It is a measurment on an EKG that shows the hearts electrical ventricular activity along with the QRS complex measurement. They should use a QTc (the c stands for corrected) reading when calculating it to see if a drug you are using is doing any harm to your hearts electronics. In women the QTc should not go past 430 and actually 420 is getting a bit high. If a drug harms your hearts electronics then you will be at risk for some bad heart rhythms and worse. Effexor has more potential to do this to a person than Paxil but Paxil can and has done it. Prozac also has some bad reports. Doctors have been encouraged to learn about this but they are resistant, when they could be preventing some bad heart rhythms they cause to people with drugs they perscribe by simply doing routine EKGs on people that they have on risky drugs. Another good example of this is Erythromycin and it is not a psychotrophic med it is an antibotic. Here is a medical definition.
The Q-T interval represents the time for both ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential. This interval can range from 0.2 to 0.4 seconds depending upon heart rate. At high heart rates, ventricular action potentials shorten in duration, which decreases the Q-T interval. Because prolonged Q-T intervals can be diagnostic for susceptibility to certain types of tachyarrhythmias, it is important to determine if a given Q-T interval is excessively long. In practice, the Q-T interval is expressed as a "corrected Q-T (QTc)" by taking the Q-T interval and dividing it by the square root of the R-R interval (interval between ventricular depolarizations). This allows an assessment of the Q-T interval that is independent of heart rate. Normal corrected Q-Tc intervals are less than 0.44 seconds.
Lisa