The left ventricle responds to the persistent
hypertension with a compensatory concentric hypertrophy aiming to decrease
wall tension. Excessive hypertrophy compromises diastolic filling leading to
a reduced stroke volume. The hypertrophy may be associated with poor capillary
blood flow to the subendocardial myocardium and result in dysrhythmias and reduced
In the kidneys a persistent increase
in glomerular pressure results in glomerulosclerosis and loss of functional nephrons.
This may lead to proteinuria and elevated blood urea and creatinine.
Hypertensive retinopathy is a well recognised
feature in small animals. Sustained hypertension results in a reactive vasoconstriction
of the arteriolar vessels in the retina. This may be seen (on ophthalmoscopy)
as a tortuosity of the retinal vessels. Perivascular blood leakage may be seen,
there may be focal areas of ischaemia and degeneration, and choroidal vascular
haemorrhage may lead to retinal detachment. In severe cases the animal may present
with complete retinal detachment, intraocular haemorrhage or glaucoma.
The common clinical signs of hypertension
are listed in
Treatment should be directed towards
the underlying cause (
Sodium restriction may help in mild hypertension.
Diuresis reduces sodium and water retention.
In the presence of renal disease frusemide would be the drug of choice. Spironolactone
is used for the treatment of hyperaldosteronism.
B blockers will reduce cardiac output
and renin release and are indicated in hyperthyroid cats or in hypertension due
to renal disease.
B blockers, e.g. prazosin, may be used
in animals producing a mixed peripheral vasodilation.
Hydralazine is a direct-acting arterial
vasodilator that will reduce systemic blood pressure but may result in a reflex
sympathetic drive producing a tachycardia and increased renin production.
Angiotensin converting enzyme inhibitors
(e.g. enalapril or benazepril) decrease the production of angiotensin II and
aldosterone, causing a mixed vasodilation and sodium and water excretion.
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