June 2025
In this VETgirl online veterinary continuing education blog, Dr. Natasha Yeh and Dr. Christopher Kennedy, DACVECC, DECVECC review how focused cardiac ultrasonography (FCU) can help identify overt right heart (RH) disease. By assessing key views and integrating findings with the clinical exam, FCU can highlight right heart enlargement and fluid intolerance, aiding in timely and appropriate treatment decisions.

Recognizing Right Heart Disease with Focused Cardiac Ultrasound

By Dr. Natasha Yeh and Dr. Christopher Kennedy, DACVECC, DECVECC

The right heart (RH) is a complex structure consisting of the right atrium, tricuspid valve, right ventricular inflow region, right ventricular apex, right ventricular outflow region and the pulmonary valve apparatus. Unlike the left heart, the peculiar shape of the RH complicates imaging and measuring.1 In FCU, the study is limited to right-sided views only, which further limits our evaluation of the RH. We focus on the overt findings, which improves our specificity for recognizing a RH problem, though at the expense of our sensitivity. An important reminder is that detailed cardiac assessments remain the purview of cardiologists and recognizing mild and perhaps even moderate RH disease is beyond our scope in FCU.

Recall in blog #1 we discussed the systematic approach to FCU. The second question in each view is “is there a RH problem/is the RH bigger than the left?” In this blog post, we will consider ways to recognize RH problems.

Is the right heart big?

In FCU, the RH can be divided simply into the right atrium (RA) and the right ventricle (RV).

In the PLAX4 view, we can compare the ratio of the RA diameter to the left atrial diameter (RAD:LAD, figure 1), with normal being <1:1.2 Remember, both image acquisition error and measurement error can affect accuracy: in cases with subtle size differences, it may be best not to make measurements, whereas in cases with obvious differences, measurements may not be necessary (figure 2).

Figure 1 – PLAX4 measuring RAD:LAD. The RAD is in red and the LAD is in blue. The red and blue lines at the top right show the two measurements next to each other for comparison. As can be seen in this image, measuring the RAD can be difficult, as its size might not fit on the screen and its shape might not permit easy measurements.

Figure 2 – PLAX4 with overtly increased RAD. A) There is no need to measure the RAD, as RAD:LAD is clearly > 1:1. B) The same image as A, with the right atrium outlined in red and the left atrium in blue, showing an obvious size difference.

Considering the RV, the RV lumen diameter and free wall thickness should be < 50% the LV lumen diameter and wall thickness. If the RV measurements are > 50% their respective LV measurements, there might be a right heart problem; if the RV measurements are the same size or greater, there is a right heart problem.1,2

Video 1 – PLAX4 showing a concentrically thickened right heart. Notice how the wall of the RV is thicker than the wall of the LV. The RA is also enlarged.

Video 2 – PSAX-pap showing a right ventricular concentric and eccentric hypertrophy. Concentric means the RV wall is thickened and eccentric means the RV lumen is dilated (volume-filled). Notice how the “cap” of the “mushroom” flattens. This is the phenomenon of interventricular septal flattening and indicates elevated right heart pressures.

Video 3 – PSAX-base showing right atrial enlargement and concentric hypertrophy of the right ventricular outflow tract. Imaging the right heart this way is less familiar and is not something we should focus on in FCU; we should focus on the PSAX-pap and PLAX4 views. This example is included for your interest and for when you find something similar on your FCU journey!

Figure 3 – still image of video 3 with labels. RA, right atrium; TV, tricuspid valve; RVOT, right ventricular outflow tract; PV, pulmonary valve; LA, left atrium; Ao, aorta.

Pulmonary artery:pulmonary vein ratio (PA:PV)

We discussed PA:PV in a previous blog post. Recall, if the PA > PV, pulmonary hypertension and secondary RH disease should be suspected (figures 4 & 5).3 M-mode may be useful here: aligning the cursor through the PV and the PA can allow you to measure and compare their sizes.

Figure 4 – PLAX4 showing the PA and the PV. Compare with figure 5.

Figure 5 – PLAX4 showing PA > PV.

Caudal vena cava (CVC) and hepatic veins

The CVC can be imaged via the SX-CVC view as it crosses the diaphragm on its way to the RA. A normal CVC shows respirophasic variations, meaning it decreases in size during inspiration and increases in size during expiration. With right heart disease, right heart pressure increases. As the RA is downstream of the CVC, increased RA pressure causes CVC congestion, resulting in a) dilation and b) reduced respirophasic variations (video 4). This can be used to infer elevated RH pressures. Venturing south of the diaphragm, severe congestion manifests as dilation of the hepatic vasculature (video 5).

Video 4 – SX-CVC showing a dilated CVC that demonstrates minimal respiratory variations.

Video 5 – Modified SX-CVC view showing dilated hepatic vasculature. This is a sign of systemic venous congestion, potentially secondary to right heart disease, and indicates fluid intolerance.

What does an enlarged right heart mean?

The enlarged right heart is fluid intolerant. This means that bolus fluid administration is contraindicated even if the left heart appears underloaded. Cautious fluid administration may be appropriate in some cases: consultation with a criticalist or cardiologist is recommended. Oppositely, furosemide administration may be indicated; however, aggressive diuretic use is not advised without consulting a cardiologist and it can be detrimental in some cases of cor pulmonale. Generally, if right heart disease is causing respiratory distress, it is either due to a) pulmonary hypertension, which does not respond to diuretics; b) marked ascites, which requires abdominocentesis; c) cardiogenic shock, which may require inotropic support to improve cardiac performance and decongest the venous circulation.

References and further reading:

  1. Ware A & Bonagura JD. Cardiovascular disease in companion animals: Dog, cat and Horse. CRC Press 2022, Boca Raton, USA.
  2. Sankisov JN, Visser LC, Davis KE, et al. Two-dimensional echocardiographic right heart ratios for assessment of right heart size in dogs: Reference intervals and reproducibility. J Vet Intern Med. 2024;38(6):3005-3015.
  3. Roels, E.et al. Diagnostic value of the pulmonary vein-to-right pulmonary artery ratio in dogs with pulmonary hypertension of precapillary origin. Journal of Veterinary Cardiology, 2019;24:85–94.

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