Limited Dose-Effect Relationship of Adenosine for Detection of Atrioventricular Nodal Duality in Patients with Supraventricular Tachycardias

OBJECTIVE: The purpose of the study was to test the dose-effect relationship of adenosine for the diagnosis of dual atrioventricular (AV) nodal physiology in patients presenting with supraventricular tachycardia. SUBJECTS AND METHODS: The study population consisted of 57 patients (mean age 50 +/- 14 years; 36 females, 21 males) with palpitations related to supraventricular tachycardia. Adenosine was injected as bolus during sinus rhythm at rest in order to unmask dual AV nodal physiology by a PR jump on surface ECG (defined as a sudden increase by > or = 50 ms measured from the onset of the P-wave to the R-wave between two consecutive sinus beats). According to a stepwise clinical approach, adenosine was administered as bolus in incremental dosages (6 mg followed by 12 mg, if necessary up to 18 mg). Once a PR jump > or = 50 ms or a high-grade AV block was noted on surface ECG, the injection was stopped at that dose. RESULTS: A significant PR jump was noted after injection of 6 mg (n = 21, 99 +/- 30 ms) or 12 mg (n = 13, 94 +/- 35 ms), but not after 18 mg (n = 4, 35 +/- 10 ms) adenosine. Provocation of temporary first-grade AV block (n = 13) was associated with the longest increment of PR interval, whereas high-grade AV block (n = 36) produced a significantly shorter PR jump (105 +/- 35 vs. 65 +/- 40 ms, p = 0.0024). Electrophysiological study and ablation were performed in 37 highly symptomatic patients. AV nodal reentrant tachycardia was diagnosed in 33 patients and orthodromic AV reentrant tachycardia in 4 patients. CONCLUSION: The adenosine test was characterized by a reverse dose-effect relationship as far as identification of AV nodal duality was concerned.