By VIN Community Contributors
Robert Prosek DVM, MS, DACVIM-Cardiology, DECVIM-CA
What is Pulmonary Hypertension?
Pulmonary hypertension (PHT) is high blood pressure in the arteries leading in and out of your pet's lungs. If the high blood pressure becomes too severe, it can cause disease and failure of the right side of the heart.
Generally speaking, PHT is a sign resulting from another disease that the pet already has, so it's referred to as a secondary disease rather than primary. Those other diseases can include heartworm disease and pulmonary thromboembolism, both of which block the arteries in the lung; diseases within the lung, such as pulmonary fibrosis or chronic obstructive pulmonary disease; or diseases affecting the left side of the heart, such as degenerative mitral valve disease or dilated cardiomyopathy. However, in some instances, it can be the primary, or only, disease. If a disease has no known cause, it’s called idiopathic, and primary PHT has no known cause.
PHT is seen far more commonly in dogs than in cats.
What Signs are Displayed in Dogs with PHT?
Dogs with PHT tend to appear drowsy, cough, are short of breath, and can faint. They have difficulty exercising, if they can exercise at all. Some will collapse from the effort of trying to walk across a room. Sometimes pets with moderate to severe cases of PHT have enough trouble breathing that their gums become bluish from lack of oxygen. Some have heart murmurs, and some get a swollen stomach. Not all of these signs are from PHT as they can be caused by the primary disease causing the PHT. For example, heart murmurs can be caused by diseased heart valves. Sometimes unusual noises such as crackles, wheezes, and harsh breathing sounds can be heard from the chest; these sounds are from underlying lung disease. If the pet has pulmonary thromboembolism, he can cough up blood. Sudden death is also a sign of severe PHT.
Severe cases are debilitating, and if the pet was a person, he would be considered disabled.
How is PHT Diagnosed?
The diagnostic test of choice is a cardiac ultrasound (also called Doppler echocardiography). It provides a noninvasive and readily available method of diagnosis, but should be given by a person experienced in doing these ultrasounds. It does not require the pet to be anesthetized or sedated.
See a PHT Classification Chart to better understand levels of the disease.
How is PHT Treated?
PHT can be difficult and frustrating to treat. The veterinarian will attempt to identify its cause and treat the underlying disease. Medications can be used with the aim of improving the patient’s quality of life.
When PHT just appears suddenly and seriously (those cases are called acute), treatment focuses on giving oxygen because most patients with PHT improve with oxygen; significant exercise restriction; and alleviating congestive heart failure and any underlying diseases. At-home oxygen cages can be used to help provide relief for dogs with severe PHT. Longer-term management generally relies on the medication sildenafil citrate (Viagra – yes, the Viagra you’ve heard about, but it also works well to relieve signs of PHT as it was originally developed to treat PHT in humans). Additionally, your veterinarian might prescribe pimobendan, a heart medication. Newer human drugs that decrease pulmonary pressure (e.g., iloprost and bosentan) are currently very expensive and cost tens-of-thousands of dollars per year.
Treating whatever disease is causing secondary PHT - heart failure, heartworm disease, pulmonary thromboembolism, acute respiratory distress syndrome - will often help reduce the PHT.
Prognosis for a dog with pulmonary hypertension depends on the underlying disease and how advanced it is. One study shows that in dogs who survive the first week of therapy, the probability of survival at 6 months was 84%, and 73% at 1 year. Pulmonary hypertension is a truly debilitating disease, but on occasion it is cured or at least managed well with drugs: patients’ clinical signs improve when they take Viagra. However, many patients die suddenly as a result of PHT or have a quality of life that the owners consider intolerable.