inotrope

An inotrope, or inotropic agent, is a substance that influences the force of the heart’s contraction, or inotropy. Positive inotropes increase contractile strength, while negative inotropes reduce it. Inotropism results from changes in intracellular calcium handling or calcium sensitivity of the contractile apparatus, and from signaling pathways that regulate calcium cycling and myofilament function.

Positive inotropes are used to raise cardiac output in conditions such as heart failure with reduced ejection fraction or cardiogenic shock. Common examples include dobutamine, which chiefly stimulates beta-1 adrenergic receptors to raise cAMP and calcium entry; dopamine and epinephrine, which have broader adrenergic effects; milrinone, a phosphodiesterase-3 inhibitor that raises cAMP and produces vasodilation; and the calcium sensitizer levosimendan. Digoxin increases contractility by inhibiting the Na+/K+ ATPase, raising intracellular calcium, and it can also help control ventricular rate in atrial fibrillation. Negative inotropes, such as certain calcium channel blockers (verapamil, diltiazem) and some beta-blockers, decrease contractile force and are used with caution or avoided in acute decompensated states.

Clinical considerations include balancing improved cardiac output against risks such as tachyarrhythmias, increased myocardial oxygen demand, hypotension, and electrolyte disturbances. Inotropes are typically used for short-term hemodynamic support, including during acute stabilization, postoperative care, or in severe heart failure with low output. The term inotropy is distinct from chronotropy (heart rate) and lusitropy (relaxation), though many agents affect more than one aspect of cardiac function.