Aspirin resistance in Indian patients with coronary artery disease and cardiovascular events

BACKGROUND: Aspirin resistance is a major problem and its incidence and clinical significance in Indian patients with documented coronary artery disease are not known. AIM: We sought to study the incidence of aspirin resistance and its clinical significance in a cohort of Indian patients with coronary heart disease on therapy with aspirin using urinary 11-Dehydrothromboxane B2 levels as a surrogate marker for antiplatelet efficacy. SETTING AND DESIGN: Non randomized single center prospective study in cohort of patients with stable cardiovascular disease on chronic aspirin therapy attending the cardiology outpatient clinic of a tertiary care hospital. MATERIALS AND METHODS: Urinary dehydrothromboxane levels were analyzed in a cohort of 63 patients with stable documented coronary artery disease and in 21 healthy volunteers. The cases were followed up prospectively for a median period of 36 (1-53) months. The clinical endpoint was a composite of acute coronary syndrome, stroke, revascularization and death. STATISTICAL ANALYSIS: Comparison of urinary dehydrothromboxane concentration values between various risk factors was done using Mann Whitney U test, a non parametric alternative of independent t test. All statistical analyses were done using SPSS 11.0 (Chicago, USA) software. RESULTS: The median (range) absolute values of urinary11- dehydrothromboxane B2 levels for the healthy volunteers and cases were 440 (286-2050) pg/ml and 320 (72-2600) pg/ml (P=0.007). The corresponding normalized values were 87.3 (43-143) and 60.8 (16.7-943) ng/mmol of creatinine (P=0.131). Among the various vascular risk factors, patients who were overweight had higher absolute levels of 11- urinary dehydrothomboxane B2 levels (P=0.016). There were significantly more clinical events in patients with absolute urinary 11-dehydrothromboxane B2 levels in the upper two quartiles compared to the lower two quartiles (P=0.04). CONCLUSION: The incidence of aspirin resistance in the cohort of patients with documented heart disease was 38.1%. Patients with elevated absolute urinary dehydrothomboxane levels (>320 pg/ml) on chronic aspirin therapy constitute a high risk subset for recurrent vascular events.