inotropa

Inotropy refers to the contractile strength of the heart muscle, the force generated during systole. The term is used to describe the inotropic state of the heart, and is distinct from chronotropy (heart rate) and lusitropy (relaxation). An inotrope is a substance or factor that modifies this contractile force.

Positive inotropes increase myocardial contraction strength, which can improve stroke volume and cardiac output in conditions such as systolic heart failure or cardiogenic shock. Negative inotropes decrease contractile force and may be useful in certain situations to reduce oxygen demand or control arrhythmias, though they can worsen heart failure if used inappropriately.

Physiologically, positive inotropy arises mainly from mechanisms that raise intracellular calcium during contraction or increase the calcium sensitivity of the myofilaments. The beta-adrenergic pathway is central: activation of beta-1 receptors raises cyclic AMP, which enhances calcium influx and calcium release from the sarcoplasmic reticulum, and modulates pacing and contractile proteins. Other routes include phosphodiesterase inhibition, which sustains cAMP signaling, calcium sensitizers, and changes in myofilament responsiveness.

Clinical agents commonly described as positive inotropes include dobutamine, dopamine, epinephrine, and norepinephrine; phosphodiesterase inhibitors such as milrinone; and calcium-sensitizing agents like levosimendan. Digoxin also increases contractility, primarily by altering intracellular ion balance rather than calcium handling alone. Adverse effects of inotropes can include arrhythmias, increased myocardial oxygen consumption, and hemodynamic instability, so their use is carefully titrated and monitored.