Automaticity

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Contents 1 More Specific Terms 2 Introduction 3 Additional Terms 4 References

More Specific Terms

• parasystole

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

Additional Terms

• cardiac arrhythmia

References

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

automaticity