Circus movement in the heart.

It is well known that the reentry or circus movement is one of important mechanisms underlying the generation of arrhythmias. This is recently clasified into three category such as ordered reentry which means circus movement in an anatomically defined pathway, random reentry which means circus movement without the involvement of an anatomic obstracle and reflected reentry which does not require the reentrant circuit. In this article I describe some recent progress in studies on designed to present the characteristics of the circus movement. On the theoretical considerations, the reentry has been regularly explained for by terms such as conduction velocity (V), refractory period (R) and length of circuit (L). Basic contribution of appearance of reentry in heart tissue needs the following conditions : (1) slow conduction (2) shortening of refractory period and (3) existence of unidirectional block. The reflected reentry which does not require the circuitous pathway and unidirectional block complexed the conception of reentry itself. On the other hand, experimental technique used to investigate mechanism of arrhythmias including simulations were developed to document the spread of activation in the heart tissues. Simultaneous multi-recordings display the sequence of reentry in pathological conditions. However, direct evidence of reentry is very rare in clinical fields. Moreover, there is no complete methods distinguishing reentry from other mechanism such as abnormal automaticity. The progress in this field is expected.