Contractility

• Contractility:

  • aka inotropy
  • is a degree of emptying
  • determined by force of contraction
  • an increase in contractile force that is not a consequence of muscle stretch/length, so therefore is not a consequence of increase filling
  • graph shows that at any length, you produce more force through contractility than through pre-load

  
• What causes contractility:

  • various causes such as SNS, hormones, drugs
  • the main cause is the activation sympathetic nervous system along with catecholamines (specifically epinephrine)
  • these target the sympathetic receptors on the ventricular muscle fibres -> increase calcium induced calcium release -> increase cross bridge formation -> increase contractility = inotropy
• Inotropic agents:

  • can increase or decrease contractility
  • positive inotropes increase contractility
  • SNS
  • drugs - increase calcium induced calcium release - used in short term acute heart failure with hypotension, not used long term
  • digoxin
  • dobutamine
  • dopamine
  • negative inotropes decrease contractility
  • altered metabolic states - myocardial ischemia, or acidosis
  • drugs
  • beta blockers
  • atenolol
  • propanolol
  • calcium channel blockers
  • amlodipine
  • diltiazem
  • verapamil