Previous studies have shown that platelets are activated during atrial fibr
illation (AF). However, prophylactic therapy with aspirin is not associated
with a reduction of thromboembolic complications in patients with AF. Stim
ulation of platelet thrombin and ADP receptors causes a release of P-select
in, which is not affected by aspirin. The purpose of this study wets to ass
ess the influence of AF on platelet P-selectin expression. Blood samples fr
om 30 patients were studied ex vivo. Nineteen patients had chronic AF ( > 3
months), 11 patients were in sinus rhythm (SR). P-selectin expression was
determined by flow cytometry (antibody binding capacity [BC]) at baseline a
nd after platelet stimulation with adenosine diphosphate (ADP) and thrombin
receptor activating peptide (TRAP). To determine the effect of heart rate
and atrial pressure (RAP), measurements were repeated after 10 minutes of v
entricular pacing (120 beats/min) in patients with SR. P-selectin expressio
n was increased in patients with AF at baseline (AF: 1329 +/- 81 BC vs SR:
968 +/- 108 BC; P < 0.05) and after stimulation with ADP (AF: 1445 +/- 101
BC vs SR: 1061 +/- 109 BC; P < 0.05) and TRAP (AF: 13783 +/- 2442 BC vs SR:
5977 +/- 800 BC; P < 0.05). RAP (2.0 +/- 0.5 vs 6.0 +/- 0.8 mmHg; P < 0.01
) and atrial rate (75 +/- 5 vs 114 +/- 5 beats/min; P < 0.001) increased du
ring ventricular pacing. However, P-selectin levels remained stable. AF was
accompanied by increased P-selectin expression, in contrast, increased ven
tricular rate and elevated atrial pressure alone had no effect on platelet
activity. Further studies are needed to determine if platelet ADP receptor
inhibitors offer a therapeutic benefit in patients with AF.