July 2019 By PsychDB.com

QTc Prolongation and Monitoring

QTc Prolongation can lead to Torsades de Pointes (TdP), which can be fatal. Many psychotropic medications can prolong the QTc, and hence baseline ECGs are important prior to starting these medications. There are few guidelines on the monitoring of QTc, but it is generally recommended that an ECG be ordered when a QTc-prolonging agent is being started, or if there are there is a dose increase.

  • 500 for men[1]
  • 450 for women[2]

If the QTc is not normal, i.e. > 500, order Mg and K levels. If these levels are low, then it should be replaced and the ECG repeated again.

Methadone and other drugs can also affect QTc.

QTc doesn't tell the whole story. Combining QTc with T-wave morphology better predicts the risk for Torsades de Pointes. Some patients whose QTc falls above the traditional upper limits can take medications that alter cardiac repolarization without developing Torsades.[3]