T. Yamashita et al., SLOW ABNORMAL CONDUCTION IN THE LOW RIGHT ATRIUM - ITS ANATOMIC BASISAND RELEVANCE TO ATRIAL REENTRY, The American heart journal, 127(2), 1994, pp. 353-359
To characterize slow abnormal conduction in the low right atrium, whic
h is known to be responsible for atrial flutter, electrophysiologic fi
ndings were correlated with anatomic features in a canine model of atr
ial flutter with ligation of the crista terminalis in the midright atr
ium. Activation in the low right atrium was mapped with a patch electr
ode containing 52 bipolar electrodes and a multiplexing system. A part
icular region in the low right atrium showed atrioventricular node-lik
e electrophysiologic properties, a rate-dependent conduction delay, an
d Wenckebach periodicity. This area coincided with an area responsible
for slow conduction during atrial flutter and unidirectional block at
its initiation. Both pilsicainide and E-4031 preferentially blocked c
onduction in the specific area, leading to the termination of atrial f
lutter. Although refractoriness could not explain the abnormal conduct
ion, anatomic studies consistently found the specific region to be in
or around a thick muscle bundle, that is, the crista terminalis, or a
thick pectinate muscle branching from the crista, located perpendicula
r to the wavefront of the pacing impulse and atrial flutter. These ele
ctrophysiologic and anatomic findings suggest that slow abnormal and a
trioventricular node-like conduction over a thick muscle bundle, which
is a normal anatomic feature of the low right atrium, plays a role in
the initiation, maintenance, and termination of atrial reentry.