automaticity can further be subdivided into ( 1 ) automaticity caused by the normal automatic mechanism ( a normal property of cardiac cells in the sinus node , in some parts of the atria , in the atrioventricular junctional region , and in the his-purkinje system ) and ( 2 ) automaticity caused by an abnormal mechanism ( resulting from a decrease in membrane potential of cardiac fibers , which normally have a high level of membrane potential ) .
C0018792
atria
C0018787
cardiac