What Is Pulmonary Hypertension in Dogs?
Pulmonary hypertension (PH) refers to the development of high blood pressure within a dog’s lungs. It primarily affects older, smaller-breed dogs and can pose a significant threat if left untreated. Fortunately, this condition is relatively rare and complex. While genetic factors can contribute to its occurrence, it typically arises as a secondary condition due to various underlying health issues.
The lungs of dogs contain a complex network of blood vessels akin to the branches of a tree. Starting with larger branches like the pulmonary artery, these vessels gradually branch out into smaller arteries and eventually into capillaries. The capillaries play a crucial role in the exchange of fluids and gases between lung tissue and blood vessels. They oxygenate unoxygenated blood from the body, facilitating vital oxygenation. In dogs with pulmonary hypertension, these blood vessels experience elevated pressure, resulting in heart enlargement, reduced oxygen levels in the bloodstream, and potential heart failure.
What Is the Difference Between Pulmonary Hypertension and Systemic Hypertension?
Pulmonary hypertension denotes elevated blood pressure specifically within the lungs, whereas systemic hypertension refers to increased blood pressure in arteries throughout the body.
Systemic hypertension, commonly known as high blood pressure, is a prevalent condition affecting the entirety of the body. It can be easily diagnosed using a blood pressure cuff. On the other hand, pulmonary hypertension affects only the blood pressure within the vessels of the lungs. Its diagnosis typically requires more advanced imaging techniques.
Symptoms
- Reduced tolerance to exercise
- Persistent cough
- Episodes of fainting
- Labored breathing
- Rapid breathing patterns
- Swelling in the abdomen
- Cyanosis (bluish tint) of the gums
- Lethargy and lack of energy
- Unexplained weight loss
- Unexpected instances of sudden death
Causes
Pulmonary hypertension primarily arises as a secondary condition due to untreated underlying diseases. For instance, conditions like heartworm disease and pulmonary thromboembolic (PTE) disease can induce pulmonary hypertension through obstructions. This obstruction occurs when pulmonary arteries become blocked by factors such as worms, clots, or tumors, resulting in increased blood pressure within the lungs.
Numerous systemic diseases, including Cushing’s disease, immune-mediated hemolytic anemia (IMHA), protein-losing enteropathy (PLE) or nephropathy (PLN), trauma, or sepsis, can elevate the risk of blood clots formation leading to pulmonary hypertension in dogs.
Chronic underlying lung diseases like pulmonary fibrosis, bronchitis, pneumonia, or chronic obstructive pulmonary disease (COPD) can also elevate pressure within the lungs. This increase in pressure stems from the accumulation of scar tissue within the lungs, which constricts vessels and capillaries. Notably, West Highland White Terriers exhibit a predisposition to developing this form of pulmonary hypertension.
Primary heart diseases affecting the right side of the heart, such as mitral valve disease or dilated cardiomyopathy, can impede heart function and consequently raise blood pressure within the lungs.
Lastly, pulmonary hypertension can stem from congenital heart shunts or idiopathic conditions unrelated to any identifiable underlying cause.
Diagnosis
If there’s suspicion of pulmonary hypertension in dogs, typically arising from symptoms like exercise intolerance, coughing, breathing difficulties, or fainting, the initial step for the primary veterinarian is a comprehensive physical examination. During this examination, the veterinarian might identify unusual heart sounds such as a split S2 sound, detect fluid in the abdomen (ascites), notice rough lung sounds, or observe a bluish tint (cyanosis) in the gums.
Upon suspecting pulmonary hypertension, the primary veterinarian will likely conduct laboratory tests to screen for underlying diseases and perform heart x-rays. Essential screenings include bloodwork, urinalysis, and heartworm testing to identify primary conditions that could lead to pulmonary hypertension.
More advanced diagnostic tests may also be recommended. Typically, the primary veterinarian will refer the dog to a veterinary cardiologist for a confirmed diagnosis of pulmonary hypertension. The most straightforward and least invasive method for diagnosis is through an echocardiogram, which is essentially an ultrasound of the heart.
In some cases, cardiologists may opt for a more invasive procedure known as right heart catheterization. This involves inserting a long wire into the jugular vein, guiding it to the heart and pulmonary artery to obtain pressure readings. However, this test is less commonly performed due to its invasiveness.
Stages of Pulmonary Hypertension in Dogs
Pulmonary hypertension in dogs is often categorized into stages based on their functional class. This staging system aids pet owners in understanding the severity of their dog’s condition and helps veterinarians determine when to initiate treatment and which treatment options may be most suitable for managing the disease. The numerical order of the stage correlates with the severity of the dog’s condition.
Functional Class 1: Dogs in this class exhibit pulmonary hypertension but can engage in physical activities without any evident issues. They can run, jump, and play without experiencing shortness of breath, breathing difficulties, or fainting.
Functional Class 2: Dogs classified in this stage appear normal when at rest but may display signs of pulmonary hypertension during exercise, such as difficulty breathing, fatigue, or fainting.
Functional Class 3: Dogs in this category struggle with breathing difficulties, fatigue, chest pain, or even collapse when attempting mild physical activity or exercise.
Functional Class 4: Dogs in this class experience symptoms of pulmonary hypertension even while at rest.
Treatment
The treatment of pulmonary hypertension in dogs aims at alleviating clinical symptoms such as exercise intolerance, coughing, difficulty breathing, and fainting. Various medications prove beneficial for managing PH in pets, including sildenafil and tadalafil (Cialis), which function by dilating the arteries within the lungs to lower arterial pressure.
Given that many pets with pulmonary hypertension also suffer from heart disease, medications are typically initiated to slow down the progression of the dog’s heart condition, such as pimobendan (Vetmedin) and/or enalapril. Dogs diagnosed with PH resulting from heart failure might require hospitalization and oxygen therapy until they stabilize. Additionally, if heart failure is present, medications to alleviate lung fluid buildup may be administered to enhance the dog’s comfort, such as furosemide (Lasix) or spironolactone. Regular blood work is recommended while on these medications to monitor kidney tolerance, and increased drinking and urination may be observed in dogs undergoing such treatment.
For dogs with underlying lung disease, treatment may involve the use of theophylline, a bronchodilator, or anti-inflammatory drugs like steroids or non-steroidal agents to widen the airways and enhance breathing comfort.
Moreover, additional medications may be necessary to manage underlying conditions like Cushing’s disease, immune-mediated hemolytic anemia, and protein-losing nephropathy or enteropathy. While these diseases are typically not curable, they can be managed with medications and regular follow-up visits to adjust dosages as needed.
Recovery and Management
Pulmonary hypertension in dogs is a condition that requires long-term management with medications rather than being curable. Once your pet receives a diagnosis and begins treatment, it’s crucial to minimize their stress levels as much as possible. Your veterinarian might advise limiting their activity to prevent undue strain on the heart and lungs. It’s also important to avoid environmental conditions that can exacerbate lung issues, such as high altitudes or extreme temperatures, and to reduce exposure to cigarette smoke. Additionally, your veterinarian may suggest a prescription diet if your dog has co-existing heart disease.
Preventing pulmonary hypertension involves safeguarding pets against preventable diseases and detecting underlying conditions early. For instance, regular administration of heartworm prevention can help protect your pet from heartworms. Bringing your pet for annual checkups allows the veterinarian to promptly identify any genetic or acquired medical issues, such as heart disease or Cushing’s syndrome, enabling early diagnosis and management before secondary pulmonary hypertension develops.
The prognosis for pulmonary hypertension varies based on the severity of clinical symptoms and the response to medications. Dogs with severe pulmonary hypertension (Class 4) may have a lifespan of only a few days or weeks. However, with careful monitoring and treatment, some dogs with less severe pulmonary hypertension can live for months or even years.
