[Pharmacological study of a case of alternating right bundle branch block in the rat]

The Author has, occasionally, registered in an old rat an "alternans" right bundle branch block. Assuming that, as in human pathology, such block is due to an increase of refractory period of the interested branch, the Author wanted to study the effect of substances which, acting in various ways, are able to eliminate the block. Adrenaline (10 mcg intravenously), because of its positive dromotropic action, improving the conduction, made, at first, disappear the block. Later, because of its direct positive chronotropic action and consequent increase of sinus rate, the block appears again and becomes stable. Later on, lowering sinus rate to the beginning values, the block becomes once again "alternans". A calcium-antagonist (verapamil, mg 0.10 intravenously), causing a decrease of sinus rate, makes the block disappear. The Author, by these observations, is induced to make some clinical considerations. This conduction disturbance is similar to that one which is observed in human pathology and which has always been treated successfully by vasodilators (best of all nicotinic acid), recently associated to antiaggregant drugs too.