Ischemia--a coagulation problem?

PAI-1 in Diabetes: Pathophysiology and Role as a Therapeutic Target

Hypofibrinolysis is a key abnormality in diabetes and contributes to the adverse vascular outcome in this population. Plasminogen activator inhibitor (PAI)-1 is an important regulator of the fibrinolytic process and levels of this antifibrinolytic protein are elevated in diabetes and insulin resistant states. This review describes both the physiological and pathological role of PAI-1 in health and disease, focusing on the mechanism of action as well as protein abnormalities in vascular disease with special focus on diabetes. Attempts at inhibiting protein function, using different techniques, are also discussed including direct and indirect interference with production as well as inhibition of protein function. Developing PAI-1 inhibitors represents an alternative approach to managing hypofibrinolysis by targeting the pathological abnormality rather than current practice that relies on profound inhibition of the cellular and/or acellular arms of coagulation, and which can be associated with increased bleeding events. The review offers up-to-date knowledge on the mechanisms of action of PAI-1 together with the role of altering protein function to improve hypofirbinolysis. Developing PAI-1 inhibitors may form for the basis of future new class of antithrombotic agents that reduce vascular complications in diabetes.

PKC and CaMK-II inhibitions coordinately rescue ischemia-induced GABAergic neuron dysfunction

Cerebral ischemia leads to neuronal death for stroke, in which the imbalance between glutamatergic neurons and GABAergic neurons toward neural excitotoxicity is presumably involved. GABAergic neurons are vulnerable to pathological factors and impaired in an early stage of ischemia. The rescue of GABAergic neurons is expected to be the strategy to reserve ischemic neuronal impairment. As protein kinase C (PKC) and calmodulin-dependent protein kinase II (CaMK-II) are activated during ischemia, we have investigated whether the inhibitions of these kinases rescue the ischemic impairment of cortical GABAergic neurons. The functions of GABAergic neurons were analyzed by whole-cell recording in the cortical slices during ischemia and in presence of 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (CaMK-II inhibitor) and chelerythrine chloride (PKC inhibitor). Our results indicate that PKC inhibitor or CaMK-II inhibitor partially prevents ischemia-induced functional deficits of cortical GABAergic neurons. Moreover, the combination of PKC and CaMK-II inhibitors synergistically reverses this ischemia-induced deficit of GABAergic neurons. One of potential therapeutic strategies for ischemic stroke may be to rescue the ischemia-induced deficit of cortical GABAergic neurons by inhibiting PKC and CaMK-II.

MASP-2 activation is involved in ischemia-related necrotic myocardial injury in humans

BACKGROUND/OBJECTIVES

Insufficient blood supply to the heart results in ischemic injury manifested clinically as myocardial infarction (MI). Following ischemia, inflammation is provoked and related to the clinical outcomes. A recent basic science study indicates that complement factor MASP-2 plays an important role in animal models of ischemia/reperfusion injury. We investigated the role of MASP-2 in human acute myocardial ischemia in two clinical settings: (1) Acute MI, and (2) Open heart surgery.

METHODS

A total of 187 human subjects were enrolled in this study, including 50 healthy individuals, 27 patients who were diagnosed of coronary artery disease (CAD) but without acute MI, 29 patients with acute MI referred for coronary angiography, and 81 cardiac surgery patients with surgically-induced global heart ischemia. Circulating MASP-2 levels were measured by ELISA.

RESULTS

MASP-2 levels in the peripheral circulation were significantly reduced in MI patients compared with those of healthy individuals or of CAD patients without acute MI. The hypothesis that MASP-2 was activated during acute myocardial ischemia was evaluated in cardiac patients undergoing surgically-induced global heart ischemia. MASP-2 was found to be significantly reduced in the coronary circulation of such patients, and the reduction of MASP-2 levels correlated independently with the increase of the myocardial necrosis marker, cardiac troponin I.

CONCLUSIONS

These results indicate an involvement of MASP-2 in ischemia-related necrotic myocardial injury in humans.

Accuracy of continuous central venous oxygen saturation monitoring in patients undergoing cardiac surgery

OBJECTIVE

Continuous assessment of central venous oxygen saturation (S(cevox)O(2)) with the CeVOX device (Pulsion Medical Systems, Munich, Germany) was evaluated against central venous oxygen saturation (S(cv)O(2)) determined by co-oximetry.

METHODS

In 20 cardiac surgical patients, a CeVOX fiberoptic probe was introduced into a standard central venous catheter placed in the right internal jugular vein and advanced 2-3 cm beyond the catheter tip. After in vivo calibration of the probe, S(cevox)O(2), S(cv)O(2), mixed venous oxygen saturation (S(mv)O(2)) haemoglobin (Hb), body temperature, heart rate, central venous and mean arterial pressure, and cardiac index were assessed simultaneously at 30 min intervals during surgery and at 60 min intervals during recovery in the intensive care unit. Agreement between S(cevox)O(2), and S(cv)O(2) was determined by Bland-Altman analysis. Simple regression analysis was used to assess the correlation of S(cevox)O(2), and S(cv)O(2) to Hb, body temperature and haemodynamic parameters.

RESULTS

Values of S(cevox)O(2) and S(cv)O(2) (84 data pairs during surgery and 106 in the intensive care unit) ranged between 45-89% and 43-90%, respectively. Mean bias and limits of agreement of S(cevox)O(2) and S(cv)O(2) were -0.9 (-7.9/+6.1)% during surgery and -1.2 (-10.5/+8.1)% in the intensive care unit. In 37.9% of all measured data pairs, the difference between S(cevox)O(2) and S(cv)O(2) was beyond clinically acceptable limits (> or =1 s.d.). Mean bias was significantly influenced by cardiac index. Sensitivity and specificity of S(cevox)O(2) to detect substantial (> or =1 s.d.) changes in S(cv)O(2) were 89 and 82%, respectively.

CONCLUSIONS

In adult patients during and after cardiac surgery, the current version of the CeVOX device might not be the tool to replace S(cv)O(2) determined by co-oxymetry, although sensitivity and specificity of S(cevox)O(2 )to predict substantial changes in S(cv)O(2) were acceptable.

Activated Protein C in the Cardioplegic Solution on a Porcine Model of Coronary Ischemia-Reperfusion has Deleterious Hemodynamic Effects

PURPOSE

In reperfusion injury activation of coagulation and inflammation contribute to organ dysfunction. Activated protein C (APC) exhibits anticoagulant and anti-inflammatory properties in models of reperfusion injury. We hypothesized that APC could be cardioprotective after ischemia and cardiopulmonary bypass (CPB).

METHODS

20 pigs, undergoing 120 min of CPB and aortic cross-clamping, were randomized to receive 1 mg of human APC or placebo to the last cardioplegic solution given 15 min before declamping to the systemic circulation. After aortic declamping the heart was supported by continuing CPB for 30 min followed by 30 min surveillance. Thrombin-antithrombin complexes, neutrophil L-selectin expression in blood and myeloperoxidase activity (MPO) of myocardial biopsies were measured.

RESULTS

There was no indication of APC-induced increased bleeding. Thrombin levels were significantly lower in the APC group than in the placebo group and so were the rates of thrombin formation during the first 3 min of reperfusion and between 10 and 30 min after declamping. There were no differences in MPO or in the proportion of L-selectin (+) to L-selectin (-) neutrophils between groups. Significant systolic hypotension in the APC group was observed at 30 and 45 min compared with the placebo group which associated with the increased mortality observed in the APC group (p = 0.019).

CONCLUSIONS

Human APC in cardioplegic solution during CPB in pigs, decreased reperfusion induced thrombin formation with no associated bleeding. No anti-inflammatory effects of human APC were seen. However, in this setting, APC caused hemodynamic deterioration. The observed phenomenon could be explained by systolic hypotension potentially produced by the release of vasoactive substances generated by the APC activation of PARs in the endothelium.

Association between early postoperative coagulation activation and peri-operative myocardial ischaemia in patients undergoing vascular surgery

We investigated the association of peri-operative myocardial ischaemia with activation of coagulation and endogenous fibrinolysis in patients undergoing vascular surgery. In 50 patients, continuous Holter monitoring was performed to assess peri-operative myocardial ischaemia and 12-lead electrocardiography was recorded preoperatively and 72 h postoperatively to assess myocardial infarction. Serial blood samples were drawn peri-operatively to determine the concentrations of fibrin monomers (for activation of coagulation), D-dimer (for endogenous fibrinolysis) and cardiac troponin T and I. Patients with myocardial ischaemia showed higher concentrations of fibrin monomers at 48 h, and higher concentrations of d-dimer preoperatively and at 24 and 48 h postoperatively. In patients with peri-operative myocardial ischaemia, strong positive correlations were observed between fibrin monomer and D-dimer concentrations at 15 min and 4 h postoperatively, and cardiac troponins at 15 min and at 4, 24, 48 and 72 h postoperatively. Early postoperative activation of coagulation and fibrinolysis is associated with peri-operative myocardial cell damage among patients who are at risk for, or have a history of, coronary artery disease plus peri-operative myocardial ischaemia.

The impact of cardiac ischemia and reperfusion on markers of activated haemostasis and fibrinolysis during cardiopulmonary bypass: comparison of plasma levels in arterial and coronary venous blood

INTRODUCTION

Activation of coagulation and fibrinolysis is common among patients undergoing cardiopulmonary bypass (CPB) surgery. Little is known, however, about the impact of myocardial ischemia and reperfusion on coagulation activation and fibrinolysis in this clinical setting.

STUDY DESIGN AND METHODS

We determined the levels of coagulation activation and fibrinolysis markers (CAFM) in 19 patients with severe coronary heart disease (CHD) during CPB surgery. FXIIa, tissue factor (TF), FVIIa, tissue plasminogen activator/plasminogen activator inhibitor-1 complexes (tPA/PAI-1), prothrombin fragments 1+2 (F1+2), D-dimers (DD) and plasmin-plasmin inhibitor complexes (PPI) were measured at baseline, prior to and after cardioplegic myocardial ischemia. Simultaneous blood samples were drawn from the aorta and the coronary sinus to evaluate arteriovenous CAFM plasma level gradients.

RESULTS

Myocardial ischemia induced significant increases in gradients of FXIIa and F1+2 levels across the coronary circulation without influencing systemic levels of these markers significantly. Systemic levels of FXIIa, tPA/PAI-1, F1+2, DD and PPI increased significantly during CPB operation. There was a significant linear correlation between FXIIa, FVIIa, F1+2, DD and PPI.

CONCLUSIONS

Myocardial ischemia induces contact activation and thrombin generation rather than release of tPA and might thus contribute to postoperative thromboembolic complications. Surgery itself and CPB cause activation of coagulation and fibrinolysis as already described. A significant association between FXIIa, FVIIa, F1+2, DD and PPI suggests a relationship between contact activation, thrombin generation, fibrin formation and fibrinolysis.

The response to activated protein C after cardiopulmonary bypass: impact of factor V leiden

Activated protein C (aPC) resistance is a recognized hypercoagulable phenotype that is associated with increased risk for thrombosis in multiple clinical settings. Factor V Leiden (FVL) represents a specific inherited cause of aPC resistance, but the perioperative thrombotic risk of FVL is unclear. In this investigation, we sought to quantify whether cardiopulmonary bypass produces alterations in aPC resistance in FVL carriers and noncarrier controls, testing the hypothesis that FVL is associated with a relatively hypercoagulable postoperative state. Two-hundred-five adult cardiac surgery patients were prospectively enrolled into a genetic registry whose purpose was to study the impact of genetic variables on clinical outcomes. For this study, 8 subjects heterozygous for FVL were identified (group L), as well as 2 control groups: group MC, matched controls, 18 matched subjects without FVL; and group UC, unmatched controls, 11 consecutive subjects without FVL. Plasma was sampled at the beginning of surgery, 10 min after protamine administration, and on postoperative day 1, and assayed for resistance to aPC (normal aPC ratio is >2.0). Both MC and UC groups exhibited normal aPC ratio at baseline (2.40 and 2.36, respectively), which increased significantly (to 2.76 and 2.75, P = 0.007 and 0.021, respectively) on postoperative day 1, indicating increased postoperative sensitivity to aPC. Conversely, group L subjects exhibited aPC resistance at baseline (aPC ratio 1.80), and did not change significantly postoperatively (P = 0.867). Patients without FVL therefore show laboratory evidence consistent with relative protection from postoperative thrombosis, whereas FVL carriers do not. These findings provide mechanistic support for previous speculations of increased postoperative thrombotic risk associated with FVL.

Coagulation and fibrinolytic markers in a two-month follow-up of coronary bypass surgery

OBJECTIVES

The alterations of the coagulation-fibrinolytic profile immediately and up to few days after cardiac surgery have been widely documented. However, less information is available on whether these alterations persist for prolonged periods of time after the operation. In this study we have evaluated the coagulation-fibrinolytic profile of patients who underwent coronary artery surgery with cardiopulmonary bypass during a 2-month follow-up period.

METHODS

Twenty-six patients (age range, 50-75 years) were studied. Blood samples were collected before the intervention and at different time points postoperatively up to 2 months after the operation. Measurement of selected coagulation-fibrinolytic variables was carried out in plasma from 16 patients. Evaluation of tissue factor activity determined as procoagulant activity was performed in peripheral blood mononuclear leukocytes obtained from 10 patients.

RESULTS

Antigenic levels of clottable fibrinogen, prothrombin fragment F1.2, D-dimer, and thrombin-antithrombin complex were significantly increased during the first week after the intervention compared with preoperative values. Prothrombin fragment F1.2 levels returned to normal within 15 days, fibrinogen levels normalized within 30 days, and thrombin-antithrombin complex levels normalized at 45 days, whereas D-dimer values were still significantly higher 60 days postoperatively respective to baseline values. There was a trend toward an increased procoagulant activity from peripheral blood mononuclear leukocytes 4 days after the operation, whereas no changes of factor VII measured either as antigen or in its coagulant and activated forms were recorded throughout the study.

CONCLUSIONS

A marked activation of the coagulation-fibrinolytic system occurs after cardiopulmonary bypass and lasts for at least 2 months thereafter. This finding suggests that these alterations might account for the increased thrombotic risk of these patients during the postoperative period.

Local anesthetic actions on thromboxane-induced platelet aggregation

Some local anesthetics (LA), in concentrations present in blood during IV or epidural infusion, inhibit thrombus formation in the postoperative period. Studies on thromboxane A2 (TXA2) signaling in a recombinant model suggest that interference with TXA2-induced platelet aggregation may explain, in part, the antithrombotic actions of epidural analgesia and IV LA infusion. In this study we investigated the effects of clinically used LAs (lidocaine, ropivacaine, and bupivacaine) on TXA2-induced early platelet aggregation (1-5 s) by using quenched-flow and optical aggregometry. Our findings demonstrate that the LAs tested seem to have only a limited ability to inhibit TXA2-induced platelet aggregation assessed at early times (1-5 s). Therefore, the clinical effects of LAs on thrombi formation are unlikely to be explained by this manner alone. At large LA concentrations, moderate effects were obtained. Prolonged incubation with LA did not significantly increase effectiveness, and the lack of an effect could not be explained by generation of secondary mediators. The results were independent of the anesthetic studied. Local anesthetic effects on TXA2-induced early platelet aggregation (1-5 s) are unlikely to play a major role in the clinically observed antithrombotic effects of local anesthetics.

IMPLICATIONS

Local anesthetic effects on thromboxane A2-induced early platelet aggregation (1-5 s) are unlikely to play a major role in the clinically observed antithrombotic effects of local anesthetics. Thus, other potential targets need to be explored.

Changes in coronary vessel resistance during postischemic reperfusion and effectiveness of nitroglycerin

OBJECTIVE

Microvascular incompetence after ischemia and reperfusion may compromise the normal postischemic coronary perfusion and additionally jeopardize the recovery of the myocytes. We investigated whether such a form of acute endothelial dysfunction occurs in the routine operative setting despite the use of protective measures. For this purpose, we measured pressure-flow relations in the coronary vasculature during heart operations before and after ischemia and after reperfusion and their reaction to the nitric oxide donor nitroglycerin.

METHODS

Forty-eight patients with a low risk profile scheduled for routine coronary artery bypass surgery were included. During normothermic extracorporeal circulation, the fibrillating heart was completely excluded from bypass by clamping of the ascending aorta and snaring of the caval veins. It was relieved of blood by opening the right atrium and venting the left atrium and ventricle to avoid distention. The coronary vessels were perfused under controlled flow, and the perfusion pressures were monitored. This protocol was performed in 24 patients before and immediately after ischemia and after a reperfusion period.

RESULTS

Compared with the preischemic control, vascular resistance was decreased by 17% (P <.003) immediately after ischemia but increased again by 46% (P <.0001) during an average of 25 minutes of reperfusion and, even more important, by 23% (P <.028) in comparison with the preischemic values. In two groups of 12 patients, nitroglycerin was added to the perfusate either in a dosage of 3 microg. kg. min(-1) or as a bolus injection of 2 mg. Low-dose nitroglycerin did not reduce the elevated postreperfusion resistances significantly, but bolus injection did (P <.0002). Coronary vessel resistance increased during reperfusion in particular in patients with a history of hypertension.

CONCLUSION

Coronary vasoconstriction during postischemic reperfusion is regularly present in the routine operative setting in cardiac surgery, despite myocardial protection measures. The amount of vasoconstriction varies considerably and is particularly increased in patients with hypertension. The nitric oxide donor nitroglycerin can normalize the elevated resistances, but only in high dosages. This demonstrates a preserved ability of vascular smooth muscle to relax. The phenomenon had no sequelae in our low-risk patients having elective operations. However, it may gain significance in the case of severe left heart hypertrophy and in patients at risk with both a postoperative low-output syndrome and reduced mean arterial pressures during reperfusion.

Protective effects of leukopenia and tissue plasminogen activator in microvascular ischemia-reperfusion injury

Ischemia shifts the anticoaugulant/procoagulant balance of the endothelium in favor of activation of coagulation. We studied whether cheek pouch microcirculation of leukopenic hamsters was protected by tissue plasminogen activator (tPA) (50 microg/100 g body wt) against ischemia-reperfusion injury. Adherent leukocytes, total perfused capillary length (PCL), permeability increase, and arteriolar and venular red blood cell (RBC) velocity were investigated by fluorescence microscopy. Measurements were made at control, 30 or 60 min of ischemia, and at 30 or 60 min of reperfusion. Hamsters were made leukopenic by treatment with cyclophosphamide (20 mg/100 g body wt ip, 4 days before the experiment), which decreased circulating leukocyte count by 85-90%. Leukopenic hamsters undergoing 30 min of ischemia followed by 30 min of reperfusion showed no significant decrease in PCL or increased permeability. Leukopenic hamsters undergoing 60 min of ischemia followed by 60 min of reperfusion presented a significant decrease in microvascular perfusion where PCL was 28 +/- 7% of baseline, low-flow conditions, and increased permeability. In leukopenic hamsters treated with tPA there was complete protection of capillary perfusion with no significant changes in permeability or arteriolar and venular RBC velocity. In conclusion, thrombus formation may be an additional and independent factor that with leukocyte-mediated mechanisms determines ischemia-reperfusion injury.

Cardiopulmonary bypass and activation of antithrombotic plasma protein C

OBJECTIVE

We hypothesized that antithrombotic plasma-activated protein C plays a defensive antithrombotic role during coronary ischemia and postischemic reperfusion.

METHODS AND RESULTS

We evaluated protein C activation during cardiopulmonary bypass and coronary reperfusion in 20 patients undergoing coronary bypass surgery. During cardiopulmonary bypass and during the 10 minutes after aortic unclamping, the plasma levels of protein C (mean +/- standard error of the mean) decreased from 123% +/- 7% to 74% +/- 5% of normal mean. In contrast, the levels of activated protein C in plasma increased from 122% +/- 8% to 159% +/- 21%, and the activated protein C/protein C ratio increased from 1.04 +/- 0.08 to 2.29 +/- 0. 31 (P =.006, 2-tailed Wilcoxon signed rank test). Patients were stratified on the basis of the increase in activated protein C in the coronary sinus plasma at 10 minutes after reperfusion by means of the arbitrary value of 1.5 for the activated protein C/protein C ratio. Within 24 hours, the patients with low increases in activated protein C (ratio < 1.5, n = 8) had a significantly (P <.05) lower cardiac output and mean pulmonary artery pressure, as well as a higher systemic vascular resistance, than patients (n = 11) with high increases in activated protein C (ratio > 1.5). The rapid increase in activated protein C during the first 10 minutes after aortic unclamping indicated protein C activation in the reperfused vascular beds.

CONCLUSIONS

The antithrombotic protein C pathway was significantly activated during cardiopulmonary bypass mainly during the minutes after aortic unclamping in the ischemic vascular beds. Suboptimal protein C activation during ischemia may impair the postischemic recovery of human heart and circulation.

Mechanism of the sympathoinhibition produced by the clonidine-like drugs rilmenidine and moxonidine

The mechanism of the sympathoinhibition produced by two new derivatives of clonidine, rilmenidine and moxonidine, was studied. One aim was to determine the receptor responsible for the central sympathoinhibition by these drugs. Rilmenidine and moxonidine were injected into the cisterna cerebellomedullaris. They decreased blood pressure and the plasma noradrenaline concentration. After rilmenidine and moxonidine, two selective alpha 2-adrenoceptor antagonists (devoid of affinity for I1 binding sites), yohimbine and SK&F86466, were given intracisternally. They completely counteracted the hypotensive effects of rilmenidine and moxonidine, indicating that alpha 2-adrenoceptors are involved in the central sympathoinhibition produced by these drugs. The other aim was to determine if peripheral presynaptic inhibition of noradrenaline release from postganglionic sympathetic neurons contributes to the overall reduction of sympathetic tone. Rilmenidine and moxonidine were injected i.v. in pithed rabbits with electrically stimulated sympathetic outflow. They dose-dependently lowered blood pressure and the plasma noradrenaline concentration and inhibited stimulation-evoked cardioacceleration. Moreover, the doses necessary for these peripheral effects were identical to the doses that reduce the sympathetic nerve firing rate and blood pressure in conscious rabbits. These observations indicate that peripheral presynaptic inhibition of noradrenaline release from postganglionic sympathetic neurons contributes to the overall reduction of sympathetic tone produced by rilmenidine and moxonidine in intact animals.

Central I1-imidazoline receptors as targets of centrally acting antihypertensive drugs. Clinical pharmacology of moxonidine and rilmenidine

Moxonidine and rilmenidine are moderately selective I1-receptor stimulants. The imidazoline (I1) agonists cause peripheral sympathoinhibition, triggered at the level of central nervous imidazoline receptors. Imidazoline receptor stimulants are effective antihypertensive agents with a hemodynamic profile that is attractive from a pathophysiologic point of view. The antihypertensive activity of these agents is caused by vasodilatation and reduced peripheral vascular resistance. Left ventricular end-diastolic and end-systolic volume is reduced, whereas heart rate, stroke volume, cardiac output, and pulmonary artery pressures are largely unchanged. Long-term left ventricular hypertrophy is reduced. Both drugs, when applied in a once-daily dosage schedule, appear to control hypertension in most patients. Both drugs have been compared with representative agents from the major classes of antihypertensive drugs in controlled trials and found to be equally effective in blood pressure control. The incidence and severity of side effects are lower than those for clonidine, particularly with respect to sedation. A rebound (withdrawal) phenomenon has so far not been reported for moxonidine and rilmenidine. Therefore, I1-receptor stimulants offer the possibility of developing centrally acting agents with a better side-effect profile than do the classic alpha 2-adrenoceptor stimulants.

Central imidazoline (I1) receptors as targets of centrally acting antihypertensives: moxonidine and rilmenidine

Clonidine, guanfacine, guanabenz and alpha-methyl-dioxyphenylalanine (DOPA), the prototypes of centrally acting antihypertensives, are assumed to induce peripheral sympathoinhibition and a reduction in blood pressure via the stimulation of alpha2-adrenoceptors in the brain stem. More recently, central imidazoline (I1)-receptors have been recognized to be another target of centrally acting antihypertensive drugs. Clonidine is considered to be a mixed agonist that stimulates both alpha2- and I1-receptors. Moxonidine and rilmenidine are considered to be moderately selective I1-receptor stimulants, although it still remains unknown whether these agents act directly on the receptor as genuine agonists. A survey is given on the location, characteristics and functional aspects of imidazoline I1-receptors as targets of centrally acting antihypertensives. Furthermore, the pharmacology and clinical potential of selective I1-receptor agonists such as moxonidine and rilmenidine are discussed. Although far from perfect, these compounds have shown that it may potentially be possible to develop agents with which the well-known side effects caused by alpha2-receptor agonists can be separated from the central antihypertensive mechanism.

Endothelial cell injury in cardiovascular surgery: ischemia-reperfusion

Myocardial ischemia and reperfusion is a common occurrence in cardiovascular surgery patients. Acute ischemia results in a spectrum of derangements, which range from transient reversible stunning of the myocardium to severe irreversible abnormalities such as infarction. Many of these abnormalities are accentuated upon reperfusion with oxygenated blood. Recently, the endothelium has been shown to play a key role in the injury suffered after ischemia and reperfusion. When rendered hypoxic and then reoxygenated, endothelial cells become activated to express proinflammatory properties that include the induction of leukocyte-adhesion molecules, procoagulant factors and vasoconstrictive agents that increase vasomotor tone. These changes may contribute to the no-reflow phenomenon by promoting endothelial edema, neutrophil and platelet plugging, microthrombosis, and enhanced vasomotor tone. An increased understanding of the role that hypoxic endothelial cell activation plays in myocardial dysfunction after ischemia/reperfusion may allow therapies to be designed to further attenuate this response.

Endothelial cell injury in cardiovascular surgery: the procoagulant response

The vascular endothelium plays a critical role in the regulation of coagulation through the constitutive expression and release of anticoagulants and the inducible expression of procoagulant substances. Cardiopulmonary bypass dysregulates this process by activating endothelial cells, initially promoting bleeding and then thrombosis. Endothelial cell activation in response to circulating inflammatory mediators leads to the initiation of coagulation when tissue factor is expressed throughout the intravascular space. This results in the widespread consumption of coagulation factors. Additionally, there is a cardiopulmonary bypass-related qualitative platelet defect that is exacerbated by thrombocytopenia as platelets are consumed from the circulation by clot and adherence to the cardiopulmonary bypass circuit. Finally, cardiopulmonary bypass results in the endothelial release of plasminogen activators, which lead to an increase in systemic fibrinolysis. The diffuse generation of thrombin, driven by the inducible intravascular expression of tissue factor, plays a major role in all of these processes. Efforts to understand the critical role of the endothelium in coagulation may lead to novel therapies to prevent bleeding or thrombosis in cardiovascular surgery patients.