Abnormal Platelet Function Is Common in Pediatric Congenital Cardiac Surgery Patients.

Background: Hemostasis in cardiac surgery patients requires functional platelets. Acquired platelet function defects are well recognized in high shear aortic lesions in adults and have been described in some congenital cardiac patients with ventricular septal defects (VSDs) and with pulmonary hypertension. Abnormal shear flow is characteristic of many congenital cardiac defects. We hypothesized that platelet function abnormalities might be common in this patient group. The Platelet Function Analyzer -100 (PFA-100) is commonly used to test for platelet function defects. Pediatric reference ranges are the same as adult. Prolongation of closure times to collagen/epinephrine are common in patients on aspirin and related antiplatelet agents, with prolongation to collagen/ADP being characteristic of many clinically significant platelet disorders (congenital and acquired vonWillebrand’s disease, other platelet function defects).

Methods: We used the PFA-100 to preoperatively screen pediatric patients aged 2 mos-18 years coming to surgical repair of cardiac lesions at our institution. All aortic valve surgery patients were screened as of July 2004, and all cardiac surgery cases as of Jan 2005. For analysis only patients with platelet counts of > 100 and hematocrits of > 28 were included. If PFA-100 closure times to collagen/epi were normal, collagen/ADP testing was not performed. For study purposes PFA-100 results were counted as abnormal only when closure times for collagen/ADP were prolonged beyond the 95% confidence intervals for normal controls. No special hematological interventions were ordered preoperatively on the basis of an abnormal PFA-100 alone.

Results: PFA-100 results were available on 38 patients. 28 of 38 (74%) were abnormal, with underlying cardiac pathology strongly correlated with abnormal PFA-100 values (see table). 6 patients were on aspirin, discontinued preoperatively, and none on other antiplatelet agents. 3 of these 6 had normal PFAs to collagen/epi when tested. Although patient groups were not homogeneous, patients with abnormal PFA-100 results had higher overall intraoperative and postoperative red cell and platelet transfusion requirements on a cc/kg basis (55.3 vs 17.6 for RBCs p=.008 and 12.8 vs 6.5 for platelets p=.038). 24 hour post-operative chest tube drainage (cc/kg) did not differ between groups (23.2 vs 22.7 p=0.95). There were 2 reexplorations for hemorrage, both in patients with abnormal PFAs.

Conclusions: Prevalence of platelet function abnormalities appears high in pediatric congential cardiac surgery patients. The etiology of these abnormalities is unclear and there may possibly be a correlation with aortic valve pathology and other high shear lesions. Patients with abnormal platelet function also had increased transfusion requirements. However it is unclear is this finding is related to the platelet function defect or to differences in patient age and complexity of surgery. Larger studies that better define the population at-risk for bleeding and the significance of abnormal platelet function are needed.