- QTc (corrected QT interval) prolongation greater than 450 msec (male) or QTc greater than 470 msec (female) by Bazetts formula or use of medications that may cause QTc interval prolongation. A comprehensive list of agents with the potential to cause QTc prolongation can be found at http://www.azcert.org/medical-pros/drug- lists/bycategory.cfm.