Summary

Two theories of spread of electrical activation in atrial flutter have been proposed in the past and both of them found their supporters (and deniers) based on experimental studies and clinical observations. They are: 1. unifocal origin with radial spread of activation from a rapidly firing single focus and 2. circus movement, i.e. activation spreading in a circular fashion around the central obstacle (the focus initiating this circular movement has not been established). In earlier experiments, aconitine was applied topically and more recently electrical stimulation was used.

In our experiments, atrial flutter was produced in 16 large mongrel dogs by local application of aconitine or by electrical stimulation. Atrial electrograms were recorded with five bipolar electrodes attached to each atrium. Approximately 300 paroxysms were produced using both methods. Two distinct responses were observed:

1. Aconitine produced atrial tachycardia (or flutter?) with atrial rates ranging from 200 per minute to 440 per minute with radial spread of atrial activation from one focus (the area of local application). Atrial activation occupied from approximately 15 to 50 percent of the P-P interval.

2. Electrical stimulation produced two major types of activation patterns:

a. Unifocal radial spread of atrial activation was observed in one distinct group, which included "rapid" ectopic atrial rhythms (flutter) with rates between 480 and 570 per minute. Atrial activation appeared to initiate most of the time in the area of the S-A node regardless of the location of the stimulating electrode and stimulus parameters.

b. Spread of activation compatible with the so-called circus movement, in a caudad direction over the right atrium and in a cephalad direction over the left atrium (or sometimes reversed) was observed in "slow" ectopic atrial rhythms (flutter) with rates from 350 to 400 per minute. Activation of ectopic foci in the area of the A-V node and the S-A node is a possibility. 

Atrial activation in electrically induced atrial flutter occupied from approximately 70 to 95 percent, and on occasion even more, of the P-P interval with  the right atrium accounting for approximately 60 to 80 percent of the atrial activation time.

Publication:

1. New Evidence of Dual Mechanism of Electrical Activation in Experimentally Induced Atrial Flutter. Waldemar J. Wajszczuk, M.D., F.A.C.C. and Elliot Corday, M.D., F.A.C.C. Actas del VI Congreso Europeo de Cardiologia, Madrid, Spain, 1972, (Published by Editorial Paz Montalvo, Madrid, 1974).