CASE 4 Tachycardia in a 61-Year-Old Woman Background

A 61-year-old woman presents to the emergency department (ED) after being referred from her primary care provider's (PCP) office for evaluation of tachycardia. She had been seen by her PCP for routine placement of a purified protein derivative (PPD) tuberculin skin test and was incidentally noted to have a pulse of 160 bpm. The patient currently denies any specific complaints other than occasional palpitations. On review of her systems, however, she notes having night sweats; a 110-lb (50-kg) weight loss over the preceding 12 months; and 2-3 months of anxiety, diarrhea, and occasional diplopia. She denies having any fever, chills, chest pain, dyspnea, or swelling in her extremities. She has a past medical history of an unspecified thyroid problem. She does not take any daily medications and has no medication allergies. She has a 50-pack-year smoking history, with occasional alcohol consumption. She had been homeless for a period of time but is currently living in an apartment.
On examination, the patient is awake and fully oriented. She is diaphoretic but in no apparent distress. Her temperature is 97.0°F (36.1°C); her pulse is 160 bpm; her respiratory rate is 24 breaths/min, with an oxygen saturation of 98%; and her blood pressure is 190/117 mm Hg. She has bilateral exophthalmos with exotropia of the right eye. Her visual acuity and extraocular movements are intact. The neck examination reveals a diffuse, nontender goiter, without nodules or thyroid bruits. The heart is tachycardic, intermittently irregular, and without murmurs. The lungs are clear to auscultation bilaterally. The abdomen is nondistended, soft, and nontender, with no palpable masses. There is no edema of the extremities. The neurologic examination reveals normal mentation, intact cranial nerves, intact motor strength and sensation, and normal reflexes. No tremor is noted.
The initial laboratory studies reveal complete blood count, electrolytes, renal function, and cardiac marker findings that are all within normal limits. A plain chest radiograph is interpreted as normal (not pictured). An electrocardiogram (ECG) is obtained (see Figure 1).