Modification of atrioventricular node conduction increases RR variability but not RR irregularity nor atrial fibrillation rate in atrial fibrillation patients

We aimed at studying whether variability and irregularity of RR are modified by the selective A1 adenosine receptor agonist tecadenoson, the beta-blocker esmolol and their combination in patients with atrial fibrillation (AF). Twenty-one patients with AF were randomly assigned to either 75, 150 or 300 µg i.v. tecadenoson, administered alone and in combination with esmolol. The ECG was recorded continuously in the following 10-min phases: i) baseline1, ii) post-tecadenoson-dose1, iii) baseline2, ending at the time of the esmolol injection, iv) esmolol maintenance, v) post-tecadenoson-dose2. For every segment, heart rate (HR) and atrial fibrillatory rate (AFR) were estimated as well as variability and irregularity of RR intervals. Variability and irregularity parameters include SDNN, rMSSD, pNN50 and the regularity index, approximate entropy, respectively. In all groups, HR decreased after tecadenoson and esmolol further decreased HR. The AFR was unaffected after tecadenoson. All the variability parameters were increased after tecadenoson. On the contrary, irregularity parameters did not change after tecadenoson. In conclusion, modification of AV node conduction using beta-blockade and A1-adenosine receptor agonist can increase RR variability but does not affect irregularity of RR intervals.