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We chat with Dr. Michael Lanspa, intensivist and director of the Intermountain Critical Care Echocardiography Core Lab, about common pitfalls among bedside POCUS users and tricks for doing it better.
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Takeaway lessons
- It’s a fallacy to think that any quantitative method of EF evaluation is truly objective; cardiologists eyeball the EF and adjust their calculation if it seems wrong.
- EF is always loading sensitive, and will not reflect stroke volume accurately if the chamber is small or large. The eyeball/gestalt method is usually harder with non-symmetric contraction (i.e. RWMA).
- LVOT VTI is often compromised by an off-axis angle of insonation (within 15 degrees will introduce negligible inaccuracy), and a poor signal (the VTI should ideally be hollowed out).
- In general, tracking the VTI alone using a similar technique will yield more consistent results than attempting a full cardiac output calculation.
- TAPSE fails when the free wall contracts more or less than the longitudinal contraction. This is common in PAH, where the free wall may be more impacted than the longitudinal function. The converse may occur in the LV in hypovolemia, where radial contraction may appear hyperdynamic but longitudinal shortening remains diminished.
- s’ tends to “see” better with a poor view than TAPSE, as tissue doppler is more sensitive than M-mode.
- With more severe TR, the doppler gradient tends to underestimate the RVSP, as the pressure equilibrates faster during systole.
- A sniff test during IVC ultrasound is part of the standard echo method of estimating CVP. It is not well-proven to approximate volume responsiveness.
- Remember that when dynamic LVOT obstruction occurs, LVOT VTI may be extremely high, but the stroke volume is not elevated — it’s balanced out by the reduction in effective orifice size (i.e. the LVOT diameter is not the diameter of the jet, which has been narrowed).
- In general, eyeball assessment of regurgitation using color doppler and B-mode is probably all that’s needed for POCUS; attempting additional quantification is rarely high-yield.
- Assessing aortic stenosis is generally an unreasonable ask for bedside POCUS users. The easiest tool is probably to get the best possible 2d view of the valve and eyeball its opening; a reasonable visualized valve excursion is probably not consistent with severe stenosis. Beyond that, obtain a full study.