Inotrope - Positive / Negative Cronotrope

The inotropic adjective belongs to any agent capable of altering the contraction force of a muscle. The term inotropic is widely used in the medical field, especially in reference to the action of some drugs on myocardial contractility. This effect can be:

positive inotrope: increase in the contractile strength of the heart muscle;

negative ionotropic: decreased contractile strength of the heart muscle.

The adjective chronotropic belongs to any agent capable of altering the frequency of contraction of the heart muscle. The term chronotropic is widely used in the medical field in reference to the ability of some drugs to alter the heart rate. This effect can be:

positive chronotropic: increase in heart rate (tachycardia action);

negative chronotropic: decrease in heart rate (bradycardia action);

Drugs such as digitalis have a positive inotropic action, given the ability to increase the contraction force of the myocardium. These medicines are used to support the cardiac function in case of heart failure, cardiomyopathy, heart rate control in case of atrial fibrillation or supraventricular tachycardia (therefore they have a positive inotropic and negative chronotropic action).

Other medicines, such as beta blockers, produce instead a negative and negative chronotropic inotropic effect, reducing the frequency and strength of myocardial contraction; this effect translates into a reduction in cardiac output and heart work. These medicines are generally used in the treatment of arterial hypertension, chronic heart failure and angina pectoris, as well as in the early intervention of acute myocardial infarction (reduce cardiac oxygen consumption by arresting the extension of the necrotic area) .

Among the endogenous molecules, therefore produced by our body, hormones such as thyroxine, noradrenaline and adrenaline exert an inotropic and chronotropic positive effect, while acetylcholine exhibits a negative chronotropic effect.