Summary

Authors present a review of the normal cardiac electrophysiology and a study of the genesis of arrhythmias.

The electrophysiologic properties of the excitable cell membrane are analysed. When an electrical stimulus exceeds the resting threshold, the permeability characteristics of the membrane are altered and rapid ion inflow is initiated, generating an action potential.

A review of the of voltage-gated channels, with emphasis on the sodium channel, clarifies how transmembrane ionic currents are elicited.

The generation of impulses at the sinusatrial node, its conduction through the miocardium and the expression of the current flow in the electrocardiogram are explained.

Following the normal cardiac electrophysiology discussion, the genesis of arrhythmias is reviewed. Among the many types of arrhythmias, special emphasis is given to reentry, the main cause of arrhythmia in patients. The occurrence of reentry can be understood in terms of anatomical findings, i.e. the Purkinje terminal loop model, or through the leading circle concept.

These mechanisms underlie all types of cardiac arrhythmias.