Electrocardiogram in a 55-year-old woman with an endocrine disorder
D. Luke Glancy, MD, and Wilson L. Wang, MD
The salient features of the electrocardiogram in Figure 1 are sinus bradycardia, low QRS voltage, flat T waves in all leads in the absence of ST-segment depression, and a long QT interval. Each of these findings is typical of hypothyroidism, and the combination of all four in the same electrocardiogram has a high positive predictive value (1, 2). Indeed, the patient's serum levels of thyroid-stimulating hormone (183.71 µIU/mL; reference range, 0.50-5.00) and free thyroxine (<0.15 ng/dL; reference range, 0.60-1.15) indicate profound hypothyroidism. An earlier electrocardiogram, recorded when the patient was euthyroid, shows sinus bradycardia but otherwise is normal (Figure 2).
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