Result of obstruction to circulation. In right ventricle usually. In
auricle from narrow auriculo-ventricular opening. Pure dilatation from
sudden extreme blood pressure as in inflammations of the lungs. In fat
cattle from fatty obstructions around the heart and great vessels.
Weakness of cardiac muscles in fatty degeneration, fevers, debility,
etc. Symptoms, dyspnœa under slight exertion, unsteady walk, cold,
dropsical limbs, venous pulse, pulse small, weak, irregular,
intermittent, with palpitations. Treatment, in early stages arrest the
causes, arsenic, digitalis, fatten for butcher.
Dilatation of the right cavities of the heart is one of the most common
heart diseases of the horse. It is an almost constant condition in
advanced broken wind, and is a frequent concomitant of hypertrophy and
an occasional one of atrophy of the heart. Its usual direct cause is
some obstacle to the free escape of blood from the cavity affected. Thus
in broken wind the difficulty of the circulation through the lungs
causes accumulation in the pulmonary artery and right ventricle of the
heart, the walls of which are distended because of the unwonted internal
pressure. When the dilatation of this ventricle reaches a certain stage
the auriculo-ventricular opening is equally widened, the valves become
insufficient to close it and the right auricle and venæ cavæ participate
in turn in the internal pressure and dilatation. The right ventricle is
more often affected than the left, because of the greater frequency of
obstruction in the circulation through the lungs than in that through
the general system, and because of the thinness of its walls which more
readily give way under internal pressure. Dilatation may result from
disease of the great arteries, from diminution of their calibre by the
pressure of tumours, or by narrowing of their openings at the heart,
whether as the result of diseased valves or other morbid condition. As
affecting the auricles primarily its usual cause is narrowing of the
auriculo-ventricular opening from some abnormal deposit. The extreme
thinness of the walls of the auricles allows these to give way under
internal pressure even much more readily than the right ventricle.
The causes it will be seen are similar to those inducing hypertrophy,
and hence the frequent coexistence of the two. Pure dilatation occurs
especially when internal pressure takes place suddenly and to excess,
and while the nutritive functions are to a great extent in abeyance.
Such conditions are found in acute inflammations of the respiratory
organs, or of the inner or outer membranes of the heart, and the rapid
deposit in the lungs of tubercles or other abnormal material.
Dilatation of the right side of the heart is a common complaint in
overfed cattle, and is apparently due to the diminished power of
resistance in the walls of the heart, the muscular substance of which is
partly replaced by fatty granules, and to the obstruction offered to the
circulation by the extraordinary accumulation of fat around the base of
the heart and the commencement of the large blood vessels. Though a
diseased condition this rarely shortens life or interferes with the uses
to which cattle are put.
The heart walls are similarly weakened and yield more readily to the
internal blood pressure in endocarditis, myocarditis, pericarditis, high
fever, infectious diseases, poisonings, anæmia, and debilitating
diseases generally. Debility and incapacity to resist the blood pressure
is the essential prerequisite to dilatation.
The _symptoms_ which have been already enumerated in the table given
under the head of _hypertrophy_ are mainly these: Loss of appetite,
spirit and endurance; faintness and difficulty of breathing on the
slightest exertion; habitual coldness with a tendency to dropsy of the
extremities; loss of control over the extremities when walked or trotted
far; venous pulsation in the jugulars; heart’s impulse weak and
undulatory or tremulous, or under exertion tumultuous or palpitating;
murmur often present with the first sound; the first or more commonly
the second sound may be doubled; pulse small, weak, irregular, and often
intermittent, and frequently livid spots in the nasal mucous membrane.
Paroxysms of unsteady gait from irregular circulation in the brain is
frequent, and Dyer asserts that he has repeatedly seen blindness as a
result of this condition.
In _treatment_ the main purpose should be to put a stop to the cause of
the disease before it has been developed to a dangerous extent. When the
malady is manifested by the symptoms above enumerated the subject is
rendered permanently unfit for service and will probably die suddenly
under some slight exertion. Fattening animals in a condition of quietude
will often lay on flesh for an indefinite length of time notwithstanding
that the heart is considerably dilated. (See note on digitalis,
strophanthus and arsenious acid in dilated heart, under the head of
_hypertrophy_). To relieve the asthmatic attacks attending on an
overtaxed heart Zuill strongly recommends the combination of iodide of
potassium, digitalis, nux vomica and coca. But heart tonics are often
much more affective after the bowels and portal system have been
unloaded by a laxative.