Combined effect of acute altitude exposure and vigorous exercise on platelet activation

Exposure to high altitudes and exercise alters body's physiology and may cause acute cardiovascular events. Platelet activation is one of the key players in these events. Therefore, we investigated the effect of vigorous exercise at higher altitude (2650 m) on platelet aggregation and serum markers of platelet activation. 14 healthy subjects performed a step incremental ergometer test until exhaustion at the Environmental Research Station (UFS, 2650 m) at Zugspitze. Platelet aggregation and serum levels of endothelin-1, soluble p-selectin, platelet factor 4 and Chromogranin A were measured. Platelet activation was significantly enhanced after exercise at high altitude compared to measures immediately prior exercise. We detected significantly enhanced serum levels of endothelin-1 and soluble p-selectin whereas chromogranin A and platelet factor 4 remained unchanged. This effect might be due to increased endothelin-1 levels causing pulmonary vasoconstriction, rheological changes and direct platelet activation. This might be of clinical relevance, especially in patients with pre-existing diseases.

Effect of Acute Altitude Exposure on Serum Markers of Platelet Activation

Background: Platelets are the key factor in primary hemostasis. It has been shown that chronic altitude exposure increases platelets' aggregability. Nevertheless, data about acute effects and the underlying mechanisms are sparse. Methods: Sixteen healthy volunteers were examined in our hospital (519 m alt.) and 30 minutes after arrival in the environmental research station on the Zugspitze Mountain (2656 m alt.). Serum levels of soluble p-selectin were examined to elucidate platelet activation. In addition, serum levels of chromogranin A (CGA) as a measure of adrenergic activation, endothelin 1 (ET-1) representing pulmonary vascular tone and monocyte chemoattractant protein-1 (MCP-1) as a measure of inflammatory response were examined. Results: Acute altitude exposure induced a significant increase of p-selectin (116 ± 4.8 pg/mL vs. 132 ± 6.2 pg/mL; p < 0.01). Whereas MCP-1 was significantly lowered (538 ± 50.6 pg/mL to 470 ± 41.1 pg/mL; p = 0.02) and CGA was not altered significantly (88 ± 47.4 ng/mL vs. 79 ± 44 ng/mL; p = 0.22), ET1 was increased significantly from 0.8 ± 0.07 pg/mL to 1.15 ± 0.09 pg/mL (p < 0.01). Conclusion: Our study could demonstrate relevant platelet activation that was accompanied by a 44% increase of ET-1. This activation might obtain clinical relevance in patients with pre-existing cardiovascular disease as a trigger for acute events.

Myeloperoxidase is not useful for detecting stress inducible myocardial ischemia but may be indicative of the severity of coronary artery disease

Background and Objectives

Elevated levels of myeloperoxidase (MPO) have been found in patients in different stages of coronary artery disease (CAD). The aim of this study was to assess whether the MPO liberation is increased by stress inducible myocardial ischemia and could be used to improve the diagnostic accuracy of non-invasive evaluation for myocardial ischemia.

Subjects and Methods

Seventy-six patients with suspected myocardial ischemia who underwent stress myocardial perfusion scintigraphy (MPS) were enrolled. 59 patients with an acute coronary syndrome (ACS) who received a percutaneous coronary intervention along with 12 healthy volunteers were also included in the study. In every subject the MPO plasma levels were assessed by enzyme linked immunosorbent assay. In patients undergoing MPS, the MPO levels were measured serially before and after the stress testing.

Results

Of the 76 patients undergoing MPS, 38 were diagnosed with a stress inducible myocardial ischemia. The patients with a stress induced ischemia had significantly higher basal MPO levels than those without it (32±3 ng/mL vs. 24±4 ng/mL, p=0.03). However, there was no relevant change in the MPO levels after the stress test compared to the baseline. The patients with ACS showed significantly higher MPO levels than the patients undergoing MPS (131±14 ng/mL vs. 28±2 ng/mL, p<0.01) and the healthy subjects (131±14 ng/mL vs. 26±2 ng/mL, p<0.01).

Conclusion

Since the MPO plasma levels did not increase after the stress MPS, MPO appears not to be a useful biomarker for detecting a stress inducible myocardial ischemia. Yet, the MPO levels correlate with the different stages of CAD and may hold significance as an indicator for its clinical severity.

Clinical management of clopidogrel inefficiency by point of care platelet function testing and individual adjustment of anti-platelet therapy--initial experiences

Insufficient inhibition of ADP dependent platelet aggregation by clopidogrel is associated with an increased risk for adverse coronary events, such as stent thrombosis, after percutaneous coronary intervention. Here, we describe an approach to the clinical management of patients with insufficient inhibition of ADP dependent platelet aggregation by clopidogrel involving dose adjustment or switching of the thienoyridine. We put special emphasize on a patient who experienced recurrent acute myocardial infarction due to stent thrombosis associated with severe clopidogrel non response following elective coronary drug eluting stent implantation. In this patient, an inadequate clopidogrel effect at maintenance doses was confirmed by repeated platelet function assessment with a multiple electrode impedance point of care platelet function test. Subsequent dose adjustments still did not result in sufficient inhibition of ADP dependent platelet aggregation. Only after switching to the then shortly available new thienopyridine prasugrel could a sufficient platelet inhibition be obtained. However, our data from further patients show that although this may overcome inadequate clopidogrel efficiency in many cases, even under prasugrel suboptimal platelet inhibition may occur.