automaticity

noun

au·​to·​ma·​tic·​i·​ty ˌȯ-tə-mə-ˈti-sə-tē, -ma- 

plural automaticities

: the capacity of a cell to generate an action potential spontaneously without an external stimulus

Atrial tachycardias due to abnormal automaticity or triggered activity are particularly difficult to abolish with antiarrhythmic drugs.

—Leonard I. Ganz and Peter L. Friedman, The New England Journal of Medicine

All adult cardiac myocytes can respond to electrical stimuli and conduct action potentials, but the working cells of the atria and ventricles generally lack automaticity …

—Arnold M. Katz, Physiology of the Heart, 5th edition