“Implantable devices are well suited to monitor and record several parameters that carry prognostic information. Specifically, the primary function of implantable cardioverter defibrillators (ICDs) is to monitor for changes in heart rhythm and treat both tachyarrhythmias and bradyarrhythmias. They are efficient in monitoring the heart rate, incidence of arrhythmias, and patient activity level, which provide prognostic information. Parameters such as thoracic impedance, heart sounds, and respiratory rate and patterns may further refine prognostic information available from ICDs. Combining parameters may provide a better way to interpret and use the available information.”