Dromotropic

Dromotropic refers to the effect on the rate at which electrical impulses travel through the heart, especially through the atrioventricular (AV) node. Dromotropy describes changes in AV nodal conduction velocity, which can influence the time between atrial activation and ventricular response. It is one aspect of cardiac modulation that is distinct from chronotropy (heart rate) and inotropy (contractile force). In clinical terms, dromotropic effects are often inferred from changes in the PR interval on an electrocardiogram.

Positive dromotropic effects increase conduction velocity through the AV node, shortening the conduction time. They are typically produced by sympathetic stimulation or beta-adrenergic receptor activation, and can facilitate faster transmission of impulses from atria to ventricles. Negative dromotropic effects slow AV nodal conduction, lengthening the PR interval. These effects are usually mediated by parasympathetic (vagal) activity and acetylcholine acting on M2 receptors, or by drugs that enhance vagal tone.

Pharmacologic agents illustrate the spectrum of dromotropy. Beta-adrenergic agonists (eg, isoproterenol) have positive dromotropic effects; acetylcholine and other anticholinergic influences can produce negative dromotropic effects. Antimuscarinic drugs like atropine reduce vagal tone and can yield a positive dromotropic effect. Digitalis glycosides increase vagal tone and commonly exert a negative dromotropic effect.

Clinically, dromotropy is relevant in the management of arrhythmias and AV block, and is considered when evaluating drug effects on AV nodal conduction and PR interval.