Hypertension, defined as a blood pressure consistently >160 mmHg, is a frequently observed symptom in cats.
Common causes, such as age (>10 years), chronic renal disease, hyperthyroidism, diabetes mellitus, hyperadrenocorticism and acromegaly, are diagnosed more often due to heightened awareness of these diseases by feline practitioners.
End-organ damage associated with hypertension include the heart and vessels, the brain, the kidney, and probably most importantly, the eye.
- Regulation of blood pressure
- Pathogenesis of hypertension
- Role of the renin-angiotensin aldosterone system
- Chronic renal disease - 19-65% of CRD cats have hypertension. CRD-induced hypertension is most likely due to sodium retention, increased activity of the renin-angiotensin-aldosterone system, volume expansion, increased norepinephrine levels, and an increased vascular responsiveness to catecholamines.
- Aldosterone (mineralocorticoid) imbalance
- Idiopathic hypertension (unknown origin)
- Primary aldosteronism - (Conn's syndrome)
Hypertension develops in 15-50% of acromegalic humans due to volume expansion and possibly an increased tissue responsive to angiotensin II. The incidence of hypertension in acromegalic cats has not been reported.
- A pheochromocytoma is associated with episodic hypertension due to the release of catecholamines from a tumour of the chromatin cells in the adrenal gland.
- Administration of Megestrol acetate (Ovarid®)
- Administration of corticosteroids
- Diabetes mellitus
- Chronic anaemia
Left untreated, hypertension inevitably damages delicate capillaries in end-artery organs (eyes, kidneys, heart, and brain). Hypertension may manifest as blindness, polyuria, polydipsia, cardiac irregularities, seizures, nystagmus (neurological signs), and hind limb paresis. Retinal detachment and acute blindness, the most common presenting complaints for hypertensive cats, are recognized by retinal haemorrhages, tapetal hyperreflectivity, and vascular tortuosity on fundic examination.
Treatment is firstly aimed at addressing the primary cause of hypertensionm such as chornic renal disease, hyperthyroidism, etc.
Management of hypertensive effects due to increased β-receptor sensitivity may best be achieved with specific beta-blocker therapy. The most commonly recommended drug for cats is atenelol which decreases the neuromuscular and cardiovascular effects of hyperthyroidism.
- Low sodium diet - a diet moderately restricted in sodium should be offered, although no evidence as yet exists to correlate dietary salt intake and hypertension in cats.
- An antihypertensive agent (such as those listed below) should be instigated in cats with a repeatable systolic blood pressure exceeding 160 mm Hg using a oscillometric blood pressure monitor. Regular (monthly) monitoring of blood pressure should coincide with repeated prescriptions for ongoing use of blood pressure medication.
|Furosemide||1 - 2 mg/kg q 12-24 hrs|
|Enalapril||0.35 - 0.5 mg/kg q 24-48 hrs|
|Benazepril||0.25 - 0.5 mg/kg q 24 hrs|
|Atenolol||6.25 - 12.5 mg/kg q 24hrs|
|Calcium channel blockers|
|Diltiazem||1.5 - 2.5 mg/kg q 8 hrs|
|Amlodipine||0.625 mg/cat q 24 hrs|
|Spironolactone||1-2 mg/kg every 12 hrs|
- Syme, HM et al (2002) Prevalence of systolic hypertension in cats with chronic renal failure at initial evaluation. J Am Vet Med Assoc 220:1799
- Jensen J, Henik RA, Brownfield M, Armstrong J. (1997) Plasma renin. activity and angiotensin I and aldosterone concentrations in cats with hypertension associated with chronic renal disease. Am J Vet Res 58:535–540
- Nelson, RW & Couto, GG. (1998) Small Animal Internal Medicine, 2nd ed. St. Louis: Mosby pp:721–726
- Walker, DJ et al (2009) Urinary cortisol/cortisone ratios in hypertensive and normotensive cats. JFMS 11:442-448