Pacemaker, ArtificialSick Sinus SyndromeHeart BlockCardiac Pacing, ArtificialBiological ClocksSinoatrial NodeEquipment FailureAtrioventricular BlockBradycardiaHyperpolarization-Activated Cyclic Nucleotide-Gated ChannelsCircadian RhythmElectrodes, ImplantedInterstitial Cells of CajalSuprachiasmatic NucleusDevice RemovalArrhythmias, CardiacEquipment SafetyHeart Conduction SystemElectrocardiographyCyclic Nucleotide-Gated Cation ChannelsPeriodicityAction PotentialsAtrioventricular NodeElectrophysiologyDefibrillators, ImplantableFlufenamic AcidArrhythmia, SinusPeriod Circadian Proteins