Difference Between Inotropic, Chronotropic And Dromotropic

An inotrope is agent that alters the force or energy of muscular contractions. There are two categories of inotrope that is negatively inotropic agents and positively inotropic agents. Positively inotropic agents such as dopamine, Epinephrine, Isoproterenol, Amiodarone, etc. increase the strength of muscular contraction while negatively inotropic agents such as labetol and propanolol weakens the force of muscular contraction.

Chronotropic are drugs that affect the heart rate and rhythm by affecting the electrical conduction system of the heart and the nerves that influence it, such as by changing the rhythm produced by the sinoatrial node.

Just like Inotropes, there are positive and negative Chronotropes. Positive Chronotropes increase heart rate and they include Atropine, Milrinone and Theophylline. Negative chronotropes on the other hand, decrease the heart rate; examples include digoxin, acetylcholine and metoprolol.

Dromotropic are drugs which affects the conduction speed in the AV node and subsequently the rate of electrical impulses in the heart. Positively dromotropy such as is phenytoin increases conduction speed while Negative dromotropy such as verapamil decreases conduction speed.

Key Differences

Description

Inotropic are medicines that alter the force or energy of heart’s muscular contraction.

Chronotropic are drugs or medicines that change the heart rate and rhythm by affecting the electrical conduction system of the heart and the nerves that influence it.

Dromotropic are drugs that affect the conduction of electric impulses through the heart.

Targeted Effects

• Inotropic Drugs: These drugs primarily target the force of cardiac muscle contraction, enhancing or reducing the strength of contractions.
• Chronotropic Drugs: These drugs primarily target the heart rate, increasing or decreasing the number of heartbeats per minute.
• Dromotropic Drugs: These drugs primarily target the speed and efficiency of electrical impulses conduction through the heart’s conduction system.

Main Use

• Inotropic Drugs: They are used to treat conditions where the heart’s pumping ability is compromised, such as heart failure or cardiogenic shock.
• Chronotropic Drugs: Used to manage heart rate abnormalities, like tachycardia (fast heart rate) or bradycardia (slow heart rate).
• Dromotropic Drugs: Employed in cases of abnormal electrical conduction, such as certain types of arrhythmias or heart block.

Mechanism of Action

• Inotropic Drugs: Act on cardiac muscle cells to influence calcium handling and increase or decrease the force of contraction.
• Chronotropic Drugs: Target the autonomic nervous system to affect the release of neurotransmitters that regulate heart rate.
• Dromotropic Drugs: Impact the heart’s electrical conduction system, affecting the speed of electrical impulses through the heart.

Effects on Cardiac Output

• Inotropic Drugs: Can increase cardiac output by improving the force of contractions.
• Chronotropic Drugs: Can influence cardiac output by increasing or decreasing heart rate.
• Dromotropic Drugs: May have an impact on cardiac output by optimizing the coordination of heart contractions.

Side Effects

• Inotropic Drugs: Potential side effects may include arrhythmias, increased oxygen demand, and electrolyte imbalances.
• Chronotropic Drugs: Side effects may include fatigue, dizziness, and disturbances in blood pressure.
• Dromotropic Drugs: Side effects may include heart block, bradycardia, and hypotension.

Clinical Indications

• Inotropic Drugs: Used in acute decompensated heart failure, cardiogenic shock, and certain cases of heart muscle dysfunction.
• Chronotropic Drugs: Utilized in conditions where the heart rate needs to be adjusted, such as certain arrhythmias.
• Dromotropic Drugs: Employed in cases where the electrical conduction is abnormal, leading to irregular heartbeats.

Examples of Drugs

• Inotropic Drugs: Dobutamine, Digoxin, Milrinone.
• Chronotropic Drugs: Beta-blockers (e.g., propranolol), Atropine.
• Dromotropic Drugs: Calcium channel blockers (e.g., verapamil), Beta-blockers.

Categorization

The drugs are categorized into positive or negative depending on their role.

Positive

• Positive inotropic – strengthens the force of cardiac contraction.
• Positive chronotropic -plays a role of accelerating the heart rate.
• Positive dromotropic -speeds up conduction of electric impulse through the heart.

Negative

• Negative inotropic – weakens the force of cardiac contraction.
• Negative Chronotropic – slows down the heart rate.
• Negative Dromotropic– slows down conduction of electric impulse through the heart.

Examples

Positive

• Positive inotropic drugs include dopamine, Epinephrine, Isoproterenol, Amiodarone, etc.
• Positive chronotropic , a good example is Atropine, Milrinone and Theophylline.
• Positive dromotropic, a good example of the drug is phenytoin.

Negative

• Negative inotropic, a good example is labetol and propanolol.
• Negative chronotropic, a good example is digoxin, acetylcholine and metoprolol.
• Negative dromotropic, a good example is verapamil.

Also Read: Difference Between Test C And Test E

Difference Between Inotropic, Chronotropic And Dromotropic In Tabular Form