Fig. 2. Appropriate implantable cardioverter-defibrillator (ICD) therapy according to ICD therapy zones (high-rate ICD therapy zone vs. low-rate ICD therapy zone) in group 1 (A), 2 (B), and 3 (C). Group 1, heart failure (HF) and ICD for primary prevention; group 2, HF and ICD for secondary prevention; group 3, non-HF and ICD.