Comparison of the Prevalence of APC-resistance in Vascular Patients and in a Normal Population Cohort in Western Germany

Vascular graft thrombosis secondary to activated protein C resistance: a case report and literature review

Hypercoagulability is a well-documented and prominent risk factor for venous thromboembolism. The role of thrombophilia in arterial thrombotic events is less well defined. A 52-year-old male patient with multiple atherogenic risk factors was admitted for non-healing pedal ulcer and absent distal pulses. Based on the clinical presentation, Doppler ultrasound and angiography findings, the patient underwent elective in situ bypass arterial reconstruction. The saphenous vein graft was of satisfactory quality and the procedure went routinely. Acute graft thrombosis on postoperative day 0 was recognized immediately and prompted an emergent surgical revision. No technical errors or anatomical/mechanical causes for failed reconstruction were found and the graft was successfully thrombectomized using a Fogarty balloon-catheter. Graft rethrombosis, however, ensued after several hours. Considering the absence of threatening limb ischemia and the idiopathic recurrent thrombosis, raising suspicion of prothrombotic state, conservative treatment was pursued. Postoperative thrombophilia testing proved positive for activated protein C resistance, mandating introduction of chronic oral anticoagulation. Six months later, the operated extremity is viable. Inexplicable vascular graft thrombosis, particularly if early and recurrent, should raise suspicion of underlying thrombophilia. If confirmed by laboratory testing, long-term secondary antithrombotic prophylaxis may be required.

Increased tissue factor pathway inhibitor activity is associated with myocardial infarction in young women: results from the RATIO study

BACKGROUND

The tissue factor pathway inhibitor (TFPI)/protein S anticoagulant system is a potent inhibitor of blood coagulation. TFPI and protein S are major determinants of thrombin generation (TG) tests determined at low tissue factor (TF) and at high TF concentrations in the presence of activated protein C (APC). Both TFPI and protein S protect against venous thrombosis, but the importance of the TFPI/protein S system in arterial thrombosis remains unclear.

OBJECTIVES

To investigate the influence of the TFPI/protein S anticoagulant system on the risk of myocardial infarction (MI) in young women.

METHODS

The RATIO study is a case-control study in women under 50 years of age, including 205 patients and 638 controls. TFPI and protein S were quantified using ELISA. The TFPI/protein S activity (nTFPIr) and the APC sensitivity ratio (nAPCsr) were determined using TG tests. Odds ratios (ORs) adjusted for putative confounders and corresponding 95% confidence intervals (95% CI) were determined.

RESULTS

Women with MI had higher TFPI levels than controls (135.9 ± 40% vs. 124.2 ± 41%), resulting in increased TFPI/protein S activities and increased APC sensitivity. Furthermore, an increased TFPI activity was associated with MI [nTFPIr: adjusted OR Q1 vs. Q4 = 2.1 (95%CI 1.1-4.1)]. Additionally, an increased APC sensitivity was associated with MI [nAPCsr: adjusted OR Q1 vs. Q4 = 1.7 (95% CI 0.9-3.2)]

CONCLUSION

Women with MI had increased TFPI levels compared with controls. Consequently, the TFPI/protein S activity and APC sensitivity are increased in women with MI. Whether this increase in TFPI activity acts as a compensating mechanism for an increased procoagulant state or is a marker of endothelial damage remains to be investigated.

Arterial thrombosis in mice with factor V Leiden mutation

The factor V Leiden (FVL) mutation has been demonstrated to be associated with the development of venous thrombosis in humans. Whether such a propensity also exists in the arterial circulation remains controversial. In an effort to minimize the variability that clouds the clinical study of arterial thrombosis, we studied FVL-associated arterial thrombosis in an experimental model of homozygous, heterozygous, and wild-type mice. Heterozygous FVL mice were crossbred to C57BL/6J mice over several generations. The genotypes of the resulting three genotype groups (wild type, heterozygous FVL, and homozygous FVL) were blinded to the investigators. Arterial injury was produced with the injection of ferric chloride into an isolated segment of carotid artery. Arterial thrombosis was assessed with an ultrasonic flow probe and the time to occlusion (TTO) was recorded. The carotid artery occluded within 60 minutes of injury in 72 of the animals studied (97.3%). The carotid artery remained patent at 60 minutes in the remaining two animals, both of whom were subsequently found to be genotypically wild type. There was a statistically significant relationship between TTO and genotype (p = .002). TTO was greatest in the wild-type mice (p < .001 vs heterozygous, < .001 vs homozygous) and least in the homozygotes (p < .001 vs heterozygotes). Increased thrombogenicity is present in mice with the FVL mutation and is more prolonged in homozygotes than heterozygotes. These findings provide some corroboration to the clinical studies that suggest an increased risk of arterial events in patients with the FVL mutation.

Inherited Thrombophilia in Arterial Disease: A Selective Review

Thrombophilia may be defined as an acquired or congenital abnormality of hemostasis predisposing to thrombosis. Because arterial thrombosis is usually linked with classical risk factors such as smoking, hypertension, dyslipidemia, or diabetes, a thrombophilia workup is usually not considered in case of arterial thrombosis. The most accepted inherited hemostatic abnormalities associated with venous thromboembolism are factor V Leiden (FVL) and factor II (FII) G20210A mutations, as well as deficiencies in antithrombin (AT), protein C (PC), and protein S (PS). This review focuses on the link between these abnormalities and arterial thrombosis. Overall, the association between these genetic disorders and the three main arterial complications (myocardial infarction [MI], ischemic stroke [IS], and peripheral arterial disease [PAD]) is modest. Routine screening for these disorders is therefore not warranted in most cases of arterial complications. However, when such an arterial event occurs in a young person, inherited abnormalities of hemostasis seem to play a role, particularly when associated with smoking or oral contraceptive use. These abnormalities also seem to play a role in the risk of premature occlusion after revascularization procedures. Therefore thrombophilia tests may be informative in a very restricted population with arterial events. Anticoagulants rather than antiplatelet therapy may be preferable for these patients, although this remains to be proven.