Mathematical relationship between automaticity of the sinus node and the AV junction

Stable sinus and AV junctional rates (each in the same animal) were obtained in 50 open-chest dogs anesthetized with pentobarbital. After cannulation of both the sinus node and the AV node arteries, the control sinus rate was 135 ± beats per minute (mean ± 1 SD), the range being 84 to 192. Following selective eserinization of the sinus node (10 or 100 μg per milliliter, 2 ml.), which progressively slows the sinus node until a stable AV junctional rhythm emerges, the mean AV junctional rate was 88 ± 19 beats per minute, ranging between 48 and 126. The plot of AV junctional rates (AVJR) versus corresponding sinus rates (SR) from each dog demonstrates a 2:3 ratio between these two variables. On mathematical analysis of these data there is a consistent correlation (r = 0.942; p < 0.001) for the linear relationship between AVJR and SR, with a β̂ estimate of the slope being 0.64979. This value is reasonably close to a useful premise that the resting AV junctional rate amounts to 66 per cent or two thirds of the control sinus rate. The model AVJR = β̂. SR is adequate to explain the relationship between the two variables AVJR and SR.