Platelet dysfunction in acute type A aortic dissection evaluated by the laser light-scattering method

Platelet dysfunction contributes to bleeding tendency in acute type A aortic dissection. Particle counting by new laser light-scattering methods more accurately quantifies changes in the number of different-sized platelet aggregates than do conventional optical density methods. We studied platelet aggregation kinetics and patterns of aggregation deficiency in acute-phase aortic dissection with laser light scattering. Blood from 20 acute type A aortic dissection patients undergoing surgery was sampled during acute (9.1 ± 6.8 hours from onset) and chronic (postoperative day 20, control) phases of aortic dissection. Platelet count and aggregability were assessed by optical density and laser light-scattering methods after aggregation was induced (addition of 2.0 μg/mL collagen to samples). Optical density showed significant reduction in acute-phase platelet aggregation (acute vs chronic: 65 ± 27% vs 77 ± 17%, P < .03). Laser light scattering showed significant reduction in medium (25-50 μm) and large (50-70 μm) but not small aggregate (9-25 μm) generation (acute vs chronic: small, 1.2 ± 0.6 × 107 vs 1.5 ± 1.0 × 107, NS; medium, 0.6 ± 0.3 × 107 vs 1.1 ± 0.5 × 107, P < .001; large, 1.4 ± 1.2 × 107 vs 2.6 ± 1.7 × 107, P < .001). Acute- versus chronic-phase platelet counts were significantly decreased (1.7 ± 0.1 × 105/μL vs 3.6 ± 0.3 × 105/μL, P < .001). Platelet aggregation is suppressed in acute-phase aortic dissection. This suppression does not occur in the initial phase of small aggregate formation; rather, it occurs during the conglomeration of small aggregates into larger aggregates.