The Mechanism of Auricular Flutter and Auricular Fibrillation

A DISCUSSION of the mechaniism of auricular flutter or fibrillation requires first a precise definition of what is meant by those terms. They were coined originally to designate more or less characteristic clinical syndromes, but they are now applied loosely to a heterogeneous group of experimental results that may bear only a superficial resemblance to those syndromes. Thus, it is possible to define flutter and fibrillation exclusively on the basis of rate, as was done recently by Prinzmetal and his associates.4 This definition, however, is undesirable, because it groups together conditions which have quite different features; for example, it does not distinguish fast auricular activity that is stopped by acetylcholine from activity with the same frequency that is not stopped by acetylcholine. As pointed out by Wiener and Rosenblueth,7 the structure and properties of auricular muscle are such that they allow for at least two modes of recurrent activity. In the first, impulses start at one or several points, they spread through the muscle and disappear at its boundaries; recurrence cannot take place without reinitiation; we may designate these impulses as beats. In the second, an impulse travels continuously in one direction over a closed circuit and recurs cyclically because the front of the impulse meets always nonrefractory tissue; we may designate this activity as cyclically recurrent or circus movement. That mammalian auricular muscle is capable of exhibiting automatic beats in the absence of connections with nodal tissue has been shown by Rosenblueth and Garcia Ramos.A 6 Two different types of automatic activity were observed, a slow and a fast activity. The dif-