Bathmotropic

Bathmotropic often refers to modifying the degree of excitability specifically of the heart; in general, it refers to modification of the degree of excitability (threshold of excitation) of musculature in general, including the heart. It especially is used to describe the effects of the cardiac nerves on cardiac excitability. Positive bathmotropic effects increase the response of muscle to stimulation, whereas negative bathmotropic effects decrease the response of muscle to stimulation. In a whole, it is the heart's reaction to catecholamines (norepinephrine, epinephrine, dopamine). Conditions that decrease bathmotropy (i.e. hypercarbia) cause the heart to be less responsive to catecholaminergic drugs. A substance that has a bathmotropic effect is known as a bathmotrope.

While bathmotropic, as used herein, has been defined as pertaining to modification of the excitability of the heart, it can also refer to modification of the irritability of heart muscle, and the two terms are frequently used interchangeably.

The term "bathmotropic" is derived from the Ancient Greek word (bathmós), meaning "step" or "threshold".

In 1897 Engelmann introduced four Greek terms to describe key physiological properties of the heart: inotropy, the ability to contract; chronotropy, the ability to initiate an electrical impulse; dromotropy, the ability to conduct an electrical impulse; and bathmotropy, the ability to respond to direct mechanical stimulation. A fifth term, lusitropy, was introduced in 1982 when relaxation was recognized to be an active process, and not simply dissipation of the contractile event. In an article in the American Journal of the Medical Sciences, these five terms were described as the five fundamental properties of the heart.

The bathmotropic effect modifies the heart muscle membrane excitability, and thus the ease of generating an action potential. The ease of generating an action potential is related both to the magnitude of the resting potential and to the activation state of membrane sodium channels.

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