Hypertension (high blood pressure) is an insidious foe. Like you, your cat can have high blood pressure for a long time without any obvious, overt signs, says Larry Cowgill, DVM, chief of the small animal internal medicine service at the University of California Davis School of Veterinary Medicine. In cats, unlike in humans, hypertension is usually secondary to some underlying condition, most often hyperthyroidism or kidney disease. Less common causes include diabetes mellitus and primary adrenal diseases. Stress is not believed to be a cause of sustained hypertension but can cause transient hypertension.
Often, the first inkling that a cat is hypertensive is a sudden onset of blindness. Increased pressure in the blood vessels of the eye can cause the retina to detach. This is not a life-or-death emergency, says Cowgill, who is board certified by the American College of Veterinary Internal Medicine. But it is an emergency in terms
of whether your cat is going to keep his eyesight or not. The cat needs to be hospitalized, and antihypertensive drugs need to be tried aggressively. If the blood pressure is not brought under control rapidly – within hours – there’s reduced hope of getting the eye to repair.
If treated quickly and aggressively, the retinas of most affected cats will re attach, probably within a few days. The longer the retina remains detached, the less likely the cat will regain vision.
Other indications of hypertension include acute onset of life-threatening neurological disorders. Some animals will have seizures and can develop strokes, just like people do. Sometimes those are reversible, and sometimes they’re not, says Cowgill.
Measuring feline blood pressure
Hypertension can worsen the condition that precipitates it and predispose affected cats to other problems. The major organs affected – the overt targets – are the brain, heart, kidney, and eye, says Cowgill. But subtly, below the surface, just like in humans, there’s a lot of chronic vascular disease and other organ damage going on that’s not as precipitous.
The only way to know whether an animal has hypertension is to measure its blood pressure, emphasizes Cowgill. Routine measuring of feline blood pressure is not yet standard veterinary practice. Because a cat’s arteries are so small, equipment designed for humans can’t be used, but the process is similar. The two measurement techniques commonly used involve a cuff wrapped around the cat’s tail or leg.
The indirect oscillometer measures changes (oscillations) in pulse pressure and yields reliable measurements for all three blood pressures of interest: systolic, diastolic, and mean. The Doppler ultrasonic flowmeter – a less expensive and more commonly used device – detects arterial blood flow and measures only systolic pressure reliably.
Obtaining reliable, consistent measurements is tricky. Like humans, cats are subject to the white coat effect. Until your cat learns that the test is something he need not fear, just taking measurements will raise his blood pressure.
Blood pressure should be measured in a highly consistent, systematic way, in a calm, non-threatening environment. It’s important that the cat become acclimated to tester, device, and technique. At our hospital, we usually test with the cat on the client’s lap, says Cowgill. The tester’s experience and patience is key. It takes experience, rather than any particular skill, to do this well, he notes. Most people who have experience have a sense when the cat just has anxiety or is actually hypertensive.
Focus treatment on underlying cause
A diagnosis of hypertension should not be based on a single reading. Tests should be repeated, ideally over the course of multiple visits. We recommend that the diagnosis of hypertension be made either on sequential, reproducibly high blood pressure measurements taken on several different occasions, or on a high measurement in the presence of other known consequences of hypertension, says Cowgill.
Some cats have mild hypertension, and are not quite as predisposed to some of the clinical consequences. Some veterinarians would not recommend routine treatment at that stage; others would. Typically, though, there’s a growing consensus that once the systolic blood pressure is consistently greater than 175mm Hg, the cat is at risk for hypertensive consequences.
Once a diagnosis is confirmed, treatment focuses on management of the underlying causative condition and generally includes some combination of antihypertensive drugs and restricting dietary salt. Prognosis depends both on the course of the underlying disease and the success of the antihypertensive regimen.