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, capillariesand 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.
• Passive pulmonary hypertension: It is caused by difficulty in pulmonary vein outflow, generally as a result of left heart failure.
• Angio-occlusive pulmonary hypertension: It results from increased vascular resistance in the lungs. It is the most common form of severe pulmonary hypertension.

Often, the only clinical signs seen in dogs with mild pulmonary hypertension are those related to the primary cause of hypertension.

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

• Cough.
  
  
• Exercise intolerance.
  
  
• Dyspnea (difficulty breathing): Initially, only dyspnea on exertion may occur, but in severe cases, dyspnea at rest may also occur.
  
  
• Right-sided heart failure may be accompanied by abdominal distention caused by ascites, a jugular pulse, and pleural effusion.
  
  
• 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.

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.
  
  
• 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.
  
  
• Obstructive diseases of the pulmonary circulationb: such as heartworms, angiostrogillosis, neoplasia, septicemia, autoimmune hemolytic anemia, hyperadrenocorticism, nephrotic syndrome, and disseminated intravascular coagulation. They lead to angio-occlusive pulmonary hypertension.
  
  
• 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.

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.
  
  
• 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.
  
  
• 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.
  
  
• Laboratory analysis: especially important in dirofilariosis and angiostrongylosis.
  
  
• 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.
  
  
• 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.

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.

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.
  
  
• 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.

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.
  
  
• Puppies: it is important to perform good cardiopulmonary auscultation early to detect congenital abnormalities that may be the cause of pulmonary 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.

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.