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 specialized conduction system (SCS). We have used microelectrode techniques to characterize action potential properties of the murine SCS, as well as epicardial and endocardial muscle preparations for comparison. In the RBB, action potential duration at 50%, 70%, and 90% repolarization (APD50,70,90) was 6±0.7, 35±6, and 90±7 ms, respectively. Maximum upstroke velocity (dV/dtmax) was 153±14 V/s, and conduction velocity averaged 0.85±0.2 m/s. APD90 was longer in the Purkinje network of fibers (web) than in the RBB (P <0.01). Web APD50 was longer in the left than in the right ventricle (P <0.05). Yet, web APD90 was longer in the right than in the left ventricle (P <0.001). APD50,70 was significantly longer in the endocardial than in the epicardial (P <0.001;P <0.003). APD90 in the epicardial and endocardial was shorter than in the RBB (≈36 ms versus ≈100 ms). 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 (≈2-fold) longer than in the myocardium and implicate the role of the murine SCS in arrhythmias. The differences should have important implications in the use of the mouse heart to study excitation, propagation, and arrhythmias.

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