Systemic hypertension

Most animals are presented for target organ damage or for their underlying disease rather than for high blood pressure itself. Eye lesions are the most common: exudative retinal detachment causing blindness, with retinal, vitreous or anterior-chamber haemorrhage and tortuous retinal vessels; they are reported in about half (ISFM) to as many as all (ACVIM) hypertensive cats. Neurological signs include lethargy, disorientation, altered behaviour, seizures, head tilt, nystagmus and focal deficits from stroke. Cardiac signs include a gallop rhythm from left ventricular hypertrophy and, rarely, heart failure or aortic dissection. Kidney involvement shows as proteinuria and progressive kidney disease.

Systemic hypertension is a sustained rise in arterial blood pressure. It is classed as situational (a stress response to the clinic that needs no treatment), secondary (the large majority of feline cases, driven by another disease) or idiopathic (no cause found, 13-20% of feline cases). Chronically raised pressure injures tissues that depend on tight blood-flow control. The kidney normally autoregulates across a systolic range of about 80-160 mmHg; above that, glomerular capillaries are exposed directly, leading to glomerulosclerosis, arteriosclerosis and proteinuria. In the eye it causes exudative retinal detachment and haemorrhage. In the brain, pressure produces hypertensive encephalopathy with cerebral oedema, and in the heart concentric left ventricular hypertrophy. In cats with kidney disease, systemic renin-angiotensin activation appears limited, and sympathetic activation seems to play a larger part than in people.

Hypertension is common in older cats and is underdiagnosed. It accompanies chronic kidney disease in 19-65% of affected cats and 10-23% of newly diagnosed hyperthyroid cats, with further cats becoming hypertensive after hyperthyroidism is treated. In dogs, reported prevalence varies widely: 9-93% of dogs with chronic kidney disease, 20-80% with hyperadrenocorticism and 24-67% with diabetes mellitus. Other causes include pheochromocytoma and primary hyperaldosteronism. The white-coat effect can raise systolic pressure by up to 80 mmHg in a healthy cat during a simulated clinic visit, so screening is aimed at older animals and those with risk diseases rather than healthy young animals.

The key distinction is between true hypertension and situational hypertension caused by stress during measurement: readings should be taken after acclimatisation, repeated over several sessions, and interpreted with caution because no indirect device is fully validated in conscious animals. The guidelines differ on the normal cut-off: ACVIM treats systolic pressure under 140 mmHg as normal, while the ISFM guidelines follow the IRIS staging, which sets the boundary at 150 mmHg. Once confirmed, secondary causes must be sought and separated from idiopathic hypertension: chronic kidney disease, hyperthyroidism in cats, hyperadrenocorticism and diabetes in dogs, pheochromocytoma and primary hyperaldosteronism. Retinal detachment or encephalopathy in an older animal should prompt pressure measurement.

Cardiovascular system, arteries and arterioles, eyes (retina, choroid, vitreous), brain, heart (left ventricle), kidneys (glomeruli)

No primary prevention described; screening finds it before organ damage. ACVIM: yearly from 9 years. ISFM (cats): at least yearly from 7 years, every 6-12 months from 11 years, every 3-6 months with kidney or thyroid disease.

Treatment lowers proteinuria and can reattach retinas, but vision returns in a minority; complete detachment with blindness is usually permanent. Pressure control has not been shown to prolong survival in cats; proteinuria predicts shorter survival.