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 atrioventricular 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 the resulting ventricular rate during high atrial rate remains unclear. This study provides quantitative description of complex AVN input-output correlations determining the ventricular rate during random high atrial rate. METHODS AND RESULTS 12 rabbit heart preparations were used to evaluate the ventricular 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 correlations were used to quantify the ventricular rate under different pacing protocols. Small alternations in the sequence of activation of P and A resulted in substantial changes of the organization of the intranodal cellular responses and the ventricular rate. The ventricular rate was shown to be significantly dependent on the site of high rate pacing (P < 0.01) and on the resulting 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 versa (P < 0.05). CONCLUSIONS The prevailing ventricular rate during high atrial rate is a complex dynamic parameter that depends not only on the global mean atrial rate but, in a major part, on the differential bombardment of the AVN inputs and on the site of initiation of the atrial wave fronts.