Action potential characteristics and arrhythmogenic properties of the cardiac conduction system of the murine heart

Studies have characterized conduction velocity in the right and left bundle branches (RBB, LBB) of normal and genetically engineered mice. However, no information is available on the action potential characteristics of the sp ecialized conduction system (SCS). We have used microelectrode techniques t o characterize action potential proper-ties of the murine SCS, as well as e picardial and endocardial muscle preparations for comparison. In the RBB, a ction potential duration at 50%, 70%, and 90% repolarization (APD(50.70.90) ) was 6 +/-0.7, 35 +/-6, and 90 +/-7 ms. respectively, Maximum upstroke vel ocity (dV/dt(max)) was 153 +/- 14 V/s, and conduction velocity averaged 0.8 5 +/-0.2 m/s. APD(90) was longer in the Purkinje network of fibers (web) th an in the RBB (P<0.01), Web APD(50) was longer in the left than in the righ t ventricle (P<0.05). Yet, web APD(90) was longer in the right than in the left ventricle (P<0.001). APD(50.70) was significantly longer in the endoca rdial than in the epicardial (P<0.001; P<0.003). APD(90) in the epicardial and endocardial was shorter than in the RBB (<approximate to>36 ins versus approximate to 100 ins). Spontaneous electrical oscillations in phase 2 of the SCS occasionally resulted in early afterdepolarizations. These results demonstrate that APDs in the murine SCS are significantly (approximate to2- fold) longer than in the myocardium and implicate the role of the murine SC S in arrhythmias. The differences should have important implications in the use of the mouse heart to study excitation, propagation, and arrhythmias.