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Basics ⬇

Basics

Definition

Sustained elevation in systolic or diastolic (or both) arterial blood pressure. In dogs and cats, systolic BP >160 mmHg or diastolic BP >120 mmHg obtained by any method is considered abnormal. BP elevation may be transient and related to measurement artifact (stress-induced or white-coat effect), or sustained and pathologic. In veterinary patients, HT is usually due to another disease process and is termed secondary hypertension. If an underlying disease is not present or cannot be determined, the terms primary, essential or idiopathic HT are used.

Pathophysiology

  • Arterial BP is the product of cardiac output and systemic vascular resistance; cardiac output is determined by HR and stroke volume.
  • BP regulation depends on integration of complex mechanisms within the central and peripheral nervous systems, renal and cardiac tissues, and humoral factors, which synergistically affect cardiac output and vascular resistance.
  • Baroreceptors in the carotid sinus and aortic arch respond to changes in BP; a fall in BP increases sympathetic discharge, causing vasoconstriction and increased cardiac contractility and HR. Humoral substances that modulate BP include catecholamines, vasopressin, kinins, renin, angiotensin, aldosterone, prostaglandins, and atrial natriuretic peptide.
  • Primary HT is not fully understood in veterinary patients, but some cases have a hereditary component. Secondary HT is most commonly associated with chronic kidney disease and endocrinopathies in dogs and cats.
  • HT may also occur secondary to fluid therapy, vasoconstricting drugs, steroid administration, or erythropoietin therapy.
  • Persistent elevation of BP causes tissue injury and is termed target organ damage (TOD).

Systems Affected

  • Cardiovascular
  • Nervous
  • Ophthalmic
  • Renal/Urologic

Genetics

Colonies of hypertensive dogs have been produced by mating dogs with essential HT; mode of inheritance not known.

Incidence/Prevalence

  • Varies with criteria for HT and method of measurement.
  • Dogs: prevalence of HT in chronic kidney disease (9–93%; most studies support a rate of 25%), hyperadrenocorticism (73–80%), diabetes mellitus (24–46%).
  • Cats: prevalence of HT in chronic kidney disease (19–65%), hyperthyroidism (9–23%).

Signalment

Species

Dog and cat

Breed Predilections

None

Mean Age and Range

  • Usually older dogs and cats.
  • Younger animals may be affected if renal disease due to infection (e.g., leptospirosis) or heritable disease (e.g., polycystic renal disease, dysplasia).

Clinical Signs and Findings

  • Ocular: acute blindness, intraocular hemorrhage, dilated pupils, exudative retinal detachment, retinal vessel tortuosity, retinal perivascular edema, papilledema, retinal degeneration (late).
  • Neurologic: depression, head tilt, seizures, nystagmus, paresis, ataxia, circling, disorientation.
  • Renal: polyuria/polydipsia associated with progression of chronic renal disease, hematuria, proteinuria.
  • Cardiovascular: murmur, gallop rhythm, cardiomegaly, rarely CHF, epistaxis.

Causes

Primary or Essential

Not known; familial in some dogs

Secondary

  • Accounts for most cases in dogs and cats
  • Renal disease-tubulointerstial or glomerular disease, amyloidosis, polycystic kidney disease, dyplasia
  • Hyperadrenocorticism
  • Hyperthyroidism
  • Diabetes mellitus-less common
  • Pheochromocytoma-less common
  • Hyperaldosteronism-less common
  • Central nervous system disease-less common

Risk Factors

Underlying renal disease or endocrinopathy

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Cardiovascular-hypertrophic cardiomyopathy, thyrotoxic heart disease, aortic stenosis, arterial thromboembolic disease.
  • Ophthalmic-ocular trauma, systemic infections (bacterial, fungal, viral), coagulopathies, vasculopathy.
  • Neurologic-primary brain, spinal cord, or peripheral nerve disease.

CBC/Biochemistry/Urinalysis

  • CBC: usually normal; decreased PCV with severe chronic renal disease; increased PCV with hyperadrenocorticism.
  • Biochemistry profile: azotemia, hyperphosphatemia, hypokalemia (renal insufficiency); hyperglycemia (diabetes mellitus); high ALP (hyperadrenocorticism); increased ALT (hyperthyroidism); hypokalemia (hyperaldosteronism).
  • Urinalysis: proteinuria (glomerulonephritis, amyloidosis, hyperadrenocorticism); hematuria; poor urine concentrating ability (renal insufficiency, hyperadrenocorticism); glucosuria (diabetes mellitus).

Other Laboratory Tests

  • Glomerulonephropathy-increased urine protein:urine creatinine ratio (>0.5 in dogs, >0.4 in cats), decreased creatinine clearance.
  • Renal dysfunction-decreased creatinine clearance.
  • Hyperadrenocorticism-exaggerated ACTH response test, failure to suppress with dexamethasone, increased urine cortisol:creatinine ratio.
  • Hyperthyroidism (cats)-increased T4, inadequate suppression with a T3 suppression test.
  • Hypothyroidism (dogs)-decreased T3, T4, free T3, free T4; possibly increased T3 and T4 auto-antibodies, increased endogenous TSH.
  • Pheochromocytoma-increased urinary catecholamine metabolites.
  • Hyperaldosteronism-increased plasma aldosterone.

Imaging

  • Echocardiography to evaluate hypertensive heart disease (findings include left ventricular free wall and/or interventricular septal hypertrophy, diastolic dysfunction, or normal structure and function).
  • Thoracic radiography to evaluate secondary cardiac changes (typically mild cardiomegaly without CHF).
  • Abdominal radiography to evaluate liver, adrenals, and kidneys.
  • Abdominal ultrasonagraphy to evaluate kidneys, liver, adrenal glands, and bladder.
  • CT or MRI scan if brain tumor, hemorrhage, hyperadrenocorticism suspected.
  • CT, MRI, or myelogram to determine cause for paresis.
  • Thyroid scintigraphy to evaluate hyperthyroidism.

Diagnostic Procedures

Definitive diagnosis of HT requires documentation of high arterial BP via direct or indirect methods in the population at risk. There is no evidence that BP should be measured in all animals. Although correlation with direct BP measurements may vary, indirect measurements in the appropriate clinical population are invaluable in the treatment of HT and prevention of TOD.

Direct (Invasive)

Considered the gold standard, but seldom performed on an outpatient basis in awake animals; reserved for intraoperative monitoring or emergency management of severe HT.

Indirect (Non-invasive)

  • Indirect BP measurement is easily performed in a clinical setting, and are most commonly obtained with oscillometric or Doppler techniques, depending on the size of the animal.
  • An inflatable cuff is wrapped around an extremity; the width of the cuff should be approximately 30–40% (cats) or 40% (dogs) of the circumference of the limb or tail at the site of placement. The cuff should be at or near the level of heart when measuring BP.
  • A cuff that is too small will result in a falsely high BP measurement, while too large a cuff will result in a falsely low measurement.
  • An average of 5–7 measurements should be obtained for the BP session; discard the first measurement.
  • A permanent record of the BP measurement session should include: technique used, cuff size, limb used, time of day, time of medication, animal's disposition, and operator name.
  • Consistent techniques yield more reliable results. Interpret results in light of the animal's excitement level during the procedure and repeat if results are questionable.

Oscillometric Technique

  • Oscillometric technique (Cardell, Memoprint, PetMap) detects pulse pressure oscillations beneath the cuff bladder that result from changes in arterial diameter.
  • Place the animal in lateral or sternal recumbency in a calm environment. Place the artery arrow marker on the cuff on the caudomedial aspect of forearm (or proximal to the carpus with arrow pointed medially), over the dorsomedial metatarsal region (or distal to the tarsus) or on the ventral aspect of the tail in a snug position. The machine can inflate the cuff automatically with display of systolic, diastolic, and mean BP and the heart rate.
  • The oscillometric technique is not as reliable as the Doppler method for animals with fast heart rates, very small arteries, or muscle tremors. However, a recent study showed that high definition oscillometry is accurate in cats. In both cats and dogs, the oscillometric devices tend to underestimate BP by increasing amounts as pressure increases.

Doppler Technique

  • Doppler flow meters (Parks, Vet-Dop, Jorgensen) detect blood flow as a change in the frequency of reflected sound (Doppler shift) due to the motion of underlying red blood cells. For measurements taken from the front limb, a pneumatic cuff is wrapped snugly around the forearm above the carpus. An aneroid manometer connects to the occluding cuff. The Doppler transducer is placed over the median artery on the ventral aspect of the forepaw, between the metacarpal and carpal pads (distal to the cuff). The hair between the pads should be moistened to remove air pockets prior to applying the transducer with gel. Shaving the area is not necessary.
  • After inflating the cuff to 30–40 mmHg higher than the expected systolic pressure, the cuff is deflated at approximately 3–4 mmHg/sec. An audible blood flow signal is heard by the operator and denotes systolic BP.
  • The major limitation of the Doppler technique is the imprecise discrimination of the sounds designating the diastolic, and therefore mean, pressures.
  • The Doppler technique is the preferred method of BP measurement in cats.

Pathologic Findings

  • Arteriolar hypertrophy, tunica media vasorum hyperplasia, and destruction of the internal elastic lamina layer; vascular damage in the eye, kidney, cardiovascular and nervous system tissues leads to hemorrhage, thrombosis, edema, and necrosis.
  • Ventricular hypertrophy develops in response to an increased workload.

Treatment ⬆ ⬇

Treatment

Treatment Guidelines for Dogs and Cats

  • In order to reduce the risk of TOD, BP should ideally be reduced to a systolic BP <150 mmHg and a diastolic BP <100 mmHg.
  • The ACVIM Hypertension Consensus Panel and International Renal Interest Society have recommended that treatment for high BP be based on classifications of the patient which depends upon both reliable BP measurements and knowledge of TOD.
  • Antihypertensive treatment is indicated in any dog or cat with a sustained systolic BP >200 mmHg or a diastolic BP >120 mmHg, regardless of other clinical findings.
  • In both species, any animal with clear evidence of ongoing TOD generally should be considered a candidate for antihypertensive therapy.
  • Animals with no clinical signs and mildly elevated BP should not be treated.

Appropriate Health Care

Usually managed on an outpatient basis. Inpatient care may be necessary depending upon the underlying condition (e.g., fluid therapy with renal failure) or serious complications related to HT (e.g., neurologic signs or acute retinal hemorrhage).

Activity

No restrictions unless acute blindness present

Diet

  • Influenced by underlying cause; sodium restriction is controversial since it will activate the renin-angiotensin aldosterone axis. Sodium restriction alone is unlikely to lower BP.
  • Avoid high salt intake.

Client Education

  • Unless underlying cause is curable (e.g., hyperthyroidism) or controllable (e.g., hyperadrenocorticism), the patient is likely to be on antihypertensive medication for life.
  • Alert owners to TOD of uncontrolled HT (e.g., retinal hemorrhage, retinal detachment, progressive renal impairment, cardiac disease, neurologic signs).

Surgical Considerations

May be indicated for hyperthyroidism, pheochromocytoma, hyperaldosteronism, and some forms of hyperadrenocorticism.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Treat underlying cause if possible, although HT may persist even if underlying disease is well controlled.
  • Cats-amlodipine is first-line oral drug, with an ACE inhibitor added if proteinuria (UPC >0.4) is present.
  • Dogs-ACE inhibitor (e.g., enalapril, benazepril) is first-line drug due to frequency of underlying proteinuria (UPC >0.5), with amlodipine added as second drug if necessary.
  • Spironolactone and hydralazine may be added to the antihypertensive regime if ACE inhibitors and amlodipine are ineffective in lowering BP to <150 mmHg.
  • In a hypertensive emergency, parenteral hydralazine, sodium nitroprusside, or labetolol can be used. Continuous direct BP monitoring is necessary.

Dihydropyridine Calcium Channel Blockers

  • Lower peripheral vascular resistance by vasodilation.
  • T1/2 of amlodipine is 30 hours in dogs, so this is a drug for chronic, not acute, management of HT.
  • Amlodipine-dogs, 0.1–0.5 mg/kg PO q24h; cats, 0.625–1.25 mg/cat PO q24h.

ACE Inhibitors

  • Lower peripheral vascular resistance and stroke volume by blocking the conversion of angiotensin I to angiotensin II; renoprotection; decrease vascular remodeling.
  • Enalapril-dogs, 0.5 mg/kg PO q12h; cats, 0.25–0.5 mg/kg PO q12h.
  • Benazepril-dogs and cats, 0.5 mg/kg PO q12h.

Angiotensin Receptor Blockers (ARBs)

  • Blocks the activation of angiotensin II AT1 receptors and directly causes vasodilation, reduces secretion of vasopressin, and reduces production and secretion of aldosterone.
  • Telmisartan-dogs, 1.0 mg/kg PO q24h.

Direct-Acting Vasodilators

  • Lower peripheral vascular resistance.
  • Hydralazine-dogs, 0.5 mg/kg PO q12h, with a stepwise increase to 3 mg/kg PO q12h if needed. Caution if high-dose amlodipine also used.

Alpha-Receptor Antagonists

  • Most commonly used with beta-receptor antagonists in cases of pheochromocytoma.
  • Phenoxybenzamine-dogs, 0.25 mg/kg PO q12h; cats, 2.5 mg/cat PO q12h.

Diuretics

  • Spironolactone-dogs and cats, 1–2 mg/kg PO q12h; primarily used for antialdosterone effects to limit fibrosis; weak diuretic.
  • Furosemide-dogs, 2–4 mg/kg PO q12h; cats, 1–2 mg/kg PO q12h; not routinely used in antihypertensive therapy.

Beta-Receptor Antagonists

  • Lower HR and cardiac output and suppress renin secretion.
  • Blocks the effects of excess thyroid hormone, although additional drugs are needed to control BP.
  • Rarely used in dogs unless pheochromocytoma present.
  • Propranolol-dogs, 0.2–1 mg/kg PO q8h; cats, 2.5–5 mg/cat PO q8–12h.
  • Atenolol-dogs, 0.25–1 mg/kg PO q12h; cats, 6.25–12.5 mg/cat PO q12h.

Contraindications

Taper or discontinue steroids, vasoconstricting drugs (e.g., phenylpropanolamine).

Precautions

  • Arterial vasodilators can cause reflex tachycardia; rapidly acting drugs and multiple vasodilators used together increase the risk of hypotension and acute renal failure.
  • Beta blockers may worsen bronchiolar disease, CHF, conduction disturbances (e.g., second- and third-degree AV block).
  • High volume IV fluid therapy increases BP.

Possible Interactions

  • Combinations of drugs increase risk of hypotension.
  • Hyperkalemia may result from ACE inhibitors and spironolactone, especially with underlying renal disease.

Alternative Drug(s)

In a hypertensive emergency, hydralazine (0.2 mg/kg SC or IM), sodium nitroprusside (1–5 µg/kg/min up to 10 µg/kg/min CRI), or labetolol (0.25 µg/kg q10min; 20–30 µg/kg/min CRI) can be used. Continuous direct BP monitoring is necessary.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • BP measurements of <150/100 are the treatment goal, although systolic BP <160 mmHg is reasonable and will minimize risk of TOD.
  • BP and hypertensive complications (especially retinopathy) should be checked weekly until BP is controlled.
  • Laboratory tests to measure side effects of medications and clinical disease response (e.g., proteinuria, hematuria, anemia, thrombocytopenia, potassium balance, sodium balance, azotemia, albumin).

Possible Complications

  • CHF (rare).
  • Glomerulonephropathy (proteinuria, hematuria).
  • Renal failure.
  • Retinopathy (hemorrhage, detached retina).
  • Cerebral vascular accident (various central nervous system signs).
  • Gingival hyperplasia may develop with amlodipine treatment in dogs.

Expected Course and Prognosis

  • Dictated by underlying cause of HT.
  • BP can be controlled with appropriate/combined therapy in most patients, but antihypertensive therapy does not necessarily improve survival time.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

Chronic renal disease, endocrinopathies

Zoonotic Potential

None, unless Leptosirosis determined to cause renal disease and HT

Pregnancy/Fertility/Breeding

Pregnancy is a high volume state, and would be expected to make HT more severe.

Age-Related Factors

Chronic renal disease, hyperthyroidism, and hyperadrenocorticism-more common in older animals.

Synonyms

  • High blood pressure
  • Systemic arterial hypertension

Abbreviations

  • ACE = angiotensin converting enzyme
  • ACTH = adrenocorticotropic hormone
  • ALP = alkaline phosphatase
  • ALT = alanine aminotransferase
  • ARBs = angiotensin receptor blockers
  • AV = atrioventricular
  • BP = blood pressure
  • CBC = complete blood count
  • CHF = congestive heart failure
  • CT = computed tomography
  • HR = heart rate
  • HT = systemic hypertension
  • MRI = magnetic resonance imaging
  • PCV = packed cell volume
  • T3 = triiodothyronine
  • T4 = thyroxine
  • TOD = target organ damage
  • TSH = thyroid stimulating hormone

Author Rosie A. Henik

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Client Education Handout Available Online

Suggested Reading

Brown S, Atkins C, Bagley R, Carr A, et al. ACVIM consensus statement: Guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. J Vet Intern Med 2007, 21:542–558.

Brown S, Elliot J, Francey T, Polzin D, Vaden S. ACVIM consensus statement: Consensus recommendations for standard therapy of glomerular disease in dogs. J Vet Intern Med 2013, 27:S27–S43.

Brown SA, Henik RA. Systemic hypertension. In: Tilley LP, Smith FWK, Oyama MA, Sleeper MM, eds., Manual of Canine and Feline Cardiology, 5th ed. St. Louis, MO: Saunders Elsevier, (in press).

Jepson R. Feline systemic hypertension: Classification and pathogenesis. J Fel Med Surg 2011, 13:25–34.