Overproduction of platelet microparticles in cyanotic congenital heart disease with polycythemia.

OBJECTIVES

We sought to clarify the role of platelets in the pathogenesis of abnormal coagulation in patients with cyanotic congenital heart disease (CCHD) with polycythemia; we evaluated the production of platelet microparticles (MPs), platelet degranulation and aggregation response, as well as the correlations of these variables with polycythemia.

BACKGROUND

A shortened life span and suppressed aggregability of platelets are well known in patients with CCHD. Although platelet MPs are overproduced and play an important role in the coagulation process in various hematologic and cardiovascular disorders, the production of MPs remains to be elucidated in CCHD. We studied 19 patients who had CCHD with polycythemia and 21 age-matched subjects with acyanotic congenital heart disease (ACHD). Flow cytometry, using monoclonal antibodies, showed the presence of MPs as particles positive for the surface antigen (glycoprotein IIb/IIIa) specific to platelets, and platelet alpha-degranulation was recognized as platelets positive for the surface antigen of P-selectin. Platelet aggregation was assessed as the response to adenosine diphosphate (ADP). Relationships between these indexes and hematocrit (Hct) values were also evaluated.

RESULTS

Production of MPs correlated positively with Hct and markedly increased at Hct values above 60% in patients with CCHD. Surface P-selectin and the mean platelet volume in patients with CCHD were comparable with those in patients with ACHD. The platelet aggregation response to ADP significantly and negatively correlated with Hct. In two subjects who showed hemoptysis and underwent phlebotomy, MPs were reduced 6 h after the procedure.

CONCLUSIONS

Platelet MPs are overproduced in patients who have CCHD with polycythemia, probably due to a high shear stress derived from blood hyperviscosity. Circulating incompetent platelets, which have already been activated, as well as MPs, might play an important role in the coagulation abnormalities identified in such patients.