Assessment of atrioventricular nodal physiology in the mouse

Transgenic mice are increasingly being utilized for understanding cardiac e lectrophysiologic abnormalities. However, little is known about the normal atrioventricular nodal and infraHisian physiology in the mouse because of t he prior inability to record a His-bundle deflection. We present the first comprehensive examination of the murine atrioventricular nodal and His-Purk inje systems employing His-bundle recordings. Normal, healthy, male C57BL/6 J mice (n = 48) underwent an in vivo electrophysiology study using a 2 F oc tapolar electrode catheter. Effective refractory periods were determined du ring premature atrial and ventricular stimulation. The PR interval measured 44 +/- 6 ms with a mean sinus cycle length of 185 +/- 42 ms. Baseline AH i ntervals were 36 +/- 5 ms and HV intervals were 10 +/- 2 ms. At a pacing cy cle length of 140 ms the atrioventricular nodal effective refractory period (AVNERP) and atrial effective refractory period (AERP) were 86 +/- 19 ms a nd 57 +/- 17 ms, respectively. The mean AV Wenckebach and 2:1 paced cycle l ength were 103 +/- 14 ms and 84 +/- 13 ms, respectively. Premature atrial s timulation curves were asymptotic without discontinuity. A subset of nine m ice was studied after administration of isoproterenol. The sinus cycle leng th, AVNERP and AERP decreased significantly from baseline measurements. Thi s method establishes a practical and feasible technique to record in vivo H is-bundle electrograms in the mouse to assess atrioventricular nodal and in fraHisian physiology. Use of this model will allow for the examination of a bnormalities of atrioventricular nodal and infraHisian conduction in transg enic murine models.