Q-ATC INTERVAL AS A CLINICAL INDICATOR OF HYPER-CALCEMIA

The charts were reviewed of more than 200 patients discharged from the hospital between 1972 and 1977 with a diagnosis implying abnormal calcium metabolism. When all other variables known to affect the Q-T interval were eliminated, serum calcium concentrations on 65 occasions in 39 patients were found to correlate significantly (P < 0.001 or better) with the following electrocardiographic intervals: Q-aTc (beginning of QRS complex to apex of T wave), Q-oTc (beginning of QRS complex to onset of T wave) and Q-Tc (beginning of QRS complex to end of T wave). Of these, the Q-aTc interval was the more easily and precisely measured at elevated calcium levels and exhibited the strongest correlation (P < 0.0001) over the range of calcium levels measured. The relation was linear and could be used to estimate serum calcium levels from measured Q-aTc intervals. For a Q-aTc interval of 0.29 second or less (range 0.23 to 0.29) the serum calcium was estimated to ±1.9 mg/dl with 95 percent confidence. For a Q-aTc interval of 0.27 second or less, the correspondence with hypercalcemia in the study series was 90 percent or better. When all other factors known to affect the Q-T interval are ruled out, the shortening of the Q-aTc interval appears to be a useful clinical indicator of hypercalcemia. © 1979.