Kawamura M, et al. - Whether upgrade cardiac resynchronization therapy (CRT) has an anti-arrhythmic impact on ventricular arrhythmia (VA) with implantable cardioverter-defibrillator (ICD) patients and has a relationship with the incident of VA and left ventricular (LV)-lead threshold was investigated in this study. Participants included 384 patients with the implantation of CRT-defibrillator (CRT-D), of whom, an upgrade from ICD to CRT-D was received by 102 patients. Patients were defined as having an anti-arrhythmic effect after upgrade (n=22), pro-arrhythmic effect (n=14) and unchanging-VA events (n = 66). Findings revealed the association of upgrade-CRT with reduction of VA, ICD therapies and ventricular tachycardia cycle length (VT-CL). A significantly slower VT-CL was evident following upgrade vs before upgrade. While 14 patients demonstrated a pro-arrhythmic impact and LV lead threshold might be related to VA-incidents.