30 Jan 2023
Gerardo Poli
Job Title
Systemic hypertension (SH) alone is often asymptomatic until it is severe, making early detection difficult. For this reason, it is important to know the diseases, illnesses, and other causes that can contribute to SH and recognise their clinical signs.
From there, through thorough diagnostic investigations, a diagnosis will, hopefully, result then help with the long-term management of the hypertension; as well as underlying diseases, if any.
SH can be classified as physiological, primary or secondary.
Physiological SH tends to be transient and non-sustained, often caused by the activation of the sympathetic flight or fight response from excitement, fear and/or anxiety.
With primary SH – also known as idiopathic SH – the underlying cause is unknown. This is characterised by a persistent increase in blood pressure (BP), but with normal findings on complete blood counts, serum biochemistry, urinalysis, and other diagnostic imaging and hormone tests.
Secondary SH is by far the most common form (80% of cases in dogs and cats). It can be caused by other systemic diseases, as well as certain medications.
Diagnosis of hypertension is relatively straight forward; however, it does rely on the clinician to have a high index of suspicion based on the history, clinical signs and physical examination findings to achieve a diagnosis. In secondary SH, the clinical signs will be associated with the underlying disease.
Three categories of clinical signs are most often observed in the hypertensive patient: ocular, cardiac and neurological.
Diagnosis of SH relies on a combination of BP measurements and various laboratory tests. BP measurements can be achieved via various direct and indirect methods.
Regardless of the method used, the main thing to consider is sympathetic stress response can increase BP by approximately 20mmHg in dogs and cats. Therefore, it is essential to disregard once off, atypically high measurements, and take the average of at least three to seven subsequent measurements to get a more accurate measurement. Sometimes, hospitalisation may be required and the BP monitoring to be done over several days to accurately diagnose a persistently elevated BP.
While serial BP monitoring are being done, it is important to have the baseline laboratory tests done to rule in or out underlying diseases. The minimum tests that should be performed include a complete blood count, serum biochemistry, and urinalysis.
Diagnosis of SH is often difficult due to the absence of clinical signs during the early stages. With diligent history taking and physical examinations, SH can be diagnosed at the milder stages.
Once a diagnosis of SH has been made and all underlying disease managed, it is then vital to determine the risk of target organ damage and formulate an acute and long term management plan for SH.
