Hypertension, or persistent elevation in blood pressure, is a relatively common and potentially serious threat to feline health. In cats, secondary hypertension, which is related to an underlying systemic disease process that disrupts the body’s regulatory systems responsible for maintaining normal blood pressure, is the most common form of this hypertension. The most common of these diseases is chronic kidney disease (CKD). At least 60% of cats diagnosed with hypertension also have signs of CKD. About 20% of cats diagnosed with hyperthyroidism, another common disease of older felines, are diagnosed with hypertension as well. Less common diseases such as hyperaldosteronism, hyperadrenocorticism, or pheochromocytomas can also be related to hypertension in cats. In some cases, however, no underlying cause is identified, indicating primary hypertension.
Blood pressure is measured in the veterinary clinic or hospital using either a Doppler ultrasound device or an oscillometric device attached to a cuff placed on a cat’s front leg or tail. For accurate readings, it is important that this measurement be taken several times by an experienced practitioner using the appropriate cuff size, and excessive movement or restraint can lead to inaccurate measurements. Because the stress of veterinary visits can lead to a situational increase in blood pressure, or white coat hypertension, it is recommended that these measurements be taken before other stressful procedures, in a quiet room where the cat has had at least 5-10 minutes to acclimate. Even with these precautions, it is often recommended to repeat the measurement on a separate day before confirming a diagnosis of hypertension, unless the cat has consistent clinical signs or a predisposing condition.
Systolic blood pressure, or the blood pressure in the arteries that is recorded when the heart contracts, is the most important measurement when diagnosing a cat with hypertension. Because most cats are expected to experience some degree of white coat hypertension, it is unlikely to get a truly normal blood pressure reading in the hospital. Veterinarians take this into consideration when making a diagnosis. A consistent measurement of systolic blood pressure below 150mmHg is considered low risk for systemic hypertension, while readings above 180mmHg put a cat in the category of high risk. Readings between 150 and 180mmHg are in the category of mild or moderate hypertension.
As mentioned above, systemic hypertension is very often related to underlying diseases in the cat, so it is recommended that cats diagnosed with other common health conditions - such as chronic kidney disease, hyperthyroidism, or heart disease - have their blood pressure monitored regularly. Conversely, if a cat is diagnosed with systemic hypertension, screening tests for these underlying conditions should be carried out.
Chronically increased pressure within a cat’s blood vessels can cause injury to tissues and organs within the body. This consequence of systemic hypertension is called target organ injury, and the organs most at risk for damage in cats with high blood pressure are the eyes, brain, kidney and heart.
Ocular problems are the most common target organ injury seen in cats with hypertension, ranging from retinal detachment causing blindness to more subtle signs such as bleeding or swelling in the back of the eye that can be observed during a clinical eye exam. In some cases, blindness caused by hypertension can be reversed if treated very quickly, but in the majority of cases, it is unfortunately permanent.
Neurologic changes can be seen in between 15-40% of cats with hypertension. These signs can include disorientation, lack of balance, seizures, altered mentation or behavior, or weakness in the limbs. These signs are most common when the blood pressure rises very quickly, and they often resolve if treatment is initiated in the early stages of the disease.
Hypertension often causes damage to the kidneys in cats, but since many cats with chronic kidney disease also have hypertension, it can be difficult to distinguish kidney damage resulting from CKD from kidney damage resulting from hypertension. Research shows that hypertension increases protein loss through the kidneys (known as proteinuria) in cats with and without CKD. Proteinuria is associated with a shorter survival time in cats with CKD, underscoring the importance of hypertension in cats who have this disease.
With systemic hypertension, the heart has to beat against higher pressure, which can lead to cardiac changes in up to 60% of cats. However, unlike in humans, cardiac disease is rarely the cause of increased blood pressure in cats, but the result of hypertension. These changes involve thickening of the heart walls, and a veterinarian may be able to hear a heart murmur or other abnormal heart sounds on a physical exam. Luckily, though these heart changes are common in cats with hypertension, life-threatening complications such as congestive heart failure are infrequent.
The goal of treatment for hypertension is to reduce the risk of target organ damage. Treatment generally involves medication and monitoring for the remainder of a cat’s life, in conjunction with treatment for any underlying medical conditions such as CKD or hyperthyroidism. The first-line medication for treating feline hypertension is generally a calcium channel blocker called amlodipine, available as a small pill given once daily. If giving pills is not an option for the cat or owner, transdermal preparations which are rubbed on the inside of the ear are available, but not always as reliable. In some cases, particularly in cats that have proteinuria, other medications such as the angiotensin receptor blocker telmisartan or the ACE inhibitor benazepril may be added or used in place of amlodipine. With any treatment, frequent checkups and regular blood pressure monitoring are used to ensure that blood pressure remains below 160mmHg and that there is no evidence of continuing target organ damage.
Feline hypertension is generally a manageable condition with regular medication. Some of the consequences of hypertension, such as blindness, cannot be reversed with treatment, while others, such as neurologic abnormalities, may improve. There are few good studies on the long-term prognosis for cats being treated for hypertension, likely because this can be heavily influenced by the underlying disease process.
Without treatment, feline hypertension can have serious side effects, including blindness, seizures, and cardiac damage. It is important to have cats examined regularly by a veterinarian, as early signs of hypertension, such as changes to the eyes or a heart murmur, may be present on a physical exam. Cats with any underlying condition, especially CKD or hyperthyroidism, should have their blood pressure screened regularly, as prompt treatment of hypertension can help prevent potentially catastrophic target organ damage.
Last updated 2021