[Diagnostic value of the isoproterenol test in effort tachycardia]

An isoproterenol test was performed in 69 patients during electrophysiological investigation to assess its diagnostic value in adrenergic supraventricular or ventricular tachycardia. Sixteen control subjects had no symptoms on exercise and routine exercise stress testing did not trigger any hyperexcitability. Sixteen patients had reproducible documented supraventricular tachycardia induced by exercise (13 paroxysmal junctional tachycardias, 3 focal atrial tachycardias). Eight patients had ventricular hyperexcitability related to effort. Twenty-nine patients had supraventricular and/or ventricular hyperexcitability only at rest. Electrophysiological investigations included paired atrial stimulation during sinus rhythm and paced rhythm followed by programmed ventricular stimulation using one and then two extrastimuli delivered during sinus rhythm and paced ventricular rhythm. These stimulation studies were carried out under basal conditions and then during low dose isoproterenol infusion (10 to 40 micrograms) which accelerated the heart rate to 130/mn. Electrophysiological and conduction parameters and the mode of induction of the tachycardia (defined as at least 5 successive echos with a configuration similar to the clinical tachycardia) were studied. We observed an acceleration of anterograde and retrograde conduction and a shortening of the effective atrial and ventricular refractory periods but these changes were found equally in the different groups of patients and were not related to the induction of tachycardias. The induction of paroxysmal junctional tachycardia by isoproterenol was a very sensitive (92%) and specific (100%) diagnostic method. Its diagnostic value was much greater than Holter monitoring (25%) and exercise stress testing (12.5%). Induction of ventricular tachycardia by isoproterenol was also very sensitive (75%) and specific (95%). The diagnostic value was higher than exercise stress testing (71%) and Holter monitoring (62%). Isoproterenol did not affect the induction of spontaneous tachyarrythmias unrelated to effort and even suppressed the triggering of some episodes. In conclusion, the induction by atrial or ventricular pacing or spontaneous supraventricular or ventricular tachycardia during isoproterenol infusion was very specific and correlated with the concept of tachycardia induced by exercise and therefore of adrenergic nature. The sensitivity of this test was excellent in patients with supraventricular tachycardia (95%) and very good in ventricular tachycardia (75%). On the other hand, the changes in the electrophysiological parameters were not specific for a group of patients.