Disturbances Of The Heart In General

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Sources: Disturbances Of The Heart

Of prime importance in the treatment of diseases of the heart is a

determination of the exact, or at least approximately exact,

condition of its structures and a determination of its ability to

work.



This is not the place to describe its anatomy or its nervous

mechanism or the newer instruments of precision in estimating the

heart function, but they may be briefly itemized. It has now been

kn wn for some time that the primary stimulus of cardiac contraction

generally occurs at the upper part of the right auricle, near its

junction with the superior vena cava, and that this region may be

the "timer" of the heart.



This is called the sinus node, or the sino-auricular node, and

consists of a small bundle of fibers resembling muscle tissue. Lewis

[Footnote: Lewis: Lecture in the Harvey Society, New York Academy of

Medicine, Oct. 31, 1914.] describes this bundle as from 2 to 3 cm.

in length, its upper end being continuous with the muscle fibers of

the wall of the superior vena cava. Its lower end is continuous with

the muscle fibers of the right auricle. From this node "the

excitation wave is conducted radially along the muscular strands at

a uniform rate of about a thousand millimeters per second to all

portions of the auricular musculature."



Though a wonderfully tireless mechanism, this region may fall out of

adjustment, and the stimuli proceeding from it may not be normal or

act normally. It has been shown recently not only that there must be

perfection of muscle, nerve and heart circulation but also that the

various elements in solution in the blood must be in perfect amounts

and relationship to each other for the heart stimulation to be

normal. It has also been shown that if for any reason this region of

the right auricle is disturbed, a stimulus or impulse might come

from some other part of the auricle, or even from the ventricle, or

from some point between them. Such stimulations may constitute

auricular, ventricular or auriculoventricular extra contractions or

extrasystoles, as they are termed. In the last few years it has been

discovered that the auriculoventricular handle, or "bundle of His,"

has a necessary function of conductivity of auricular impulse to

ventricular contraction. A temporary disturbance of this

conductivity will cause a heart block, an intermittent disturbance

will cause intermittent heart block (Stokes-Adams disease), and a

prolonged disturbance, death. It has also been shown that

extrasystoles, meaning irregular heart action, may be caused by

impulses originating at the apex, at the base or at some point in

the right ventricle.



In the ventricles, Lewis states, the Purkinje fibers act as the

conducting agent, stimuli being conducted to all portions of the

endocardium simultaneously at a rate of from 2,000 to 1,000 mm. per

second. The ventricular muscle also aids in the conduction of the

stimuli, but at a slower rate, 300 mm. per minute. The rate of

conduction, Lewis believes, depends on the glycogen content of the

structures, the Purkinje fibers, where conduction is most rapid,

containing the largest amount of glycogen, the auricular musculature

containing the next largest amount of glycogen, and the ventricular

muscle fibers the least amount of glycogen.



Anatomists and histologists have more perfectly demonstrated the

muscle fibers of the heart and the structure at and around the

valves; the physiologic chemists have shown more clearly the action

of drugs, metals and organic solutions on the heart; and the

physiologists and clinicians with laboratory facilities have

demonstrated by various new apparatus the action of the heart and

the circulatory power under various conditions. It is not now

sufficient to state that the heart is acting irregularly, or that

the pulse is irregular; the endeavor should be to determine whit

causes the irregularity, and what kind of irregularity is present.