What Is Pulmonary Hypertension in Dogs?
Pulmonary hypertension (PH) is when high blood pressure develops in the dog’s lungs. It occurs more frequently in older, smaller-breed dogs, and can be fatal if not properly treated. Fortunately, this complex syndrome is not very common. While it can be caused by a genetic condition, it is more often a secondary disease that results due to multiple underlying conditions.
The lungs have an intricate network of blood vessels that are like branches in a tree. You start with the big branches, like the pulmonary artery, and where the branches get the thinnest, they turn into twigs—these are the capillaries. The capillaries are where the smallest arteries connect with the smallest veins. The capillaries are where fluids and gasses are exchanged between lung tissue and blood vessels. Unoxygenated blood from the body is oxygenated in these tiny vessels in the lungs. Dogs with pulmonary hypertension have too much pressure in these blood vessels, which leads to an enlargement of the heart, less oxygen in the bloodstream, and potentially heart failure.
What Is the Difference Between Pulmonary Hypertension and Systemic Hypertension?
Pulmonary hypertension is increased blood pressure in the lungs, while systemic hypertension is increased blood pressure in arteries throughout the rest of the body.
Systemic hypertension, also known as high blood pressure, is much more common and affects the entire body. It is readily diagnosed with a blood pressure cuff, whereas pulmonary hypertension only affects the blood pressure in vessels inside the lungs themselves. It requires more advanced imaging to diagnose.
Symptoms of Pulmonary Hypertension in Dogs
Cyanotic (blue-tinted) gums
Causes of Pulmonary Hypertension in Dogs
Pulmonary hypertension is more commonly a secondary condition that arises as a consequence of an untreated underlying disease. For example, underlying diseases like heartworm disease and pulmonary thromboembolic (PTE) disease can lead to pulmonary hypertension by an obstruction. The pulmonary arteries can become blocked by the presence of worms, a clot, or a tumor, leading to increased blood pressure inside the lungs.
There are many other systemic diseases such as Cushing’s disease, immune-mediated hemolytic anemia (IMHA), protein-losing enteropathy (PLE) or nephropathy (PLN), trauma, or sepsis that can also result in dogs being more likely to have blood clots that lead to pulmonary hypertension.
Chronic underlying lung disease like pulmonary fibrosis, bronchitis, pneumonia, or chronic obstructive pulmonary disease (COPD) can also lead to an increase in pressure inside the lungs. This pressure increase is the result of the buildup of scar tissue inside the lungs, which narrows the vessels and capillaries. West Highland White Terriers are more predisposed to developing this form of pulmonary hypertension.
Primary heart diseases that affect the right side of the heart, such as mitral valve disease or dilated cardiomyopathy can lead to poor functionality of the heart and subsequent increased blood pressure inside the lungs.
Finally, pulmonary hypertension can be caused by congenital shunts in the heart that a dog is born with, or from a disease that is idiopathic—not linked to any underlying cause.
How Veterinarians Diagnose Pulmonary Hypertension in Dogs
If pulmonary hypertension is suspected based on a history of exercise intolerance, cough, difficulty breathing, or fainting, your dog’s primary veterinarian will want to start with a thorough physical examination. Sometimes a veterinarian may detect an extra heart sound that is unusual while listening to a dog's heart, called a split S2 sound. Your vet may also detect fluid in the belly (ascites) on palpation, rough lung sounds, or even cyanosis (a blue tint) of the gums.
If your dog’s veterinarian suspects pulmonary hypertension, they will likely want to run lab work to screen for underlying disease and take x-rays of the heart. Bloodwork, a urinalysis, and a heartworm test are all recommended to screen for primary diseases that may have led to pulmonary hypertension.
More advanced testing may also be recommended.
Your regular vet will likely refer your dog to a veterinary cardiologist for a confirmed diagnosis of PH. The easiest and least invasive way to diagnose pulmonary hypertension is through an echocardiogram, an ultrasound of the heart. Occasionally, cardiologists may elect to perform a right heart catheterization where a long wire is inserted into the jugular vein and threaded to the heart and into the pulmonary artery to get a pressure reading. This is a more invasive test and thus less commonly performed.
Stages of Pulmonary Hypertension in Dogs
Patients with pulmonary hypertension are often staged by determining which functional class they belong to. This classification system helps pet parents understand the severity of their dog’s pulmonary hypertension, and helps guide their veterinarians on when to institute treatment and which treatment may be best for management of the disease. The lower the stage number, the less severely the dog is affected.
Functional Class 1: This class includes dogs with pulmonary hypertension that do not have any issues with physical activity and can exercise without any immediate troubles. These dogs can still run, jump, and play without showing any shortness of breath, difficulty breathing, or fainting.
Functional Class 2: This class includes dogs that are normal while at rest but have some clinical signs of pulmonary hypertension when exercising, such as difficulty breathing, fatigue, or fainting.
Functional Class 3: This class includes dogs that cannot exercise or even do mild activity without difficulty breathing, fatigue, chest pain, or even collapse.
Functional Class 4: This class includes dogs that are symptomatic even when at rest.
Treatment of Pulmonary Hypertension in Dogs
Treatment of pulmonary hypertension is geared toward reducing clinical signs, like exercise intolerance, cough, difficulty breathing, and fainting. Several medications are beneficial for pets with PH, including sildenafil and tadalafil (Cialis), which work to dilate the arteries inside the lungs to reduce arterial pressure.
In many pets with pulmonary hypertension, heart disease is also present. Medications will likely be started to slow progression of your dog’s heart disease, like pimobendan (Vetmedin) and/or enalapril. If a dog is diagnosed with PH due to heart failure, they may have to be hospitalized and kept on oxygen until they are stable. If they are in heart failure, they may be put on medications that remove fluid that has backed up on the lungs, to help make your dog more comfortable.
Medications like furosemide (Lasix) or spironolactone may be prescribed. If your dog is started on one of these diuretics, regular blood work is recommended to ensure the kidneys are tolerating the medication. You may notice your dog drinking and urinating more frequently while on these medications.
Dogs with underlying lung disease may be put on theophylline, a bronchodilator, or anti-inflammatory drugs like steroids or non-steroidal agents, to open up the airways and help patients to be more comfortable when breathing.
Other underlying diseases like Cushing’s, immune-mediated hemolytic anemia, and protein-losing nephropathy or enteropathy may require additional medications to get under control. Unfortunately, most of these diseases are not readily cured, and are instead managed with medications and follow-up visits to adjust dosages.
Recovery and Management of Pulmonary Hypertension in Dogs
Pulmonary hypertension is not something that is cured, but rather is a diagnosis that is managed long-term with medications. After your pet is diagnosed and started on treatment, it is important to minimize their stress as much as possible. Your veterinarian may also recommend that you limit their activity to avoid excess work by the heart and lungs. Avoiding conditions that are hard on the lungs, such as high altitudes or excessively hot or cold air, and reducing exposure to cigarette smoke may also be helpful. Your veterinarian may recommend a prescription diet if your dog also has heart disease.
Prevention of pulmonary hypertension is aimed at protecting pets from preventable disease or catching underlying disease early on. For example, regular heartworm prevention can keep your pet safe from heartworms. Bringing your pet in to see their veterinarian every year for regular checkups can also help to quickly identify any genetic or acquired medical conditions like heart disease or Cushing’s, so that prompt diagnosis and management can be instituted prior to developing secondary pulmonary hypertension.
The prognosis for pulmonary hypertension depends on the severity of clinical signs and how well your dog responds to medications. Dogs with severe (Class 4) pulmonary hypertension may live only a few days or weeks. However, some dogs with less severe PH may live months or years with careful monitoring and treatment.
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