positive inotrope

A positive inotrope strengthens each squeeze of the heart, like turning up the power on a failing pump so it can move more blood with every stroke. When a weak heart cannot push out enough blood to supply the body, an inotrope boosts the force of contraction to keep vital organs perfused.

Most positive inotropes increase the calcium available inside heart muscle cells, because the strength of contraction depends on intracellular calcium. Catecholamines such as dobutamine and dopamine stimulate beta-1 adrenoceptors, raising cyclic AMP and calcium entry. Phosphodiesterase-3 inhibitors like milrinone raise cyclic AMP by blocking its breakdown. The cardiac glycoside digoxin works differently, indirectly raising calcium by inhibiting the sodium-potassium pump. Most are reserved for short-term use in acute heart failure or shock, often as intravenous infusions in critical care.

The catch is that making the heart work harder costs oxygen and electrical stability. Inotropes increase myocardial oxygen demand and can provoke arrhythmias, and several large studies show that long-term use of most inotropes increases mortality in chronic heart failure rather than helping. They are therefore generally a bridge or a rescue measure, not a long-term therapy, with digoxin being a partial exception used at low doses.