Is Epinephrine an Inotrope?
Yes, epinephrine is definitely an inotrope with positive inotropic effects through its action on beta-adrenergic receptors, increasing myocardial contractility and cardiac output. 1, 2
Mechanism of Action
Epinephrine acts on both alpha (α) and beta (β) adrenergic receptors, producing a three-fold mechanism for increasing blood pressure: direct myocardial stimulation that increases ventricular contraction strength (positive inotropic action), increased heart rate (positive chronotropic action), and peripheral vasoconstriction 2
At low doses (<0.3 mcg/kg/min), epinephrine predominantly produces β-adrenergic effects including increased inotropy and decreased systemic vascular resistance 1
At higher doses (>0.3 mcg/kg/min), epinephrine's α-adrenergic vasoconstriction effects become more prominent 1
Dose-Dependent Effects
Epinephrine demonstrates a sequential dose-response pattern: first causing vascular dilation at very low doses, then increasing heart rate at moderate doses, and finally producing significant inotropic and lusitropic effects at higher doses 3
In septic shock patients, epinephrine increases oxygen delivery by increasing cardiac index without affecting systemic vascular resistance or pulmonary artery occlusion pressure 4
Epinephrine activates both Gs (stimulatory) and Gi (inhibitory) pathways through β2-adrenoceptors, unlike norepinephrine which only activates the Gs pathway 5
Clinical Use as an Inotrope
Epinephrine is classified alongside other recognized inotropes in clinical guidelines, with dosing recommendations specifically for its inotropic effects 1
In acute heart failure management, epinephrine is listed in the European Society of Cardiology guidelines as an inotropic agent with a recommended infusion rate of 0.05-0.5 μg/kg/min 1
Experimental studies have confirmed epinephrine's ability to shift the end-systolic pressure-volume relation leftward and increase its slope, which are characteristic effects of positive inotropes 6
Important Clinical Considerations
Despite its inotropic properties, epinephrine is not recommended as a first-line inotrope in cardiogenic shock and should be restricted to use as rescue therapy in cardiac arrest 1, 7
Norepinephrine or dobutamine are generally preferred as first-line agents for cardiogenic shock requiring inotropic or vasopressor support 7, 8
In patients with cardiogenic shock after myocardial infarction, epinephrine was associated with a higher incidence of refractory shock compared to norepinephrine, despite similar effects on cardiac index 9
Epinephrine's inotropic effects come with significant metabolic consequences, including increased myocardial oxygen consumption, lactic acidosis, and hyperglycemia 2, 9
In conclusion, epinephrine is definitively classified as an inotrope based on its pharmacologic actions and clinical effects, though its use as a first-line inotropic agent is limited by its side effect profile and the availability of potentially safer alternatives in many clinical scenarios.