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Hypercalcemia.
The ECG reveals
sinus rhythm with the following abnormalities:
1. Very short
ST segment with a consequently short QT interval; and
2.
Prominent U waves (esp. in V3).
These changes are very
suggestive of hypercalcemia. The QT corrected has been found
to be inversely proportional to the calcium level in
hypercalcemic patients up to a level of about 16 mg/dl. At
higher levels, the T wave begins to prolong, essentially
making the QT interval normalize, though the ST segment
remains short. In addition, prominent U waves are often seen
in hypercalcemia. The differential diagnosis of a short QT
corrected is much narrower than that of prolonged QT. The
chief causes of a short QT are hypercalcemia and digoxin
therapy (associated with characteristic "scooping" of the
ST-T complex). Cardiac arrhythmias are unusual with
hypercalcemia, but AV block, sinus arrest, sino-atrial
block, ventricular tachycardia, and cardiac arrest have been
reported, usually in patients receiving rapid IV injections
of calcium. This patient's serum calcium was 16 mg/dl. He
was found to have hyperparathyroidism; at surgery, he had
successful resection of a parathyroid carcinoma.
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