A 27-year-old woman with no past medical history complains of one week of dizziness and palpitations, especially when she gets up quickly; she is now asymptomatic in the ED.  She states that she “gets this way from time to time”, and she is sure that it “must just be my stress”.  The woman is not taking any medications, and denies illicit substances, recent illness, or change in her diet.  Her vital signs and cardiovascular and neurologic examinations are normal, and she is not pregnant.

Her electrocardiogram shows a heart rate of 68, no evidence of pre-excitation, and no ST or T wave changes from a previous electrocardiogram done for the same complaint three months ago: QT interval 480 ms, corrected QT (QTc) 512 ms.

Which of the following would be the MOST helpful in establishing a diagnosis:

    A.    Serum potassium level
    B.    Serum magnesium level
    C.    Serum calcium level
    D.    Repeat electrocardiogram


In the meantime, a quote – 
 
“To each one of you the practice of medicine will be very much as you make it – to one a worry, a care, a perpetual annoyance; to another, a daily joy and life of as much happiness and usefulness as can well fall to the lot of man.”

–William Osler