Pulmonary hypertension in dogs: symptoms and treatment

Overview

The right ventricle pumps blood to the lungs for oxygenation. Pressure and resistance to blood flow are normally low in the pulmonary circulation. Higher pressure makes the right ventricle work harder. Prolonged strain can change its structure.

Pulmonary hypertension is an abnormal circulatory state whose underlying cause must be investigated. Causes in dogs are divided into 6 main groups. Several may affect the same dog. Care monitors both the underlying disease and clinical wellbeing.

Primary pulmonary vascular hypertension is rare in dogs. The left ventricle pumps oxygenated blood from the lungs to the rest of the body.

Causes

Pressure can rise when too much blood flows through the lung vessels. A patent ductus arteriosus or ventricular septal defect can increase blood flow to the lungs, for example. Another mechanism is increased resistance in pulmonary vessels. Vessel constriction, thickened walls or a blood clot can increase resistance.

Raised left atrial pressure can also increase pressure in lung capillaries. Progressive mitral valve degeneration is one possible cause. Dilated cardiomyopathy can cause the same problem. Chronic pressure overload on the left side may later alter pulmonary arterial structure too.

Oxygen deficiency associated with respiratory disease can constrict lung vessels. Underlying diseases include pulmonary fibrosis and tracheal or bronchial collapse. Pulmonary blood clots form a separate cause group. Heartworm and lungworm, Angiostrongylus vasorum, can cause parasitic pulmonary hypertension.

Angiostrongylus vasorum lives in the pulmonary arteries and right ventricle. Prolonged infection may involve raised pulmonary pressure. Occasionally, a tumour or another mass compresses a pulmonary vessel from outside.

Risk factors

Disease associated with a congenital cardiac shunt may appear in puppyhood. Acquired heart and lung diseases usually affect adults. Dogs with mitral valve disease and pulmonary hypertension are often older and small. Time spent in endemic areas is considered when assessing parasite exposure.

In follow-up of 25 dogs with respiratory-associated pulmonary hypertension, median age was 12.4 years. Ages ranged from 3.6–15.7 years. Median weight was 6.5 kg, ranging from 2.2–32 kg.

Cushing's disease, immune-mediated red blood cell destruction and protein-losing kidney disease can predispose to pulmonary clots and therefore pulmonary hypertension.

Typical symptoms

Signs you may notice at home include:

• Tiring more easily on walks and reduced exercise tolerance.

• Fainting, particularly during exercise or excitement.

• Faster breathing than usual, even at rest.

• Unusually slow recovery of breathing after activity.

• Coughing.

• A swollen abdomen from fluid accumulation.

• More prominent neck veins.

• Weight loss.

Coughing may mainly reflect underlying respiratory disease. Of the 25 dogs mentioned, 16, or 64%, presented because of fainting. Fourteen of 25, or 56%, coughed. Eight, or 32%, had difficulty breathing.

Complications and consequences

Ongoing right heart strain can cause heart failure. Failure may cause fluid in the abdomen. Reduced cardiac output can impair circulation throughout the body. Severe disease may also cause sudden death.

Among the 25 dogs with respiratory-associated pulmonary hypertension, 8, or 32%, died or were euthanased within the first month. Median survival for all 25 was 6 months from the start of follow-up. Nevertheless, 4 remained alive 28–60 months after diagnosis. The longest survivor lived more than 5 years.

In a series of 28 dogs with Angiostrongylus-associated pulmonary hypertension, 26, or 92.9%, survived to discharge. At 2 years, 6 of 11 dogs followed, or 54.5%, were still alive. The outlook therefore depends greatly on the underlying disease.

Some heart and lung changes remain permanent, shifting the focus to symptom relief.

Diagnosis at the vet

Heart ultrasound estimates disease likelihood

Investigations combine symptoms, history, clinical examination and cardiac imaging. Doppler echocardiography is the most common way to investigate pulmonary pressure. A blood pressure reading from a limb or tail measures systemic pressure. Direct pulmonary arterial pressure measurement requires right heart catheterisation.

Catheterisation is rarely performed in dogs because it is invasive and carries risks. Ultrasound assesses low, intermediate or high probability of pulmonary hypertension. Doppler measures findings including tricuspid regurgitation velocity, or TRV. Structural changes in the right heart and pulmonary artery contribute to assessment.

Right ventricular enlargement and wall thickening support suspicion. Flattening of the ventricular septum and right atrial enlargement may also be visible. Cooperation and laboured breathing affect measurements. An ultrasound pressure estimate alone does not reliably reflect symptom severity.

Tricuspid regurgitation may produce a right-sided heart murmur. Lung crackles may be associated with fibrosis or pulmonary oedema, for example. In disease associated with chronic left heart disease, the left atrium is usually enlarged.

The underlying disease is investigated separately

Chest X-rays assess changes in the heart, pulmonary arteries and lung tissue. An ECG helps identify arrhythmias that can cause similar symptoms. Blood counts, biochemistry and urine tests may reveal an underlying predisposing disease. Pulse oximetry or blood gas measurements can monitor oxygenation.

Raised blood NT-proBNP is not specific for pulmonary hypertension. Parasite tests depend on infection risk and travel history. Contrast-enhanced chest CT may help find a pulmonary clot.

Further investigation of lung disease may require bronchoscopy and a lavage sample. Disease resembling pulmonary fibrosis may prove to be vascular disease or chronic pulmonary thromboembolic disease. It can be classified as idiopathic, of unknown cause, only after thorough investigation. Angiostrongylus infection can be investigated with faecal larval examination or PCR. Larvae are shed intermittently in faeces.

Treatment

Acutely ill dogs need supportive care

The vet plans treatment according to the cause of pulmonary hypertension. A dog struggling to breathe may need hospital care and oxygen. Strenuous activity is restricted because it increases fainting risk. Fluid in the abdomen or chest may be drained with a needle when needed to ease breathing and discomfort.

An ultrasound finding in a symptom-free dog does not automatically lead to pulmonary pressure-lowering medication.

Medication targets the correct mechanism

Sildenafil is a phosphodiesterase type 5 inhibitor that dilates pulmonary blood vessels. It can reduce fainting. Treatment may also help manage fluid accumulation. It can improve exercise tolerance too. However, the ultrasound pressure estimate may not decrease even when wellbeing improves. Tadalafil is another option in the same class. A comparison found neither improved quality of life more than the other.

When left heart disease causes pulmonary hypertension, treatment primarily addresses that disease and heart failure. A PDE5 inhibitor is not first-line treatment in this group. Vasodilation in the wrong situation may increase pulmonary oedema risk. Nevertheless, selected cardiac patients may benefit from additional medication with close monitoring.

Respiratory-associated disease also requires management of the underlying lung or airway disorder. A stent may be considered for severe tracheal collapse. Airway narrowing in a short-muzzled dog may require corrective surgery. Pulmonary clot-associated disease needs treatment that inhibits clotting.

Parasitic disease requires treatment of the identified heartworm or Angiostrongylus infection. A significant congenital left-to-right shunt may be closed under certain conditions. Closing a right-to-left shunt may cause acute right heart failure.

Successful elimination of adult heartworms may reduce pulmonary arterial pressure. Right heart failure may then resolve too.

Follow-up focuses particularly on wellbeing

A stable patient may be reassessed 2 weeks after medication starts or changes. Reviews may then take place every 3–6 months if wellbeing remains stable. Worsening symptoms require earlier assessment. Monitoring focuses on energy, fainting, breathing effort and signs of heart failure.

In respiratory-associated pulmonary hypertension follow-up, quality-of-life scores improved at one month in the 15 dogs surviving to review. Not every stable patient needs repeated heart ultrasound.

Prevention

Managing progression risk includes preventing respiratory infection and addressing parasite risk. Vaccination also helps prevent infectious respiratory disease. Dogs acquire Angiostrongylus vasorum by eating a slug or snail containing larvae. Preventive parasite medication is planned according to risk in endemic areas.

Pregnancy is discouraged in dogs with diagnosed pulmonary hypertension. Avoiding air travel and high-altitude destinations is recommended. Unnecessary procedures requiring general anaesthesia need particularly careful consideration.

Airway narrowing in short-muzzled dogs is identified and treated early where possible.

Important for dog owners

Record fainting episodes and situations in which breathing or stamina changes. Monitor breathing rate and effort during rest or sleep too. Particularly when starting vasodilator treatment, a resting or sleeping rate persistently above 30–40 breaths per minute needs veterinary assessment to rule out pulmonary oedema.

Keep daily life as calm and low-stress as possible. Avoid tobacco smoke, excessive heat and very cold, dry air. A harness instead of a collar may reduce cough irritation in a dog with airway disease. Weight loss in an overweight dog may ease respiratory symptoms.

Follow the vet's prescribed medication. Diet is chosen according to the underlying disease. Normalisation of every heart ultrasound measurement is not the only measure of response.

Report new weakness or unusual tiredness after medication.

Frequently asked questions

Is pulmonary pressure the same as ordinary blood pressure?

An ordinary limb or tail measurement assesses systemic blood pressure. Pulmonary pressure is usually assessed with Doppler echocardiography. Confirmatory direct pulmonary arterial measurement requires right heart catheterisation. Symptoms and other findings are considered alongside ultrasound.

Can pulmonary hypertension resolve completely?

It may resolve if a treatable underlying cause is controlled. In one dog with eosinophilic lung disease, symptoms and raised pulmonary pressure disappeared with treatment of the underlying condition. Other dogs retain permanent heart and lung changes.

How long can a dog live with pulmonary hypertension?

Survival depends on the underlying disease. In follow-up of 25 dogs with respiratory-associated disease, median survival was 6 months. One lived more than 5 years. In the Angiostrongylus-associated series, 6 of 11 dogs with known follow-up were alive at 2 years.

Does every dog receive the same medicine?

Treatment depends on the cause of raised pulmonary pressure. Left heart disease is treated primarily by addressing the cardiac disease and any heart failure. Pulmonary clots require treatment that inhibits clotting. Identified heartworm or Angiostrongylus infection needs specific veterinary treatment.

How should daily life and exercise change?

Activity is restricted in severe pulmonary hypertension because of fainting risk. A calm daily routine supports care. A harness may reduce collar-related cough irritation in a coughing respiratory patient. Avoiding flight and high-altitude stays is recommended with diagnosed pulmonary hypertension.