Dromotropic Action

DROMOTROPIC ACTION (from the Greek dromos—running), the influence of various factors on the heart's ability to conduct impulses. The term dromotropic action was introduced in 1900 by Engelmann. Stimulation of the cardiac branches of the vagus nerve causes a slowing in impulse conduction (negative dromotropic action), while stimulation of the cardiac branches of the sympathetic nerve leads to an acceleration of impulse conduction (positive dromotropic action). For the most part, dromotropic action changes in the same direction as inotropic action, but exceptions to this rule occur (e.g., strongly slowed conduction with an unchanged volume of contractions during an incomplete block, etc.). Positive dromotropic action is exerted by Ca, Sr, Ba (in small quantities), adrenaline (by stimulating the endings of the sympathetic nerve), and atropine (by paralyzing the endings of the vagus nerve). The positive dromotropic action caused by the latter two substances is sometimes paralyzed due to the exhaustion of conductive capacity resulting from an increase in the number of impulses. Negative dromotropic action is exerted by K, Ba (in large quantities), high concentration of H-ions, digitalis, chloroform, chloral hydrate, atropine (in small doses), quinine (a protoplasmic poison), nicotine, sparteine, and cocaine (acting directly on the heart muscle), as well as morphine, physostigmine, and muscarine (acting as irritants on the endings of the vagus nerve). Negative dromotropic action can lead to complete dissociation of the activity of the atria and ventricles.