Complete heart block during potassium therapy in thyrotoxic periodic paralysis.

Background: Although cardiac dysrhythmia is common in patients with thyrotoxic periodic paralysis (TPP), high-degree atrioventricular (AV) block complicated by cardiogenic shock, even under KCl supplementation, is rarely described.

Objectives: To present a case of TPP in a patient who developed complete AV block with severe consequences due to paradoxical hypokalemia during KCl therapy. In addition, the management of acute hypokalemia in TPP is reviewed.

Case Report: A 41-year-old Chinese man with TPP presented to the Emergency Department with a 2-day history of paralysis in the extremities. He developed complete AV block with cardiogenic shock and respiratory failure, necessitating ventilatory support when plasma K(+) level decreased from 1.7 mmol/L to 1.3 mmol/L during KCl replacement of 30 mmol in 2 h. The administration of another 60 mmol KCl over 3 h achieved a plasma K(+) level of 2.1 mmol/L, resulting in the resolution of AV block and successful weaning. However, rebound hyperkalemia (K(+) 5.6 mmol/L) upon recovery was evident and uneventfully corrected.

Conclusion: A paradoxical fall in serum K(+) concentration with potentially life-threatening complication is still underappreciated in patients with TPP on KCl supplementation. Early recognition and prompt therapy prevent untoward consequences.