Morphological determinators of platelet activation status in patients with atrial fibrillation

Background: Stage of platelet activation is an important modulator of stroke risk associated with atrial fibrillation (AF). However, factors determining such activation status of thrombocytes in patients with AF are still not well studied.

Methods and results: We enrolled 83 patients (mean age 61 ± 10 years, 61% male, mean CHA₂DS₂-VASc 2.1 ± 1.4) with paroxysmal (75%) or persistent (25%) AF admitted for catheter ablation. Blood samples were collected directly from the left atrium (LA) and platelet activation status was measured by means of flow cytometric assessment in whole blood and light transmission aggregometry (LTA) in unstimulated and Thrombin-receptor-activated-peptide-6 (TRAP-6)-stimulated platelet rich plasma. In flow cytometry, we measured fractions of platelet microparticles and aggregates as well as P-selectin expression on platelets' surfaces. LTA findings are expressed as maximal aggregation (MA), primary slope (PS) and area under curve (AUC). Cardiac anatomy has been assessed by means of echocardiography and magnetic resonance imaging. Left atrial appendage (LAA) volume, but not LAA morphology nor morphological and functional parameters describing LA, was significantly correlated with increased pre-activation of platelets (R = 0.224, p = 0.043) and consecutive reduced response to TRAP-6 (R = 0.231, p = 0.037) measured by P-selectin expression in flow cytometry. Similarly, a reduced response to TRAP-6 in patients with larger LAA volume (PS: R = -0.240; p = 0.042; AUC: R = -0.244; p = 0.035; MA: R = -0.270; p = 0.019) as well as with heart failure (PS 54.75 vs 71.45, p = 0.026) was observed in LTA.

Conclusion: In patients with AF, LAA volume correlates with extent of platelet activation status, this effect is aggravated in patients with heart failure.