A MATHEMATICAL-MODEL OF SINUS NODE FUNCTION - VALIDATION BY RECORDINGOF SINUS NODE ELECTROGRAMS

We have applied a mathematical function to model sinus node recovery a fter atrial pacing at different cycle lengths in 13 autonomically dene rvated, anesthetized canines. This model provides ''pure'' indexes of sinoatrial conduction and of suppression of automaticity. We compared sinoatrial conduction computed from the model (SACT(c)) with sinoatria l conduction measured directly utilizing a catheter recording the sinu s node electrogram (SACT(d)) to test the validity of the model. We use d both the model and the sinus node electrogram to further define even ts after pacing. There was close agreement between SACT(c) and SACT(d) with correlation coefficients at pacing cycle lengths of 20 and 50% b elow resting of 0.86 (P < 0.0001) and 0.78 (P < 0.0001), respectively. We verified that the conventional sinus node recovery time is due bot h to suppression of automaticity and prolongation of sinoatrial conduc tion. Sinoatrial conduction time returned rapidly to normal over 1-3 b eats, whereas automaticity recovered exponentially over 20-40 postpaci ng intervals. The model accurately describes postpacing phenomena and has the potential to provide a useful adjunct to the measurement of th e sinus node electrogram for assessment of sinus node function in the experimental laboratory.