Expansion
Sympathetic drive and calcium raise it; hypoxia, acidosis and beta blockade lower it
Expansion
Positive inotropes
- Sympathetic stimulation and circulating catecholamines, through beta-1 receptors
- Increased extracellular calcium
- Digoxin, by inhibiting the sodium-potassium ATPase
- Phosphodiesterase inhibitors, by raising cyclic AMP
- Thyroid hormone
- The Bowditch (treppe) effect, in which higher rate increases force
Negative inotropes
- Hypoxia, hypercapnia and acidosis
- Beta blockers and non-dihydropyridine calcium channel blockers
- Myocardial ischaemia and infarction
- Hyperkalaemia
- Many anaesthetic agents
The common pathway is intracellular calcium. That is why acidosis is so depressant: hydrogen ions compete with calcium for troponin C binding sites.