Aged Argentina Death, Sudden, Cardiac Death, sudden Defibrillators, Implantable Defibrillators, implantable Epidemiologic Methods Female Heart Failure Heart failure, congestive/mortality Humans Male Middle Aged Placebo Effect Randomized Controlled Trials as Topic Treatment Outcome Ventricular Dysfunction, Left adult aged article clinical practice congestive heart failure controlled study defibrillator disease severity female follow up health care cost health care system heart left ventricle failure