Echocardiographic Evaluation of the Right Atrial Area Index in Dogs with Pulmonary Hypertension

Background: Right atrial area (RAA) is a prognostic factor in human patients with pulmonary arterial hypertension (PAH). Reference intervals for RAA have been described in healthy dogs.

Objectives: To evaluate RAA indexed to the body surface area in dogs with PAH as an indicator of right atrial size, PAH severity and right-sided congestive heart failure (R-CHF).

Animals: A total of 119 client-owned dogs, 48 dogs with PAH and 71 control dogs.

Methods: Prospective observational study. Pulmonary arterial hypertension was classified according to the tricuspid regurgitation pressure gradient (TRPG) as mild (36-50 mmHg), moderate (51-75 mmHg), or severe (>75 mmHg). The RAA index was calculated as the RAA divided by body surface area.

Results: The RAA index was higher in dogs with moderate PAH (13.3 cm² /m² ; range, 3.4-24.7 cm² /m² ) and severe PAH (12.1 cm² /m² ; range, 5.4-21.8 cm² /m² ) than in those with mild PAH (6.7 cm² /m² ; range, 4.8-10.7 cm² /m² ) or in controls (7.3 cm² /m² ; range, 4.2-10.2 cm² /m² ; P < 0.001). The RAA index was higher (P < 0.0001) in dogs with R-CHF (17.5 cm² /m² ; range, 12.7-24.7 cm² /m² ) compared to those without R-CHF (7.6 cm² /m² ; range, 4.4-19.4 cm² /m² ). The most accurate cutoff value of the RAA index to identify R-CHF was >12.3 cm² /m² (sensitivity, 100%; specificity, 89.5%). In dogs with PAH, severity of tricuspid regurgitation (TR) was the only independent predictor of RAA index based on multivariate analysis (P < 0.02).

Conclusions and clinical importance: The RAA index can be used to evaluate right atrial size in dogs and may be more effective than TRPG in predicting R-CHF in dogs with PAH. The severity of TR is the main determinant of the RAA index in dogs with PAH.