Circus movements

Severely depressed conduction may result in simple block, eg, atrioventricular nodal block or bundle branch block. Because parasympathetic control of atrioventricular conduction is significant, partial atrioventricular block is sometimes relieved by atropine. Another common abnormality of conduction is reentry (also known as "circus movement"), in which one impulse reenters and excites... 

Arrhythmias are caused by abnormal pacemaker activity or abnormal impulse propagation. Thus, the aim of therapy of the arrhythmias is to reduce ectopic pacemaker activity and modify conduction or refractoriness in reentry circuits to disable circus movement. The major mechanisms currently available for accomplishing these goals are (1) sodium channel blockade, (2) blockade of sympathetic autonomic effects in the heart, (3) prolongation of the effective refractory period, and (4) calcium channel blockade. 

Allessie MA, Bonke FIM, Schopman FJG Circus movement in rabbit atrial muscle as a mechanism of tachycardia. Cite Res 1973 32 54-62. 

It is generally accepted that the predominant mechanism of atrial fibrillation and atrial flutter is reentry. Atrial fibrillation appears to result from multiple atrial reentrant loops (or wavelets), and atrial flutter is due to a single, dominant reentrant substrate (counterclockwise circus movement around the tricuspid annulus). Atrial fibrillation or flutter usually occurs in association with forms of organic heart disease that causes atrial distension. Forms of heart disease that commonly lead to atrial stretch and precipitate atrial fibrillation or flutter include... 

Ischaemic damage of cardiac muscle cells delays action potentials, which can then depolarize other cells no longer refractory, setting up circus movement (a loop of depolarization)... 

The changes produced by drugs on other electrical properties of the heart may also be evaluated. For example, an alkaloid may decrease the electrical excitability of the auricles. Thus, a greater intensity of current would then be required to provoke an extra systole. The time of application of this electric shock must be precisely determined. Following each systole, the heart has a refractory period, during which time it is highly resistant to external stimuli thus, it insures the necessary rest period for the heart. Measurements of the auricular refractory period are commonly made with antifibrillatory alkaloids. If the Thomas Lewis-Mines circus movement theory of auricular fibrillation is to be believed, then any sub-... 

Allessie, M. A., Bonke, F. I. M., Shopman, F. J. G. (1977) Circus movement in rabbit atrial muscle as a mechanism of tachycardia. III. The leading circle concept A new model of circus movement in cardiac tissue without the involvement of an anatomical obstacle. Circ. Res. 41, 9 Arneodo, A., Coullet, P., Tresser, C. (1981) A possible new mechanism for the onset of turbulence. Phys. Lett. 81A, 197... 

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