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Crab view is the view of the pulmonary veins by colour Doppler using a low velocity to capture pulmonary venous flow, as it enters the left atrium (in normal configuration). Beware that pulmonary veins may partially or totally be draining in another structure than the left atrium (TAPVR or PAPVR). We attempt to locate the ostium. A PW Doppler should be done on every vein at its opening in the left atrium. The biphasic or triphasic pattern should be identified. Some flow reversal may occur during the atrial contraction. A prolonged atrial reversal duration may be associated with underlying LV diastolic dysfunction (poor compliance). This sign of diastolic dysfunction is often reported in the pediatric or adult literature. However, it has not been systematically reported in neonatal conditions with LV diastolic dysfunction (such as in the conditions with LV hypertrophy).
Right lower pulmonary vein (RLPV)
Left lower pulmonary vein (LLPV)
Left upper pulmonary vein (LUPV)
Right upper pulmonary vein (RUPV)
Right lower pulmonary vein Doppler.
Right upper pulmonary vein Doppler.
Left upper pulmonary vein. One may appreciate the Triphasic pattern (S1, S2 and D waves) of the pulmonary venous flow. There is occasional some Ar wave (during atrial contraction) with brief retrograde flow.
Right lower pulmonary vein. One may appreciate the Biphasic and Triphasic pattern of the pulmonary venous flow. There is occasional some Ar wave (during atrial contraction) with brief retrograde flow.
Two other examples of a crab view.
Two other examples of a crab view.
Nyquist (velocity filter) is set at a lower value in order to visualize the venous flow entering the left atrium.
PW-Doppler in the left lower pulmonary vein.
PW-Doppler in the left upper pulmonary vein.
PW-Doppler in the right upper pulmonary vein.
PW-Doppler in right left lower pulmonary vein.
Pulmonary venous flow typically shows a triphasic pattern: the S1 and S2 waves represent systolic forward flow into the left atrium, with S1 occurring during early systole and S2 during late systole. You can appreciate here relative to the relationship of the QRS. The D wave reflects diastolic forward flow during early ventricular filling when the mitral valve is open. The AR wave (atrial reversal) is a brief retrograde flow occurring during atrial contraction, just before mitral valve closure. This pattern provides insight into left atrial and ventricular diastolic properties.
These waveforms are influenced by the dynamic pressure relationships between the pulmonary veins, LA, and LV. The S waves reflect LA compliance and downstream LV systolic function; diminished S waves may indicate elevated LA pressures or impaired atrial relaxation. The D wave is primarily dependent on LV diastolic compliance and suction, and becomes more prominent with increased preload or restrictive physiology. The AR wave amplitude increases with reduced LA compliance or elevated LV end-diastolic pressure, as atrial contraction must overcome higher resistance. Altogether, analysis of pulmonary venous flow provides valuable insight into left-sided filling pressures, diastolic function, and atrial mechanics. More information on the website of NephroPOCUS.
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