Focal and Macroreentrant Atrial Tachycardia. Introduction: The effects of a
denosine on atrial tachycardia (AT) remain controversial, and the mechanist
ic implications of adenosine termination have not been fully established. T
he purpose of this study was to elucidate the differential effects of adeno
sine on focal and macroreentrant AT and describe the characteristics of ade
nosine-sensitive AT.
Methods and Results: Thirty patients received adenosine during AT. Tachycar
dia origins were identified as focal or macroreentrant during invasive elec
trophysiologic studies, Responses to adenosine were analyzed and characteri
zed as tachycardia termination, transient suppression, or no effect, Electr
ophysiologic studies demonstrated a focal origin of tachycardia in 17 patie
nts. Adenosine terminated focal tachycardias in 14 patients (dose 7.3 +/- 4
.0 mg) and transiently suppressed the arrhythmias in three others (dose 10.
0 +/- 6.9 mg), A macroreentrant mechanism,vas demonstrated in 13 patients;
adenosine terminated only one of these tachycardias and had no effect on th
e remaining 12 patients (dose 10.2 +/- 2.9 mg), Four classes of adenosine-s
ensitive AT were identified. Class I consisted of nine patients with tachyc
ardia arising from the crista terminalis; these tachycardias also terminate
d with verapamil (4/4). Class II consisted of four patients with repetitive
monomorphic AT arising from diverse sites in the right atrium; these eithe
r slowed or terminated in response to verapamil (2/2), Class III consisted
of the three patients with transient suppression and demonstrated electroph
armacologic characteristics consistent with an automatic mechanism, includi
ng insensitivity to verapamil (2/2), In the one patient with macroreentrant
AT that was comprised of decremental atrial tissue, adenosine terminated t
achycardia in a zone of decremental slow conduction (Class IV); this tachyc
ardia slowed with verapamil,
Conclusions: Adenosine-sensitive AT is usually focal in origin and arises e
ither from the region of the crista terminalis (inclusive of the sinus node
) or from diverse atrial sites,vith an incessant nonsustained repetitive pa
ttern. Although most forms of macroreentrant AT are insensitive to adenosin
e, rarely macroreentrant AT with zones of decremental slow conduction can d
emonstrate adenosine sensitivity.