QTc, the Multitude of Ways It Is Calculated and Implications for Clinical Practice: A Case Example

QTc stands for heart-rate corrected QT interval on the electrocardiogram and is a measure of the efficiency of repolarization of the left ventricle. Excessive prolongation, generally considered to be >500 ms, can result in a potentially fatal ventricular arrhythmia known as torsade de pointes. Some psychiatric medications can cause this arrhythmia and, therefore, this issue is important to all prescribers of psychiatric medications. It is also important to keep in mind that there are multiple algorithms used to calculate the QTc. The Bazett's algorithm, one of the most commonly used algorithms on electrocardiogram machines, can produce an artificially prolonged QTc; however, the use of this algorithm is not generally identified on the printout from the electrocardiogram machine, which can cause unnecessary concern and delay treatment of patients. For these reasons, this article explains the basic concepts of the QT interval and QTc interval and discusses why it is important for psychiatrists and other prescribers to know this information. A case report is then used to illustrate the clinical application of this knowledge so that effective treatment is not unnecessarily delayed.