Intrathoracic Impedance Monitoring Uncovered Presymptomatic Amiodarone-Induced Hypothyroidism: Another Possible Cause of Impedance Drop

Abstract

Intrathoracic impedance (ITI), measured between the right ventricular coil and the device can, reflects intrathoracic fluid status. A 78-year-old female with dilated cardiomyopathy who survived cardiopulmonary arrest received a cardiac resynchronization therapy-defibrillator equipped with an ITI monitor. She had been prescribed amiodarone since November 2008. The ITI began to decrease steadily since September 2009 without worsening of heart failure symptoms. She was relatively well until December 2009 when she became aware of swelling of the face and lower legs. She noticed increasing easy fatigability and weakness in February 2010 and entered the hospital. A chest X-ray film showed an increase in the size of the heart shadow without worsening of pulmonary congestion or pleural effusions. An echocardiogram revealed a large pericardial effusion. The free thyroxin was 0.05 ng/dL, the free triiodothyronine 0.42 pg/mL, and the TSH 200.4 µIU/mL. These findings were consistent with a diagnosis of amiodarone-induced hypothyroidism. She was treated with levothyroxine, along with dose reduction of amiodarone. All symptoms improved gradually and the ITI began to increase since March 2010 and finally restored to the baseline level in September when the pericardial effusion almost disappeared and thyroid hormone test returned to normal. Our case suggests that ITI monitoring could uncover presymptomatic amiodarone-induced hypothyroidism possibly by detecting pericardial effusions.