VPT 311: General and Systemic Veterinary Pharmacology (2+1)

CLASSES OF DRUGS ACTING ON HEART

• Drugs acting on the heart can be classified into
• Drugs that directly affect the myocardial cells which includes
  • autonomic neurotransmitters and related drugs
  • cardiac glycosides and other inotropic agents
  • antidysrhythmic or antiarrhythmic drugs
• Drugs that affect the cardiac function indirectly through actions elsewhere in the vascular system calcium antagonists acting both directly on the myocardial cells and indirectly by relaxing the arterioles.

Autonomic transmitters and related drugs

• Both sympathetic and parasympathetic systems exert a tonic effect on the heart at rest.
• The main effects of sympathetic activity on the heart are
  • positive inotropic effect (increased force of contraction)
  • positive chronotropic effect ( increased heart rate)
  • increased automaticity
  • repolarisation and restoration of function following generalised cardiac depolarisation
  • reduced cardiac efficiency.
• The parasympathetic effects include
  • cardiac slowing and reduced automaticity
  • decreased force of contraction
  • inhibition of A-V conduction