Inotropic Vs. Chronotropic Vs. Dromotropic: 5 Major Differences You Must Know

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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

1. Meaning

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.

2. 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.

3. 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

Basis of Comparison Inotropic Chronotropic Dromotropic
Definition Medicines that alter the force or energy of heart’s muscular contraction.   Drugs or medicines that change the heart rate and rhythm. Drugs that affect the conduction of electric impulses through the heart.
Categorization Positive Inotopic: Strengthens the force of cardiac contraction.    
Negative Inotropic: Weakens the force of cardiac contraction.    
Positive Chronotropic: Plays a role of accelerating the heart rate.   Negative Chronotropic: Slows down the heart rate. Positive Dromotropic: Speeds up conduction of electric impulse through the heart.  
Negative Dromotropic: Slows down conduction of electric impulse through the heart.
Examples Positive Inotropic:  Dopamine, Epinephrine, Isoproterenol, Amiodarone, etc.  
Negative Inotropic: Labetol and propanolol.
Positive Chronotropic: Atropine, Milrinone and Theophylline.      
Negative Chronotropic: Digoxin, acetylcholine and metoprolol.  
Positive Dromotropic: Phenytoin.        
Negative Dromotropic: verapamil.