HYPERTROPHY OF THE HEART.
Simple, eccentric, concentric. Ventricles chiefly affected. Causes, increased functional activity, from obstruction to the circulation, or continued extra exertion. Right ventricular hypertrophy-obstruction in the pulmonary circulation; left ventricular hypertrophy-obstruction in the systemic. Auricular hypertrophy-insufficiency of the auriculo-ventricular valves. Pericarditis as a cause. Abnormal weights. Symptoms, beats more forcible and prolonged, 1st sound low, prolonged, 2nd sound clear, often doubled, increased dulness on percussion, diagnostic signs of hypertrophy, dilatation and a combination of the two. Simple hypertrophy rarely dangerous, with dilatation grave, threatens congestions and apoplexies. Treatment, rest, laxatives, sedatives, in irregular heart action digitalis, arsenic.
An enlargement of the heart from increase of its muscular substance is by no means uncommon in the horse. It may exist without any change in the capacity of the cavities of the heart (simple hypertrophy) or it may be associated with dilatation of one or more of these cavities (hypertrophy with dilatation;—eccentric hypertrophy). A third variety has been described in which the capacity of the cavities is decreased but Cruveilhier and Budd have satisfactorily shown the nonexistence of this condition except as a congenital deformity.
It is in the ventricles that the increase is chiefly observed, the reason of which is to be found in the causes of the malady. These usually consist in some obstruction to the circulation such as chronic congestions in the lungs or elsewhere, rupture of air cells in the lungs, tuberculous and other abnormal deposits in the chest and elsewhere, tumors which by their position interfere with the circulation through the larger vessels, and the like. Where by some such cause the blood is impeded in its outward course, one or both ventricles are called upon to contract more vigorously to force a sufficient amount of blood onward and in accordance with the inherent adaptability of the animal economy, there takes place an increase of the muscular walls of the ventricle proportionate to the required energy of the contractions. The condition then is essentially due to a more active nutrition and growth of the muscular substance and finds its exact parallels in the well-developed legs of the ballet dancer or the brawny arm of the blacksmith. All alike occur in accordance with a general law that whenever there is habitually demanded of any organ an unusual activity of function, which stimulates without exhausting its power, nature adds to the active element of such organ till the required labor can be accomplished without the overwork of any particular part.
Keeping this in view we can easily explain the increase of one part of the heart without immediate implication of another. The ventricles are more commonly enlarged than the auricles because upon them devolves the work of overcoming the obstruction, whether this exists in the lungs or the system at large. The auricles fulfill little more than a passive function in receiving the blood from the veins during the contraction of the ventricles and allowing it to pass down into these when their relaxation takes place. The closure of the auriculo-ventricular valves during the ventricular contraction protects the auricles from the internal tension to which the lower part of the heart is subjected and thus all tendency to increase is obviated.
The hypertrophied part corresponds to the locality of the obstruction. If it exists in the lungs (heaves, consumption, hepatisation, chronic bronchitis), pulmonary artery, its valves at its origin from the heart, or if it consists in contraction of that orifice, the enlargement takes place primarily in the right ventricle, the right auricle remaining unchanged so long as the auriculo-ventricular valves act perfectly. The ventricle, however, tends to dilate as well as enlarge in thickness of walls, and as soon as this dilatation has proceeded so far as to widen the orifice between the auricle and ventricle and render its valves insufficient, the auricle also begins to dilate and its walls often increase in thickness. But the vicious chain does not end here. Should the animal survive and the original obstruction persist, the veins throughout the system become habitually congested because of the reflux of blood from the right auricle and ventricle, dropsies appear in different parts, the congestion of the veins is continued through the capillary bloodvessels to the arteries, the difficulty of propelling the blood comes to be experienced by the left ventricle and a corresponding series of morbid changes taking place on that side, as have already ensued on the right, the vicious circle is soon completed, and the entire organ becomes diseased, each constituent part of the organ operating injuriously on that which preceded it in the track of the circulation, and every new change forming but a stepping stone to a more dangerous modification.
On the other hand the obstruction may exist in the general circulation, on the course of the aorta, or its branches, in its valves at its origin from the heart, or in the narrowing of its orifice. Then the increase takes place first in the left ventricle, is propagated to the left auricle, leads to congestion of the veins, capillaries and arteries of the lungs, and lastly to disease of the right side of the heart. Here there is a different starting point, but the progress of the disease-changes in a direction opposed to the course of the circulation is the same.
The disease may, however, begin with the auricles, owing to disease of the auriculo-ventricular valves impeding the flow of blood into the ventricle, or to simple narrowing of the auriculo-ventricular opening. The auricle is then primarily enlarged, the corresponding veins congested, this is propagated to the capillaries and arteries, and lastly the ventricle on the opposite side of the heart is involved. This is chiefly seen with fibrinous deposits on the valves or in the case of polypus hanging into the auriculo-ventricular opening. Aneurisms, embolisms, neoplasms, atheroma and calcic degeneration of the arterial walls may be effective factors.
In addition to these causes Bouilaud and Leblanc attach a high importance to chronic inflammations of the serous membranes, which by reason of the contiguity of the latter to the muscular structure bring about a more abundant circulation in this and an increased nutrition. Another cause is unintermitting hard work which necessitates excessive exertion of the heart, to supply blood more freely to the muscular system and the lungs. Many hunters suffer from this affection it is believed because of their extraordinary exertions. The stallion Helenus had a heart of 14 ℔s.
Weight of the heart. The heart in the horse which rarely weighs over 9 ℔s. is increased from 10 ℔s. to 14 ℔s. in this disease and in one case in a cart horse, recorded by Stephenson in the Veterinarian for 1861, it is said to have reached 32 ℔s. Stephenson probably weighed the heart while filled with blood. A diseased heart weighed in this way by Thomson amounted to 34 ℔s., one by Gerlach, 19 ℔s., an ox’s heart by Herran 36 ℔s. In Stephenson’s case there was further an extraordinary dilatation of the anterior vena cara. Haycock (Veterinarian, 1850), records a case in which though the heart only weighed 10 ℔s. 8 oz., yet the walls of the ventricles were double the normal thickness, those of the left being 2¼ inches while those of the right were 1 inch. An estimate from the thickness of the walls, it must be borne in mind, is not so satisfactory as the absolute weight taken after the removal of the large vessels, the superfluous fat and the contained blood.
The usual coincidence of other complaints supports the statement that it is mostly due to obstruction to the circulation. A few cases will illustrate. Dyer reports the case of a hunter in which with general hypertrophy and dilatation of the right auricle, the pulmonary artery was so large as to admit the fist. (Veterinarian, 1861). Halloway relates a case in which there were extensive internal deposits of melanotic material, especially in the mesenteric glands, liver, spleen, and kidneys (Veterinarian, 1850). Haycock records a case with thickening of the auriculo-ventricular valves on the right side, and of several of their tendinous cords, also a diseased liver which had ruptured before death (Veterinarian, 1850). Percivall publishes a case associated with pleurisy and rheumatism (Veterinarian, 1858). Henderson furnishes a case associated with diseased right auriculo-ventricular valves and enlarged liver weighing 55 ℔s. (Veterinarian, 1847.)
Symptoms. In simple hypertrophy the heart beats are more forcible and prolonged so that the period of silence or rest is shortened. This is due to the greater length of time taken up in the contraction of the ventricles. For the same reason the pulse which may or may not be accelerated, irregular or intermittent, is full and rolling or as it were prolonged. The first sound of the heart is prolonged and low or muffled, sometimes almost inaudible while the second is unnaturally loud. Sometimes when one ventricle only is enlarged that may complete its contraction later than the other and the second sound is repeated as in the syllables lub—tip tip. A duplication of the first sound only is less common. If the sounds are heard over a greater extent of the chest’s surface than is natural, the lungs being healthy, it is probably due to hypertrophy of the heart. If very clear on the right side they indicate increase of the right ventricle. The heart’s impulse is usually strong and may be felt on both sides, and it may be over the whole chest.
Percussion usually shows a more extended dulness in the region of the heart but the blows must be pretty forcible to bring out the deeper resonance, otherwise it will come only from the thin layer of lung. These results are of the greatest value in the dog.
The pulse is usually regular and if excited to irregularity and intermission quickly returns to its natural state when the patient is left at rest.
As hypertrophy is usually associated with dilatation of the heart the following table abridged and modified from Dr. Walshe will prove valuable by presenting side by side the signs indicating hypertrophy with and without dilatation, and simple dilatation.
| TABLE CONTRASTING THE MAIN SYMPTOMS OF HYPERTROPHY AND DILATATION. | ||
|---|---|---|
| A. General Physical Signs. | ||
| SIMPLE HYPERTROPHY. | HYPERTROPHY WITH DILATATION. | SIMPLE DILATATION. |
| Heart’s impulse slow and heaving as if pressing steadily against an obstacle—in rythm regular, in force unequal. | Force increased, sharper, more knocking, may impart a shake to the body. May be felt on the right side. | Impulse conveys a feeble undulatory sensation; force of successive beats unequal; rythm irregular. |
| First sound is dull, muffled, prolonged and weakened almost to extinction. Second sound full and clanging; period of silence shortened. | Sounds gain greatly in loudness and extent of transmission, especially if the valves are thickened. | First sound short, abrupt and clear. Second sound not specially affected. |
| Murmur with the first sound present at one time and absent at another. | Murmur with the first sound may be present, from altered direction of the orifice of the aorta. | Murmur with the first sound from insufficiency of the auriculo-ventricular valves. |
| B. General Functional Symptoms. | ||
| SIMPLE HYPERTROPHY. | HYPERTROPHY WITH DILATATION. | SIMPLE DILATATION. |
| Strength unimpaired. Power of continued exertion (especially uphill) limited by shortness of breath. | Strength tends to become impaired. | Strength fails. |
| Visible mucous membranes healthy or of a bright red. | Purpleness and lividity of the mucous membranes proportionate to the valvular or pulmonary obstruction. | Lividity of the mucous membranes. Dropsical effusions of the limbs and other dependent parts which pit on pressure. |
| Difficulty of breathing occasional. | Difficulty of breathing occurs in paroxysms. | Difficulty of breathing great and constant, with occasional aggravations. |
| Pulse full, strong, firm, tense, resisting and prolonged without jerk or thrill. | Fulness of pulse continues but strength and power of resistance lost. | Pulse small and feeble, much later than the heart beat. Regular or feeble, fluttering and irregular. Venous pulse in the jugulars. |
| Rarely and never rapidly the direct cause of death. | Indirectly and more or less rapidly fatal. | Palpitation frequent. Faintness occurs from time to time, and may lapse into fainting and sudden death. |
Pure hypertrophy rarely implies imminent danger unless dependent on some pre-existing structural disease which impedes the freedom of the circulation. If excessive, however, or if associated with dilatation the animal is short-winded and unfit for all but the slowest work. It predisposes to congestion or apoplexy of the lungs when its seat is the right ventricle, and to congestions and hemorrhage in other parts of the system, brain, kidney, lungs, liver, bowels, if in the left.
Asthma (dogs), heaves (horses), emphysema and tuberculosis in cattle are occasional complications attended by grave symptoms.
Treatment. In advanced cases and such as are dependent on irremovable structural changes in the lungs or elsewhere no treatment is of any avail. In recent and uncomplicated cases in the horse and cow and in some more advanced conditions in other animals, not used for work, a palliative treatment may be profitably adopted. This consists in a nitrogenous restricted and gently laxative diet, perfect rest in fattening oxen and other animals, or in the horse moderate and carefully regulated work, and as a medicament the use of digitalis or aconite. No known remedy has any power to directly check the growth of the heart and the utmost that can be expected of these agents is to lessen the activity of the heart’s action and retard its growth. Digitalis may be given as recommended for palpitation, or aconite in the form of tincture 20 drops for horses and cattle and 1 to 2 drops for dogs, repeated four times daily. Strophanthus may replace digitalis. When depletion seems advisable purgatives or diuretics should be given as appears most applicable to the particular case. Iodide of potassium has been strongly recommended.
When extreme dilatation exists with the hypertrophy, sedatives should be given cautiously and their effects carefully watched as the heart is often dangerously susceptible to depressing influences. When the disease has advanced so far as to cause abundant dropsical effusions it is futile to resort to treatment as amelioration can rarely be looked for, not even to the extent of allowing an animal to be fattened.
The value of arsenic in most cases of broken wind (heaves) has suggested the inquiry whether it does not operate directly on the heart. Leblanc who advances this query might have quoted in explanation the known power of arsenic to retard and arrest tissue change, with its natural consequences, the diminished amount of effete matter thrown into the blood in any given time, and the lessened necessity for an active circulation to supply any great waste of structure. It may benefit such cases in this way but does so probably to a far greater extent by an influence on the nervous function analogous to its action in neuralgia and other purely nervous disorders. Dilatation of the heart which usually exists in heaves is usually benefited by tonics which like arsenic are destitute of stimulating properties.