Age related differences in the response to acidosis, hypoxia, and hyperkalaemia in canine cardiac Purkinje fibres

Objective: In the clinical setting, the response of adult and neonatal cardiac rhythms to hypoxia and to acidosis differs, the former leading to tachyarrhythmias and the latter to bradyarrhythmias. In this study, the aim was to determine whether a cellular electrophysiological substrate could be identified to explain the clinical observation. Methods: Conventional microelectrode techniques were used to study the electrophysiological responses of automatic Purkinje fibres to acidosis, hypoxia, and hyperkalaemia individually. Results: Adult Purkinje fibres showed decreases in maximum diastolic potential, activation voltage, and automaticity as pH was decreased from 7.3 to 6.1. Triggered activity due to early afterdepolarisations developed in 70% of adult Purkinje fibres at pH 6.1. Neonatal Purkinje fibres showed decreased automaticity as pH decreased and, in contrast to adults, quiescence occurred at pH 6.1 At Po2