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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.
Pulmonary venous Doppler displays a biphasic systolic forward wave and an early-diastolic forward wave, often followed by a brief atrial reversal. The systolic wave is often split into S1 and S2: S1 occurs in early systole when the left atrium (LA) relaxes as the mitral valve has just closed, causing LA pressure to fall below pulmonary venous pressure and drawing blood forward into the LA. S2 follows in mid-to-late systole and is driven mainly by longitudinal left-ventricular (LV) shortening—the descent of the mitral annulus increases LA capacitance and further lowers LA pressure, augmenting forward venous inflow. After aortic valve closure and mitral opening, the D wave reflects early-diastolic conduit flow from the pulmonary veins through the LA into the LV; its size depends on LV relaxation (“suction”), LA pressure, and preload. Finally, Ar (atrial reversal) occurs during atrial contraction; if LV end-diastolic pressure or stiffness is high, part of the LA outflow is pushed back into the pulmonary veins, increasing Ar velocity and, classically, prolonging Ar duration relative to the mitral A wave. Patterns that increase S1/S2 include robust LV longitudinal systolic function (greater annular descent), good LA compliance, low intrathoracic/LA pressure (e.g., inspiration), and situations that decompress the LA in systole such as a nonrestrictive interatrial communication with left-to-right shunting; among these, S2 is the most sensitive to LV longitudinal performance. S1/S2 decrease when LA pressure rises during systole or LA compliance is poor—most notably with mitral regurgitation (a large V-wave blunts or reverses S, especially S2), with reduced LV longitudinal function, acute volume/pressure loading of the LA, or marked tachycardia that shortens systole and diastasis. The D wave increases when early-diastolic LA→LV driving pressure is strong or pulmonary venous return is high—examples include significant PDA with left-to-right shunt, brisk LV relaxation, or high preload; it decreases with impaired LV relaxation (prolonged relaxation), low preload, or when diastolic inflow is limited by a restrictive interatrial communication or pulmonary venous obstruction. In advanced diastolic dysfunction/restrictive physiology, a characteristic pattern emerges of blunted S with tall D and prominent Ar, reflecting high LA pressure, rapid early filling, and a stiff LV that forces more retrograde flow during atrial systole.
A tall pulmonary venous S-wave reflects strong reservoir-phase forward flow into the left atrium (LA) during LV systole. When the LV shortens longitudinally, the mitral annulus descends, the LA actively relaxes, and LA pressure falls relative to pulmonary venous pressure; that suction augments systolic inflow and makes S large. Anything that enhances annular descent (good LV longitudinal systolic function), improves LA compliance, or prevents a systolic LA pressure rise will boost S—e.g., normal/hyperdynamic LV function, absence of mitral regurgitation (no V-wave), effective LA relaxation, and even decompression across a nonrestrictive ASD/PFO (LA→RA during systole lowers LA pressure further, steepening the PV–LA gradient). Transiently, inspiration can also enlarge S by dropping intrathoracic/LA pressures. Conversely, conditions that raise LA pressure in systole—most notably mitral regurgitation or poor LV longitudinal function—blunt or reverse S.
A prominent D wave reflects augmented early-diastolic forward flow from the pulmonary veins into the left ventricle. At mitral valve opening, left atrial (LA) pressure briefly exceeds left ventricular (LV) pressure and, coupled with active LV relaxation (“suction”), releases blood that has accumulated in the LA/pulmonary venous reservoir during ventricular systole. The result is a rapid “conduit” emptying into the LV, recorded as a taller, sharper D wave. Situations that increase LA preload or enhance early-diastolic LV suction—such as left-to-right shunting with high pulmonary venous return (e.g., a significant PDA) or tachycardia with shortened diastasis—accentuate the D wave, whereas impaired LV relaxation or elevated LV filling pressures tend to blunt D and may increase the atrial reversal (Ar) wave.
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