Unifying Algorithm for Mechanistic Diagnosis of Atrial Tachycardia.

BACKGROUND: No existing criteria unequivocally differentiate focal atrial tachycardia (AT) caused by microreentry, triggered activity, or enhanced automaticity. Although macroreentrant AT is readily diagnosed based on entrainment criteria, the smaller circuit dimension associated with microreentrant AT makes it challenging to validate the presence of reset with fusion. An algorithm was, therefore, developed that is independent of entrainment but which reliably identifies specific mechanisms of focal AT.

METHODS AND RESULTS: Fifty-nine patients with AT underwent adenosine testing after mapping of tacycardia. Ten ATs had nonfocal activation, with ≥90% of tachycardia cycle length identified with electroanatomical mapping, findings consistent with macroreenty. All ATs were insensitive to adenosine. Forty-nine patients had focal AT with centrifugal activation. In 32/49 (67%) ATs, electrograms were nonfractionated, and <50% of tachycardia cycle length could be mapped. Based on programmed stimulation, 26/32 (81%) of these ATs were classified as due to triggered activity and 6/32 (19%) as due to enhanced automaticity. Adenosine terminated 100% of triggered ATs and transiently slowed or suppressed 100% of automatic ATs. The remaining 17 focal ATs had localized fractionated electrograms (≥35% of tachycardia cycle length) at the site of successful ablation and were classified as microreentrant. Adenosine had no effect in these ATs. The response to adenosine accurately differentiated all subtypes of focal AT, P<0.05.

CONCLUSIONS: Adenosine-sensitivity (termination or transient slowing/suppression) in response to adenosine was 100% sensitive and specific for identifying focal AT mechanisms due to triggered activity or automaticity, respectively. Absence of adenosine effect on focal AT identifies tachycardia due to microreentry.