OBJECTIVE: To assess the potential benefits and risks associated with 
levothyroxine (LT4) therapy in patients with subclinical hypothyroidism (SH) and 
concomitant coronary artery disease (CAD).
METHODS: We enrolled 33 patients (4 male and 29 female subjects) with SH and CAD 
in this study. The study cohort consisted of 2 groups: 19 patients who were 
randomly assigned to receive LT4 therapy, titrated to maintain a normal serum 
thyrotropin level (main group), and 14 patients who did not receive any LT4 
replacement therapy (control group). Variables of the lipid profile and left 
ventricular diastolic function were measured and 24-hour electrocardiographic 
monitoring was performed before randomization and at 6-month follow-up. Medical 
therapy for the CAD remained unchanged throughout the 6-month study period.
RESULTS: In the main group, no statistically significant differences were found 
in the lipids, variables of left ventricular diastolic function, and heart rate 
pattern between the hypothyroid and euthyroid states. Individual analysis 
revealed, however, that LT4 therapy was beneficial in terms of lipid 
abnormalities in those patients with lower body mass index, shorter history of 
CAD, and higher cholesterol levels at baseline. In the control group, we noted 
statistically significant prolongation of early filling deceleration time after 
6 months, which indicated less flexibility of the left ventricular myocardium 
and diastolic myocardial dysfunction with long-term SH. In reference to adverse 
effects of LT4 therapy, 5 of the 19 patients had an increased rate of 
ventricular premature beats. These 5 patients were significantly older and 
initially had more supraventricular and ventricular premature beats than the 
rest of the main group. No ST depressions were recorded during LT4 therapy.
CONCLUSION: In patients with SH and CAD, LT4 therapy can be beneficial in 
diminishing lipid abnormalities in those with lower body mass index, briefer 
duration of CAD, and higher levels of cholesterol at baseline. Patients in our 
study who experienced adverse effects of LT4 treatment were older and had more 
supraventricular premature beats at baseline in comparison with the other 
patients.