Plasma platelet products and exercise-induced myocardial ischemia

Peripheral plasma concentrations of PF-4 and TxB2 were measured by RIA in 26 patients who underwent exercise stress testing. In group A (n = 15; age 50 +/- 16, mean +/- S.D.) in whom blood sampling was performed by venipuncture, seven patients had a positive stress test associated with an increase in PF-4 concentrations from 3.3 +/- 1.6 ng/ml to 6.9 +/- 3.6 (mean +/- S.D.); six of them demonstrated a greater than 50% increase in PF-4; and only one of eight with a negative stress test had such an increase. In group B (n = 11; 49 +/- 10 yr), patients also underwent postexercise thallium-201 scanning and blood samples were obtained through an intravenous catheter. These patients consistently demonstrated higher PF-4 values (before exercise 7.5 +/- 3.9 ng/ml; after exercise 11.9 +/- 7.1), regardless of the results of the exercise and thallium studies. TxB2 concentrations were unchanged in both groups. To further evaluate the effect of catheter-collected samples on PF-4, five healthy males had serial concurrent blood sampling in opposite arms via both venipuncture and catheter. Although PF-4 concentrations in venipuncture samples were constant, those collected through the catheter increased as a function of time. On the basis of the findings in group A, enhanced platelet activation appears to be associated with exercise-induced ischemia. The observations in group B and the healthy controls indicated that catheter-collection of samples artifactually increased PF-4 concentrations.