1058 Intermittent Heart Action. 



Etiology. The omission of ventricular contractions occurs 

 frequently in horses as a sequel of acute infectious diseases 

 especially in the course, or during the convalescence, of in- 

 fluenza; in other animals it is hardly ever observed. As the 

 actual cause a reflex or immediate excessive stimulation of the 

 N. vagus may be assumed, since in the cases observed by the 

 author the omissions could always be relieved by atropine, 

 which is known to paralyze the vagus endings. The stimula- 

 tion of the vagus becomes manifest by the intermediation of 

 the , central nervous system when the omissions occur in brain 

 affections, fo^ instance, in case of increased intracranial -pres- 

 sure (chronic Hydrocephalus interhuS, brain tumors, - inflam- 

 rbation of the brain coverings^ etc.).- Digestive disturbances 

 (enteric catarrh, obstipation) also sometimes give rise to 

 transitory intermissions which are probably produced by 

 chemical substances that have been absorbed from the intestine,- 

 in such a mariner that the poisons irritate the N. va,gu& or its 

 center either directly or reflexly. The ventricular sy-s-tole may 

 finally be omitted in certain cases in connection with diseases 

 of the heart muscle or of its nervous apparatus, for-instance, 

 in acute inflammatory processes in the heart muscle, in the 

 pericardium or in the endocardium. 



In.termissions of the heart beat which are produced by 

 additional systolic contractions occur in all animal species and 

 always depend upon an abnormal stimulation of the heart. 

 The abnormal stimulation consists either in an increased 

 diastolic pressure in any one portion of the heart (in heart 

 weakness), or it develops in acute inflammatory processes in 

 the heart muscle, in the pericardium or endocardium. Some- 

 times poisons which have been absorbed in the intestines exert 

 an abnormal stimulation upon the heart. 



Pathogenesis. The physiological irrrtability or conductivity 

 of the heart-is reduced by excessive stimulation of the N. vagus, 

 and this occurs 'first on the points of transition between the 

 auricles and the ventricles, where the compartments of the 

 heart are connected only by small muscular bundles. In con- 

 sequence single contractions of the heart muscle, omit, according 

 to the degree of disturbance either only in the ventricles or 

 also in the auricles. The same occurs in diseases of the heart. 



Under .the" influence of an abnormal stimulation at the time 

 when the respective heart segments are usually in diastole, 

 an unusual contraction, an additional systole occurs following 

 immediately upon a normal systole but preventing the occur- 

 ]"ence of the next normal systole by reducing the irritabilitj'- 

 of the heart for a time. The sooner the .additional systole 

 follows upon the immediately preceding normal contraction, the 

 less complete are the filling and contraction of the heart, the 

 aortic pressure being as yet lowered but slightly, and in con- 



