ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA IN PATIENTS WITH VENTRICULOATRIAL CONDUCTION BLOCK

OBJECTIVE: To demonstrate the reversibility of retrograde ventriculo-a trial block by isoproterenol in patients with atrioventricular nodal r eentrant tachycardia (AVNRT). DESIGN: Three case reports and their ele ctrophysiological features. PATIENTS: Three patients with documented o r suspected paroxysmal supraventricular tachycardia. INTERVENTIONS: At routine electrophysiology study, no supraventricular tachycardia was inducible in the baseline state. Infusion of isoproterenol (1 to 5 mug /min) was given and stimulation procedures were repeated. RESULTS: At baseline, all three patients had discontinuous antegrade atrioventricu lar (AV) nodal conduction, but very poor (two patients) or absent (one patient) ventriculo-atrial conduction prevented induction of AVNRT. D uring infusion of isoproterenol, retrograde conduction was enhanced so that 1:1 retrograde occurred to cycle lengths of 300,340 and 260 ms. AVNRT was then inducible in all patients, reproducing their clinical s ymptoms. CONCLUSION: Absent or poor ventriculo-atrial conduction in pa tients with suspected AV node reentry does not preclude the developmen t of tachycardia with sympathomimetic enhancement. Isoproterenol shoul d be given to attempt reversal of block in these patients.