Inotrope

An inotrope (pronounced /ˈaɪnətroʊp/) is an agent which alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction.

Most commonly, the inotropic state is used in reference to various drugs that affect the strength of contraction of heart muscle (myocardial contractility). However, it can also refer to pathological conditions. For example, ventricular hypertrophy can increase inotropic state, while myocardial infarction can decrease it.

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Cardiac inotropes

Both positive and negative inotropes are used in the management of various cardiovascular conditions.

The choice of agent largely depends on specific pharmacological effects of individual agents with respect to the condition.

One of the most important factors affecting inotropic state is the level of calcium in the cytoplasm. Positive inotropes usually increase the level, while negative inotropes decrease it. However, not all drugs involve calcium release, and among those which do, the mechanism for manipulating the calcium level can vary from drug to drug.

Positive inotropic agents

Positive inotropic agents increase myocardial contractility, and are used to support cardiac function in conditions such as decompensated congestive heart failure, cardiogenic shock, septic shock, myocardial infarction, cardiomyopathy, etc.

Examples of positive inotropic agents include:

• Calcium
• Calcium sensitisers
  • Levosimendan
• Cardiac glycosides
  • Digoxin
• Catecholamines
  • Dopamine
  • Dobutamine
  • Dopexamine
  • Epinephrine (adrenaline)
  • Isoprenaline (isoproterenol)
  • Norepinephrine (noradrenaline)
• Eicosanoids
  • Prostaglandins^[1]
• Phosphodiesterase inhibitors
  • Enoximone
  • Milrinone
  • Theophylline

Negative inotropic agents

Negative inotropic agents decrease myocardial contractility, and are used to decrease cardiac workload in conditions such as angina. While negative inotropism may precipitate or exacerbate heart failure, certain beta blockers (e.g. carvedilol) have been shown to reduce morbidity and mortality in congestive heart failure.

• Beta blockers
• Diltiazem
• Verapamil

References