automaticity

Cells in the sinus & AV nodes are slowly-conducting cells activated by opening of Ca⁺² channels. They display automaticity, in that they spontaneously depolarize at a characteristic rate. Cells in the sinus node are normally the fastest to depolarize giving rise to sinus rhythms. Factors that enhance automaticity: 1) autonomic changes a) increased sympathetic tone b) decreased sympathetic tone 2) metabolic changes a) hypoxia b) hypercarbia c) decreased pH 3) mechanical factors: atrial or ventricular stretch 4) drugs: isoproterenol 5) electrolyte abnomalities a) decreased K⁺ b) increased Ca⁺²

References

Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 60