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Sep 19, 2012

Echocardiography diagnosis of pulmonary hypertension (PH)


In this article we will discuss how echo is used to diagnose pulmonary hypertension, and  also limitation of echo, as diagnosis of PH by definition is to be made with help of right heart catheterization and by assessing mean pulmonary pressure (more than 25mmhg), but with echo we usually asses systolic pressure.
To diagnose Pulmonary hypertension (PH) peak tricuspid regurgitation (TR) velocity is used.
With help of simplified Bernoulli equation peak pressure gradient of tricuspid regurgitation is calculated

Peak pressure gradient of tricuspid regurgitation = 4 X (tricuspid regurgitation velocity)2

Pulmonary artery systolic pressure is obtained by adding RA pressure to peak pressure gradient of tricuspid regurgitation, which is calculated by IVC diameter and inspiratory collapse

If peak tricuspid regurgitation velocity is difficult to measure due to trivial/mild tricuspid regurgitation, than use of contrast echocardiography (e.g. agitated saline), this significantly increases the Doppler signal, thus allowing proper measurement of peak tricuspid
regurgitation velocity.

Pulmonary hypertension is defined as mean pulmonary pressure more than 25mmhg so to convert echo derived systolic pulmonary Pressure in to mean pressure see below

“Theoretically calculation of mean pulmonary artery pressure (PAP), from PA systolic pressure is possible i.e. (mean PAP= 0.61 X PA systolic pressure + 2 mmHg)”
Echo assessment of PH

In patient with severe TR systolic pressure by echo leads underestimation of pulmonary pressure.

In most patients, systolic pressure by TR and echo is overestimation by 10mmhg

In diagnosing PH other variable by echo can used to reinforce diagnosis but these have decreased sensitivity as they manifest later in PH
·        RV ejection time into the PA
·        Increased dimensions of right heart chambers
·        Abnormal shape and function of the interventricular septum.
·        Increased RV wall thickness.
·        Dilated main PA

Keeping in mind limitation of echo in assessing PH, one may group PH into three groups  i.e. unlikely PH, possible PH and likely PH in order of increasing specificity of diagnosis of PH.

TR peak velocity is grouped into three groups less than 2.8 m/s, 2.9-3.4 m/s and more than 3.4 m/s.
1.     If TR velocity is more than 3.4 m/s, one can make confident likely diagnosis of PH with or without other echo finding of PH.
2.     If TR velocity is less than 2.8 m/s than PH is unlikely, but if other echo finding of PH are present one may consider possibility of PH.
3.     If TR velocity is between 2.9 to 3.4 m/s than with without other echo findings PH is possible.


Arbitrary criteria for estimating the presence of PH based on tricuspid regurgitation peak velocity and Doppler-calculated PA systolic pressure at rest (assuming a normal right atrial pressure of 5 mmHg) and on additional echocardiographic variables suggestive of PH


Class
level
Echocardiographic diagnosis: PH unlikely
Tricuspid regurgitation velocity less  than 2.8 m/s, PA systolic pressure less than 36 mmHg, and no additional  echocardiographic variables suggestive of PH
1
B
Echocardiographic diagnosis: PH Possible
Tricuspid regurgitation velocity less than 2.8 m/s, PA systolic pressure less than 36 mmHg, but presence of additional echocardiographic variables suggestive of PH

IIa
C
Echocardiographic diagnosis: PH Possible
Tricuspid regurgitation velocity 2.9–3.4 m/s, PA systolic pressure 37–50 mmHg with/without additional echocardiographic variables suggestive of PH
IIa

C
Echocardiographic diagnosis: PH likely
Tricuspid regurgitation velocity more than 3.4 m/s, PA systolic pressure  more than 50 mmHg, with/without additional echocardiographic variables suggestive of PH
I
B