Hypertension

From Cat
Exhaustion and torpor in a cat with systolic arterial hypertension (systolic arterial pressure = 290 mmHg).
Sudden blindness in a cat, caused by hypertensive retinopathy.
Example of marked symmetrical concentric hypertrophy of the left ventricle in a cat with renal failure and systemic arterial hypertension
File:Bp1.jpg
Eye showing bleeding into the anterior chamber (in front of the lens) caused by hypertension

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.

Cause

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

Clinical signs

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[2].

In severe cases, hypertensive encephalopathy may occur, resulting in seizures.

Treatment

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[3].

  • 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[4].
  • 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.

Diuretics
Furosemide 1 - 2 mg/kg q 12-24 hrs
ACE inhibitors
Enalapril 0.35 - 0.5 mg/kg q 24-48 hrs
Benazepril 0.25 - 0.5 mg/kg q 24 hrs
Beta-blockers
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


References

  1. 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
  2. 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
  3. Nelson, RW & Couto, GG. (1998) Small Animal Internal Medicine, 2nd ed. St. Louis: Mosby pp:721–726
  4. Walker, DJ et al (2009) Urinary cortisol/cortisone ratios in hypertensive and normotensive cats. JFMS 11:442-448