Systemic hypertension (or high blood pressure) is quite common in humans, but it is infrequently diagnosed in veterinary practice. This is likely due to the difficulties associated with measuring blood pressure in pets, rather than an actual low prevalence of systemic high blood pressure in cats and dogs. However, in recent years, the increasing popularity of cats as pets, their longer life span, and the development of reliable blood pressure measurement tools have led to a rise in the detection of hypertension in cats, along with its associated disorders.
Hypertension is defined as a long-standing elevation of systemic arterial pressure beyond normal levels for a given species. In veterinary literature, there is some debate over the normal blood pressure values in cats. These values can vary depending on the measurement method used, any pharmacological containment (sedation) to reduce anxiety, fear, or excitement, and the animal’s behavioral state. As a general guideline, normal blood pressure in cats is considered to be: 118-170 mm/Hg for systolic blood pressure and 83-100 mm/Hg for diastolic blood pressure. A diagnosis of hypertension is made when systolic and/or diastolic pressure exceed the upper limit of the normal range (i.e., systolic pressure greater than 170 mm/Hg and/or diastolic pressure greater than 100 mm/Hg), confirmed through repeated measurements.
Primary vs. Secondary Hypertension in Cats
High blood pressure can be primary (essential hypertension) or secondary to other medical conditions (secondary hypertension). While essential hypertension is more common in humans, secondary hypertension is more often found in animals. In cats, systemic hypertension is usually associated with chronic kidney disease, hyperthyroidism, and sometimes diabetes mellitus.
As a systemic condition (involving the entire body), hypertension can affect various organs and systems, leading to a variety of signs and symptoms. Unfortunately, systemic hypertension is often asymptomatic in its early stages and may go undetected for months or even years until tissue damage manifests as dysfunctions and failures of different organs. The organs most commonly affected include the eyes, heart, kidneys, and central nervous system.
Ocular signs are caused by damage to the inner structures of the eye, particularly the retina and choroid. These can include retinal edema, intraocular hemorrhage, retinal detachment, and even sudden onset blindness. The cardiovascular system responds to high blood pressure with increased wall thickness in the left ventricle of the heart (left ventricular hypertrophy), which results from the increased workload the heart must perform to pump blood against higher arterial pressure. Neurological signs are caused by brain edema and can include seizures, disorientation, muscular incoordination, stupor, and coma. Renal damage usually occurs in the presence of pre-existing kidney disease, creating a vicious cycle where chronic kidney disease leads to hypertension, which further damages kidney function and structure.
Once a diagnosis of systemic hypertension is established, the treatment plan should be based on several factors, including the underlying medical condition, the presence of structural damage, dysfunction or failure of target organs, and the degree of increased blood pressure. In most cases, antihypertensive therapy is lifelong, even after the underlying cause (e.g., renal disease, hyperthyroidism) has been addressed. The goal is to reduce blood pressure and protect organs from further damage.
Although dietary changes are essential in human hypertension management (such as salt and calorie restrictions), they do not appear to be as effective in pets. While discontinuing high-sodium diets is always recommended, dietary restrictions should not be the foundation of antihypertensive therapy for cats. Instead, these changes should be a secondary strategy. Antihypertensive drugs are crucial in the treatment of systemic hypertension in cats, particularly angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers, and, in hypertensive hyperthyroid cats, beta-blockers.
Since pharmacological therapy is often long-term, it is ideal to use a single agent administered once daily by mouth, ensuring better owner compliance with the treatment schedule. If the initial drug’s response is inadequate, a higher dose or a drug from a different class may be added. The most common side effects of antihypertensive drugs include anorexia, vomiting, and diarrhea. Reducing blood pressure too much is unlikely with oral drug regimens. If side effects occur, the initial drug should be replaced with an alternative agent. When owners strictly adhere to the prescribed treatment plan, and the underlying cause of hypertension is adequately managed, antihypertensive therapy is generally effective in controlling the condition. This helps prevent or slow the progression of organ damage caused by prolonged high blood pressure, which, if untreated, can lead to multi-organ failure and life-threatening consequences.
