If you measure your
QTc during times with high heart rate without physical activity or anxiety, your
QTc may prolong.
What's important is that your REAL QT time, not corrected after the QTc formula, isn't above 500msec, because then (and only then) your risk of TdP increases. 95% of us have QT time at heart rate 60 of 360-440 msec (460 for women). That doesn't mean that 2,5% of us have LQTS (2,5% is above 440 and 2,5% is below 360).