Pathophysiological basis of tachyarrhythmias--re-entry.

A description is given of the principles of re-entry and circus movement, which were originally formulated on the basis of experiments on jellyfish and play an important role in cardiac arrhythmias. The essential features of re-entry are 1) the existence of two conducting pathways which communicate at their proximal and distal ends, and 2) the occurrence of uni-directional block in one pathway while conduction is maintained in the other. A retrograde wavefront may then be set up in the pathway where block was present, and the tissue from which the impulse came may be re-excited. Once this sequence is set up it may continue as a circus movement leading to tachycardia. Long re-entry circuits are present in Wolff-Parkinson-White syndrome, in which two connections between atria and ventricles exist. Micro-re-entry may occur in a variety of cardiac tissues. An example of supraventricular tachycardia due to micro-re-entry in the atrio-ventricular node of an isolated rabbit heart is shown, in which simultaneous recording of transmembrane potentials of AV nodal cells unraveled the events. The principles of the termination of circus movement tachycardias by electrically induced premature beats are discussed.