Canine Systemic Hypertension – NAVLE Study Guide

Overview and Clinical Importance

Systemic hypertension refers to sustained elevations in systemic arterial blood pressure. In dogs, systolic blood pressure consistently greater than 140 mmHg or diastolic pressure greater than 90 mmHg is considered elevated. However, the ACVIM Consensus Guidelines recommend that treatment be initiated when systolic pressure persistently exceeds 160 mmHg, as this level is associated with moderate-to-high risk for target organ damage (TOD).

Unlike in cats where hypertension is commonly recognized, canine hypertension has historically been underdiagnosed. However, it is a clinically significant condition that can cause serious complications affecting the eyes, kidneys, heart, and brain. Understanding the diagnosis, underlying causes, and treatment of canine hypertension is essential for NAVLE success.

Blood Pressure Classification

The ACVIM Consensus Guidelines (2018) classify blood pressure based on the risk of developing target organ damage (TOD). Treatment decisions should consider both the blood pressure level and the presence or absence of TOD.

Table 1: ACVIM Blood Pressure Classification Chart or Blood Pressure Measurement on Dog

Etiology of Canine Hypertension

Canine hypertension is classified as either primary (idiopathic/essential) or secondary. Secondary hypertension, which accounts for the vast majority of cases in dogs, occurs due to an identifiable underlying disease.

Common Causes of Secondary Hypertension

Causes of Canine Hypertension:

• C - Chronic Kidney Disease (most common)
• H - Hyperadrenocorticism (Cushing's disease)
• O - Obesity
• P - Pheochromocytoma
• D - Diabetes mellitus
• O - Other endocrine (hypothyroidism - uncommon)
• G - Glomerular disease (protein-losing nephropathy)

Blood Pressure Measurement Technique

You should know how a Doppler Blood Pressure Measurement device looks like…

Accurate blood pressure measurement is critical for diagnosis. The ACVIM recommends following a standardized protocol to minimize situational (white coat) hypertension, which can cause falsely elevated readings due to stress.

Standardized Measurement Protocol

• Allow the patient 5-10 minutes to acclimate to the environment
• Measure BP in a quiet, isolated area away from other animals
• Have the owner present if possible to reduce anxiety
• Position patient in lateral or sternal recumbency
• Place the cuff at heart level (right atrium)
• Select proper cuff size: width = 40% of limb circumference in dogs
• Discard first measurement; obtain 5-7 consecutive readings
• Average the readings for final BP value

Doppler vs. Oscillometric Methods

Target Organ Damage (TOD)

Sustained hypertension can cause damage to organs with rich arteriolar blood supply. The eyes, kidneys, heart, and brain are most commonly affected. Recognizing TOD is critical because its presence indicates immediate treatment is needed, regardless of how many times BP has been measured.

Figure 1: Hypertensive Retinopathy showing Retinal Hemorrhage or Detachment

Ocular (Hypertensive Retinopathy)

Ocular lesions are present in approximately 62% of hypertensive dogs. Visual disturbance or acute blindness is often the presenting complaint.

• Retinal hemorrhages - flame-shaped, punctate, or preretinal
• Retinal detachment - serous, can cause acute blindness
• Hyphema - blood in anterior chamber
• Tortuous retinal vessels - "box-carring" appearance
• Subretinal edema - fluid accumulation
• Papilledema - optic nerve swelling
• Secondary glaucoma

Renal

• Progressive glomerular damage and glomerulosclerosis
• Proteinuria (elevated UPC ratio)
• Progression of chronic kidney disease

Cardiac

• Left ventricular hypertrophy (concentric)
• Diastolic dysfunction
• Systolic murmur may develop

Neurologic (Hypertensive Encephalopathy)

• Acute onset seizures
• Altered mentation, disorientation
• Ataxia, head tilt, vestibular signs
• Cerebrovascular accident (stroke)

Antihypertensive Treatment

Treatment goals include: reducing BP to less than 160 mmHg (ideally less than 140 mmHg), preventing TOD, and treating the underlying cause. In dogs, ACE inhibitors are first-line therapy. Amlodipine is added for refractory cases. This differs from cats, where amlodipine is first-line.

RAAS System Mechanism of ACE Inhibitors

Low Blood Pressure/Volume → Kidneys release Renin.

Renin acts on liver's Angiotensinogen → Angiotensin I (Ang I).

Ang I passes through lungs → ACE converts it to Angiotensin II (Ang II).

Ang II Effects:

Vasoconstriction (narrows vessels).

Stimulates Adrenal Glands to release Aldosterone (kidneys retain Na+/Water, excrete K+).

Stimulates Pituitary to release ADH (kidneys retain Water).

Increases thirst.

Result: Increased blood volume & vasoconstriction → ? Blood Pressure

Figure 2: RAAS mechanism.

Antihypertensive Drug Summary

Treatment Algorithm for Dogs

• First-line: ACE inhibitor (enalapril or benazepril 0.5 mg/kg PO q12-24h)
• If inadequate after 1-2 weeks: Add amlodipine (0.1-0.25 mg/kg PO q24h)
• If still inadequate: Increase amlodipine to 0.5 mg/kg or add telmisartan
• Hypertensive crisis (greater than 200 mmHg with TOD): Consider hydralazine or IV therapy
• Pheochromocytoma: Phenoxybenzamine first, then add beta-blocker if needed (never beta-blocker alone!)

Dogs: ACE inhibitor first-line (enalapril, benazepril) | Cats: AMLodipine first-line

Monitoring and Follow-up

• Recheck BP: 7-10 days after starting/changing therapy
• Stable patients: Every 1-4 months depending on severity
• Monitor renal values: 5-7 days after starting ACEi/ARB (may see mild creatinine increase)
• Target BP: Less than 160 mmHg (ideally less than 140 mmHg)
• Watch for hypotension: Weakness, lethargy if BP drops below 120 mmHg
• Fundic examination: Regular monitoring for ocular TOD resolution