mean ms ecgs electrocardiograms correction corrected qt qtc interval rate 
msec qtcf fridericia qt interval formula corrected using correction ecg 
msecs qtc interval corrected qt formula using bazetts bazett prolongation 
ms qtcf fridericia qt corrected interval formula ecg screening subject 
qtcf ecg triplicate mean screening msec correction ecgs interval fridericia 
qt qtc msec syndrome long corrected interval congenital history fridericia