The actions of atropine and quinidine in fibrillation of the auricles : clinical and experimental studies second lecture / by Thomas Lewis.

Thomas Lewis

Date:: [1922]

Credit: The actions of atropine and quinidine in fibrillation of the auricles : clinical and experimental studies second lecture / by Thomas Lewis. Source: Wellcome Collection.

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$nessed. Abrupt termination of the disorder in one case, failure to terminate in another. Before leaving these effects of quinidine upon the auricular dis- order, it is to be noted that quinidine does not act on the muscle alone; it also acts on the vagus. Its effect is to paralyze this nerve partly or completely. The manner of its action is not the same as that of atropine, for atropine acts on the nerve endings, while quinidine would appear to act, according to Dale’s recent observations,! upon the nerve ganglia; the end result, so far as we are now concerned, isthesame. Vagal tone decreases. Fortunately for our theoretical consideration, this change in nerve control acts in the same directions as do the direct effects on the muscle, a fact | which is expressed correspondingly in the accompanying table. TABLE. Rate of Refractory Transmission auricular period. time. movement. Vagal stimulation, s,s al ln si ee Ge bas = a AUOWUME* Yea. sere Get oe Oe a i Quinidine (direct action) . . . . + + Quinidine (indirect action). . . . + + =< Since both the direct and indirect action of quinidine are similar in end-results to those of atropine, 1t may be asked why the last drug is not capable of bringing fibrillation to an end. The reply is that in some circumstances it does do so; for the fibrillating auricle of the dog, atropine is usually an effective remedy,’ ™ stopping the disorder immediately. It is clear however that it is not effective clinically in chronic cases of fibrillation; though it might be so in more acute cases. A statement has been made that Hering? saw fibrillation abolished by atropine in man. This does not appear to have been so, the case being a disorderly rhythm of a different kind, as Hering* has stated. In patients, fibrillation is more firmly rooted than in dogs in which it has been produced by stimulation; and atropine, though it acts in the same directions as quinidine, has a far less powerful action. It may be of interest to note that our observations upon atropine preceded our personal acquaintanceship with quinidine and its use in fibrillation. The effect of Quinidine on the ventricles in fibrillation of the auricles is a complex one. In chronic fibrillation, a rise of ventricular rate is almost constant and is usually conspicuous. ‘The rise coincides with the fall of auricular rate when single doses of the drug are given; using repeated doses, the ventricular rate often tends to fall away, although the auricular rate still remains low. ‘Three factors appear to be involved, namely, the fall of auricular rate, loss of vagal tone and a direct action of quinidine on the conducting tissues. We may consider these separately. When the auricle is beating rapidly and the ventricle is failing$