By Lori Locke, DVM, DACVIM 

Dogs diagnosed with pulmonary hypertension are most commonly small breed and middle aged to older.  The most common presenting complaints include exercise intolerance, cough, dyspnea, and syncope. Many of these patients present on emergency for acute respiratory distress.  Physical examination findings may include labored breathing, increased lung sounds, heart murmur, ascites, and cyanosis.

Routine diagnostic hematologic and biochemical diagnostics should be performed. These diagnostic tests should be reviewed with an emphasis on systemic diseases that may predispose dogs to pulmonary thromboembolism such as Cushing’s disease and PLN.  Heartworm antigen test should always be obtained. Thoracic radiography is not specific for pulmonary hypertension, but may demonstrate supportive findings, including cardiomegaly, right-sided heart enlargement, or pulmonary artery dilation. Pulmonary arteries may be tortuous in patients with heartworm disease.  Echocardiogram is the gold standard noninvasive diagnostic tool for pulmonary hypertension. The maximal tricuspid valve regurgitation velocity is the most common echocardiographic method used to diagnose systolic pulmonary hypertension. There are subjective assessments that are also informative including right-sided heart enlargement and septal flattening caused by increased pressure on the right side.Central Texas Veterinary Specialty and Emergency Hospital

Treatment

There are several phosphodiesterase 5 inhibitors, including sildenafil, tadalafil and vardenafil. These drugs promote vasodilation. Sildenafil is a short-acting PDE5 inhibitor. It has been evaluated for treating canine pulmonary hypertension in the clinical setting and has been shown to decrease pulmonary arterial pressure, improve quality of life, and improve survival time. Sildenafil has rare gastrointestinal side effects and, while relatively expensive, may be affordable for many clients. A compounded product may be more cost effective.  It is considered the drug of choice for treating pulmonary hypertension in dogs. The recommended sildenafil dose is 1 to 3 mg/kg by mouth, every eight to 12 hours.Central Texas Veterinary Specialty and Emergency Hospital

Pimobendan (Vetmedin) exerts positive inotropic effects as well as vasodilatory effects. Clinically, pimobendan has been shown to improve pulmonary hypertension secondary to degenerative mitral valve disease. Pimobendan is not considered an effective solo therapy for dogs with pulmonary hypertension but is often used in conjunction with Sildenafil.

Supportive Care and Treatment of Underlying Conditions

Patients with pulmonary hypertension often require supportive therapy and additional therapies based on the underlying cause of the pulmonary hypertension. These therapies may include oxygen supplementation, treatment of primary pulmonary disease with anti-inflammatory or bronchodilating agents, or treatment of congestive heart failure with diuretics. Patients with thromboembolic disease may benefit from anticoagulant medications and corticosteroids, and patients with heartworm disease may require heartworm adulticide therapy.

Outcomes

The prognosis for dogs with pulmonary hypertension varies and often depends on the underlying cause. Negative prognostic factors may include advanced heart disease, high right atrial pressure, or severe right ventricular dysfunction.