Usefulness of isoproterenol in facilitating atrioventricular nodal reentry tachycardia during electrophysiologic...

In some patients with documented atrioventricular (AV) nodal supraventricular tachycardia (SVT), the arrhythmia is not inducible during a standard stimulation protocol. In these patients the level of sympathetic activity may be an important factor. This study evaluates the influence of isoproterenol on anterograde and retrograde pathway properties in patients with AV nodal SVT and the mechanism by which this SVT is facilitated. Group 1 consisted of 8 consecutive patients, ages 23 to 85 years (mean +/- standard error, 57 +/- 8) who had no inducible AV nodal SVT during electrophysiologic testing until isoproterenol (0.5 to 3.0 micrograms/min) was infused. These patients were compared with 6 patients in the same age range (45 to 78 years, mean +/- standard error, 64 +/- 5) who had inducible AV nodal SVT without isoproterenol and who comprised group 2. In comparing group 1 (before isoproterenol) with group 2, there was no significant difference in the refractory periods of the anterograde slow and fast pathways, although the anterograde block cycle length was longer in group 1 patients (421 +/- 18 vs 362 +/- 14 ms, p less than 0.05). The retrograde block cycle length was also longer in 7 of the 8 group 1 (before isoproterenol) patients in whom it could be measured versus those in group 2 (411 +/- 14 vs 318 +/- 27 ms, p less than 0.05). During isoproterenol, the anterograde and retrograde block cycle lengths in group 1 were not different from group 2. Therefore, AV nodal SVT may not be inducible in some patients during routine electrophysiologic testing.(ABSTRACT TRUNCATED AT 250 WORDS)