Utility of the Total Thrombus-Formation Analysis System as a Tool for Evaluating Thrombogenicity and Monitoring Antithrombotic Therapy in Pediatric Fontan Patients

BACKGROUND

There is no consensus regarding thromboprophylaxis after Fontan procedure, and novel tools to assess thrombogenicity are needed to establish optimal thromboprophylaxis. The Total Thrombus-formation Analysis System (T-TAS) was developed for the quantitative analysis of thrombus formation using microchips with thrombogenic surfaces. This prospective study evaluated the utility of T-TAS in the assessment of thrombogenicity in pediatric Fontan patients.

METHODS AND RESULTS

The participants included 20 consecutive Fontan patients who underwent cardiac catheterization and 30 healthy controls. Blood samples collected without and with antithrombotic therapy (aspirin or aspirin and warfarin) were used for T-TAS to compute the area under the curve (AUC) in the atheroma (AR₁₀-AUC₃₀) and platelet (PL₁₈-AUC₁₀) chips. A higher AUC indicates higher thrombogenicity. T-TAS values showed that patients in the Fontan group without antithrombotic therapy had lower thrombogenicity than those in the control group [PL₁₈-AUC₁₀, median (interquartile range) 356 (313-394) vs. 408 (392-424); AR₁₀-AUC₃₀, median (interquartile range) 1270 (1178-1351) vs. 1382 (1338-1421)]. Aspirin and warfarin therapies significantly decreased PL₁₈-AUC₁₀ and AR₁₀-AUC₃₀, respectively, compared with those of patients without antithrombotic therapy (P < 0.001 for each comparison). Subgroup analysis divided by low (< 9 mmHg) or high (≥ 9 mmHg) central venous pressure (CVP) showed that CVP affects the reduction in AR₁₀-AUC₃₀ with antithrombotic therapy.

CONCLUSIONS

T-TAS may be a useful tool for monitoring thrombogenicity and antithrombotic therapy in Fontan patients.

Platelet volume indices correlate to severity of heart failure and have prognostic value for both cardiac and thrombotic events in patients with congenital heart disease

Patients with heart failure (HF) reportedly have activated platelets with increased platelet distribution width (PDW) and mean platelet volume (MPV), which lead to thrombotic events. These platelet indices are easily measured by routine blood tests and have been proposed as potential markers of cardiac events. We performed the present study to clarify whether platelet indices correlate to the severity of HF and to the prognosis of patients with congenital heart disease (CHD). We performed a retrospective single-center study including 400 patients with CHD [median age, 34 years (range 12-76); 49% males] hospitalized between 2014 and 2017. We assessed their clinical data, correlation between platelet indices and severity of HF, and prognosis of HF-related hospitalization and thrombus formation. In multivariate analysis, a significant correlation was found between PDW and logBNP (log-transformed brain natriuretic peptide; r = 0.30, p < 0.001), as well as between MPV and logBNP (r = 0.24, p < 0.001). After treatment for heart failure, a significant reduction was found in PDW (average value before treatment: 14.2; after: 13.2, p = 0.017). In multivariate logistic regression analysis, PDW [hazard ratio (HR) 1.365; 95% confidence interval (CI) 1.005-1.768] and MPV (HR 1.472; 95% CI 1.055-2.052) were predictors of HF-related hospitalization. Similarly, PDW (HR 1.998; 95% CI 1.461-2.630) and MPV (HR 1.792; 95% CI 1.155-2.781) were predictors of thrombus formation. Platelet volume indices correlate to severity of heart failure and have prognostic value for both cardiac and thrombotic events in patients with CHD.

Properties of Plasma Clots in Adult Patients Following Fontan Procedure: Relation to Clot Permeability and Lysis Time-Multicenter Study

Objectives: thromboembolic complications are a major cause of morbidity and mortality following Fontan (FO) surgery. It is also well established that altered FO circulation results in systemic complications, including liver and endothelium damage. We sought to evaluate whether dysfunctions of these sources of hemostatic factors may result in changes of fibrin clot properties. Methods: a permeation coefficient (K_s) and clot lysis time (CLT) were assessed in 66 FO patients, aged 23.0 years [IQR 19.3–27.0], and 59 controls, aged 24.0 years [IQR 19.0–29.0]. K_s was determined using a pressure-driven system. CLT value was measured according to assay described by Pieters et al. Endothelium and liver-derived hemostatic factors along with liver function parameters were evaluated. The median time between FO operation and investigation was 20.5 years [IQR 16.3–22.0]. Results: FO patients had lower K_s (p = 0.005) and prolonged CLT (p < 0.001) compared to that of controls. K_s correlated with CLT (r = −0.28), FVIII (r = −0.30), FIX (r = −0.38), fibrinogen (r = −0.41), ALT (r = −0.25), AST (r = −0.26), GGTP (r = −0.27) and vWF antigen (r = −0.30), (all p < 0.05). CLT correlated with the time between FO operation and investigation (r = 0.29) and FIX (r = 0.25), (all p < 0.05). After adjustment for potential cofounders, TAFI antigen and GGTP were independent predictors of reduced K_s (OR 1.041 per 1% increase, 95% CI 1.009–1.081, p = 0.011 and OR 1.025 per 1 U/L increase, 95% CI 1.005–1.053, p = 0.033, respectively). Protein C and LDL cholesterol predicted prolonged CLT (OR 1.078 per 1% increase, 95% CI 1.027–1.153, p = 0.001 and OR 6.360 per 1 μmol/L increase, 95% CI 1.492–39.894, p = 0.011, respectively). Whereas elevated tPA was associated with lower risk of prolonged CLT (OR 0.550 per 1 ng/mL, 95% CI 0.314–0.854, p = 0.004). GGTP correlated positively with time between FO surgery and investigation (r = 0.25, p = 0.045) and patients with abnormal elevated GGTP activity (n = 28, 42.4%) had decreased K_s, compared to that of the others (5.9 × 10⁻⁹ cm² vs. 6.8 × 10⁻⁹ cm², p = 0.042). Conclusion: our study shows that cellular liver damage and endothelial injury were associated with prothrombotic clot phenotype reflected by K_s and CLT.

Thromboembolic Events Are Independently Associated with Liver Stiffness in Patients with Fontan Circulation

Background: Thromboembolism (TE) and Fontan-associated liver disease (FALD) are common and lead to significant morbidity in Fontan circulations. Risk factors for TE and the potential link between TE and FALD are not well understood. The objective of this study was to evaluate the association between TE and the severity of FALD based on radiologic liver stiffness. Methods: Using a retrospective cohort study design, 85 Fontan patients (aged 27.7 ± 8.2 years) who had liver stiffness measurement were included. Multivariable logistic regression was used to determine independent associations with TE. Results: Sixteen patients (19%) had a history of TE after the Fontan procedure at a mean age of 21.4 ± 15.0 years. Patients with TE were significantly older at the time of the last evaluation (33.8 ± 11.7 vs. 26.3 ± 6.5 years, p = 0.03). Liver stiffness by MRI and ultrasound was higher in the TE group (5.1 ± 1.4 vs. 4.3 ± 1.2 kPa, p = 0.04 and 2.8 ± 0.4 vs. 2.4 ± 0.5 m/s, p = 0.04, respectively). On multivariable analysis, higher liver stiffness (odds ratio (OR): 2.12, p = 0.03) and older age (OR: 1.11, p = 0.03) were associated with TE. Conclusions: This study found an association between TE, age, and radiologic liver stiffness.

Pathophysiology of thrombosis and anticoagulation post Fontan surgery

The Fontan procedure has transformed the lives of children born with single-ventricle physiology, previously deemed inoperable. Worldwide, there are an increasing number of children with Fontan circulation, with the potential for survival into adulthood. Due to the abnormal circulation, Fontan patients have an increased risk of thromboembolic (TE) events, with up to 25% of events leading to death. Despite the importance of preventing TE events in this patient population, there is currently no clinical consensus on the optimal monitoring, thromboprophylaxis therapies, and treatment of these events. This paper reviews the available literature regarding anticoagulation in the pediatric and adult Fontan population, including the mechanisms for thrombosis and current antithrombotic therapies.

Strategies for thromboprophylaxis in Fontan circulation: a meta-analysis

BACKGROUND

The Fontan circulation is associated with an increased risk of thromboembolic events (TEs). As many as 25% of these thrombotic events result in fatality. More subtle adverse effects on the pulmonary circulation from embolic thrombi may further impair adequate functioning of the circuit. Despite these well-documented phenomena, the most optimal approaches to thromboprophylaxis are still not clearly defined.

OBJECTIVE

A meta-analysis of published trials in English on PubMed and Cochrane libraries that evaluated the role of using TE prophylaxis in patients who underwent the Fontan procedure was conducted.

METHODS

10 studies with a total number of 1200 patients with an average follow-up time of 7.1 years were identified. A random effect model was used.

RESULTS

The incidence of TE was significantly less in patients who received TE prophylaxis (using either aspirin or warfarin) compared with patients who did not receive TE prophylaxis (OR 0.425, 95% CI 0.194 to 0.929, p<0.01, I(2)=37%). The incidence of TE was significantly lower in patients who received aspirin compared with no TE prophylaxis (OR 0.363, 95% CI 0.177 to 0.744, p<0.01, I(2)=0%) and who received warfarin compared with no TE prophylaxis (OR 0.327, 95% CI 0.168 to 0.634, p<0.01, I(2)=2.5%). There was no significant difference in incidence of TE between warfarin and aspirin (OR 0.936, 95% CI 0.609 to 1.438, p=0.54, I(2)=0%). Furthermore, there was no significant difference in incidence of early TE (within 6 months of the operation) or late TE (>6 months) between patients receiving warfarin and aspirin (OR 0.784, 95% CI 0.310 to 1.982, p=0.37, I(2)=8%) and (OR 0.776, 95% CI 0.249 to 2.42, p=0.3, I(2)=45%), respectively. When only total cavopulmonary connection patients were included, there was again no difference between warfarin and aspirin in the incidence of TE (OR 0.813, 95% CI 0.471 to 1.401, p=0.34, I(2)=11%).

CONCLUSIONS

This study shows a significantly lower incidence of TE after Fontan procedure if either aspirin or warfarin is used. This meta-analysis suggests no significant difference in incidence of early or late TE in patients receiving aspirin compared with warfarin.

Thromboembolic complications in Fontan patients: population-based prevalence and exploration of the etiology

After the Fontan procedure, patients face an increased risk for thromboembolic events (TE). The etiology for this increased thrombogenecity is incompletely understood. This study aimed to determine the prevalence of TE in Danish Fontan patients and to bring new insights into the etiology of TE. Using a population-based design, we retrospectively identified all TEs in 210 Fontan patients. Whole blood assays (thromboelastography, thromboelastography functional fibrinogen and Multiplate) reflecting global hemostasis, clot strength and platelet aggregation were analyzed prospectively in 112 patients and plasma was analyzed in 76 patients for biomarkers reflecting endothelial-, glycocalyx-, platelet-, and fibrinolysis function (histone-complexed DNA fragments, Protein C, soluble CD40 ligand, soluble thrombomodulin, syndecan-1, tissue-type plasminogen activator). The results were compared in groups stratified according to age, antithrombotic therapy, TE, and glycocalyx degradation (syndecan-1 < or ≥ median). Correlation between biomarkers and demographic-, anatomical-, clinical- and biochemical parameters was investigated. The prevalence of TE was 8.1 % after a mean follow-up of 8.4 years. None of the stratified groups demonstrated evidence of hypercoagulability in the whole blood assays and no unexpected significant differences were found between the groups. All biomarkers, except protein C, correlated with one another and after stratification of glycocalyx degradation only syndecan-1 levels ≥ median correlated with other biomarkers. The prevalence of TEs was 8.1 % after mean follow-up of 8.4 years. Overall, the hemostatic profile appeared normal, however, in a subset of patients, evidence of some endothelial activation/damage including glycocalyx degradation and fibrinolysis was found, identifying a potentially more thrombogenic group.

Usefulness of peripheral vascular function to predict functional health status in patients with Fontan circulation

After the Fontan operation, patients are at a substantial risk of the development of impaired functional health status. Few early markers of suboptimal outcomes have been identified. We sought to assess the association between peripheral vascular function and functional health status in Fontan-palliated patients. Asymptomatic Fontan patients (n = 51) and age- and gender-matched healthy controls (n = 22) underwent endothelial pulse amplitude testing using a noninvasive fingertip peripheral arterial tonometry (PAT) device. Raw data were transformed into the PAT ratio, an established marker of vascular function. Cardiopulmonary exercise testing was performed using the Bruce protocol. In the Fontan cohort, 94% of patients were New York Heart Association functional class I and 88% had a B-type natriuretic peptide level of <50 pg/ml. The baseline pulse amplitude, a measure that reflects the arterial tone at rest, was greater in the Fontan patients than in the controls (median 2.74, interquartile range 1.96 to 4.13 vs median 1.86, interquartile range 1.14 to 2.79, p = 0.03). The PAT ratio, a measure of reactive hyperemia, was lower in Fontan patients (median 0.17, interquartile range -0.04 to 0.44, vs median 0.50, interquartile range 0.27 to 0.74, p = 0.002). The key parameters of exercise performance, including peak oxygen consumption (median 28.8 ml/kg/min, interquartile range 25.6 to 33.2 vs median 45.5 ml/kg/min, interquartile range 41.7 to 49.9, p <0.0001) and peak work (median 192 W, interquartile range 150 to 246 vs median 330, interquartile range 209 to 402 W, p <0.0001), were lower in Fontan patients than in the controls. The PAT ratio correlated with the peak oxygen consumption (r = 0.28, p = 0.02) and peak work (r = 0.26, p = 0.03). In conclusion, in an asymptomatic Fontan population, there is evidence of reduced basal peripheral arterial tone and vasodilator response, suggesting dysfunction of the endothelium-derived nitric oxide pathway. Vasodilator function appears to correlate with exercise performance.

Loxosceles gaucho spider venom and its sphingomyelinase fraction trigger the main functions of human and rabbit platelets

Loxosceles venoms can promote severe local and systemic damages. We have previously reported that Loxosceles gaucho spider venom causes a severe early thrombocytopenia in rabbits. Herein, we investigated the in vitro effects of this venom and its sphingomyelinase fraction on the main functions of platelets. Whole venom and its fraction induced aggregation of both human and rabbit platelets. Aggregation was dependent of plasma component(s) but independent of venom-induced lysophosphatidic acid generation. There was no increase in the levels of lactate dehydrogenase during platelet aggregation, ruling out the possibility of platelet lysis. The increased expression of ligand-induced binding site 1 (LIBS1) induced by L. gaucho venom and its sphingomyelinase fraction, as well as of P-selectin by the whole venom, evidenced the activation state of both human and rabbit platelets. Adhesion assays showed an irregular response when platelets were exposed to the whole venom, whereas the sphingomyelinase fraction induced a dose-dependent increase in the platelet adhesion to collagen. These findings evidence that L. gaucho venom and its sphingomyelinase fraction trigger adhesion, activation, and aggregation of both human and rabbit platelets. Thus, this work justifies the use of rabbits to investigate Loxosceles venom-induced platelet disturbances, and it also supports research on the role of platelets in the pathogenesis of loxoscelism.

Antiplatelet versus anticoagulation therapy after extracardiac conduit Fontan: a systematic review and meta-analysis

The benefits of prophylactic anticoagulation or antiplatelet therapy for patients undergoing extracardiac conduit (ECC) Fontan procedure still are a matter of debate. Through a systematic review and meta-analysis, this study aimed to determine the incidence of thromboembolism among patients undergoing ECC Fontan who received anticoagulation or antiplatelet therapy. Until February 2010, MEDLINE studies describing the incidence of thromboembolic events after ECC Fontan were reviewed. Information on type of drugs and clinical outcome was extracted. The 20 studies analyzed involved 1,075 patients: 220 (20.4%) in the antiplatelet group and 855 (79.5%) in the anticoagulation group. The mean follow-up period ranged from 2 to 144 months. The overall thromboembolism rate was 5.2% (95% confidence interval [CI], 3.8-7%; I(2) = 0%; p(het) = 0.32). The effect of different therapeutic strategies on the occurrence of thromboembolic and bleeding events was analyzed. Interestingly, the anticoagulation therapy compared with the antiplatelet therapy was not associated with a significant reduction in the incidence of overall thromboembolic complications (5% vs 4.5%, respectively; I(2) = 0%; p(het) = 0.80). Only two cases of bleeding were observed among patients receiving anticoagulant therapy at the time of the event. For patients undergoing ECC Fontan, the rate of thromboembolic and bleeding events associated with antiplatelet therapy is similar to that associated with anticoagulation therapy.