Introduction: Ultrasonographic indices of the inferior vena cava are useful for predicting right heart filling pressures in people.

Objectives: To determine whether ultrasonographic indices of caudal vena cava (CVC) differ between dogs with right-sided CHF (R-CHF), left-sided CHF (L-CHF), and noncardiac causes of cavitary effusion (NC).

Materials and methods: 113 dogs diagnosed with R-CHF (n = 51), L-CHF (30), or NC effusion (32) were enrolled. Seventeen of the R-CHF dogs had pericardial effusion and tamponade. Focused ultrasound was performed prospectively to obtain 2-dimensional and M-mode subxiphoid measures of CVC maximal and minimal size (CVCmax and CVCmin), CVCmax indexed to aortic dimension (CVC:Ao), and CVC collapsibility index (CVC-CI). Variables were compared between study groups using Kruskal-Wallis and Dunn’s-Bonferroni testing, and receiver operating characteristics curves were used to assess sensitivity and specificity.

Results: All sonographic CVC indices were significantly different between R-CHF and NC dogs (P < 0.001). Variables demonstrating the highest diagnostic accuracy for discriminating R-CHF versus NC were CVC-CI <33% in 2D (91% sensitive and 96% specific) and presence of hepatic venous distension (84% sensitive and 90% specific). L-CHF dogs had higher CVC:Ao and lower CVC-CI compared to NC dogs (P = 0.016 and P = 0.043 in 2D, respectively) but increased CVC-CI compared to the R-CHF group (P < 0.001).

Conclusions: Ultrasonographic indices of CVC size and collapsibility differed between dogs with R-CHF compared to NC causes of cavitary effusions. Dogs with L-CHF have CVC measurements intermediate between R-CHF and NC dogs.