automaticity

Introduction

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:

• autonomic changes
  • increased sympathetic tone
  • decreased sympathetic tone
• metabolic changes
  • hypoxia
  • hypercarbia
  • decreased pH
• mechanical factors: atrial or ventricular stretch
• drugs: isoproterenol
• electrolyte abnomalities
  • decreased K+
  • increased Ca+2

More specific terms

• parasystole

Additional terms

• cardiac arrhythmia