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R.V. Barrs1
1Sydney School of Veterinary Science, The University of Sydney, NSW 2006
Pathophysiology and incidence of systemic hypertension
Systemic hypertension (SH) occurs secondary
to a number of diseases, including chronic
kidney disease (CKD), hyperthyroidism, primary hyperaldosteronism, hyperadrenocorticism and phaeochromocytoma. Of these, CKD is the most commonly detected cause of SH, followed by pre- and post-treatment cases of hyperthyroidism. In up to 20% of cats with SH no underlying cause is identifiable and hypertension is classified as idiopathic1. Cats with idiopathic SH are geriatric (> 12 years of age) and subclinical renal disease is suspected to be the cause of hypertension in at least some of these cases.
SH is diagnosed in up to 40% of cats with CKD seen in primary care clinics in up to 65% of CKD cases in the referral practice setting. Most cats with CKD and SH have creatinine concentrations of < 300 μmol/L (3.4 mg/dL) (IRIS stage I-III). In humans with CKD, SH is associated with impaired renal sodium handling, excessive activation of the renin–angiotensin–aldosterone system (RAAS) and sympathetic nervous system, structural changes
to arterioles, endothelial dysfunction, oxidative stress and genetic factors. Investigations into RAAS activation in cats with SH and CKD have yielded heterogeneous results, and the pathogenesis of SH is yet to be fully elucidated 2.
Measuring blood pressure in clinics
The two indirect methods of blood pressure recommended for diagnosis of SH in conscious cats in clinics are Doppler sphygmomanometry and High Definition Oscillometry (HDO). However, only systolic blood pressure (SBP) readings are accurate using either of these methods. Thus, in clinical practice diagnosis of SH in cats is on the basis of elevated SBP.
In the largest single study to measure SBP in 780 apparently healthy cats3 using the Doppler method,
Your Singapore, the Tropical Garden City
the median SBP was 120.6 (110.4–132.4) mmHg. Factors independently associated with a higher SBP were increasing age category, being more nervous during assessment, being male, being neutered, and being a stray.
Minimisation of stress is critical to prevent stress- related “white-coat” hypertension in the clinic environment, which can result in large transient increases in BP. Standardised protocols minimise stress and help ensure accurate and consistent BP measurements are readily available1, and should include time for the cat to acclimatise in a stress free environment, minimal use of restraint and
use of a cuff width 30-40% of the circumference of the limb/tail where it is used. The International Renal Interest Society has standardised definitions of hypertension ( guidelines/staging.html) for cats with CKD that can also be applied to other causes of hypertension
in cats (Table 1). The International Society of Feline Medicine (ISFM) consensus guidelines
on hypertension include recommendations for frequency of BP monitoring in cats (Table 2). It should be noted that
Table 1. International Renal Interest Society (IRIS) Classification of Blood Pressure Sub-stages
Table 2 ISFM Panel Recommendations for monitoring of Systemic Blood Pressure (SBP)1
Treatment protocols
For cats with CKD treatment for hypertension is usually initiated when the SBP is 160-179 mmHg and ocular/cardiac/neurological TOD is detected or, in the absence of TOD if SBP is persistently160-179 mmHg (as measured on > 1 occasion on separate visits ideally measured over one to two months), if SBP is ≥ 180 mmHg and TOD is present or, in the
     Systolic blood pressure (mm Hg)
  Blood Pressure Substage
  Risk of Future Target Organ Damage (TOD)
 < 150
 Borderline hypertensive
   ≥ 180
  Severely hypertensive
  Frequency of SBP monitoring
  Healthy cats 7 – 10 years of age
  At least every 12 months
 Healthy cats ≥ 11 years of age
  At least every 6 – 12 months
  Risk factors present including:
- underlying diseases that cause secondary hypertension, e.g. CKD, hyperthyroidism
- evidence of target organ damage (TOD), e.g. ocular changes, arrhythmia/gallop/heart murmur, CKD, ocular signs, CNS signs
   When risk factor first detected and at least every 3 – 6 months

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