Scenario: A 30-year-old man was admitted to the intensive care unit for head injuries due to a motor vehicle accident. He had an emergent craniotomy for skull fractures, bilateral subdural hematomas, and subarachnoid hemorrhage. The first ECG (A) was obtained at admission and the second (B) was obtained a few hours after admission.

(A) Sinus rhythm at 75/min, (B) sine-wave pattern at 110/min

One complication of traumatic injury is rhabdomyolysis, a condition that leads to the breakdown of muscle fibers, resulting in the release of myoglobin into the bloodstream. A buildup of serum myoglobin can lead to altered kidney function and elevated potassium. Although the patient’s serum potassium was only moderately elevated to 6.3 mmol/L, his ECG revealed a sine-wave pattern. Because atrial myocytes are sensitive to hyperkalemia, the P wave flattens and eventually disappears. As hyperkalemia progresses, the QRS complex widens and blends with the T wave, resulting in...

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