Endogenous fibrinolysis-Relevance to clinical thrombosis risk assessment

Platelet reactivity and activated clotting time predict hemorrhagic site complications in patients with chronic coronary syndromes undergoing percutaneous coronary interventions

BACKGROUND

Radial access is preferred in patients with chronic coronary syndromes (CCSs) treated with ad hoc percutaneous coronary intervention (PCI). Antithrombotic and antiplatelet treatment before PCI may affect outcomes at vascular access sites. QuikClot Radial is a kaolin-based band that may shorten hemostasis time. Using point-of-care testing, we investigated the effect of antithrombotic and antiplatelet treatment on access-site complications.

METHODS

This prospective observational study included consecutive patients with CCS on chronic aspirin therapy referred for ad hoc PCI. The activated clotting time (ACT), global thrombosis test and VerifyNow P2Y 12 test were done sequentially after unfractionated heparin (UFH) and clopidogrel administration. Patients were monitored for radial artery patency, bleeding and local hematoma until discharge.

RESULTS

We enrolled 40 patients [mean age, 68.8 ± 8.8 years; men, 30 (75%)] who received UFH (median dose, 8000 IU; interquartile range, 7000-9000 IU) and clopidogrel (600 mg). All radial arteries remained patent during follow-up. Local bleeding and hematomas were noted in 11 patients (27.5%) each. Patients with bleeding had lower mean platelet activity at 2 h [122.5 ± 51 platelet reactivity units (PRU) vs. 158.7 ± 43 PRU, P  = 0.04] and higher ACT (216.9 ± 40 s vs. 184.6 ± 28 s, P = 0.006) than patients without bleeding. An ACT >196 s at 2 h predicted bleeding or hematoma (AUC, 0.72; 95% CI, 0.56-0.85, P = 0.008).

CONCLUSION

Lower platelet activity and higher ACT after PCI were associated with higher bleeding risk at a vascular access site. Point-of-care testing of ACT after the procedure may help identify patients with CCS undergoing PCI who are at higher risk of access-site bleeding.

Vulnerable atherosclerotic plaque features: findings from coronary imaging

Pathological studies have suggested that features of vulnerable atherosclerotic plaques likely to progress and lead to acute cardiovascular events have specific characteristics. Given the progress of intravascular coronary imaging technology, some large prospective studies have detected features of vulnerable atherosclerotic plaques using these imaging modalities. However, the rate of cardiovascular events, such as acute coronary syndrome, has been found to be considerably reduced in the limited follow-up period available in the statin era. Additionally, not all disrupted plaques lead to thrombus formation with clinical presentation. If sub-occlusive or occlusive thrombus formation does not occur, a thrombus on a disrupted plaque will organize without any symptoms, forming a “healed plaque”. Although vulnerable plaque detection using intracoronary imaging is focused on “thin-cap fibroatheroma” leading to plaque rupture, superficial plaque erosion is increasingly recognized; however, the underlying mechanism of thrombus formation on eroded plaques is not well understood. One of intravascular imaging, optical coherence tomography (OCT) has the highest image resolution and has enabled detailed characterization of the plaque in vivo. Here, we reviewed the status and limitations of intravascular imaging in terms of detecting vulnerable plaque through mainly OCT studies. We suggested that vulnerable plaque should be reconsidered in terms of eroded plaque and healed plaque and that both plaque and circulating blood should be assessed in greater detail accordingly.

Fibrinolysis in Platelet Thrombi

The extent and duration of occlusive thrombus formation following an arterial atherothrombotic plaque disruption may be determined by the effectiveness of endogenous fibrinolysis. The determinants of endogenous fibrinolysis are the subject of much research, and it is now broadly accepted that clot composition as well as the environment in which the thrombus was formed play a significant role. Thrombi with a high platelet content demonstrate significant resistance to fibrinolysis, and this may be attributable to an augmented ability for thrombin generation and the release of fibrinolysis inhibitors, resulting in a fibrin-dense, stable thrombus. Additional platelet activators may augment thrombin generation further, and in the case of coronary stenosis, high shear has been shown to strengthen the attachment of the thrombus to the vessel wall. Neutrophil extracellular traps contribute to fibrinolysis resistance. Additionally, platelet-mediated clot retraction, release of Factor XIII and resultant crosslinking with fibrinolysis inhibitors impart structural stability to the thrombus against dislodgment by flow. Further work is needed in this rapidly evolving field, and efforts to mimic the pathophysiological environment in vitro are essential to further elucidate the mechanism of fibrinolysis resistance and in providing models to assess the effects of pharmacotherapy.

Ethnic Difference of Thrombogenicity in Patients with Cardiovascular Disease: a Pandora Box to Explain Prognostic Differences

Arterial and venous atherothrombotic events are finely regulated processes involving a complex interplay between vulnerable blood, vulnerable vessel, and blood stasis. Vulnerable blood ('thrombogenicity') comprises complex interactions between cellular components and plasma factors (inflammatory, procoagulant, anticoagulant, and fibrinolytic factors). The extent of thrombogenicity may determine the progression of atheroma and the clinical manifestation of atherothrombotic events, with the highest thrombogenicity in African Americans and lowest in East Asians. Inherent thrombogenicity may influence clinical efficacy and safety of specific antithrombotic treatments in high-risk patients, which may in part explain the observation that East Asian patients have reduced anti-ischemic benefits and elevated bleeding risk with antithrombotic therapy compared to Caucasian patients. In this review, we discuss available evidence regarding the racial differences in thrombogenicity and its impact on clinical outcomes among patients with atherosclerotic cardiovascular disease.