Role of the differential bombardment of atrial inputs to the atrioventricular node as a factor influencing ventricular rate during high atrial rate

Objectives: The role of the atrial inputs for the conduction through the at rioventricular node (AVN) at slow rates and during reentrant tachycardia is well acknowledged, although still controversial. However, the relationship between the sequence and rate of atrial engagement of the AVN inputs and t he resulting ventricular rate during high atrial rate remains unclear. This study provides quantitative description of complex AVN input-output correl ations determining the ventricular rate during random high atrial rate. Met hods and results: 12 rabbit heart preparations were used to evaluate the ve ntricular rate during programmed regular high atrial rate pacing or random pacing from eight atrial sites. Electrograms were recorded at the posterior (P) and anterior (A) AVN inputs, and at the bundle of His along with nodal cellular action potentials. Lorenz-plots and input-output-rate correlation s were used to quantify the ventricular rate under different pacing protoco ls. Small alternations in the sequence of activation of P and A resulted in substantial changes of the organization of the intranodal cellular respons es and the ventricular rate. The ventricular rate was shown to be significa ntly dependent on the site of high rate pacing (P<0.01) and on the resultin g mean rate of inputs activation. Furthermore, the asymmetry between P- and A-bombardment was an important determinant, so that high ventricular rate was associated with large difference between the inputs' rates and vice ver sa (P<0.05). Conclusions: The prevailing ventricular rate during high atria l rate is a complex dynamic parameter that depends not only on the global m ean atrial rate but, in a major part, on the differential bombardment of th e AVN inputs and on the site of initiation of the atrial wave fronts. (C) 1 999 Elsevier Science B.V. All rights reserved.