Bradycardia despite hyperthyroidism

Hyperthyroidism is usually associated with tachycardia, hypothyroidism with bradycardia. After observing clinically inapparent hyperthyroidism in pati ents requiring pacemaker implantation, we studied the occurrence of hyperth yroidism in patients receiving a first permanent pacemaker. Of 237 patients (age 71.4 +/- 8.9 years; 54.9% females), 16 (6.75%) had subclinical (TSH < 0.1 mE/l and fT3 less than or equal to 9.0 pmol/l) and 4 (1.69%) overt hyp erthyroidism (TSH < 0.1 mE/l and fT3 > 9.0 pmol/l). Prevalence of hyperthyr oidism was similar to that in the general population. Compared to euthyroid patients, in the patients with subclinical or overt hyperthyroidism there were significantly more females (n = 16) than males (n = 4; p = 0.018). Hyp erthyroid patients were older (75.0 +/- 9.6 vs. 70.7 +/- 8.9 years; p = 0.0 15). At follow-up, all patients had a relevant proportion of pacemacer-indu ced beats. Clinical signs of hyperthyroidism or cardiac symptoms were not d ifferent between groups. In conclusion, bradycardia does not exclude the presence of hyperthyroidism . Temporary pacing is recommended in thyreotoxicosis with bradycardia. In c ontrast, primary implantation of a permanent pacemaker appears to be adequa te in patients with bradycardia, cardiovascular disease and an additional d iagnosis of hyperthyroidism.