Assessing Pulmonary Pressures

    Assessing Pulmonary Pressures

    February 15, 2018
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    63F presents with acute bilateral segmental PE’s demonstrated on CTA. Her troponin is negative. BNP is minimally elevated. Her HR is 105, BP 110/78, SpO2 94% on room air. 

    As you mull over the appropriate disposition for this patient, you pause to perform a bedside echo which suggests pulmonary hypertension. You reconsider your medicine-telemetry disposition, and admit the patient to a stepdown unit. You get the relevant subspecialty services involved early in her care, and she goes on to do exceptionally well.

    Introduction:

    By interrogating a tricuspid regurgitation jet using continuous wave doppler, you can obtain the maximum velocity of that jet. The practice of many echo labs is to use the modified Bernouli equation to relate pressure and velocity, and obtain the peak systolic pressure gradient between the RA and the RV. However, if the beam is not perfectly in line with the TR jet, the gradient is underestimated. IVC collapsibility is often used to estimate the right atrial pressure, despite a compelling pool of literature demonstrating the inaccuracies of this practice.¹ The estimated RA pressure to the peak pressure gradient between the RA and RV in order to obtain the RV systolic pressure pressure. The net is a dubious, rough estimate of the pulmonary artery systolic pressure.

    While right heart catheterization is the gold standard for the diagnosis of pulmonary hypertension, echocardiography can suggest the possibility that your patient has pulmonary hypertension. The European Society of Cardiology and European Respiratory Society’s joint 2015 Guidelines on the Diagnosis and Treatment of Pulmonary Hypertension acknowledge the limitations of echocardiography for the diagnosis of pulmonary hypertension.²

     

     

    Nuts and bolts:

    First, you need to find a view that gives you a tricuspid regurgitation jet which is parallel to the doppler beam. This can be done from the apical 4 chamber view, but you’re often going to be off axis. The next-level move is to obtain the right ventricular inflow view. You first obtain the parasternal long axis view, and then tilt the tail of the probe towards the patient’s left shoulder.

    PARASTERNAL LONG AXIS VIEW 

    RV INFLOW VIEW

    Here’s an echo clip alternating between the parasternal long axis and RV inflow views

    Now, once you’ve got the RV inflow view, try to get the TR jet lined up with the continuous wave doppler beam

     

    The negative velocities (those traveling away from the probe) represent the TR jet. When you measure the peak velocity (3.3 m/sec), most cardiac packages will also give you the peak gradient. This represents the pressure gradient between the RA and RV (in this case 44 mmHg).

    A TR jet with a peak velocity above 2.9 m/s suggests the patient probably has pulmonary hypertension, and a TR jet above 3.4 m/s suggests they almost definitely have pulmonary hypertension.  At 3.3 m/s, this patient’s probability of having pulmonary hypertension is quite high. In the right clinical context, this could be a critical data point.

    References

    1. Magnino, Corrado, et al. “Inaccuracy of Right Atrial Pressure Estimates Through Inferior Vena Cava Indices.” American Journal of Cardiology 120.9 (2017): 1667-1673.

    2. Galiè, Nazzareno, et al. “2015 ESC/ERS guidelines for the diagnosis and treatment of pulmonary hypertension: the Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT).” European heart journal 37.1 (2015): 67-119.