The effects of ouabain on induction of atrioventricular nodal re entrant paroxysmal supraventricular tachycardia

Electrophysiological studies utilizing His bundle recordings and atrial extra stimulus technique were performed in 17 patients (pts) with documented paroxysmal supraventricular tachycardia (PSVT) before and after 0.01 mg/kg, i.v., ouabain. Before ouabain, echo zones (EZ) were demonstrated in 11 patients. After ouabain, EZ were abolished in two, decreased in five, unchanged in three, and increased in one. In one patient, EZ was demonstrated only after ouabain. Eleven patients could sustain PSVT before ouabain; after ouabain, only six patients could sustain PSVT. Analysis of A₁-A₂, H₁-H₂ curves revealed 11 patients with discontinuous (dual pathway) and six patients with smooth conduction curves. In dual pathway patients, both the fast and slow pathway curves were shifted rightward and upward after ouabain. The changes in EZ were dependent upon the relative rightward shifts of the two pathways. In patients with smooth curves, EZ tended to shift rightward with a critical A H being achieved at longer A₁-A₂ intervals after ouabain. In conclusion, the effects of ouabain on PSVT were variable. Beneficial effects included abolition or decrease of EZ and loss of the ability to sustain PSVT. Potentially deleterious effects included widening or new development of EZ.