Adenosine is an endogenous nucleoside that has been used in the diagnosis and treatment of tachycardias, including those with normal QRS durations and those with wide QRS complexes in both children and adults. The electrophysiologic basis for the use of adenosine is primarily its depressant effect on conduction in the atrioventricular node and its antiadrenergic effect an the ventricular myocardium. In our study, adenosine was administered intravenously via bolus dose to 43 patients with supraventricular and ventricular tachycardias as well as ventricular extrasystoles. Adenosine successfully terminated 11 of 12 tachycardias using the atrioventricular node as reentrant circuit. It induced transient complete atrioventricular nodal block, unmasking the typical appearance of the flutter and fibrillation waves on the surface electrogram. It was also useful in terminating and therefore diagnostic in ventricular ectopic activity in two patients and ventricular tachycardias in five patients, suggesting that the mechanism is triggered activity. Adenosine's rapid metabolism ensures that a bolus injection is rapidly removed from the circulation; consequently no serious side effects were seen in our study
