Figure-3: The main mechanism of the “troubleshooting”: the slow conduction of the scar zone of posterior inferior left ventricle and interventricular septum due to the old myocardial infarction. EGM 1:Atip to Aring;EGM 2:Can to RV coil;EGM 3: RVtip to RVring . (AVN:atrioventricular node;OMI:old myocardial infarction;PVC: premature ventricular contraction;VS1:ventricular sense of ventricular activation transmitted through the AVN;VS2:ventricular sense of PVC originated from the scar of posterior inferior left ventricle)