Differential effects of adenosine on focal and macroreentrant atrial tachycardia

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.