An inotrope (//; from Greek in-, meaning fibre or sinew) is an agent that 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.
The term inotropic state is most commonly 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, enlarged heart muscle (ventricular hypertrophy) can increase inotropic state, whereas dead heart muscle (myocardial infarction) can decrease it.
Both positive and negative inotropes are used in the management of various cardiovascular conditions. The choice of agent depends largely 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 of the muscle cell. Positive inotropes usually increase this level, while negative inotropes decrease it. However, not all drugs involve calcium release, and, among those that 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 sensitisers
- Cardiac myosin activators
- Phosphodiesterase inhibitors
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, bisoprolol and metoprolol) have been believed to reduce morbidity and mortality in congestive heart failure. Quite recently, however, the effectiveness of beta blockers has come under renewed critical scientific scrutiny.
Class IA antiarrhythmics such as
Class IC antiarrhythmics such as