A simple method for evaluating abnormal lengthening of the QT interval during the face immersion test

The slope of the relation between the unadjusted QT interval and heart rate during the face immersion test has been reported to be useful as an index for predicting an abnormal lengthening of the QT interval for children with nonfamilial long QT syndrome. Our goals were to determine whether we can replace the slope of the QT/heart rate relation calculated from all data with that calculated from fewer data and to determine whether we can replace the slope with the corrected QT value by heart rate (QTc value) at the minimum heart rate. We studied 19 children with a prolonged QT interval and 54 control children by using statistical analysis. The slope calculated from the selected data points (at least four) was in agreement with the slope calculated from all data, and the relationship between the slope and the QTc value at the minimum heart rate showed a high correlation. It was determined that we can replace the slope calculated from all data with that calculated from at least four data points and replace the slope with the QTc value at the minimum heart rate as an index for predicting an abnormal lengthening of the QT interval.