Disorders of impulse formation

on 7.12.08 with 0 comments

  • altered normal automaticity—for examples, SA node

  • abnormal automaticity: cells that don’t usually have automaticity exhibit it

  • triggered activity

    • early afterdepolarizations (EADs)

    • delayed afterdepolarizations (DADs)

Altered normal automaticity

  • occurs when normal pacemaker cells (SA, AV nodes) begin pacing at a non-physiologic rate

  • example: junctional tachycardia in the AV node; this can overdrive the pacemaker cells and drive the heart too quickly

Abnormal automaticity

  • occurs when automaticity arises from cells that are not the normal pacemaker cells in the heart

  • example: accelerated idioventricular rhythm

    • ischemia creates a current of injury between normal and ischemic cells

    • cells that don’t usually fire begin to fire themselves

    • occurs 24 to 72 hrs after myocardial infarction

Triggered activity

  • caused by oscillations in the membrane potential induced by the previous beats; these are classified by how closely they occur relative to the previous beat

  • two types

    • early afterdepolarizations (EADs)

    • delayed afterdepolarizations (DADs)

Category: Cardiology Notes



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