Inotropes are drugs that alter the strength (force) of the heart’s contractions. Positive inotropes increase contractility, boosting cardiac output when the heart is failing to pump effectively. Negative inotropes reduce contractility and are used therapeutically in conditions where a less forceful contraction is beneficial, most notably beta-blockers and some calcium channel blockers used in heart failure and arrhythmia management.
Positive inotropes are most commonly used in the intensive care unit for patients with severely impaired cardiac function following cardiac arrest, cardiogenic shock or major cardiac surgery. The principal agents are: dobutamine (a beta-1 adrenergic agonist that increases contractility and reduces afterload, first-line for most cases of cardiogenic shock), milrinone (a phosphodiesterase inhibitor that increases contractility and causes vasodilation, often used when beta-blockers are already on board and beta stimulation may be less effective), and levosimendan (a calcium sensitiser that improves contractility without increasing oxygen demand, used in selected cases of acute decompensated heart failure). Adrenaline (epinephrine) has both inotropic and vasopressor effects and is used in severe shock and during cardiac arrest itself.
The use of positive inotropes carries risks. Increased myocardial contractility increases the heart’s oxygen consumption, which can worsen ischaemia in an already-compromised heart. Positive inotropes also lower the threshold for arrhythmias, including ventricular tachycardia and ventricular fibrillation. For this reason, they are used at the lowest effective dose for the shortest necessary duration, with continuous ECG monitoring.
In the post-cardiac arrest ICU, inotropes and vasopressors are often used together to maintain adequate blood pressure and cardiac output during the period of myocardial stunning. As the stunned myocardium recovers over 24 to 72 hours, inotropic support is gradually weaned. Failure to wean from inotropes may indicate more severe underlying structural heart disease requiring further investigation or mechanical circulatory support.
« Back to Glossary Index