The Heart Cell—Electrophysiological Aspects

A short review is given of the ionic fluxes associated with the action potential in Purkinje fibres, and in sinus and AV-node, and of the influence of variations in the extracellular concentrations of K+, Na+, Ca2+ and Mg2+ on basic electrophysiological parameters. Variations in serum potassium concentration often play an important role in the genesis of arrhythmias by changing several electrophysiological parameters, whereas only extreme variations in the serum calcium level produce electrophysiological effects of clinical importance. Hypo- and hypernatremia within the ranges observed clinically most probably do not produce significant electrophysiological changes. Variations in extracellular magnesium concentration seem to have effects on electrophysiological parameters particularly when they occur simultaneously with changes in the concentrations of calcium and potassium.