Pulmonary hypertension commonly results from cardiovascular, pulmonary, or systemic disease. Clinical signs include dyspnea, syncope, exercise intolerance, lethargy, and\/or coughing. Diagnostics can begin with thoracic radiography; more advanced techniques include Doppler echocardiography and pressure measurement by catheterization under fluoroscopic guidance.<\/p>\n
Although certain abnormalities may indicate pulmonary hypertension on radiographs, a radiographic assessment of the intrathoracic structures as a whole can help screen for comorbidities, which may either be a cause or sequela of pulmonary hypertension and may require further diagnostic work-up. Early diagnosis and treatment can help prevent progression to right-sided heart failure. Management depends on the underlying cause.<\/p>\n
Take-Home Points<\/strong><\/p>\n Pulmonary hypertension is defined as increased pulmonary arterial pressure, commonly secondary to cardiovascular, pulmonary, or systemic disease.1,2<\/sup> Right-sided cardiomegaly can ensue, possibly followed by cardiac decompensation into right-sided heart failure with increased severity. More commonly, dogs and cats with pulmonary hypertension exhibit signs of dyspnea, syncope, exercise intolerance, lethargy, or coughing.1<\/sup> A diagnosis is most practically achieved with Doppler echocardiography due to its accessibility and noninvasiveness. However, a definitive diagnosis is best obtained by using more invasive catheterization techniques under fluoroscopic guidance to directly measure pulmonary arterial pressure,1,2<\/sup> although the risks, higher cost, and training needed to perform such a procedure make it a less favorable choice for routine clinical use.1<\/sup> Thoracic radiography may precede and is more accessible than echocardiography and may show abnormalities supportive of pulmonary hypertension and changes indicative of the underlying cause. Although thoracic radiography is reported to be insensitive for patients with mild pulmonary hypertension, abnormalities may be more reliably observed in dogs and cats with at least moderate pulmonary hypertension.2<\/sup> Management of pulmonary arterial hypertension depends on the underlying cause. The American College of Veterinary Internal Medicine recently published a consensus statement with guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs.1<\/sup> This article focuses on the use of thoracic radiographs to support a diagnosis of pulmonary hypertension. <\/span><\/p>\n Radiographic features of pulmonary hypertension include right-sided cardiomegaly and pulmonary arterial distension. Right-sided cardiomegaly is characterized by rounding of the cranial and right lateral margins of the cardiac silhouette with associated caudal and left displacement of the cardiac apex, resulting in a \u201creverse D\u201d appearance of the cardiac silhouette on a ventrodorsal\/dorsoventral projection (<\/strong><\/span>FIGURE 1<\/span><\/strong>)<\/strong>.2,3<\/sup> <\/span><\/p>\n Figure 1A. Lateral projections of a dog with severe right-sided cardiomegaly. The cranial and right lateral margins of the cardiac silhouette are severely rounded (arrowheads).<\/p><\/div>\n Figure 1B. Dorsoventral projections of a dog with severe right-sided cardiomegaly. The cranial and right lateral margins of the cardiac silhouette are severely rounded (arrowheads), and the apex of the cardiac silhouette is displaced to the left (arrow). The cardiac silhouette has a \u201creverse D\u201d appearance.<\/p><\/div>\n In the absence of concurrent left-sided cardiomegaly, the cardiac silhouette may become wider in relation to its height.3<\/sup> An objective means of measuring this change, the \u201c3\/5 to 2\/5 cardiac ratio\u201d method involves drawing a line from the carina, extending ventrally parallel to the caudal border of the heart. Approximately 3\/5 of the cardiac silhouette surface area (right heart) should be cranial to this line, and 2\/5 of the cardiac silhouette surface area (left heart) should lay caudal to this line (<\/strong><\/span>FIGURE 2<\/span><\/strong>)<\/strong>.4<\/sup> If the cardiac silhouette cranial to this line has a fractional surface area greater than 3\/5, right-sided cardiomegaly should be considered.4<\/sup> <\/span><\/p>\n Figure 2A. Right lateral thoracic radiograph of a dog without right-sided cardiomegaly. In the absence of cardiomegaly, a line drawn from the carina and extending ventrally parallel to the caudal border of the heart divides the cardiac silhouette into a normal \u201c3\/5 to 2\/5 cardiac ratio,\u201d as correlated by comparing the surface areas of a:b.<\/p><\/div>\n Figure 2B. Right lateral thoracic radiographs of a dog with right-sided cardiomegaly. In patients with right-sided cardiomegaly, more than 3\/5 of the cardiac silhouette surface area is identified cranial to this line (i.e., a:b is greater than 3\/5:2\/5).<\/p><\/div>\n Using the clockface analogy (<\/strong><\/span>FIGURE 3<\/span><\/strong>)<\/strong>, an opaque soft tissue bulge confluent with the cardiac silhouette at the 1 to 2 o\u2019clock position on the dorsoventral or ventrodorsal projections is suggestive of main pulmonary artery enlargement (<\/strong><\/span>FIGURE 4<\/span><\/strong>)<\/strong>. This finding may be associated with lobar pulmonary artery enlargement. <\/span><\/p>\n\n
Radiographic Features of Pulmonary Hypertension<\/h2>\n
Dogs<\/h3>\n
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<\/a><\/a><\/a><\/a>Figure 3A. Clockface representation of cardiac chambers location on a right lateral radiograph. L aur, left auricle; MPA, main pulmonary artery.<\/span><\/a><\/div><\/div>