Bradycardia. 1057 



Etiology. The cause of a decided slowing- of' the heart 

 beat lies either in an excessive stimulation of the vagus or 

 in certain affections of the heart muscle. 



An excessive stimulation of the N. vagus may follow upon 

 a bilateral compression of this nerve (in the thorax cavity, 

 in the medulla oblongata), it may be due to slight inflammation, 

 to compression of the vagus center in certain brain affections, 

 and finally, it may be a reflex effect from the stomach' or in- 

 testine, from the peritoneum or from the skin (Albrecht). Cer- 

 tain chemical substances (e. g., tannates) are also capable of 

 irritating the vagus. Certain diseases of the heart muscle 

 frequently cause bradycardia, for instance, degeneration of the 

 muscle in acute infectious diseases, chronic myocarditis, 

 atrophy of the heart, affections of the coronary arteries, finally 

 insufficient nutrition of the heart muscle in inanition. 



Prom what has been said it is readily seen that bradycardia indeed occurs 

 as an accompaniment of various diseases, but that it must, nevertheless, be 

 considered separately because in many cases a cause cannot be ascertained. 



Symptoms. In horses a reduction in the number of heart 

 beats has been observed to as few as 9 (Zimmermann), in most 

 cases only to 12-20 (Dieckerhoff, Nordheim, Vogel, Zschokke), 

 in dogs to 20-18 (Frohner, Albrecht). The heart beat remains 

 vigorous and the heart sounds are clear. The animals are 

 apparently quite well; only in severe cases they show, aside 

 from the symptoms of the underlying disease, languor, somno- 

 lence, lassitude, attacks of heart spasms or of heart weakness. 



Diagnosis. Bradycardia is easily recognized and the cause 

 may often be ascertained. It is possible to determine by sub- 

 cutaneous injections of atropine (for large animals 0.02-0.05; 

 for dogs 0.005-0.008 gm.) whether the cause lies in the vagus 

 or in the heart, because bradycardia which is due to an excessive 

 stimulation of the vagus disappears for a time after the ad- 

 ministration of atropine.. Symptoms of heart weakness, which 

 may become manifest only on motion, point to an organic dis- 

 ease of the heart. 



Treatment. Nerve stimulants are indicated in all cases, 

 such as injections of atropine, alcohol, ether, also sponging, 

 and the relief of any digestive disturbances that may be present. 



Literature. Albrecht, W. f. Tk., 1895. 225 (Lit.). — Frohner, Monh., 1891. 

 IL 548. — Gutbrod, W. f. Tk., 1901. 493. — Nordheim, Z. f.'Vk., 1890.' 275. — 

 Sonnenberg, B. t. W., 1909. 171. — Vogel, Eep., 1888. 1. — Zimmermann, O. M., 

 1900. 289. 



3. Intermittent Heart Action. Actio Cordis Intermittens. 



(Arhythmia cordis.) 



Intermittent heart action is a disturbance of the heart beats 

 which may be produced by the total omission of one or several 

 ventricular contractions or by additional systolic contractions. 



Vol. 1—67 



