Postoperative low aspirin response in vascular surgery: A pilot study

Background and Goal of Study: The efficacy of Aspirin (ASA) in primary and secondary prevention of vascular diseases has been widely documented. However, patients taking ASA may show low response to treatment, related to genetic polymorphisms, poor compliance or other factors that are not yet fully understood. Patients undergoing vascular surgery are at risk of myocardial infarction in the perioperative period because of the high prevalence of risk factors. The goal of our study was to measure the efficacy of ASA after major aorta and peripheral vascular surgery by using whole blood impendance aggregometry (IA) (Multiplate® analyzer). Our hypothesis is that surgical trauma, postoperative inflammation and thrombocytosis may reduce the efficacy of ASA, partially explaining the increased incidence of postoperative myocardial infarction in this population. Materials and Methods: We performed a monocentric, observational, cohort study. Patients presenting for elective abdominal aorta or peripheral vascular surgery, chronically treated by ASA were included. Blood samples for platelet count and IA measurements were collected on the morning of surgery (baseline) and once daily until the fifth postoperative day (POD). The primary outcome measure was platelet response expressed in AU in the Aspi-test using the Multiplate® analyzer. The Aspi-test specifically measures platelet response to ASA. Low aspirin response (LAR) was defined as an impedance of less than 50 UA. Secondary outcomes were postoperative thrombotic and hemorrhagic complications on POD 30. Baseline and postoperative values were compared using paired student-t test. The fraction of patients showing LAR was compared using Fisher's test. Results and Discussion: 17 patients were included. Mean baseline platelet count was 256 G/l and decreased in the postoperative period (188 G/l at POD2). LAR increased from 12% at baseline (2/17 patients) to 41 % (5/17) postoperative (p=0.3) Mean preoperative platelet reactivity was 23 ± 18 AU compared to 45 ± 22 AU postoperative (p=0.003). 4 patients suffered peripheral thrombosis, 2 of whom showed postoperative LAR. No patient had cardiac or cerebral ischemic complication. One patient had a hemorrhagic complication related to surgery. Conclusion: We observed a postoperative increase in LAR in patients undergoing vascular surgery. Large clinical trials need to evaluate whether postoperative LAR is correlated to an increased incidence in thrombotic complications.