Chronotropic

Not to be confused withChronotypeorChronotope.

Chronotropiceffects (fromchrono-,meaning time, andtropos,"a turn" ) are those that change theheart rate.

Chronotropicdrugsmay change theheartrate andrhythmby affecting theelectrical conduction system of the heartand thenerves that influence it,such as by changing therhythm produced bythesinoatrial node.Positive chronotropes increase heart rate; negative chronotropes decrease heart rate.

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

Many positiveinotropesaffectpreloadandafterload.

Positive chronotropes

• MostAdrenergic agonists
• Atropine
• Dopamine
• Epinephrine
• Isoproterenol
• Milrinone
• Theophylline

Negative chronotropes

Chronotropic variables can be considered in systolic myocardial left and right sides. 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 ofdigitalis,though it turns out that digitalis has aninotropiceffect rather than a chronotropic effect.

• Beta blockerssuch asmetoprolol
• Acetylcholine
• Digoxin
• Pacemaker current (i.e.HCN channel) inhibitors (e.g.ivabradine)