Atrial Complexes in Patie& Without Structural Heart Disease

Adenosine is an endogenous nucleoside that produces multiple electrophysiologic effects in the heart, including sinoatrial slowing and depression of atrioventricular (AV) conduction.’ When administered clinically as an intravenous bolus, adenosine is effective in terminating AV nodal reentry and AV reciprocating supraventricular tachycardias by producing transient AV nodal conduction block.2,3 Adenosine effects on reentrant arrhythmias within atria1 myocardium are less well characterized. Adenosine has been shown to increase local activation frequency during atria1 fibrillation4 and may occasionally decrease atria1 cycle length and terminate atria1 flutter.5,6 However, most studies indicate that adenosine is generally not effective in terminating these reentrant atria1 arrhythmias but may be useful as a diagnostic tool by producing AV block.3,7,X The use of adenosine to treat supraventricular tachycardia is occasionally associated with induction of atria1 fibrillation.’ Adenosine effects on atria1 tissue are similar to those observed with acetylcholine in experimental preparations’0-‘2 and, because adenosine activates the same potassium channel as acetylcholine, l3 we hypothesized that adenosine shortens atria1 wavelength in a similar fashion. The present study was designed to estimate the effect of adenosine on the wavelength of premature atria1 complexes in patients undergoing electrophysiologic study. . . . The effects of intravenous adenosine and premature atria1 stimulation were evaluated in 11 patients without structural heart disease undergoing electrophysiologic study for supraventricular tachycardia. Mean age was 47 +- 14 years. No patients had a history of atria1 flutter or atria1 fibrillation and none had been taking class I or III ant&rhythmic drugs, After sedation with intravenous midazolam or propofol, or both, multipolar electrode catheters were introduced percutaneously and positioned in the high right atrium, right ventricular apex, and coronary sinus, and across the tricuspid valve in a position that allowed recording of His bundle and low right atria1 electrograms. In some patients, an Ag-AgCl monophasic action potential catheter (EP Technologies,