VETgirl October 2024 Beat e-Magazine

QUARTERLY BEAT / OCTOBER 2024

WEBINAR HIGHLIGHTS

primary pulmonary diseases. Finally, a single dose of a diuretic can shrink pulmonary vessels in less than 30 minutes, which will mask this normally present and important clue in dogs. Unfortunately, cats love to be very different than dogs in many ways. First, cardiomegaly may only be mild in the face of fulminant L-CHF. When present, cardiomegaly is often generalized without appreciable chamber enlargement. A valentine-shaped cardiac silhouette is commonly seen on DV or VD radiographs and is most often caused by left atrial enlargement. 2 Second, the presence of enlarged pulmonary lobar veins is inconsistent in cats and further masked with a single dose of a diuretic. Third, pleural and pericardial effusion commonly occur with L-CHF in cats because their visceral pleura is drained by pulmonary veins. In the dog, pleural and pericardial effusion are primarily associated with right- sided CHF. Finally, cardiogenic pulmonary edema will sometimes increase pulmonary opacity only around the bronchi in cats, which creates a reticulonodular pattern, mimicking the appearance of a bronchial pulmonary pattern that occurs with inflammatory airway disease. Without cardiac or pulmonary lobar venous enlargement, the findings of a pulmonary pattern with or without pleural effusion are very nonspecific and caused by other etiologies such as neoplasia and infectious disease. PULMONARY HYPERTENSION The etiology and pathophysiology of pulmonary hypertension (PH) is well reviewed elsewhere. 3 However, it is worth noting that it is a common sequela to other causes of dyspnea. In dogs and cats, PH is most commonly caused by heartworm or other parasitic disease, L-CHF, or chronic airway disease. Thromboembolic disease, shunts, and idiopathic PH are uncommon causes. Although echocardiography is needed to definitively diagnosis PH, several radiographic features help differentiate this disease from L-CHF in dogs. Cardiomegaly is common, but typically right sided in nature. 4,5 Right ventricular enlargement causes increased width and sternal contact of the cardiac silhouette on lateral projections and rounding of the right side of the cardiac silhouette on the VD/DV. Many dogs will also have a bulge in the region of the main pulmonary artery, located around the 1-2 o’clock region (when imagining a clockface superimposed over the cardiac silhouette) on the VD/DV projection. Variably pulmonary lobar artery enlargement with or without tortuosity occurs, more commonly affecting the caudal vasculature. A recent study demonstrated that comparing the artery to its corresponding vein may be helpful to detect enlargement. 6 A caudal pulmonary lobar artery to vein ratio of 1.1 demonstrated 91% specificity and 31% sensitivity in predicting PH. In other words, seeing pulmonary lobar arterial enlargement supports the diagnosis of PH but its absence cannot rule out the disease. Pulmonary infiltrates are seen in approximately 2/3 of cases, most often as a patchy or diffuse unstructured interstitial or alveolar pulmonary pattern. Unfortunately, the appearance and distribution of pulmonary infiltrates with PH is identical to diseases such as L-CHF, non-

radiographs as they only evaluate the pleural space, heart, and surface of the lungs. 1 Large lesions or regions of abnormal lung can easily be missed by ultrasound due to the negative effects of reverberation artifact that results from gas within the pulmonary parenchyma. Additionally, thoracic radiographs provide a global view of the thorax, evaluating structures that may influence interpretation of cardiopulmonary or pleural space pathology. As a result, thoracic radiographs are essential and should be acquired when safe to do so. A complete thoracic radiographic study involves acquiring three projections: right lateral, left lateral, and either ventrodorsal (VD) or dorsoventral (DV) projections. A DV projection is likely safer in most patients with dyspnea as it maximizes ventilation. It also makes the caudal pulmonary lobar vessels easier to see. The only downside is that if pleural effusion is present, it is more likely to decrease visualization of the cardiac silhouette on a DV projection as compared to a VD. The author prefers to start with the DV (or VD) projection for all thoracic studies as it will decrease the odds of atelectasis from lateral recumbency causing increased opacity throughout the pulmonary parenchyma on lateral projections that could be confused with true disease. Finally, it is prudent to keep in mind that each lateral projection only evaluates the pulmonary parenchyma of the opposite side because of recumbent atelectasis. For example, when looking at a right lateral radiograph, only the left cranial and caudal lung lobes are evaluated. Beyond imaging, other routine diagnostics helpful during the initial work up of dyspneic patients include a complete blood count, a chemistry profile, urinalysis, retrovirus testing (for cats), and heartworm antigen/antibody testing. More advanced testing includes echocardiography, diagnostic thoracic ultrasound, and computed tomography with contrast.

NO, IT'S NOT HEART FAILURE: A THORACIC RADIOGRAPHIC CASE SERIES

MARC SEITZ Marc Seitz, DVM, DACVR, DABVP (Canine and Feline Practice) College of Veterinary Medicine, Department of Clinical Sciences Mississippi State University, Mississippi State, MS, USA

In this VETgirl webinar, No, it’s Not Heart Failure: A Thoracic Radiographic Case Series on August 21, 2024, Dr. Marc Seitz, MS, DACVR, DABVP (canine and feline) uses a case series to review the radiographic diagnosis of non-cardiogenic pulmonary edema, chronic lower airway disease, pulmonary hypertension, pulmonary thromboembolism, atypical appearing metastatic neoplasia, and pulmonary hemorrhage. Tune in HERE and learn what key radiographic findings can help you to get a diagnosis!

Dyspnea of any cause is a common reason dogs and cats present acutely unstable. While heart failure is common, it tends to get overdiagnosed in patients presented with dyspnea if the heart appears big and an abnormal pulmonary pattern is present. Unfortunately, many breeds of dog have a larger but still normal cardiac silhouette relative to their thoracic cavity and most causes of respiratory distress cause an abnormal pulmonary pattern. Imaging is a vital part of diagnosing the underlying cause of dyspnea. However, triaging and stabilizing patients is imperative before pursuing imaging studies as stress and non-sternal recumbency can alter ventilation, disrupting the delicate balance that comes with compensation for hypoxemia. This is especially true for pleural space disease and hypoventilation. All patients benefit from remaining in sternal recumbency and some form of oxygen therapy. Many patients benefit from a mild sedative (e.g., butorphanol) or an anxiolytic drug. If pleural space disease is present, thoracocentesis should be performed prior to radiographs as it will improve evaluation of the pulmonary parenchyma and make the study safer. Other stabilization therapies should be tailored to triage exam findings. For example, bronchodilators can be given to patients with suspected lower airway disease. A diuretic like furosemide can be given to patients with suspected heart failure. Furosemide can also function like a diagnostic test in that lack of radiographic improvement following diuretic therapy makes heat failure unlikely. A clinical response to furosemide is not

pathognomonic for heart failure as patients with airway disease will respond to the drug’s bronchodilatory effects.

POCUS AND THORACIC RADIOGRAPHS

LEFT SIDED CONGESTIVE HEART FAILURE

Thoracic point-of-care ultrasound (POCUS) is an imaging technique that can safely be performed after the initial triage exam and while patient stabilization is being performed. Thoracic POCUS is easily performed with the patient standing or in sternal recumbency. A detailed description of various techniques and interpretation is beyond the scope of this presentation and well-reviewed elsewhere (references below). However, POCUS is invaluable at rapidly diagnosing pleural effusion, pericardial effusion, and alveolar-interstitial disease. When combined with the history, signalment, and physical exam findings, results from a POCUS exam can help localize the cause of dyspnea as well as guide stabilization therapies and further diagnostics. Thoracic POCUS ultrasound findings can also be used to complement radiographic findings. Specific examples include confirming the presence of pleural effusion, guiding diagnostic or therapeutic thoracocentesis, and differentiating cardiogenic pulmonary edema secondary to left sided congestive heart failure (L-CHF) from lower airway disease. Although thoracic POCUS findings are rapid and quite useful, they are never a replacement for thoracic

Left sided congestive heart failure (L-CHF) is most commonly caused by mitral valve disease in small-breed dogs, dilated cardiomyopathy in large-breed dogs, and hypertrophic cardiomyopathy in cats. CHF is a clinical diagnosis that is made based on physical exam and radiographic findings. Echocardiography is rarely needed for the diagnosis. In dogs, the classic triad of findings includes left-sided cardiomegaly, pulmonary lobar venous enlargement, and an unstructured interstitial to alveolar pulmonary pattern. The distribution of the pulmonary pattern varies and depends on the direction and symmetry of the mitral valve jet. Pulmonary patterns are most commonly patchy to diffuse and most severe caudodorsally. The pulmonary pattern can be either symmetric or asymmetric. Contrary to popular belief, a perihilar pattern is less common. In dogs with dilated cardiomyopathy, cranioventral distributed patterns are common, which can mimic aspiration pneumonia. Pulmonary patterns associated with L-CHF tend to be less severe as compared to

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