<prompt> A 50 year old man presents with central chest pain. He collapsed while his ECG was being recorded. What is the cause of this ECG?R on T phenomenonMacro-reentrant CircuitEarly after depolarizationAV nodal Re-entry  <response>: ECG shows ST segment changes in lead II, III indicating inferior wall MI BLUE ARROW Ventricular extra-systole after the first beat RED MARK In the fouh beat, ventricular Extra-systole YELLOW is occurring at time of T wave triggering a polymorphic Ventricular tachycardia. The R-on-T phenomenon is the superimposition of an ectopic beat on the T wave of a preceding beat which triggers Polymorphic VT. 