OBJECTIVE: To study the effect of adequacy of thyroid hormone replacement 
therapy on coronary atherosclerosis.
DESIGN: Retrospective cohort study of elderly hypothyroid patients with 
coexisting coronary artery disease. The association between the adequacy of 
thyroid replacement and the progression of angiographic coronary artery disease 
was investigated. Fisher's exact test was used for statistical analysis.
SETTING: Coronary angiographies were performed at the Cardiac Catheterization 
Laboratory of the Victoria General Hospital, Halifax, Nova Scotia, the only 
tertiary referral centre for Nova Scotia and Prince Edward Island. Information 
about the past and current thyroid status of the subjects was collected from 
their family physicians.
PATIENTS: Of 4103 patients admitted for coronary angiography during 1992 and 
1993, 25 were on thyroid replacement therapy to treat hypothyroidism. Ten 
patients who underwent more than one coronary arteriography were selected (seven 
females and three males, mean age 65 +/- 10 years).
RESULTS: Of five patients inadequately treated for hypothyroidism, all 
demonstrated angiographic evidence of coronary atherosclerosis progression. 
However, five of seven who were treated adequately did not show atherosclerosis 
progression (P = 0.02, OR = 0.72, 95% CI 1.36 to infinity). Decreasing or 
maintaining the dose of L-thyroxine at 100 micrograms or less resulted in 
coronary atherosclerosis progression in six of six patients, whereas five of six 
patients taking fixed or increasing doses of L-thyroxine 150 micrograms or 
higher were spared from disease progression (P = 0.015, OR = 0.41, 95% CI 2.4 to 
infinity).
CONCLUSIONS: Angiographic coronary artery disease progression may be prevented 
by adequate thyroid replacement in hypothyroidism. With the help of modern, 
sensitive thyroid stimulating hormone assays higher doses of L-thyroxine may be 
safer and more effective in the atherosclerosis management of this patient 
population. Thyroid hormones can protect against atherosclerosis, presumably due 
to their metabolic affects on plaque progression.