Pulmonary Thromboembolism in Dogs

Pulmonary thromboembolism (PTE) occurs when a blood clot lodges in one of the arteries that feed into the lungs. Slow-flowing blood and blood vessel damage, in addition to blood which clots too easily, can predispose a dog to thrombus (blood clot) formation. Most of the time, pulmonary PTE is caused by another underlying disease process.

Pulmonary thromboemboli (blood clots) can originate in the right atrium of the heart, or in many of the major veins throughout the body. As the dog's body makes oxygenated blood to deliver to the heart and lungs, this clump of blood cells is carried through the bloodstream toward the lungs, where it gets caught in a narrow portion of one of the passages of the arterial network that feeds oxygenated blood to the lungs. In this way, the blood flow through that artery is halted, and oxygenated blood is not able to reach the lung. The severity of the condition is, to a degree, dependent on the size of the blood clot.

PTE can affect both dogs and cats. If you would like to learn how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

• Fatigue
• Cough
• Lack of appetite (anorexia)
• Sudden difficulty breathing
• Inability to sleep or get comfortable
• Increased breathing rate
• Spitting up blood
• Exercise intolerance
• Pale or bluish-colored gums

Causes

• Cancer
• Heart disease
• Liver disease
• Heartworm disease
• Cushing's disease
• Inflammation of the pancreas
• Protein-losing kidney disease, or intestinal disease
• Immune-mediated hemolytic anemia (destruction of red blood cells)
• Musculoskeletal trauma
• Recent surgery
• Bacterial infection of the blood
• Disseminated intravascular coagulopathy (DIC) -- extensive thickening and clotting of the blood throughout the blood vessels

Diagnosis

Your veterinarian will perform a thorough physical exam on your dog, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. In most cases, the bloodwork will be necessary for pinpointing an underlying disease.

You will need to give a thorough history of your dog's health, including a background history of symptoms, and possible incidents that might have precipitated this condition. The history you provide may give your veterinarian clues to the clot's origin.

Arterial blood gases will be taken to check for low oxygen in the blood. A coagulation profile will be done to detect a clotting disorder; these tests include the one-stage prothrombin time (OSPT) and activated partial thromboplastin time (APTT). Heartworm serology will also be performed.

X-ray images of the dog's chest will allow your doctor to visually examine your dog for pulmonary artery abnormalities, enlargement of the heart, lung patterns, or fluid in the lungs. Your veterinarian may choose the more sensitive echocardiogram (an ultrasound image of the heart) to see the motion and size of the heart and its surrounding structures more clearly, because since a thrombus in the right chamber of the heart, or in the main pulmonary artery, will sometimes show up on an echocardiogram.

Electrocardiogram (ECG) readings can indicate cor pulmonale, enlargement of the right ventricle of the heart due to increased blood pressure in the lungs. Serious heart rhythm abnormalities (arrhythmias) will be evident on an ECG. 

There is also pulmonary angiography, which uses an injection of a radiocontrasting agent into the dog's lung arteries to improve visibility on the X-ray, and spiral computed tomography (CT), which is three-dimensional X-ray imaging for non-selective angiography.