Chronotropic

Chronotropic effects (from chrono-, meaning time) are those that change the heart rate.

Chronotropic drugs may change the heart rate by affecting the nerves controlling the heart, or by changing the rhythm produced by the sinoatrial node. Positive chronotropes increase heart rate; however, negative chronotropes decrease heart rate.

A dromotrope affects Atrioventricular node (AV node) conduction. A positive dromotrope increases AV nodal conduction, and a negative dromotrope decreases AV nodal conduction. A lusitrope is an agent that affects diastolic relaxation.

Many positive inotropes affect preload and afterload.

Negative Chronotropes

Chronotropic variables in systolic myocardial performance can be split left and right. Left sided systolic chronotropy can be appreciated as Aortic Valve open to close time. Right sided variables are represented by Pulmonary valve open to close time. Inverted as diastolic chronotropy, the variables are aortic valve close to open and pulmonic close to open time. Pharmaceutical manipulation of chronotropic properties was perhaps first appreciated by the introduction of digitalis, though it turns out that digitalis has an inotropic effect rather than a chronotropic effect.

• Beta-blockers such as Metoprolol
• Acetylcholine
• Digoxin
• The Non-DHP Calcium Channel Blockers, Diltiazem and Verapamil
• Ivabradine
• quinidine

Positive Chronotropes

• Atropine
• Dopamine
• Dobutamine
• Epinephrine
• Isuprel

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