title: Aspirin-induced platelet inhibition in patients undergoing cardiac surgery.
abstract: Platelet function and response to pharmacological inhibition are altered by cardiac surgery. For example, aggregation is increased early after aortic valve replacement (AVR) and platelet response to aspirin is often insufficient after coronary artery bypass grafting (CABG). We hypothesized that the effect of aspirin administration after cardiac surgery might be impaired due to platelet activation. Therefore, the antiplatelet effect of aspirin was compared in patients (n = 20 per group) after CABG and AVR surgery (bileaflet prosthesis). Arachidonic acid-induced aggregation (turbidimetry) and thromboxane formation (radioimmunoassay) were determined before and 1, 5, and 10 days after surgery. In CABG-patients, antiplatelet treatment had been discontinued 10 days before surgery. Oral aspirin was started on day 1 after CABG. AVR-patients did not receive oral aspirin. Before surgery, platelet aggregation and thromboxane formation were significantly higher in patients with aortic stenosis. After CABG, thromboxane formation was not significantly changed from control values before surgery (66 +/- 13% on day 10) despite oral aspirin treatment, whereas thromboxane formation in patients undergoing AVR significantly increased compared to values before surgery (216 +/- 29% on day 10). In both groups of patients, 100 micromol/l aspirin in vitro largely inhibited platelet function before surgery, with markedly attenuated effects after surgery. In conclusion, thromboxane formation increased after AVR but not after CABG. The antiplatelet effect of aspirin, therefore, may be impaired after CABG by increased platelet activity. An additional in vitro "resistance" of platelets was seen after both CABG and AVR.
authors.affiliation: Federal Institute for Drugs and Medical Devices, Bonn, Germany. nzimmermann@bfarm.de
authors.forename: Norbert
authors.initials: N
authors.lastname: Zimmermann
authors.forename: Muhammed
authors.initials: M
authors.lastname: Kurt
authors.forename: Joachim
authors.initials: J
authors.lastname: Winter
authors.forename: Emmeran
authors.initials: E
authors.lastname: Gams
authors.forename: Folker
authors.initials: F
authors.lastname: Wenzel
authors.forename: Artur Aron
authors.initials: AA
authors.lastname: Weber
authors.forename: Thomas
authors.initials: T
authors.lastname: Hohlfeld
mesh_terms: D001021:Aortic Valve / Q000601:surgery; D001241:Aspirin / Q000494:pharmacology*; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D001026:Coronary Artery Bypass / Q000009:adverse effects*; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011446:Prospective Studies; D013931:Thromboxanes / Q000378:metabolism*
chemical_list: D010975:Platelet Aggregation Inhibitors; D013931:Thromboxanes; D001241:Aspirin