Pulmonary veins on cardiac ultrasound
In a recent twitter poll showing this parasternal long axis (PLAX) image, only 36% (N = 301) were able to identify the pulmonary vein. Even though the purpose of POCUS is to answer yes/no questions, having a thorough knowledge of the anatomy is important to distinguish normal from abnormal structures. Moreover, we all know the quote “the eyes do not see what the mind does not know”.
Left pulmonary veins seen on PSAX view, aortic valve level.
These images (black & white print of color Doppler) nicely illustrate the anatomic location of all the four pulmonary veins. PSAX view obtained from a patient with atrial septal defect (ASD). LAA = left atrial appendage; DAO = descending aorta.
Here is an interesting view of all four pulmonary veins from the suprasternal window called the ‘crab view’.
Interestingly, the normal pulmonary vein waveform is very similar to that of hepatic vein Doppler that we use to assess venous congestion except that the majority of the flow is above the baseline (flow towards LA = transducer). It essentially comprises of 2 forward (flow into LA) – S (systolic) and D (diastolic) waves and 1 backward wave – AR (atrial reversal). S wave has 2 components – early systolic/S1 and late systolic/S2, though it is difficult to distinguish between these two in ~70% of the patients. Following figures illustrate the normal waveform as well as key determinants of each of these waves. Having a simultaneous EKG makes your life much easier (helps precisely identify phases of the cardiac cycle).
Detailed discussion of the waveform analysis is beyond the scope of this post but just remember that in normal adults, the S wave is greater than the D wave and S/D ratio is greater than 1. As the LA pressure increases, particularly with elevated LV filling pressures/mitral regurgitation, the S wave velocity decreases and the S/D ratio falls to less than 1. This is similar to S<D pattern seen in the hepatic venous Doppler with increasing right atrial pressure. Having said that, S<D on PV Doppler may be seen in healthy adolescents and young adults with excellent LV elastic recoil that manifests fast LV relaxation and thus rapid LV filling in early diastole, with only minor contribution to filling during atrial contraction.