ECG of the "newborn" mouse (Mus domesticus) with specific reference to comparative AV transmission

Comparative AV Transmission. Introduction: The objective of this study was to record the ECG of the smallest living mammal to extend the domain of dat a for comparative AV nodal electrophysiologic purposes. These data are need ed to establish the relationship between the PR interval and heart size in mammalian species of all sizes. Methods and Results: In recently born mice (age 1.5 to 8 weeks) weighing be tween 2.5 and 10 g and with estimated heart weights between 15 and 60 mg, E CGs, using bipolar limb leads, were recorded during general anesthesia. The PR interval, representing AV transmission time was about 40 msec, which is quite long for hearts of this size. On the basis of detailed analysis of t he data, we postulate the presence of a fixed delay or discontinuous propag ation in the AV node not only in newborn mice, but in mammals of all sizes. Conclusion: AV transmission times obtained in mammals (including humans) ca nnot be explained on the basis of generally accepted, classic AV conduction theories. The acceptance of the presence of a fixed delay in the AV node m ay ultimately be of value to better understand AV node function during sinu s rhythm and supraventricular arrhythmias.