Studies on components of the plasma kallikrein-kinin system in patients undergoing cardiopulmonary bypass

Probing the coagulation pathway with aptamers identifies combinations that synergistically inhibit blood clot formation

Coordinated enzymatic reactions regulate blood clot generation. To explore the contributions of various coagulation enzymes in this process, we utilized a panel of aptamers against factors VIIa, IXa, Xa, and prothrombin. Each aptamer dose-dependently inhibited clot formation, yet none was able to completely impede this process in highly procoagulant settings. However, several combinations of two aptamers synergistically impaired clot formation. One extremely potent aptamer combination was able to maintain human blood fluidity even during extracorporeal circulation, a highly procoagulant setting encountered during cardiopulmonary bypass surgery. Moreover, this aptamer cocktail could be rapidly reversed with antidotes to restore normal hemostasis, indicating that even highly potent aptamer combinations can be rapidly controlled. These studies highlight the potential utility of using sets of aptamers to probe the functions of proteins in molecular pathways for research and therapeutic ends.

Alterations to haemostasis following cardiopulmonary bypass and the relationship of these changes to neurocognitive morbidity

Cardiopulmonary bypass (CPB) is routinely utilized to provide circulatory support during cardiac surgical procedures. The morbidity of CPB has been significantly reduced since its introduction 50 years ago; however, cerebral injury remains a potentially serious consequence of otherwise successful surgery. The risk of stroke postoperatively is approximately 1-5%. Incidence rates for neurocognitive deficit, however, vary markedly depending on the detection method, although typically it is reported in at least 50% of patients. The aetiology of this cerebral injury remains open to debate, although evidence shows that ischaemia secondary to microembolism may be the principal factor. Emboli originate from bubbles of air, atheroemboli released on aortic manipulation and thromboemboli generated as a result of haemostatic activation. Significant generation of thrombin occurs during CPB resulting in fibrin formation, although the trigger of this activation is not fully understood. Rather than originating from contact activation as previously thought, the primary trigger may be via the activated factor VII/tissue factor pathway of coagulation, with an additional role of contact activation in amplification of coagulation as well as the fibrinolytic response to CPB. Haemostatic activation is inhibited with systemic heparin therapy. The relationship between haemostatic activation and emboli formation during CPB is not known. Interventions to reduce cerebral injury in the context of cardiac surgery depend, in large part, on the minimization of emboli. This review investigates cerebral injury after cardiac surgery and evidence showing that microembolism is the principal causative agent. Fibrin emboli are postulated to be an important source of cerebral embolism. The mechanism of haemostatic activation during CPB is therefore also discussed.

FXII levels, FXIIa-like activities and kallikrein activities in normal subjects and patients undergoing cardiac surgery

A new chromogenic peptide substrate assay kit was used to measure factor XII (FXII) levels in plasma samples from 115 male patients with heart disease awaiting cardiac surgery, 40 age-matched normal healthy male blood donors and 20 patients before, during and after cardiopulmonary bypass surgery (CPB). Kallikrein-like and FXIIa-like activities were also determined in the CPB patient group. FXII levels were significantly lower (p = 0.0049) in the heart disease patients awaiting surgery when compared with values for the healthy donors and 13 patients (11.3%) had FXII levels below 50% compared with 1 normal donor (2.5%). During CPB significant decreases in FXII levels and significant increases in FXIIa-like and kallikrein-like activities were found indicating activation of the FXII-plasma kallikrein pathway during CPB.

Heparin-coated bypass circuits (Carmeda) suppress the release of tissue plasminogen activator during normothermic coronary artery bypass graft surgery

OBJECTIVES

To study fibrinolysis in a homogeneous first-time coronary artery bypass surgery (CABG) population in whom heparin-coated circuits were used.

DESIGN

A prospective, blinded, randomized, placebo-controlled study.

SETTING

A university hospital, tertiary care, intraoperative and postoperative intensive care unit.

PARTICIPANTS

Twenty-one adult elective primary CABG patients.

INTERVENTIONS

Randomized circuit-type centrifugal pump, membrane oxygenator, rigid cardiotomy reservoir, either placebo (n = 10) or heparin-coated (n = 11) (Carmeda; Medtronic Inc., Anaheim, CA).

MEASUREMENTS AND MAIN RESULTS

Blood samples were analyzed for tissue plasminogen activator (TPA) activity, TPA antigen, plasminogen activator inhibitor-1 (PAI-1) activity, prothrombin complex F1.2, and antithrombin III (AT-III) at the following times: before cardiopulmonary bypass (CPB), during CPB (30 and 60 minutes), post-CPB, and day 1 postsurgery. TPA activity and antigen increased fivefold in the placebo group during CPB, whereas it did not even double in the heparin-coated group. PAI-1, F1.2, and AT-III were not different between groups.

CONCLUSIONS

Heparin-coated CPB circuits reduced TPA release in this homogeneous CABG population with routine heparin/protamine management.

Role of factor XII in thrombin generation and fibrinolysis during cardiopulmonary bypass

During cardiopulmonary bypass, thrombin is generated, which is thought to be initiated by activation of factor XII on the surface of the bypass equipment. We present a patient with severe factor XII deficiency who underwent cardiac surgery. As much thrombin was formed during cardiopulmonary bypass (measured by the prothrombin activation fragment F1 + 2 and thrombin-antithrombin complexes) as in normal patients, showing that factor XII was not necessary for thrombin generation. Factor X, but not factor IX, was activated (as measured by their activation peptides), and this activation correlated with F1 + 2 and thrombin-antithrombin complexes, suggesting that the tissue-factor/factor-VIIa pathway is the trigger for thrombin formation.