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July 28, 1978

The QT Interval and Serum Ionized Calcium

Author Affiliations

From the Department of Anesthesiology (Mr Rumancik), The Milton S. Hershey Medical Center, Pennsylvania State University, Hershey; the Department of Anesthesiology (Dr Denlinger), University of California Medical Center, San Diego; the Department of Anesthesiology (Dr Nahrwold), University of Michigan Hospital, Ann Arbor; and the Department of Anesthesiology (Dr Falk), Lancaster General Hospital, Lancaster, Pa.

JAMA. 1978;240(4):366-368. doi:10.1001/jama.1978.03290040044020

The correlation between serum ionized calcium (Ca++) levels and three ECG QT intervals (Q-O TC, Q-A Tc, and Q-E TC) was assessed in 20 adult patients. The relationship between each QT interval and Ca++ level, based on 209 Ca++ determinations through a range of 1.0 to 4.0 mEq/liter, is best described by a hyperbolic function. Although Q-O TC and Q-A TC predict Ca++ levels more accurately than Q-E TC, all QT intervals are clinically unreliable as guides to the presence of hypercalcemia. Similarly, the usefulness of the QT intervals in the diagnosis of hypocalcemia is limited by the wide distribution of normal values.

(JAMA 240:366-368, 1978)