by Rebecca Quinn, DVM, DACVIM (Internal Medicine and Cardiology)
Systemic hypertension (HT) is a well-recognized condition in geriatric feline medicine. Systemic hypertension can be defined as either primary or secondary. Primary HT is diagnosed when an underlying cause cannot be identified; primary HT is the most common cause of HT in the human population. Secondary HT is defined as HT due to an underlying disease process. Almost all HT in cats is secondary; the most common causes of feline HT are hyperthyroidism and chronic kidney disease. Other more unusual causes of secondary HT in cats can include pheochromocytoma, Cushing’s disease, hyperaldosteronism, and multiple myeloma. In theory, other conditions such as acromegaly may cause or contribute to HT. If left untreated, HT can lead to severe end organ damage. Affected organs can include the eyes (vision loss, optic nerve damage), brain (hemorrhage, edema), kidneys (proteinuria, ischemia, fibrosis), and the heart.
Cardiovascular Symptoms and Exam Findings
Cats with HT may develop clinical symptoms at home indicating cardiovascular damage. These can include exercise intolerance, breathing difficulties, epistaxis, or collapse. Physical exam findings suggestive of cardiovascular damage or stress include a gallop rhythm (the presence of an S4 heart sound), a soft systolic heart murmur, or an arrhythmia. Some patients may have abnormal lung sounds or abnormal mentation.
Cardiovascular Consequences of Uncontrolled Systemic Hypertension
In human medicine, HT is often associated with stroke and myocardial infarction. This occurs as a result of microscopic artery wall tears and associated build-up of cholesterol and platelets. Arteries may become narrow enough to result in complete loss of arterial blood flow, or plaques may become dislodged and travel to vital organs. People may also experience hemorrhagic strokes, in which high arterial pressure leads to rupture and bleeding of a vital artery. Unlike people, cats rarely have high cholesterol or primary vascular disease, factors which contribute greatly to stroke and myocardial infarction. Therefore, while these events may occur in feline HT, they are considered very rare.
Left ventricular hypertrophy is likely the most common cardiovascular consequence of prolonged HT in cats. Systemic hypertension is associated with narrowing of the arteries, which in turn increases the workload of the heart. In order for the heart to adapt, the heart walls must become thicker. If left uncontrolled, ventricular hypertrophy results in relaxation abnormalities, poor coronary blood flow, and left atrial enlargement. Cats with these changes may be more likely to experience congestive heart failure. Additionally, the thickened ventricular muscle is more sensitive to sympathetic stimulation, and these cats may also be more likely to develop cardiac arrhythmias.
More unusual cardiovascular complications of HT in cats have been reported. Aortic dissection occurs when HT causes the layers of the aorta to separate and tear. The tear can extend along the length of the ascending aorta, and allow blood to flow within the wall of the aorta itself. Aortic dissections can lead to aortic rupture, and are considered potentially life threatening.
Diagnosis & Treatment
Blood pressure measurements in cats are most commonly obtained non-invasively using either the oscillometric technique (an automated system) or Doppler sphygmomanometry. Diagnosis of HT should be made when patient blood pressures are obtained in a calm and quiet setting, and after repeat readings indicate persistently elevated blood pressure. While the “white coat effect” must be taken into account, systolic blood pressure readings of greater than 180 mmHg support the diagnosis of HT. Because feline HT is so commonly associated with other illnesses, it is very important that these patients undergo full medical evaluations. This typically includes labwork (complete blood count, chemistry panel, T4 +/- free T4, urinalysis +/- urine protein:creatinine, and endocrine testing as needed). Abdominal ultrasound or additional imaging may be required in some cats. If an underlying disease process can be identified, treatment of that condition should be initiated and the blood pressure rechecked within the appropriate time frame.
It is very important to recognize that some cats with appropriately treated underlying diseases still require anti-hypertensive therapies. Depending on the underlying cause, treatment options may include an angiotensin converting enzyme inhibitor (enalapril, benazepril), calcium channel blockers (amlodipine), or selective β blockers such as atenolol. Some patients may require more than one medication in order to appropriately control HT.
Long-term adequate control of the underlying disease process and HT may lead to improvement, or even reversal, of cardiovascular changes. Patient symptoms and physical exam findings such as gallop sounds may resolve; control of HT is associated with improved left ventricular wall structure. Perhaps most importantly, control of HT has been linked to improved quality of life and decreased morbidity in our feline patients.
For more information, please contact Dr. Rebecca Quinn at firstname.lastname@example.org, send a message to the general Cardiology inbox at email@example.com, or call the Cardiology Service at 617-541-5038.
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