Pulsatile vessel: carotid artery or internal jugular vein?
I recently shared an image on Twitter, asking viewers to identify whether the pulsating vessel was the internal jugular (IJ) vein or the carotid artery. Out of the 902 respondents, approximately half believed it to be an artery. This misconception likely comes from the common belief that veins do not exhibit pulsations, while arteries do. However, it is important to note that blood flow in veins can indeed be pulsatile, particularly in those situated close to the heart. These pulsations are more pronounced in hyperdynamic states, such as volume depletion or high-output cardiac conditions.
Upon closer examination, one can observe that the pulsating vessel overlies the carotid artery, as indicated in the labeled image below. This is the commonest anatomical position of the IJ vein, as illustrated. Furthermore, when the patient takes a breath (note the movement of the trachea), the shape of the vessel changes (from oval to drop-like) and collapses, demonstrating respiratory variation. Carotid arteries typically do not exhibit such respiratory variation. In the long axis, the vein displays a paint brush appearance, whereas the carotid artery would be expected to resemble a pipe. The height of the collapse point of the vein can be used to estimate right atrial pressure (RAP) analogous to the visual estimation of JVP (collapse point = highest point of venous pulsations visually), which is low in this case.
Below image demonstrates transition from IJ vein (paint brush) to carotid artery (pipe) upon fanning the transducer.
Of note, the image in question was captured from a patient with cirrhosis and acute kidney injury. Visualizing the inferior vena cava (IVC) from the subxiphoid window was challenging; however, it was visible from the right lateral window. Despite the diameter appearing to be less than 2 cm, it is crucial to clarify that this measurement does not reflect the anteroposterior diameter, and the vessel did not exhibit respiratory variations. Notably, IVC POCUS can be unreliable in patients with cirrhosis.
In the images provided below, you can observe the IVC and parasternal long axis views. The left ventricular outflow tract velocity time integral (LVOT VTI) was found to be low, averaging around 14 cm. This finding suggests volume depletion in the given clinical context. It is worth noting that cirrhosis-induced hyperdynamic state may exhibit similar characteristics (Supranormal LV EF, low RAP), although patients with cirrhosis are typically chronically volume expanded with high VTI. With a blood pressure reading of 123/85 mmHg in this particular patient, a distributive picture is less likely (diastolic not low).
Tricuspid regurgitation is another situation where you can see pulsatile IJ vein. But as most hospitalized patients with functional or structural TR tend to be hypervolemic, we often see pulsatile but distended IJ veins (unless scanning at high head elevation). Here is an example.