History: Approximately 5 month old MN Lab mix, just adopted from the Humane Society; A heart murmur was ausculted on physical exam, but the dog is otherwise healthy
Radiographic Findings: There is right sided cardiomegaly which is causing a shift of the left ventricle/apex to the left on the VD view. Also on the VD view, the right atrium is markedly enlarged. The heart has a rounded appearance on the lateral views but not on the VD view. The left heart is normal. The pulmonary vasculature and parenchyma are normal. There is a sternal abnormality with shortened 5th and 6th sternebrae, with irregularity of the 5th sternebra.
Radiographic Interpretation/Synthesis: Severe right sided cardiomegaly with marked right atrial enlargement most likely due to tricuspid dysplasia. Cor triatriatum dexter is possible. An atrial septal defect would be much less likely. Other congenital cardiac abnormalities such as pulmonic stenosis or Tetralogy of Fallot are not likely due to the radiographic signs that are present. A right atrial mass or myxomatous degeneration of the tricuspid valve are not likely in a patient of this age. The sternal abnormality is likely congenital, or may be due to prior trauma.
Most candidates realized tricuspid dysplasia was a top rule-out. More successful candidates were able to reason through the other possibilities and kept the differential list short. They also recognized that, although there was a sternal anomaly, the radiographic findings did not otherwise fit with a PPDH, so left that off the rule-out list. Less successful candidates struggled with cardiovascular physiology and included rule-outs that were not likely, based on radiographic findings – these included Tetralogy of Fallot, PDA, PPDH. They sometimes over-interpreted the left heart as being enlarged, which led them to inappropriate differentials.