Comparison and recalculation of the very different QTc interval durations in young healthy women

The aim was to use some simple way for easier comparison, other expression or recalculation of the QTc duration from one formula to another in order to remove the large QTc differences.

The QT interval duration in 138 young healthy women was taken from our archive. The measured QT interval was corrected for heart rate (QTc) according to nine published regression equations (Bazett, Fridericia, Hodges, Sarma, Lecocq, Rautaharju, Sagie=Framingham, Arrowood, Malik) and compared mathematically by the Pearson correlation coefficient R and graphically by linear correlation.Correlation between two different QTc durations can be of three kinds: small (e.g. Bazett's versus Malik's formulas, R=0.0525, p=0.5405, the QTc values are much dispersed in the graph), larger (Malik's versus Sarma's formulas, R=0.939, p<0.01, the values are less dispersed), and identical (the Rautaharju's versus Arrowood's formulas, R=1.000, p<0.01, all QTc points are situated on one line). The linear correlation QTc1 = a+b·QTc2 enables recalculation from one QTc formula into another, if necessary.In conclusion, the QTc interval durations are differently long according to the QTc formula used. The correlations with the large Pearson R coefficient indicate the QTc pairs inappropriate for recalculation, the small R values indicate the appropriate pairs for recalculation.