Col. San Miguel Chapultepec, Del. Miguel Hidalgo, México D.F., México
Introduction
The presence of a heart murmur may or may not be associated with cardiovascular disease in dogs. In order to assess the clinical significance of a murmur, several diagnostic modalities need to be considered. Thoracic radiography is necessary for the evaluation of the patient with cardiovascular disease. During the process of diagnosis cardiovascular disease in small animals, an excellent knowledge of radiographic anatomy and pathophysiology is necessary.
Radiography provides a rapid, noninvasive tool for evaluating structures within and around the thorax. A systematic approach should be used to provide the necessary tools in the investigation of cardiovascular disease. It should be noted that radiographs are a complementary technique to echocardiography and an understanding of the benefits and limitation of this modality is imperative.
Degenerative mitral valve disease is by far the most common cause of heart pathology in small animal medicine accounting for 75% of all heart disease. Other cardiac diseases both acquired and congenital can present clinically with a murmur. Considering this, it is important to determine the radiographic characteristics that occur in the evolution of the natural disease process to best tailor treatment.
Canine chronic valvular heart disease (CVHD) is one of the most common causes of heart pathology in small animals. In most cases 40% of the patients diagnosed with CVHD will develop congestive heart failure.1
For an adequate approach to the patient with CVHD the consensus guidelines for canine chronic valvular disease2 are very useful to classify and orient diagnostic and treatment protocols.
Based on this classification the following radiographic considerations can be established for each staging system. It is important to reiterate that thoracic radiography should be performed in every patient with an ausculted heart murmur, not only for clinical evaluation but also as a baseline image to monitor disease progression.
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CVHD stage
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Radiographic findings
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A
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None
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B1
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Radiographically normal
Slightly enlarged LA, LV or both (with normal systolic function evaluated echocardiographically)
Normal vertebral heart score
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B2
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Clearly enlarged LA, LV or both
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C
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Clearly enlarged LA, LV or both
Evidence of previous or current pulmonary edema
Alveolar pattern
Border effacement
Air bronchograms
Increased pulmonary opacity
Generally alveolar pattern distribution is symmetrical and bilateral
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D
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Refractory congestive heart failure (see radiographic findings expected explained in Stage C)
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Considerations when interpreting cardiac silhouette must include chest anatomy, whether the film is inspiratory or expiratory and patient positioning, as these can affect the morphology of cardiac silhouette significantly.3 Since all of these factors exists, it is important to delineate that thoracic radiographs, although important in the diagnosis of cardiac chamber enlargement is limited. With that, the left atrium is the easiest assessed with certainty and since left atrial enlargement precedes congestive heart failure, then radiology´s utility is still significant. Furthermore, a diagnosis of cardiogenic pulmonary edema without moderate to severe left atrial enlargement cannot be supported.4
When evaluating pulmonary patterns in CVHD, alveolar pattern differential diagnosis includes pneumonia, which is common in patients with acute signs that do not respond well to conventional treatment. In addition to the prior, neoplasia in older dogs must be regarded.4
Pulmonary hypertension is a common occurrence in patients with CVHD in advanced stages and can cause clinical signs like syncope and worsen exercise intolerance. Thoracic radiography is insufficient in the diagnosis of pulmonary hypertension. Radiographic findings that support the diagnosis of pulmonary hypertension are: right sided chamber enlargement, pulmonary artery enlargement, pulmonary arterial tortuosity or pruning when heartworm is present.5 The reason why thoracic radiography lacks sensitivity in the diagnosis of pulmonary hypertension is that the radiographic changes are not associated with the severity of the cardiopulmonary disease.
Conclusions
Thoracic radiology is one of the most important diagnostic tools for patients with CVHD, particularly to rule our congestive heart failure. It is a noninvasive means to indirectly assess cardiac performance. Finally, pulmonary hypertension is a common complication of patients with advanced CVHD and thoracic radiology is not sufficiently sensitive to adequately diagnose this clinical entity.
References
1. Bonagura JD, Twedt DC. Kirks Current Veterinary Therapy XIV. St Louis, MO: Sanders Elsevier; 2009.
2. Atkins C, Bonagura J, Ettinger S, et al. Guidelines for the diagnosis and treatment of canine chronic valvular heart disease. J Vet Intern Med. 2009;23:1142–1150.
3. Thrall DE. Textbook of Veterinary Diagnostic Radiology. 6th ed. St Louis, MO: Elsevier; 2013.
4. Tilley LP, Smith FWK, Oyama MA, Sleeper MM. Manual of Canine and Feline Cardiology. 4th ed. St Louis, MO: Elsevier; 2007.
5. Kellihan HB, Stepien RL. Pulmonary hypertension in dogs: diagnosis and therapy. Vet Clin North Am Small Anim Pract. 2010;40:623–641.