Platelet reactivity in response to mental stress in syndrome X and in stable or unstable coronary artery disease

Introduction: Previous studies showed differences in platelet reactivity in response to exercise in patients with syndrome X (SX) and those with obstructive coronary artery disease (CAD). In this study, we investigated whether similar differences could be detectable in response to a mental stressful stimulus. Materials and methods: We studied 30 SX patients (60±8 years, 8 men), 20 patients with stable angina and angiographically documented CAD (SA, 66±8 years, 14 men), and 11 patients with unstable angina (UA, 67±8 years, 6 men). A control group of 22 healthy controls (50±7 years, 5 men) was also studied. All subjects underwent a mathematical mental stress test (MST) consisting of rapid consecutive subtractions of number 7 for a period of 5 min. A venous blood sample was collected at baseline and immediately after MST. Platelet reactivity was measured on flowing blood as time necessary to occlude a ring coated with collagen-adenosine diphosphate (ADP; closure time, CT), using the platelet function analyzer (PFA-100) system. Results: At rest, CT was lower in UA patients (87±19 s) compared to controls (109±24 s, p=0.02) and SA patients (105±37 s, p=0.055), and also tended to be lower in SX patients (96±18 s) compared to controls (p=0.07). The CT response to MST differed significantly among groups (p=0.0009). At peak MST, CT did not change in controls (110±27 s, p=0.88), whereas it decreased in SA patients (96±29 s, p=0.003) and tended to decrease in UA patients (82±15 s, p=0.25). In contrast, a significant increase in CT with MST was shown in SX patients (103±21 s, p=0.007). Conclusions: Platelet reactivity is increased by MST in patients with CAD, whereas it paradoxically decreases in SX patients, which may constitute a protective effect against stress-induced events in these patients.