Serum Free Triiodothyronine and the Responsiveness to Clopidogrel in Patients Undergoing Elective Percutaneous...

Both thyroid dysfunction and low responsiveness to clopidogrel have been reported to be associated with increased cardiovascular risk. Our study aims at determining the relationship between free triiodothyronine (FT3) and low responsiveness to clopidogrel in patients undergoing elective percutaneous coronary intervention (PCI).

Consecutive patients undergoing elective PCI were enrolled. All patients received a loading dose of 300 mg clopidogrel, and platelet function was assessed by thromboelastography at least 12 h later. Low responsiveness to clopidogrel was defined by an adenosine diphosphate-induced platelet-fibrin clot strength > 47 mm and adenosine diphosphate-induced platelet inhibition rate < 50%. Major adverse cardiovascular events (MACEs) were defined as a composite of cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, and ischemia-driven revascularization.

Of 812 patients included in the study, 289 showed low responsiveness to clopidogrel. The FT3 level was significantly lower in low responders (4.61 ± 0.60 pmol/l versus 4.94 ± 4.66 pmol/l, p = 0.002). Moreover, the percentage of low responders was greater among patients with low FT3 level than among those without (56.1% versus 34.5%, p = 0.007). Logistic regression analysis showed that a FT3 level was independently associated with the risk of low responsiveness to clopidogrel (odds ratio 0.720, 95% confidence interval [CI] 0.533-0.973, p = 0.033). In patients with low responsiveness to clopidogrel, low FT3 was independently associated with increased risk of MACEs (adjusted hazard ratio 3.040, 95% CI 1.077-8.580, p = 0.036) at a median of 19-month follow-up.

Low FT3 was independently associated with increased risks of both low responsiveness to clopidogrel and cardiovascular events in patients undergoing elective PCI.