Feline Hypertension Study Guide

Overview and Clinical Importance

Systemic hypertension is defined as a persistent elevation in systemic arterial blood pressure. In cats, hypertension is predominantly a secondary condition, most commonly associated with chronic kidney disease (CKD) and hyperthyroidism. Often called the "silent killer," feline hypertension frequently remains asymptomatic until severe and often irreversible target organ damage (TOD) occurs. The four primary target organs affected are the eyes, brain, kidneys, and heart.

Understanding feline hypertension is critical for the NAVLE as it represents a common clinical presentation in geriatric feline patients. Questions frequently focus on blood pressure measurement techniques, identification of target organ damage (particularly ocular lesions), recognition of underlying causes, and appropriate pharmacological management with amlodipine as the first-line treatment.

Definition and Classification

Normal systolic blood pressure (SBP) in cats ranges from 120-140 mmHg. Hypertension is diagnosed when SBP is persistently elevated above normal values. The ACVIM and ISFM consensus guidelines classify feline blood pressure based on risk of target organ damage:

Etiology and Pathophysiology

Primary vs Secondary Hypertension

Secondary hypertension accounts for approximately 80-90% of feline hypertension cases. Unlike humans where essential (primary) hypertension predominates, cats almost always have an identifiable underlying cause.

Causes of Feline Hypertension

Pathophysiology of Target Organ Damage

The organs most vulnerable to hypertensive damage have rich arteriolar blood supplies. Sustained elevated blood pressure causes progressive vascular injury through multiple mechanisms:

• Arteriolar hyalinosis: Plasma protein deposition in vessel walls
• Fibrinoid necrosis: Smooth muscle destruction in arteriolar walls
• Hyperplastic arteriolosclerosis: Intimal proliferation with vessel narrowing
• Autoregulatory failure: When BP exceeds autoregulatory capacity, leading to hyperperfusion injury

Clinical Signs and Target Organ Damage

Many hypertensive cats are asymptomatic until severe TOD develops. The four major target organs are the eyes, brain, kidneys, and heart.

Ocular Target Organ Damage (Most Common)

Ocular lesions occur in 80-100% of severely hypertensive cats and are often the presenting complaint. Fundoscopy is essential for diagnosis.

Neurological Target Organ Damage

Hypertensive encephalopathy occurs in 15-40% of hypertensive cats. When blood pressure exceeds the brain's autoregulatory capacity, hyperperfusion leads to vasogenic cerebral edema, predominantly affecting white matter.

Clinical Signs of Hypertensive Encephalopathy:

• Seizures (generalized or focal/partial)
• Ataxia and vestibular dysfunction
• Altered mentation (obtundation, stupor, coma)
• Behavioral changes
• Head tilt, circling, abnormal nystagmus
• Cervical ventroflexion, paresis

Cardiac Target Organ Damage

Approximately 60% of hypertensive cats develop cardiac changes. The heart must pump against increased afterload, leading to concentric left ventricular hypertrophy (LVH). This is termed hypertensive cardiomyopathy.

Clinical and Diagnostic Findings:

• Auscultation: Systolic heart murmur, gallop rhythm (S3 or S4)
• Echocardiography: LV wall thickness greater than or equal to 6 mm (diastole), possible left atrial enlargement
• Important: Distinguish from primary HCM; requires ruling out hypertension and hyperthyroidism

Exam Focus: Hypertensive cardiomyopathy may be indistinguishable from primary HCM on echo alone. ALWAYS measure blood pressure and thyroid levels before diagnosing HCM in cats!

Renal Target Organ Damage

Hypertension causes glomerular hypertension and hyperfiltration, worsening proteinuria and accelerating CKD progression. The relationship between CKD and hypertension is bidirectional - CKD causes hypertension, and hypertension worsens CKD. Proteinuria (urine protein:creatinine ratio greater than 0.4) is an important marker of renal damage and an independent risk factor for mortality in cats with CKD.

Diagnosis

Blood Pressure Measurement Techniques

Accurate blood pressure measurement requires proper technique and patient acclimation. The two primary indirect methods are Doppler sphygmomanometry and oscillometric devices. Doppler is generally preferred for cats as it is more reliable in patients with small limb circumference and low blood pressure.

Measurement Protocol

• Allow 5-10 minutes for cat to acclimate in quiet environment
• Position cat in sternal or lateral recumbency; ensure cuff is at heart level
• Use minimal restraint; avoid scruffing
• Select appropriate cuff size (30-40% limb circumference)
• Take 5-7 readings; discard first reading
• Calculate average of remaining readings

White Coat Hypertension

Situational or "white coat" hypertension refers to elevated BP due to stress in the clinical environment. This is common in cats! If elevated BP is found without evidence of TOD, repeat measurements on another day before initiating treatment. However, if TOD is present, treat immediately regardless of potential white coat effect.

Diagnostic Workup for Hypertensive Cats

• Complete blood count and serum biochemistry: Assess renal function (BUN, creatinine, SDMA)
• Urinalysis with UPC: Evaluate proteinuria
• Total T4: Rule out hyperthyroidism
• Fundoscopic examination: Assess for hypertensive retinopathy/choroidopathy
• Echocardiography: Evaluate for LVH if murmur present
• Abdominal ultrasound: If hyperaldosteronism suspected (hypokalemia)

Treatment

First-Line Therapy: Amlodipine

Amlodipine besylate is the first-line and gold standard treatment for feline hypertension. It is a dihydropyridine calcium channel blocker that acts primarily on vascular smooth muscle, causing arteriolar vasodilation and reducing peripheral vascular resistance.

Adjunctive and Second-Line Therapies

Monitoring and Prognosis

Monitoring Protocol

• Initial recheck: 7-14 days after starting therapy
• Acute TOD present: Recheck within 24-72 hours
• Stable patients: Every 3-4 months
• Each visit: BP measurement, fundoscopic exam, renal parameters
• Dose adjustment: Increase amlodipine if SBP greater than 160 mmHg at recheck

Prognosis

• Cats with controlled hypertension can live normal lifespans
• Prognosis primarily determined by underlying disease (CKD, hyperthyroidism)
• Early detection and treatment prevent irreversible TOD
• Blindness from retinal detachment may be reversible if treated within 24-48 hours
• Cardiac hypertrophy may regress with BP control

Clinical Pearls Summary

Memory Aid - "CATS-BP" for Feline Hypertension: C = CKD is the most common cause (60%+) A = Amlodipine is the treatment of choice T = Target organs: Eyes, Brain, Kidneys, Heart S = SBP greater than or equal to 180 = Severe (high risk) BP = Blood Pressure measurement is essential in seniors

NAVLE Quick Facts: • Sudden bilateral blindness + mydriasis in senior cat = Measure BP immediately • Amlodipine 0.625-1.25 mg/cat PO q24h is first-line treatment • ACE inhibitors alone are NOT effective for hypertension in cats • Cuff size: 30-40% of limb circumference • Always rule out hyperthyroidism and CKD in hypertensive cats • LVH on echo could be hypertensive cardiomyopathy, not primary HCM