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Complete Heart Block in a Patient With Metastatic Papillary Thyroid Carcinoma

Following a 2-day history of exertional dyspnea and palpitations, diagnostic images revealed a soft tissue mass in the right ventricular overflow tract. Can you guess the cause?

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A 74-year-old woman presented with a 2-day history of exertional dyspnea and palpitations. Her past medical history was significant for metastatic papillary thyroid carcinoma treated with total thyroidectomy and radioactive iodine ablation with levothyroxine for chronic suppressive therapy.

On examination, the patient was afebrile with an oxygen saturation of 98% on room air, heart rate of 92 beats/min, and blood pressure of 100/54 mm Hg. There was trace bilateral lower extremity edema, and her cardiopulmonary examination was unremarkable. The laboratory studies showed a white blood cell count of 24,300/µL (3,400-9,800); platelets 86,000/µL (142,000-362,000); thyroid stimulating hormone 0.009 mlU/L (0.4-4.1); free T4 2.07 ng/dL (0.8-2.0); thyroglobulin antibody titer < 1:10 (< 1:160); thyroid microsomal antibody titer < 1:100 (< 1:1600); and thyroglobulin 17.9 ng/mL (2.0-35.0). Her initial troponin T was undetectable.

An electrocardiogram showed a first-degree atrioventricular block and subsequently a new intermittent third-degree atrioventricular block. A computed tomography angiogram (Figure 1) and cardiac magnetic resonance imaging (Figure 2) revealed a 2.6-cm soft tissue mass in the right ventricular outflow tract along with multiple pulmonary emboli and previously diagnosed pulmonary metastases. A positron emission tomography (PET) scan (not shown) revealed a 3.5-cm PET-avid lesion within the right ventricular outflow tract.

  • What is your diagnosis?
  • How would you treat this patient?

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