Is enlargement by hypertrophy due to an increase in size of the muscular fires, or does it involve an abnormal multiplication of the fibres? If the term hypertrophy be applied exclusively to morbid growth, it implies that the enlargement is due to the former, that is, to an increase in size of the muscular fibres. The term is thus restricted by Virchow and others. The multiplication of fibres, on the other hand, is called hyperplasia, or hypergenesis. Measurements in normal hearts, and in hearts more or less hypertrophied, show an increase of size of the muscular fibres, their diameter in the latter sometimes being four times greater than in the former. The heart may, therefore, be enlarged so that the volume will be four times greater than in health, by hypertrophy, in the restriction sense of the term. This, however, will probably not account for the increase of the muscular substance in all cases; and, if not, the multiplication of fibres must be admitted. Enlargement of the heart by hypertrophy, therefore, may be due wholly to hyper-nutrition, or increased growth of the muscular fibres, and hyperplasia may be superadded.
What causes the pathological processes, namely, hyper-nutrition and hyperplasia, which increase the quantity of the muscular substance of the heart?
Generally, if not invariably, enlargement by hypertrophy is the result of prolonged abnormal force of the heart’s action. It is difficult to account for this form of enlargement, except as caused by augmented muscular power continued for a long period; and generally there are present obvious causes which account, in this way, for the enlargement. The mechanism is the same as in the familiar examples of certain voluntary muscles becoming disproportionately developed when inordinately exercised. The muscles of the arms of the blacksmith are strikingly in contrast with the muscles of the lower limbs; and the reverse is true of pedestrians and dancers. Involuntary muscles, aside from the heart, also present examples. For instance, the muscular structure of the urinary bladder may become enormously hypertrophied, when the power of contraction of this organ has been for a long time increased in consequence of obstruction to the expulsion of the urine. Clinical observation shows, that in most cases of enlargement of the heart by hypertrophy, there are prior morbid conditions which stand to it in a causative relation. The practical bearing of this pathological view of hypertrophy is vastly important. It follows, that enlargement of the heart by hypertrophy, as a rule, is compensatory; or, in other words, a conservative provision to meet the difficulties incident to the morbid conditions upon which the hypertrophy depends. This truth cannot be too strongly impressed.
In the great majority of cases, enlargement by hypertrophy is consecutive to, and dependent upon, morbid conditions within the heart, namely, on valvular lesions. These give rise to hypertrophy when they involve over-repletion of the cavities, in consequence either of obstruction to the free passage of the blood through the orifices, or of regurgitation due to valvular insufficiency. The organ being unduly distended and stimulated by the accumulation of blood, its action becomes abnormally forcible; the causes of accumulation being permanent, and often progressively increasing, the increased power of action continues and augments, and hypertrophy is the result. The hypertrophy commences in that portion of the heart which is primarily affected, but the several portions sustain to each other, in their anatomical structure and functions, relations so close and reciprocal, that causes which at first are limited to one portion, affect, ultimately, the whole organ. The enlargement, however, preponderates in the portion which is first affected.
Directing attention, with some detail, to the mode in which valvular lesions give rise to enlargement, we shall be led to consider the development of the affection in the different anatomical divisions of the heart, respectively, taking them up in the order of their greater relative liability to become hypertrophied.
Of the several portions, the left ventricle is oftenest enlarged; next in liability to enlargement, is the left auricle; next, the right ventricle; and, last, the right auricle.
the valvular lesions which especially lead to hypertrophy of the left ventricle, are seated at the aortic orifice. Lesions in this situation may involve, as will be seen hereafter, either contraction, and consequently obstruction; or incompetence of the valves, and consequent regurgitation of the blood from the aorta into the ventricular cavity.
Obstruction seated in the aorta, either near to or at some distance from the heart, such as is incident to aortic aneurism, may lead to hypertrophy of the left ventricle primarily, and subsequently of the other portions. Enlargement commences in the left ventricle, in connection with lesions affecting the mitral orifices and valves, and involving either contraction or insufficiency, or both these immediate effects.
Contraction and valvular insufficiency at the orifice of the pulmonary artery occasion, primarily, enlargement of the right ventricle, precisely as aortic lesions induce, first, enlargement of the left ventricle.
Lesions at the tricuspid orifice being extremely infrequent, enlargement of the right auricle rarely occurs, except consecutively to an affection of the right ventricle.
Enlargement of the heart, not associated with valvular lesions, may be due to obstruction at a distance from the centre of the circulation. Obstruction to the pulmonary circulation incident especially to emphysema of the lungs, and occasionally to chronic pleurisy, collapse, and dilated bronchi, leads to enlargement.
The researches of Larcher, Ducrest, and other, show that a certain amount of hypertrophy, limited to the left ventricle, is incident to pregnancy. It would seem that the hypertrophy, under these circumstances, is to be regarded as normal, and that it disappears after confinement.
The changes which occur in the muscular structure of the uterus, in connection with gestation, are thus represented, on a small scale, in the heart. The increase in weight of the heart in pregnancy, it is estimated, may amount to one-fifth of the previous weight of the organ. Doubtless this temporary hypertrophy is compensatory or conservative, as it is when it occurs in other connections.
It was formerly supposed, that the prolonged functional disorder of the heart frequently eventuated in the development of hypertrophy. This supposition does not derive much support from clinical experience. At first view, the statement just made may appear inconsistent with the fact that the abnormal growth of the muscular walls of the heart is the result of abnormal muscular action of the organ. The inconsistency disappears when it is considered that functional palpitation, even when intense, does not involved the increase of power or strength of muscular action which is incident to the over-accumulation of blood from an impediment to the circulation.
(See “Functional Disorders,” page 50, where this opinion is controverted. Hale.)
Enlargement by hypertrophy, as already stated, is almost always a secondary affection. In the great majority of cases it is consecutive to valvular or aortic lesions. It is also an effect of certain chronic pulmonary diseases, more especially emphysema of the lungs. It occurs in certain cases of Bright’s disease. It is a physiological event in pregnancy. It may be produced – but the examples are very rare – by long-persisting functional disorder. Its occurrence, when it is not evidently a secondary affection, is so infrequent, that there is room for doubting whether it ever be a truly idiopathic affection. (Flint.)
SYMPTOMS AND PATHOLOGICAL EFFECTS OF HYPERTROPHY.
The symptoms of hypertrophy, in the cases which come under the cognizance of the physician, are generally intermingled with those of concomitant cardiac or other affections, of which the hypertrophy is an effect. Cases of hypertrophy not associated with, and dependent upon, other affections, are so rare, that its clinical history cannot be said to have been established by observation. The symptomatic phenomena which are described as distinctive of it, are determined inferentially, rather than by facts observed in well-authenticated cases. Rationally considered, it is clear that the symptoms would be those indicative of abnormal power of the heart’s action. Undue determination of blood to the head might be expected to occasion certain phenomena, such as cephalalgia, flushing of the face, throbbing, epistaxis, vertigo, etc. These symptoms have relation especially to hypertrophy affecting the left ventricle. Assuming the absence of aortic and of mitral lesions involving obstruction or regurgitation, the pulse would represent by its force, fullness, and incompressibility, the power of the ventricular systole. Dyspnoea, when, from any cause, the action of the heart is increased, as, for example, after exercise, would denote that the hypertrophy affected the right ventricle. Of the powerful action of the heart the patient would be conscious when his attention was directed to it, and it would be apparent from the movements of parts of the body and the dress. The digestive and assimilative functions would not be expected to offer any marked symptoms of disorder. The muscular strength would not be diminished; nutrition would not be impaired; nor the functions of secretion and excretion interrupted. (Flint.)
Hale wrote Lectures On Diseases Of The Heart, Materia medica and special therapeutics of the new remedies Volume 1, Materia Medica And Special Therapeutics Of The New Remedies Volume 2, Saw Palmetto: (Sabal Serrulata. Serenoa Serrulata), The Medical, Surgical, and Hygienic Treatment of Diseases of Women, New Remedies: Their Pathogenetic Effects and Therapeutic Application, Ilex Cassine : the aboriginal North American tea, Repertory to the New Remedies with Charles Porter Hart, The Characteristics of the New Remedies, Materia Medica and Special Therapeutics of the New Remedies, The Practice of Medicine, Homoeopathic Materia Medica of the New Remedies: Their Botanical Description etc.