A Critical Evaluation of the Radiographic Findings in Canine Cardiovascular Diseases

SUMMARY The increasing importance of the radiographic examination in diagnosing heart disease in the dog initiated a critical evaluation of the methods presently used in interpreting thoracic radiographs. Radiographs of 131 dogs that included signs compatible with heart disease were retained from a large number of routine examinations, and detailed empirical evaluation and cardiac mensuration were done. The result of empirical evaluation was compared to results of cardiac mensuration and clinical and necropsy findings. Cardiac mensuration lacked sensitivity in diagnosing heart disease when only slight changes were present. The use of only one projection and the frequent shifting of the cardiac apex toward the uninvolved side were among the main reasons for the inaccurate diagnoses. Empirical evaluation tended to overdiagnose cardiac enlargement. So that the results will be as reliable as possible and less dependent on the subjective impression of the interpreter, it is essential to use all signs visible on the radiograph. The mere evaluation of the cardiac silhouette seems inadequate. Signs indicating deficient pulmonary circulation or impaired venous return to the right heart, such as pulmonary congestion, pleural effusion, or abdominal effusion, are valuable adjuncts to diagnosis. The large vascular structures in the thorax must be scrutinized for changes secondary to heart failure. The signs should be evaluated as a group of concurrent changes resulting from the affection of a particular functional segment of the circulation. Familiarity with the hemodynamic changes to be expected is therefore required. Since most radiographic signs are nonspecific, careful differential diagnosis is always indicated. Repeat radiographs and special studies when indicated, such as angiocardiography or cardiac catheterization, will usually provide the diagnosis even in complicated cases.