<P> Again, here QT and QTlc are in milliseconds and RR is measured in seconds . </P> <P> A recent retrospective study suggests that Fridericia's method and the Framingham method may produce results most useful for stratifying the 30 - day and 1 - year risks of mortality . </P> <P> Definitions of normal QTc vary from being equal to or less than 0.40 s (≤ 400 ms), 0.41 s (≤ 410ms), 0.42 s (≤ 420ms) or 0.44 s (≤ 440ms). For risk of sudden cardiac death, "borderline QTc" in males is 431--450 ms; and, in females, 451--470 ms . An "abnormal" QTc in males is a QTc above 450 ms; and, in females, above 470 ms . </P> <P> If there is not a very high or low heart rate, the upper limits of QT can roughly be estimated by taking QT = QTc at a heart rate of 60 beats per minute (bpm), and subtracting 0.02 s from QT for every 10 bpm increase in heart rate . For example, taking normal QTc ≤ 0.42 s, QT would be expected to be 0.42 s or less at a heart rate of 60 bpm . For a heart rate of 70 bpm, QT would roughly be expected to be equal to or below 0.40 s . Likewise, for 80 bpm, QT would roughly be expected to be equal to or below 0.38 s . </P>

What are the upper limits of normal for the qtc