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Basics ⬇

Basics

Definition

Peak systolic pulmonary artery (PA) pressure >30 mmHg and/or peak diastolic PA pressure >15 mmHg

Pathophysiology

  • Causes of elevated PA pressure: (1) pulmonary arterial vasoconstriction, (2) pulmonary arterial obstruction, (3) high left atrial pressure with resultant pulmonary venous and arterial hypertension, (4) excessive pulmonary blood flow.
  • As a result of pulmonary hypertension (PHTN) right heart pressures increase to maintain pulmonary blood flow. May result in right ventricular dysfunction and decreased pulmonary blood flow. Decreased pulmonary blood flow interferes with filling of the left heart which can lead to decreased cardiac output. High right heart pressures can cause venous congestion, tricuspid regurgitation, and R-CHF.

Systems Affected

  • Cardiovascular-see Pathophysiology
  • Hepatobiliary-R-CHF may cause hepatic congestion and dysfunction
  • Respiratory-Associated pulmonary disease; R-CHF may cause pleural effusion.

Genetics

  • No specific genetic basis found.
  • Causes of primary disease (congenital heart disease-CHD, left heart disease, pulmonary disease) may have a genetic basis.

Geographic Distribution

Unknown; likely higher prevalence in heartworm-endemic areas and at high altitudes.

Signalment

Species

Dogs and cats

Breed Predilections

  • Possibly based on underlying cause of PHTN
  • Increased incidence in the terrier breeds has been suggested.

Predominant Sex

Increased incidence in female is reported

Signs

General Comments

Signs due to hypoxia and cardiac dysfunction

Historical Findings

  • Exercise intolerance
  • Dyspnea/tachypnea
  • Coughing/hemoptysis
  • Syncope
  • Abdominal distention
  • Weight loss
  • Lethargy
  • Sudden death

Physical Examination Findings

  • Dyspnea/tachypnea
  • Coughing
  • Hemoptysis
  • Loud and/or split-second heart sound
  • Pulmonary crackles and/or harsh bronchovesicular sounds
  • Cyanosis
  • Heart murmur
  • Abdominal distention
  • Jugular distention
  • Subcutaneous edema
  • Weight loss

Causes

Primary/Idiopathic/Familial PHTN

Etiology

  • Primary congenital disorders of the pulmonary vasculature identified in humans.
  • Abnormalities in endothelial derived vasodilatory/vasoconstrictor substances result in vascular obstruction and vasoconstriction.
  • Not reported in companion animals.

Pulmonary Parenchymal Disease

Etiology

  • Vascular obstruction-resulting from pulmonary lesions (e.g. fibrosis, neoplasia), vascular hypertrophy/inflammation
  • Vasoconstriction-reactive vascular constriction secondary to hypoxia and acidemia
  • Causes:
    • Pneumonia (bacterial, viral, fungal, parasitic)
    • Chronic bronchitis
    • Pulmonary fibrosis
    • Eosinophilic bronchitis
    • Pulmonary neoplasia
    • Acute respiratory distress syndrome

Pulmonary Thromboembolism (PTE)

Etiology

  • Vascular obstruction-secondary to thrombus
  • Vasoconstriction-secondary to hypoxia and vasoconstrictive substances released from the thrombus
  • Causes:
    • Hyperadrenocorticism
    • Protein-losing nephropathy/enteropathy
    • Sepsis
    • Immune-mediated hemolytic anemia
    • Neoplasia
    • Pancreatitis
    • Endocarditis
    • Disseminated intravascular coagulation
    • Primary cardiac disease (typically right heart disease)

Heartworm Disease (HWD)

Etiology

  • Vascular obstruction-vascular hypertrophy, inflammation, thromboembolism, and presence of heartworms
  • Vasoconstriction-secondary to hypoxia/thrombi

Congenital Heart Disease (CHD) with Left-to-Right Shunting

Etiology

  • Excessive pulmonary blood flow due to left-to-right shunting results in damage to pulmonary vasculature
  • Vasoconstriction/vascular obstruction-result of vascular damage and vascular hypertrophy
  • Causes:
    • Patent ductus arteriosus
    • Ventricular septal defect
    • Atrial septal defect

Left Heart Disease

Etiology

  • High left atrial pressure – results in pulmonary venous and arterial hypertension
  • Vasoconstriction/vascular obstruction – result of elevated pressure and vascular hypertrophy
  • Causes:
    • Mitral regurgitation
    • Cardio-myopathy (dilated, hypertrophic, restrictive, unclassified)
    • Mitral stenosis ° Congenital pulmonary venous obstruction (e.g., cor triatriatum sinister)
    • Left atrial tumors

Extrapulmonary Causes of Chronic Hypoxia

Etiology

  • Vasoconstriction-some environmental/extrapulmonary factors result in hypoxia and acidemia leading to pulmonary vasoconstriction and secondary vascular hypertrophy
  • Causes:
    • Hypoventilation (Pickwickian syndrome, neuromuscular disorders)
    • High altitude disease

Risk Factors

  • Cardiac and pulmonary disease
  • Heartworm disease
  • Diseases causing hypercoagulability
  • Obesity
  • High altitude

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Left-sided congestive heart failure (L-CHF)*
  • Collapsing trachea
  • R-CHF*
  • Primary pulmonary disease*
  • HWD*
  • Pneumothorax
  • Pleural effusion (pyothorax, chylothorax, hemothorax, hydrothorax)
  • Laryngeal paralysis/disease *without concurrent PHTN

CBC/Biochemistry/Urinalysis

  • Polycythemia can be seen due to hypoxemia
  • Leukocytosis seen with infectious lung disease
  • Possible evidence of hypercoagulability

Other Laboratory Tests

  • Arterial blood gases (hypoxemia)
  • Occult heartworm test
  • Workup for causes of PTE (urine protein:creatinine ratio, antithrombin III level, D-dimer, coagulation profile, urine cortisol:creatinine ratio, ACTH stimulation test, dexamethasone suppression test)
  • Cytology of effusions

Imaging

Radiography

  • Dilated pulmonary artery and/or torturous pulmonary vessels
  • Right ventricle and atrial enlargement
  • Dilated caudal vena cava
  • Pleural effusion
  • Hepatomegaly
  • Ascites
  • Evidence of primary pulmonary disease, PTE, or HWD

Echocardiography

  • RV concentric/eccentric hypertrophy
  • Flattening of the interventricular septum and/or paradoxical septal motion
  • RA dilation
  • PA dilation
  • Pleural/pericardial effusion
  • Evidence of left heart disease, HWD, CHD, or PTE
  • Asymmetric and notched pulmonary outflow envelope/tracing

Echocardiographic Assessment of PHTN Severity

  • Tricuspid valve regurgitation (TR): if present without pulmonic stenosis or pulmonary artery stenosis, the TR gradient estimates systolic PHTN severity.
  • Systolic pressure gradient between the RV and RA: estimated with spectral Doppler using the modified Bernoulli equation: 4 × (peak TR velocity)2.
    • Pressure gradient >35 mmHg (TR velocity 3.0 m/s) suggestive of PHTN.
    • Gradient determines severity: mild: 35–50 mmHg, moderate: 51–80 mmHg, severe >80 mmHg.
  • Pulmonary valve insufficiency (PI): if PI is present without pulmonary artery stenosis the PI gradient estimates diastolic PHTN severity.
  • Diastolic pressure gradient between the pulmonary artery and the RV: estimated with spectral Doppler using the modified Bernoulli equation: 4 × (peak PI velocity)2.
    • Pressure gradient >15 mmHg (PI velocity >2.0 m/s) suggestive of PHTN.

CT Scan/MRI

May be of diagnostic value if pulmonary neoplasia or other infiltrative diseases

Diagnostic Procedures

Transtracheal wash, bronchoscopy/bronchoalveolar lavage, or lung aspirate/biopsy may be of value if evidence of primary pulmonary disease

Electrocardiography

  • Right mean electrical axis deviation
  • Deep S waves leads I, II, III, and aVF
  • Widening of QRS complex
  • P-pulmonale
  • ST segment depression/elevation
  • Hypoxia-induced arrhythmias (VPCs)

Cardiac Catheterization and Pulmonary Angiography

  • The gold standard of diagnosis
  • Uncommonly performed due to risk and usefulness of echocardiography
  • Indicated if necessary to confirm diagnosis or cause

Pathologic Findings

  • Dependent on underlying disease and severity:
    • Primary pulmonary lesions
    • PTE
    • Dilated PA/RV/RA/vena cava
    • Heartworms
    • Pleural/pericardial/abdominal effusions
    • Medial hypertrophy, intimal proliferation, and sclerosis of pulmonary vasculature
    • Necrotizing arteritis

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Hospitalize patients in severe respiratory distress
  • Medical therapy as described below
  • Perform diagnostics based on patient stability

Nursing Care

  • Judicious fluid therapy may be of benefit to improve pulmonary bloodflow
  • Risk of CHF must be considered
  • Maintain low-stress environment

Client Education

  • Prognosis varies with reversibility of the underlying disease, but generally very guarded
  • Avoid environments that may predispose to respiratory distress-heat/humidity extremes, second-hand smoke, high altitudes

Surgical Considerations

Surgical heartworm extraction is a consideration in patients with severe infestation

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Treat the primary underlying disease process whenever possible
  • The ideal therapeutic agent for PHTN causes pulmonary vasodilation without causing significant systemic hypotension

Oxygen

  • Treatment of choice, but long-term administration not feasible
  • Useful in acute setting to correct hypoxia and cause vasodilation

Phosphodiesterase Type V Inhibitor (PDE5 inhibitor)

  • Inhibit the breakdown of cGMP causing increased nitric oxide and pulmonary vasodilation
  • Avoid other drugs with similar effects (nitrates)
  • Sildenafil-drug of choice for most causes of PHTN in dogs
  • Tadalafil-one published study suggests benefit in dogs
  • Vardenafil-not evaluated in companion animals

Other Vasodilators

  • Limited benefit due to concurrent systemic vasodilation and hypotension
  • Important in management of PHTN resulting from left heart disease
  • ACE inhibitors, hydralazine, and calcium channel blockers

Phosphdiesterase Type III Inhibitor (PDE3 inhibitor)

  • Pimobendan
  • Causes pulmonary and systemic vasodilation
  • Indicated if PHTN secondary to left heart disease
  • Unclear if useful with other causes of PHTN

Bronchodilators

  • May benefit patients with pulmonary disease.
  • Sympathomimetics (e.g., terbutaline) and methylxanthines (e.g., theophylline).
  • Methylxanthines may also cause mild pulmonary arterial vasodilation.

Anticoagulant Therapy

  • In humans, common therapy for all causes of PHTN due to primary and/or secondary thromboembolism.
  • Use in companion animals unclear except in patients with PTE.

Thrombolytic Therapy

  • Streptokinase and t-PA indications and effectiveness debated in companion animals.
  • Likely only indicated if acute PTE with significant cardiac compromise.

Anti-inflammatory and Antibiotic Therapy

  • Steroids may be of benefit if cause of the PHTN has an inflammatory component (e.g., heartworm disease, some cases of primary pulmonary disease).
  • Antibiotics indicated if suspect bacterial component.

Contraindications

  • Respiratory depressants
  • Cardiac myocardial depressants (e.g., beta-blockers)
  • Bronchoconstrictors (e.g. nonspecific beta-blockers)
  • Vasoconstrictors

Precautions

  • Vasodilators can cause systemic hypotension.
  • Bronchodilators can cause tachycardia and hyperexcitability.
  • Hypovolemia may result in depressed pulmonary blood flow.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Serial echocardiography to assess improvement/progression
  • Repeat thoracic radiographs, ECG, laboratory work, blood pressure as needed

Possible Complications

  • Right-sided heart failure
  • Syncope
  • Arrhythmias
  • Sudden death

Expected Course and Prognosis

  • Based on ability to reverse underlying disease
  • In general, very guarded prognosis

Miscellaneous ⬆

Miscellaneous

Abbreviations

  • ACE = angiotensin-converting enzyme
  • ACTH = adrenocorticotropic hormone
  • CHD = congenital heart disease
  • CT = computed tomography
  • ECG = electrocardiogram
  • HWD = heartworm disease
  • L-CHF = left-sided congestive heart failure
  • MRI = magnetic resonance imaging
  • PA = pulmonary artery
  • PHTN = pulmonary hypertension
  • PI = pulmonary valve insufficiency
  • PTE = pulmonary thromboembolism
  • RA = right atrium
  • R-CHF = right-sided congestive heart failure
  • RV = right ventricle
  • TR = tricuspid valve regurgitation

Authors Donald P. Schrope and Jennifer M. Mulz

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

Client Education Handout Available Online

Suggested Reading

Henik RA. Pulmonary hypertension. In: Bonagura JD, Twedt DC, eds., Current Veterinary Therapy XV. St. Louis: Saunders Elsevier, 2014, pp. 711–717.

Kellum HB, Stepien RL. Sildenafil citrate therapy in 22 dogs with pulmonary hypertension. J Vet Intern Med 2007, 21:1258–1264.