Persistent Pulmonary Hypertension of the Newborn (PPHN)
|Reviewed by Carl
Kuschel and Jon Skinner
Back to PPHN Guideline
Estimation of Pulmonary Artery Pressure (PAP) is
an important aspect of the diagnosis and treatment of Persistent Pulmonary
Hypertension of the Newborn (PPHN). There are a number of
echocardiographic indicators which help to directly or indirectly measure PAP.
- It is important to perform echocardiography
to exclude cyanotic
cardiac disease and to assess cardiac function.
- Infants with severe persistent hypoxaemia
should be assessed by an experienced paediatric echocardiographer.
- This is the most accurate way of determining PAP.
- The jet of blood leaking through the tricuspid
valve is interrogated with Doppler. The peak velocity of the tricuspid
regurgitation (TR) jet is a direct indicator of the right ventricular pressure
(and therefore PAP).
- Using the Bernoulli equation (p = 4v2,
where p is the pressure drop (mmHg) and v is the velocity of blood
flow (m/sec)), the pressure in the RV can be calculated by
RV pressure = RA pressure + (4 x (TR jet velocity)2).
on the thumbnail images to see a larger image
- The image to the left demonstrates an apical 4-chamber view of the heart.
- The chambers and valves are labelled (LA Left Atrium, MV Mitral Valve, LV Left
Ventricle, IVS Interventricular septum, RA Right Atrium, TV Tricuspid
Valve, RV Right Ventricle). The green wedge shape is the outline
of the colour Doppler field seen in the next image.
- In this image, colour Doppler has been applied.
- The TR jet is seen as the blue-yellow streak heading upwards away from the tricuspid valve.
- In this image, Doppler interrogation has been applied to determine the velocity of the TR jet.
- The velocity is in the region of 2.9 m/sec, giving a
gradient across the tricuspid valve of 34mmHg. This indicates that
that PAP is at least 34mmHg above RA pressure. The RA
pressure is generally assumed to be 5-10mmHg in ventilated infants.
- It is important to know the systemic blood pressure to determine whether PAP is above systemic BP.
- The direction and velocity of ductal blood flow can give useful information on PAP.
- Pure right-to-left flow indicates that PAP is higher than aortic pressure throughout the cardiac cycle.
- Bidirectional flow occurs when the aortic and pulmonary pressures are approximately equal. Flow is left-to-right
during diastole and right-to-left during systole (as the pulmonary arterial
pressure wave reaches the duct before the aortic pressure wave).
- Bidirectional flow is common in healthy babies in the first 12 hours but changes to pure left-to-right when aortic
pressures become higher than pulmonary pressures.
- This baby had severe PPHN (with RV
pressures calculated to be 74mmHg above RA pressure), although his
requirement for ventilatory support was minimal. The Doppler
gate is in the PDA. Left-to-right flow (above the line) and
right-to-left (below the line) are seen.
TPV/RVET Ratio and
- This ratio of Time to Peak Velocity
(TPV) of pulmonary blood flow and the Right Ventricular Ejection Time (RVET) can
indirectly indicate PAP.
- With PPHN, the TPV/RVET ratio falls as
there is a rapid acceleration of blood flow into the pulmonary artery
followed by an early deceleration of pulmonary blood flow from increased
pulmonary resistance. In severe cases, there can be a secondary
"notching" of the flow profile.
- In PPHN, the period of isovolumetric
contraction (between closure of the tricuspid valve and the opening of the pulmonary valve
- RPEP, Right Ventricular Pre-Ejection Period) is prolonged as the RV
generates enough pressure to open the pulmonary valve, resulting in an
elevated RPEP/RVET ratio.
- There can be poor repeatability of these measures but they do
have a role when you cannot measure the velocity of the TR jet.
- Some degree of right-to-left atrial shunting
through the patent foramen ovale is common, although it is rare for this to be
purely right-to-left (pure right-to-left flow is Totally
Anomalous Pulmonary Venous Drainage [TAPVD] till proven otherwise!).
- Bowing of the interatrial septum to the left is commonly seen.
- Right-to-left atrial shunting reflects right atrial filling (diastolic) pressure or ventricular filling more than right
ventricular systolic pressures.
on the thumbnail image to see a larger image
- Other shunts can be used to estimate RV pressure.
- The image to the left
demonstrates a subcostal view of the heart focusing on the
interventricular septum. This baby did not have a duct, nor
any evidence of tricuspid regurgitation from which to estimate RV
pressure. However, he was found to have a small VSD (seen as
the reddish shape in the middle of the "wedge"). The
redness of the image demonstrates left-to-right flow through the small
VSD at the point in time that the image was taken.
- Doppler interrogation of the flow through the VSD
demonstrated pure left-to-right flow, and the peak velocity was 2.2
m/sec. This indicated that the peak LV pressure was at least
19 mmHg above RV pressure.
Cardiac Function and Output
- Elevated PAP is generally associated with decreased pulmonary blood flow and increased pulmonary vascular resistance.
- Not uncommonly, there is enlargement of the RV and RA, as well as the main pulmonary artery.
- There may be flattening or even bowing of the
interventricular septum to the left if RV pressures exceed LV pressures.
- As cardiac output is dependent on venous return to the RA and LA, cardiac output (both RVO and LVO) is frequently reduced with PPHN.
- Severe PPHN may be associated with LVO below 100ml/kg/min (normal 150-300ml/kg/min)
- Quantitative assessment of cardiac function may assist with
decisions and assessments of the roles of inotropes, inhaled nitric oxide, and other
interventions affecting cardiac output.
- If the LA and LV appear under-filled, it is critical to exclude TAPVD.
|Click on the images to the
left to see larger images
- TAPVD can be missed when assessing infants with
presumed PPHN. The top images on the left are taken in the
parasternal long axis view. The RV is anterior to the
LV. The ascending aorta is labelled as AO. The RV is
enlarged and the LV is underfilled and "squashed".
This is common in severe PPHN.
- However, the lower image shows the apical 4-chamber
view. The RA and RV are grossly dilated, the LV is small, and
another structure - the pulmonary venous chamber, PVC, - is
seen (usually not as obviously as in this image).
- The PVC represents the confluence of the
abnormal pulmonary veins draining into the systemic venous
circulation (which can be at the level of portal vein, coronary
sinus, RA directly, or to an ascending vertical vein and then
- Demonstration of a left-to-right shunt at atrial
level essentially excludes TAPVD
|Skinner J, Alverson D, Hunter S (eds).
Echocardiography for the neonatologist. Churchill