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.