To the Editor: Lin et al report an observational study in 52 patients investigating whether upgrading an implantable cardioverter defibrillator (ICD), implanted predominantly for secondary prevention of cardiac resynchronisation therapy devices (CRT-D), can reduce arrhythmias.1 They failed to detect an effect of CRT on arrhythmias during a mean follow-up of 14 months. The CARE-HF extension study suggested that reduction in …