Inotropic - Positive / Negative chronotropic

The adjective inotropic refers to any agent capable of altering the force of contraction 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 inotropic: increased contractile force of the heart muscle;

negative ionotropic: decrease in the contractile force of the heart muscle.

The adjective chronotropic refers to any agent capable of altering the rate 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: increased heart rate (tachycarding action);

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

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

Other drugs, such as beta blockers, instead produce a negative inotropic and negative chronotropic effect, reducing the frequency and strength of myocardial contraction; this effect translates into a reduction in cardiac output and the work of the heart. 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 (they reduce the consumption of cardiac oxygen by stopping the extension of the necrotic area). .

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