- Central Sleep Apnea Group (Group 4) - patients with predominant central sleep apnea that will receive standard therapy (ICD/CRT-D implant + maximal medical therapy). Because the SERVE-HF Trial demonstrated a negative effect of predominantly central sleep apnea treatment on cardiovascular mortality in patients with HFrEF by using adaptive servo-ventilation therapy, patients in Group 4 will not receive any PAP therapy for treatment of sleep disordered breathing and will be followed.