Pulmonary Hypertension in Dogs - Symptoms, Causes and Treatment

Before defining what pulmonary hypertension is, we must explain in broad terms how the cardiovascular system works. The circulatory system is composed of arteries, veins, capillaries, and the heart. The cardiovascular system is composed of two circuits: the general circuit and the pulmonary circuit.

The general circuit is responsible for transporting oxygenated blood to the tissues, while the pulmonary circuit transports deoxygenated blood to the lungs so that it can be re-oxygenated. The two circuits converge in the heart, which consists of two left chambers (left atrium and left ventricle) and two right chambers (right atrium and right ventricle).

The left atrium receives oxygenated blood from the pulmonary circuit, which flows to the left ventricle where it is distributed to all tissues through the general circuit. The right atrium receives deoxygenated blood from the general circuit, which is passed to the right ventricle, where it is oxygenated and then distributed to the lungs. Blood deoxygenated from the general circuit enters the right atrium, where it is distributed to the right ventricle via the pulmonary circuit so that it can be re-oxygenated.

Having established the two different types of circuits, we can now define pulmonary hypertension, which is an increase in blood pressure in the pulmonary circuit.

There are two types of pulmonary hypertension:

• Primary pulmonary hypertension: when the cause is unknown.
  
  
• Secondary pulmonary hypertension: when it occurs as a result of another disease. It is the most common form.

Secondary pulmonary hypertension can be divided into three groups based on its etiology:

• Hyperkinetic pulmonary hypertension: it is caused by increased blood flow to the lungs, usually due to vascular malformations that allow blood to flow from the left to the right side of the heart. These malformations can exacerbate the condition if not treated promptly.
• Passive pulmonary hypertension: It is caused by difficulty in pulmonary vein outflow, generally as a result of left heart failure. This type can be particularly challenging to manage and often requires comprehensive treatment plans.
• Angio-occlusive pulmonary hypertension: It results from increased vascular resistance in the lungs. It is the most common form of severe pulmonary hypertension. This condition demands immediate attention due to its potential to rapidly progress.

Often, the only clinical signs seen in dogs with mild pulmonary hypertension are those related to the primary cause of hypertension. Recognizing these signs early can lead to a more favorable prognosis.

Clinical manifestations of pulmonary hypertension may be observed in moderate or severe patients as follows:

• Cough.
  
  
• Exercise intolerance, which can significantly affect a dog's quality of life.
  
  
• Dyspnea (difficulty breathing): Initially, only dyspnea on exertion may occur, but in severe cases, dyspnea at rest may also occur, indicating a worsening condition.
  
  
• Right-sided heart failure may be accompanied by abdominal distention caused by ascites, a jugular pulse, and pleural effusion, all of which require prompt veterinary attention.
  
  
• Syncope: a sudden loss of consciousness followed by complete recovery. Usually triggered by situations of excitement or high physical activity; however, in severe cases, a simple walk or climbing some stairs may be enough to trigger it, highlighting the importance of managing exertion levels.

There are some symptoms that are similar to asthma in dogs, to learn more about the differences between the two conditions, read this article on asthma in dogs.

The specific causes of hypertension in dogs can be divided into the following:

• Diseases that cause increased left atrial pressure: in cases of left heart failure due to degenerative mitral valve disease or cardiomyopathy. They lead to passive pulmonary hypertension and represent a significant portion of clinical cases.
  
  
• Diseases leading to volume overload at the level of the pulmonary circulation: due to vascular malformations such as atrial septal defect (persistent foramen botale), interventricular septal defect, and patent ductus arteriosus. They lead to hyperkinetic pulmonary hypertension, which can severely impact cardiac function if not addressed.
  
  
• Obstructive diseases of the pulmonary circulation: such as heartworms, angiostrongylosis, neoplasia, septicemia, autoimmune hemolytic anemia, hyperadrenocorticism, nephrotic syndrome, and disseminated intravascular coagulation. They lead to angio-occlusive pulmonary hypertension and often require complex therapeutic strategies.
  
  
• Chronic lung disease: such as interstitial lung disease or chronic obstructive disease. These situations lead to a drop in arterial oxygen pressure causing vasoconstriction of pulmonary arterioles and Angio-occlusive hypertension, emphasizing the importance of regular monitoring for early detection.

If you are interested in learning more about common respiratory diseases in dogs, do not miss our article on what is pulmonary fibrosis in dogs?

The tentative diagnosis of pulmonary hypertension may be made by:

• Clinical history and anamnesis: affected individuals usually show a clinical picture characterized by exercise intolerance, dyspnea, cough, syncope, etc. A thorough history can provide invaluable insights into the progression of the disease.
  
  
• Physical examination: signs such as abdominal distention due to ascites or dyspnea at rest may be noted on general examination. They may be detected on cardiopulmonary auscultation. Physical exams can reveal subtle signs that contribute to early detection.
  
  
• Chest radiography: dilatation of the right ventricles, pulmonary truncus, and pulmonary arteries, and pulmonary infiltrates may be noted. In addition, manifestations of the primary pathology causing hypertension may be observed, aiding in a comprehensive assessment.
  
  
• Laboratory analysis: especially important in dirofilariosis and angiostrongylosis, offering critical data for a differential diagnosis.
  
  
• Electrocardiogram: In most dogs with pulmonary hypertension, the electrocardiogram is normal, although in severe cases high, peaked P waves, deep S waves, and deviation from the right axis may be observed, which can provide essential diagnostic clues.
  
  
• Two-dimensional echocardiography and M-mode: In dogs with moderate to severe hypertension, hypertrophy and dilatation of the right ventricle and dilatation of the pulmonary artery may be observed. However, there are dogs with pulmonary hypertension who do not have echocardiographic abnormalities, so a negative result on this test should not rule out pulmonary hypertension, underscoring the need for a multifaceted diagnostic approach.

Although all of these steps contribute to the diagnosis, an increase in pulmonary circulation pressure is required to make a definitive diagnosis of pulmonary hypertension in dogs. Invasive techniques are not useful because the pulmonary arterial system is directly accessible only by cardiac catheterization. Therefore, noninvasive techniques must be used, such as Doppler echocardiography, which determines the pressure in the pulmonary artery.

Doppler echocardiography can be used especially to diagnose pulmonary hypertension when the velocity of blood in the tricuspid valve or pulmonary valve is high. Pulmonary hypertension is present when the velocity of tricuspid regurgitation exceeds 2.4 m/s and the velocity of pulmonary regurgitation exceeds 2 m/s. This method provides a reliable means of assessing pulmonary pressures.

To approach the treatment of pulmonary hypertension in dogs, the following points must be considered:

• Supportive treatment: Its goal is to control the primary pathology and its complications. Addressing underlying causes can significantly improve outcomes.
  
  
• Treatment with pulmonary arterial vasodilators: If supportive treatment succeeds in controlling the primary pathology but pulmonary hypertension and associated symptoms persist, pulmonary arterial vasodilators, such as Sildenafil, should be administered. These medications can help alleviate symptoms and improve quality of life.

In addition to these treatments, lifestyle modifications, such as weight management and controlled exercise, can play a vital role in managing the condition. Regular follow-up with a veterinarian is crucial to monitor the progression of the disease and adjust treatments as needed.

As we have explained in this article, pulmonary hypertension can be triggered by various causes. Some animals, because of their breed or age, have a strong predisposition to diseases caused by pulmonary hypertension, so preventing its occurrence is difficult or, in some cases, impossible.

Since it is difficult to prevent the occurrence of pulmonary hypertension, early diagnosis of the diseases that can cause hypertension is particularly important in order to initiate appropriate treatment as soon as possible and avoid complications. In this sense:

• Small breed dogs and older dogs: these dogs have a particular predisposition to degenerative disease of the mitral valve, regular examinations should be performed to detect the disease as early as possible and prevent the occurrence of pulmonary hypertension. Proactive care can greatly enhance longevity and quality of life.
  
  
• Puppies: it is important to perform good cardiopulmonary auscultation early to detect congenital abnormalities that may be the cause of pulmonary hypertension. Early detection and intervention can prevent progression to severe hypertension.
  
  
• Dogs living in areas that are at high altitudes above sea level: should be monitored regularly to prevent the effects of low arterial oxygen pressure. Regular veterinary check-ups can help identify potential issues before they become significant problems.

In conclusion, while prevention can be challenging, regular veterinary care and monitoring can help manage risks and improve outcomes for dogs predisposed to pulmonary hypertension.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Pulmonary Hypertension in Dogs - Symptoms, Causes and Treatment, we recommend you visit our Cardiovascular diseases category.