitude 30 mm and were tightly packed by fibrin strands at MA. In abciximab-treated whole blood, red blood cell shape was maintained at MA. The process of fibrin formation and platelet activation was also examined in PRP. Abciximab did not block platelet shape change, although the blockage of fibrin binding to platelets was shown on the TEG analyzer. In summary, we have shown structural changes of the forming clot in relation to TEG variables.