Emergency Medical Minute

​​Contributor: Travis Barlock MD Educational Pearls The QT interval represents phases 2 and 3 of ventricular plateau and repolarization, respectively. As the QT interval lengthens, more sodium and calcium channels are available and susceptible to action potentials. Prolonged QT interval is more concerning in the setting of bradycardia. This scenario increases the likelihood of R on T phenomenon.  R on T phenomenon occurs due to an early afterdepolarization event in which a premature ventricular contraction (PVC) occurs during the repolarization period (superimposed on the T wave), leading to an aberrant re-entry circuit. The re-entry circuit leads to Torsades de Pointes (polymorphic ventricular tachycardia with prolonged QT) and subsequent ventricular fibrillation. Treatment for Torsades de Pointes is 2g MgSO4. The preferred antiarrhythmic for VTach is IV lidocaine 1.5 mg/kg over 2 minutes. Avoid amiodarone due to risk of further QT prolongation. A heart rate under 80 does not need Q