NPPB and atrial flutter: ≥18 years of age; New York Heart Association (NYHA) class II, III, or IV symptoms, ejection fraction ≤ 40%; NT-proBNP ≥ 600 pg·ml−1 (or ≥ 400 pg·ml−1 if they had been hospitalized for heart failure within the previous 12 months, or NT-proBNP ≥ 900 pg·ml−1 if they are with atrial fibrillation or atrial flutter on baseline electrocardiography regardless of their history of hospitalization for heart failure)