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Aninotrope[help 1] orinotropic is adrug or any substance that alters the force or energy ofmuscular contractions. Negatively inotropic agents weaken the force ofmuscular contractions. Positively inotropic agents increase the strength of muscular contraction.
The terminotropic state is most commonly used in reference to variousdrugs that affect the strength ofcontraction of heart muscle. However, it can also refer topathological conditions. For example,enlarged heart muscle can increase inotropic state, whereasdead heart muscle 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 ofcalcium in thecytoplasm of the muscle cell. Positive inotropes usually increase this level, while negative inotropes decrease it. However, not all positive and negative drugs affect calcium release, and, among those that do, the mechanism for manipulating the calcium level can differ from drug to drug.
While it is often recommended thatvasopressors are given through acentral line due to the risk of local tissue injury if the medication enters the local tissues, they are likely safe when given for less than two hours through good peripheralintravenous catheterization.[6]
By increasing the concentration of intracellularcalcium or increasing the sensitivity of receptor proteins to calcium, positive inotropic agents can increasemyocardial contractility.[7] Concentrations of intracellular calcium can be increased by increasing influx into the cell or stimulating release from the sarcoplasmic reticulum.[8]
Once in the cell, calcium can pass through one of two channels: theL-type calcium channel (long-lasting) and theT-type calcium channel (transient). These channels respond to voltage changes across the membrane differently: L-type channels respond to higher membrane potentials, open more slowly, and remain open longer than T-type channels.
Because of these properties, L-type channels are important in sustaining anaction potential, while T-type channels are important in initiating them.[9]
By increasing intracellular calcium, via the action of the L-type channels, the action potential can be sustained for longer and therefore, contractility increases.
Positive inotropes are used to support cardiac function in conditions such asdecompensatedcongestive heart failure,cardiogenic shock,septic shock,myocardial infarction,cardiomyopathy, etc.[10]
Examples of positive inotropic agents include:[citation needed]
Negative inotropic agents decrease myocardialcontractility and are used to decrease cardiac workload in conditions such asangina. While negative inotropism may precipitate or exacerbate heart failure in the short term, certain beta blockers (e.g.carvedilol,bisoprolol andmetoprolol) have been believed to reduce long-termmorbidity andmortality incongestive heart failure.[13]
Examples of negative inotropic agents include:
Class IAantiarrhythmics such as
Class IC antiarrhythmics such as