Echocardiographic evaluation of the right atrial area index in dogs with pulmonary hypertension

Pulmonary hypertension (PH) can lead to right ventricular remodeling and failure. Right ventricular dysfunction and tricuspid regurgitation can lead to right atrial enlargement. In dogs, echocardiographic evaluation of right atrial enlargement is thusfar only based on subjective assessment. The aim was to evaluate reliability of the right atrial area index (RAAI) to characterize right atrial size and PH severity in dogs. The study was prospective, multicenter and observational. We included 103 client owned dogs: 45 dogs with PH and 58 healthy dogs as control group. PH was classified according to tricuspid regurgitation pressure gradient (TRPG) in mild (TRPG: 36-50 mmHg; n = 15 dogs), moderate (TRPG: 51-75 mmHg; n = 9 dogs) and severe (TRPG >75 mmHg; n = 21 dogs). Nine dogs with PH had right-sided congestive heart failure (CHF). Echocardiographic view of the right atrium was obtained from the left apical 4-chamber view optimized for the right heart and the right atrial area was measured by planimetry at the end of ventricular systole. RAAI was calculated as right atrial area divided by body surface area. Right atrial area showed a strong positive linear correlation with body surface area in healthy dogs (r = 0.89; P < 0.0001). RAAI was significantly higher (P < 0.05) in dogs with moderate PH (11.9 +/- 7.3 cm2/m2) and severe PH (12.0 +/- 4.5 cm2/m2) than in those with mild PH (6.9 1.5 cm2/m2) or control group (7.1 +/- 1.6 cm2/m2). No difference in RAAI was found between dogs of the two latter groups, or between dogs with moderate and severe PH. A weak positive correlation was found between RAAI and TRPG (r = 0.37; P < 0.05) and the TRPG was not different between dogs with right-sided CHF (81 29 mmHg) or without right-sided CHF (76 +/- 31 mmHg). Conversely, RAAI was significantly higher (P < 0.0001) in dogs with right-sided CHF (17.0 +/- 4.5 cm2/m2) in comparison to those without right-sided CHF (8.6 +/- 3.6 cm2/m2). The most accurate cut-off value in the prediction of right-sided CHF was >12.3 cm2/m2 (sensitivity: 89%; specificity: 89%). Intra- and inter-observer measurement variability was clinically acceptable (average coefficient of variation <10%). The study showed that RAAI increases in dogs with moderate to-severe PH and is particularly high in dogs with right-sided CHF. RAAI is expected to provide beneficial information during the assessment of PH severity in dogs and, possibly, when PH leads to remarkable hemodynamic consequences but the tricuspid regurgitation is absent or difficult to measure. Studies are needed to verify if RAAI is a prognostic factor in dogs with PH.