(Drugs) Manipulating Inotropy

• Manipulating contractility:

  • physiologically the sympathetic nervous system drives up/increases the calcium induced calcium release, producing more forceful cardiac contractions in times of need e.g. exercise or severe haemorrhage
  • drugs can also be effective in:
  • increasing contractility
  • decreasing contractility
• Drugs to decrease inotropy:

  • beta blocks: atenolol, propanolol, sotalol, nadolol, metrolol
  • block some sympathetic nervous system receptors on the myocardial sarcolemma -> limiting the opening of calcium ion channels -> decrease calcium influx -> decrease calcium induced calcium release -> decrease calcium availability to troponin -> decrease force production
  • used in those in whom myocardial blood supply is limited e.g. in coronary artery disease, due to them having less oxygen delivery to the heart, we limit oxygen needs
• Drugs to increase inotropy:

  • intropic support e.g. adrenaline, dobutamine
  • mimic the effects of the sympathetic nervous system and enhance calcium induced calcium release to produce more forceful contractions than normal
  • -> increase the opening of calcium ion channels -> increase calcium influx -> increase calcium induced calcium release -> increase calcium availability to troponin -> increase force production
  • used in critically acutely unwell e.g. acute heart failure, septicaemia