The QT interval and serum ionized calcium
W. M. Rumancik, J. K. Denlinger, M. L. Nahrwold and R. B. Falk Jr
The correlation between serum ionized calcium (Ca++) levels and three ECG
QT intervals (Q-OTC, Q-ATC, and Q-ETC) 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-OTC and Q-ATC predict Ca++ levels more
accurately than Q-ETC, 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.
