J. Ortiz et al., MECHANISM OF SPONTANEOUS TERMINATION OF STABLE ATRIAL-FLUTTER IN THE CANINE STERILE PERICARDITIS MODEL, Circulation, 88(4), 1993, pp. 1866-1877
Background. We tested the hypotheses that spontaneous termination of s
table atrial flutter is directly related to spontaneous beat-to-beat c
ycle length oscillations and that block of the circulating reentrant w
ave front occurs in an area of slow conduction. Methods and Results. W
e studied 30 episodes of spontaneous termination of stable atrial flut
ter induced by atrial stimulation in 11 conscious, nonsedated dogs wit
h sterile pericarditis. Additionally, in 5 dogs, 14 episodes of sponta
neous termination of stable atrial flutter were studied with a multisi
te mapping system to record simultaneously from 190 right atrial elect
rodes. In the conscious-state studies, atrial flutter cycle length osc
illations began 6+/-1 (mean+/-SEM) beats before termination in 26 epis
odes, stable atrial flutter evolved into atrial fibrillation in 3 epis
odes, and no cycle length change occurred before termination in 1 epis
ode. In the open-chest studies, in all instances, spontaneous oscillat
ions began 7+/-1 beats before termination. The only consistent oscilla
tion pattern occurred for the last two beats: a long cycle length (149
+/-9 milliseconds) followed by a much shorter cycle length (110+/-6 mi
lliseconds) (P<.01). Activation maps demonstrated that all cycle lengt
h oscillations were explained by changes of conduction in an area(s) o
f slow conduction in the reentrant circuit. In two instances, the last
(short) cycle length was associated with disappearance of an area of
slow conduction. In all episodes, the last circulating reentrant wave
front blocked in an area of slow conduction in the reentrant circuit.
Although not tested, during the last beat, the very early arrival of t
he circulating reentrant wave front at an area of slow conduction sugg
ests an important role for refractoriness, with head and tail interact
ions, resulting in block. Conclusions. Spontaneous termination of stab
le atrial flutter in the sterile pericarditis model (1) is preceded by
beat-to-beat cycle length oscillations that result from changes in co
nduction in areas of slow conduction in the reentrant circuit and (2)
results from block of the circulating reentrant wave front in an area
of slow conduction.