the R on T phenomenon happens when a PVC (which represents the R) occurs at a region which is in a vulnerable phase of repolarization (represented by a T wave on ECG)
this phenomenon has a potential to trigger ventricular arrhythmias such as Torsades des Pointes in specific situations
R on T which triggers ventricular arrhythmias can happen in: - patients with a prolonged QT interval which is either congenital or acquired (which can be caused by a number of drugs or electrolyte abnormalities)
patients with normal QT interval but one of these conditions: - myocardial ischemia, typically during the acute phase, although it may also occur during the healing phase of MI due to QT prolongation - electrolyte abnormalities (such as hypokalemia) - Brugada syndrome - CPVT
before the R on T phenomenon triggering TdP occurs, a pause or slowing of the rhythm can usually be observed and the TdP is described as pause-dependent
VTs occurring as a result of acute MI without QT prolongation are not pause-dependent
a PVC occurring during a T wave of the preceding beat
can be followed by an onset of ventricular arrhythmia
ECG 1 The R on T phenomenon in this example occurs in precordial leads and does not trigger a TdP, however a TdP can be seen in limb leads on the left
Oksuz, Fatih, Baris Sensoy, Ekrem Sahan, Fatih Sen, Kazım Baser, Hande Cetin, Sefa Unal, Ozcan Ozeke, Serkan Topaloglu, and Dursun Aras. 2015. “The Classical “R-On-T” Phenomenon”. Indian Heart Journal 67 (4): 392-394. https://doi.org/10.1016/j.ihj.2015.02.030.
Liu, Michael B., Nele Vandersickel, Alexander V. Panfilov, and Zhilin Qu. 2019. “R-From-T As A Common Mechanism Of Arrhythmia Initiation In Long Qt Syndromes”. Circulation: Arrhythmia And Electrophysiology 12 (12). https://doi.org/10.1161/CIRCEP.119.007571.