Antiplatelet drugs in patients with enhanced platelet turnover: biomarkers versus platelet function testing

Platelets are key players in atherothrombosis. Antiplatelet therapy comprising aspirin alone or with P2Y12-inhibitors are effective for prevention of atherothrombotic complications. However, there is interindividual variability in the response to antiplatelet drugs, leaving some patients at increased risk of recurrent atherothrombotic events. Several risk factors associated with high on-treatment platelet reactivity (HTPR), including elevated platelet turnover, have been identified. Platelet turnover is adequately estimated from the fraction of reticulated platelets. Reticulated platelets are young platelets, characterised by residual messenger RNA. They are larger, haemostatically more active and there is evidence that platelet turnover is a causal and prognostic factor in atherothrombotic disease. Whether platelet turnover per se represents a key factor in pathogenesis, progression and prognosis of atherothrombotic diseases (with focus on acute coronary syndromes) or whether it merely facilitates insufficient platelet inhibition will be discussed in this state-of-the art review.

Endogenous t-PA-antigen is an independent predictor of adverse cardiovascular events and all-cause death in patients with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with raised levels of P-selectin and an apparent prothrombotic state. However, levels of tissue plasminogen activator (t-PA)-antigen are increased also. We investigated whether high levels of endogenous t-PA-antigen or soluble P-Selectin (sP-Selectin), independently of CHADS(2-) or CHA(2) DS(2) VASc-scores, predict major adverse cardiovascular events (MACE) in patients with AF when treated according to current guidelines.

METHODS

This prospective, longitudinal single-center study included 269 patients with AF. Blood samples were analyzed for sP-Selectin and t-PA-antigen concentration by means of commercially available enzyme-linked immunoassays.

RESULTS

Patients were followed for a median duration of 1933 (1517-2277) days, during which 78 MACE and 82 deaths occurred. In multivariable analyses t-PA-antigen above the median of 4.22 ng mL(-1) was associated with MACE and all-cause death (HR 2.55 [1.43-4.57]; P = 0.002) and (HR 2.54 [1.38-4.68]; P = 0.003), respectively. There was no association of sP-Selectin with MACE or all-cause death. Furthermore, t-PA-antigen above the median independently of the CHADS(2-) or CHA(2) DS(2) VASc-scores predicted MACE and all-cause death. In patients with low and intermediate-risk for cardiovascular events according to the CHADS(2)-score the addition of high t-PA-antigen levels (> 4.22 ng mL(-1) ) had a significant impact on the patients' outcome (low-risk group, HR 3.25 [1.13-9.38]; P = 0.029 and intermediate-risk group, HR 2.33 [1.27-4.26]; P = 0.006, respectively).

CONCLUSION

High endogenous t-PA-antigen independently predicts MACE and all-cause death in patients with AF. Accordingly, t-PA-antigen as an indicator of a prothrombotic state represents a novel biomarker, which might add to risk stratification in patients with AF.

Prognostic value of plasma von Willebrand factor and its cleaving protease ADAMTS13 in patients with atrial fibrillation

BACKGROUND

The von Willebrand factor (vWF) is essential for platelet adhesion and arterial thrombosis. It is degraded into less active multimers by ADAMTS13. Patients with atrial fibrillation (AF) exhibit higher plasma vWF and lower ADAMTS13 antigen levels. The vWF/ADAMTS13-ratio might help to estimate the pro-thrombotic risk of patients with AF. We therefore investigated whether a high ratio of vWF/ADAMTS13, independently of clinical risk scores, predicts major adverse cardiovascular events (MACE) in patients with AF.

METHODS

This prospective longitudinal single center study included 269 patients with AF. Blood samples were analyzed for vWF and ADAMTS13-antigen concentration by means of enzyme-linked immunoassay kits.

RESULTS

After adjustment for all univariable predictors for MACE (p ≤ 0.1), ADAMTS13≤49.77% (HR 1.833 (95% CI 1.089-3.086); p=0.023) and vWF/ADAMTS13-ratio>27.57 (HR 2.174 (95% CI 1.238-3.817); p=0.007) remained independently associated with outcome. vWF>1434.92 mU/ml (HR 1.539 (95% CI 0.883-2.682); p=0.128) alone failed to independently predict MACE. In patients with low and intermediate risk for MACE according to the CHADS2-score the addition of high vWF/ADAMTS13-ratio levels (>27.57) had significant impact on the patients' outcome.

CONCLUSION

A high ratio of vWF/ADAMTS13 independently predicts MACE in patients with AF. Therefore, vWF and its cleaving protease ADAMTS13 might play an important role in the development and perpetuation of vascular disease in AF patients. This might be a novel target for future treatment strategies or an additional help for risk stratification in AF patients.