Brad L. Steenwyk

Qualitative thrombelastographic detection of tissue factor in human plasma

BACKGROUND:Tissue factor (TF) is the principal in vivo initiator of coagulation, with normal circulating TF concentrations reported to be approximately 23–158 pg/mL. However, patients with atherosclerosis or cancer have been reported to have TF concentrations ranging between 800 and 9000 pg/mL. Of interest, thrombelastographic (TEG®)-based measures of clot initiation and propagation have demonstrated hypercoagulability in such patients at risk for thromboembolic events. Thus, our goal in the present investigation was to establish a concentration-response relationship of the effect of TF on TEG® variables, and determine specificity of TF-mediated events with a monoclonal TF antibody. METHODS:Thrombelastography was performed on normal human plasma exposed to 0, 500, 1000, or 2000 pg/mL TF. Additional experiments with plasma exposed to 0 or 750 pg/mL TF in the presence or absence of a monoclonal TF antibody (1:360 dilution, 10 min incubation) were also performed. Clot initiation time (R) and the speed of clot propagation (MRTG, maximum rate of thrombus generation) were determined. RESULTS:The addition of TF to normal plasma resulted in a significant, concentration-dependent decrease in R and increase MRTG values. The addition of TF antibody to samples with TF significantly increased R and decreased MRTG values compared to samples with TF addition. CONCLUSIONS:In conclusion, changes in TEG® variables in conjunction with use of a TF antibody can detect pathological concentrations of TF in human plasma in vitro. Further investigation is warranted to determine if TEG®-based monitoring could assist in the detection and prevention of TF-initiated thromboembolic events.

Mechanical Circulatory Device Thrombosis: A New Paradigm Linking Hypercoagulation and Hypofibrinolysis

This review considers the perhaps unappreciated role of contact pathway proteins in the pathogenesis of thrombotic/thromboembolic morbidity associated with mechanical circulatory support. Placement of ventricular assist devices (VADs) has been associated with consumption of circulating contact proteins and persistent generation of activated contact proteins such as Factor XII and high molecular weight kininogen. Importantly, activated contact proteins are absorbed to the surface of VADs via the Vroman effect. Further, hyperfibrinogenemia and persistent platelet activation exist in patients with VADs, likely contributing to speed of clot growth. Using thrombelastographic-based analyses, it has been determined that contact pathway protein activated coagulation results in a thrombus that develops strength at a significantly faster rate that tissue factor initiated coagulation. Further, thrombelastographic analyses that include the addition of tissue-type plasminogen activator have demonstrated that contact protein pathway activation results in thrombin activatable fibrinolysis inhibitor activation to a far greater extent than that observed with tissue factor initiated coagulation, resulting in a thrombus that takes significantly longer to lyse. These observations serve as the rational basis for clinical investigation to determine if regional suppression of thrombin generation with FXII/high molecular weight kininogen inhibition in concert with thrombin-activatable fibrinolysis inhibitor inhibition may decrease mechanical circulatory support-associated thrombotic morbidity.

ε-Aminocaproic acid inhibition of fibrinolysis in vitro : should the 'therapeutic' concentration be reconsidered?

The therapeutic concentration of ϵ-aminocaproic acid (EACA) has been 130 μg/ml or greater for nearly 50 years. We tested the effects on clot growth/disintegration of EACA with a plasmatic model of hyperfibrinolysis in vitro. Human plasma was exposed to 1000 U/ml tissue-type plasminogen activator containing 0, 13, 65 or 130 μg/ml EACA, with clot growth/disintegration kinetics quantified via thrombelastography. Data were analyzed with one-way analysis of variance or Kruskal–Wallis analysis of variance as appropriate. Exposure of plasma to 1000 U/ml tissue-type plasminogen activator resulted in a brief-lived clot, lasting 2 min. EACA at all concentrations tested significantly increased the rate of clot growth compared with samples with 0 μg/ml EACA. Clot strength was significantly increased by EACA in a concentration-dependent fashion. Similarly, EACA significantly prolonged the time of onset of clot lysis and decreased the rate of lysis. Samples with 130 μg/ml EACA had no sign of lysis present for 30 min. Subtherapeutic to therapeutic concentrations of EACA significantly attenuated or abolished fibrinolysis in the presence of a concentration of tissue-type plasminogen activator more than 2000-fold that encountered systemically during cardiopulmonary bypass. Further clinical investigation is warranted to determine whether smaller concentrations of EACA could provide a reduction in bleeding with a concomitant decrease in thrombotic complications.

Clot lifespan model analysis of the effects of warfarin on thrombus growth and fibrinolysis: Role of contact protein and tissue factor initiation

Warfarin therapy has served as the backbone of chronic anticoagulation therapy for decades to prevent thrombotic morbidity secondary to blood-biomaterial interfaces. Unfortunately, thrombotic and bleeding complications are observed despite maintenance of therapeutic international normalized ratio (INR) values. We proposed to define the effects of warfarin therapy on thrombus growth and disintegration following contact pathway protein or tissue factor (TF) initiation. Normal subject or patient plasma with INR values between 1.8 and 9.6 were exposed to TF or celite and tissue-type plasminogen activator (tPA). Thrombus growth/disintegration kinetics were determined by changes in resistance over time with the clot lifespan model (CSLM), a thrombelastographic-based methodology. Data were collected until clot lysis time was observed. Linear relationships of the difference between the CLSM parameter values obtained from paired celite and TF-activated samples and corresponding INR value were determined and reported as r2. The time to clot initiation was progressively prolonged with increasing INR values in all samples, and speed of clot formation, clot strength, and time to onset of fibrinolysis decreased as INR increased. Throughout the range of INR values tested, contact activation resulted in faster growing, stronger, and longer lived thrombi when compared with matched TF-activated plasma samples. Only the time to maximum rate of lysis was correlated with INR (r2 = 0.36, p = 0.005). INR values have little correlation with the difference between contact protein and TF-activated coagulation/fibrinolysis.

Adrenal insufficiency in neonates after cardiac surgery with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) may lead to adrenal insufficiency (AI). Emerging evidence supports association of AI with morbidity after cardiac surgery.

Patient With Hypofibrinolysis-mediated Thromboembolism Converted to a Hypercoagulable/Hyperfibrinolytic State via Ventricular Assist Device Placement

Mechanical circulatory support with ventricular assist devices (VADs) for end-stage heart failure has been a focus of intense interest for nearly four decades. Despite improvements in VAD design and biomaterial composition, it is common to administer anti-coagulation (e.g., warfarin, anti-platelet agents) to prevent both device thrombosis and thromboembolism. We present a patient with pre-operative thrombophilia (pulmonary embolism, intracardiac thrombus) and hypofibrinolysis, who subsequently developed hypercoagulability with hyperfibrinolysis with normalization of clot lifespan after left VAD placement. Such complex patient-VAD-hemostatic-state interactions serve as the rationale for continuing investigation of the effects of mechanical circulation on the fibrinolytic system and thrombophilia.

Progressive lung calcification after orthotopic heart transplant

Focal, asymmetrical pulmonary airspace opacities in post-transplant setting are commonly from infection, hemorrhage, edema or infarction. Rarely, stable or mildly progressive dense pulmonary opacities are due to pulmonary calcifications. In the majority of cases, these are asymptomatic and warrant no further intervention.