Severe Pulmonary Hypertension (PAH) in an 11-Year-Old MN Yorkshire Terrier: Our Case Of the Month September 2019
Labored breathing is a common presenting complaint in small animals. Small breed dogs with a murmur pose a particular challenge, as these breeds are predisposed to both cardiac and respiratory pathology. Congestive heart failure is the most common reason for dyspnea, however pulmonary hypertension and concurrent respiratory disease must also be considered. Treatment for CHF can actually worsen clinical status in these cases, and differentiating the cause of dyspnea is crucial to selecting successful therapy. Pulmonary hypertension is a challenging diagnosis that is often overlooked or not apparent on thoracic radiographs, and echocardiography is the ideal tool to document this type of pathology.
We present a case of severe pulmonary hypertension in a Yorkshire Terrier that was initially treated for CHF.
History: Presented to the ER for difficulty breathing. History of a collapsing trachea and chronic cough. Radiographs showed cardiomegaly with questionable pulmonary changes. Placed in oxygen and treated for CHF (lasix, pimobendan, hydrcodone) but did not do well.
Diffuse thickening of mitral valve leaflets with no obvious prolapse into the left atrial lumen. Trace mitral regurgitation with normal left atrial dimension. Small LV diameter with adequate myocardial function and evidence of pseudohypertrophy. The tricuspid valve appears thickened and prolapsing, and there is severe tricuspid regurgitation. Severe right atrial enlargement; significant right ventricular dilation and hypertrophy consistent with severe pulmonary arterial hypertension. Systolic flattening of the IVS consistent with pressure overload. TR velocity consistent with pulmonary pressure gradient >90mmHg. The pulmonic and aortic valves are normal in morphology and mobility. Moderate MPA and branch dilation. No obvious pulmonic insufficiency. Normal pulmonic and aortic outflow velocities. Trace AI. No pericardial or pleural effusion noted. No cardiac tumors observed.
Severe pulmonary hypertension (PAH) is confirmed by documenting an elevated TR velocity and right heart compensatory changes. The estimated systolic pulmonary arterial pressure in this case was >90mmHg, with normal being <25mmHg. This led to severe hypertrophy and dilation of the right heart (indicating severe right-heart pressure overload). Clinical signs of weakness, heavy breathing, cyanosis, and syncope are attributed to severe PAH. Trace MR was also present, however the left heart dimensions were normal to small, indicative of dehydration.
The underlying genesis of PAH is poorly understood in cases other than heartworm infestation, though it occurs with increased frequency in a variety of forms of chronic lung disease and in patients with idiopathic pulmonary fibrosis. If not performed, a heartworm antigen test is always recommended. Given a chronic cough and collapsing trachea in this case, chronic airway disease with an acute secondary exacerbating insult (infectious or inflammatory) was suspected. Patients with this degree of PAH and pulmonary disease can develop right-sided congestive heart failure (ascites), debilitating cyanosis, labored breathing and exertional syncope if poorly controlled.
Given the recent onset of worsening respiratory signs in this case, the most common cause is an infectious or inflammatory insult causing a decline in already poor oxygenation status. A PTE cannot be ruled out. A Radiologist review of radiographs, as well as repeat films for comparison are extremely beneficial in these cases, particularly in light of echo findings. Coverage with broad spectrum pulmonary antibiotic (fluoroquinolone) was recommended, in addition to aggressive vasodilation using pimobendan and sildenafil. Lasix should be discontinued in these cases as diuretics can actually further reduce preload in cases of debilitating PAH and worsen clinical signs. Cautious fluid therapy may be helpful, due to hypotension likely due to volume depletion. Continued hospitalization for oxygen support and IV antibiotics may be necessary until stabilized.
Once stable, use of theophylline and/or taper course of anti-inflammatory steroids can also be beneficial in these cases, to treat exertional dyspnea or acute flare ups and decrease the inflammatory component as much as possible. PRN use of cough suppressants may also be beneficial. Unfortunately the prognosis overall is poor, however I am hopeful we can provide some medical relief going forward assuming the patient can be stabilized through the current crisis.