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Updated: Apr 1 2018

Sites of Action for Cardiac Drugs

Images mechanism.jpg
  • Snapshot
    • A 24-year-old woman presents with tachycardia. She reports that this happens every few years without any identifiable causes. Her pulse is 200/min. Her other vital signs are stable. An electrocardiogram shows a patient with narrow complex QRS, tachycardia to 204/min, and a regular rhythm. She is given a medication to slow down the atrioventricular node and attempt to end the narrow complex tachycardia. (Adenosine)
  • Introduction
    • Adenosine
      • mechanism of action
        • ↑ K+ out of the cells, which hyperpolarizes the cell and causes ↓ AV nodal conduction
      • background
        • action potential is initiated by the sinoatrial (SA) node
          • slowed by the atrioventricular (AV) node
          • allows for ventricular filling prior to contraction
    • Calcium channel blockers
      • mechanism of action
        • directly blocks L-type voltage-gated Ca2+ channels (dihydropyridine receptors)
      • background
        • action potential causes a rush of Ca2+ into the cell
        • Ca2+ enters via L-type voltage-gated Ca2+ channels
        • this triggers the release of more Ca2+ from the sarcoplasmic reticulum
          • via ryanodine receptors
            • blocked by the ryanodine toxin
    • Digoxin
      • mechanism of action
        • inhibits extracellular K+ binding site of the Na+-K+ATPase on myocyte cell membrane
          • when the ATPase is inhibited, ↑ Na+ intracellular concentration
          • Ca2+-Na+ exchanger decreases the amount of Ca2+ it pumps out of the cell
          • ↑ Ca2+ intracellular concentration
      • background
        • contractility is determined by intracellular Ca2+
          • positive inotropic agents increase intracellular Ca2+
    • β-blockers
      • mechanism of action
        • indirectly blocks L-type voltage-gated Ca2+ channels (dihydropyridine receptors) via ↓ cAMP
      • background
        • positive inotropy by ↑ sympathetic nervous system is mediated by β1 receptors at the SA and AV nodes
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