Echocardiographic assessment of pulmonary hypertension

A standard operating procedure for the echocardiographic assessment of pulmonary hypertension (PH) has recently been updated and published online.

The echocardiographic protocol has been developed by a group of physicians with expertise in both cardiology and PH, and is supported by the British Society of Echocardiography (BSE). The interactive e-book, complete with pictures and videos, aims to provide a standard operating procedure for the echocardiographic assessment of PH and guidance on the interpretation of the results. 

Click here to view the e-book.

Dr Luke Howard and Dr Athanasios Charalampopoulos, the Project Directors, have provided a summary of the latest guidance.

Dr Luke Howard
Consultant Pulmonologist
National Pulmonary Hypertension Service (London)
Hammersmith Hospital, Imperial College Healthcare NHS Trust, London
St Bartholomew's Hospital, Barts Healthcare NHS Trust, London

Dr Athanasios Charalampopoulos
Consultant Cardiologist with a Special Interest in Pulmonary Hypertension
Pulmonary Vascular Disease Unit
Royal Hallamshire Hospital, Sheffield

A detailed echocardiographic assessment is required in all patients where PH is suspected, not just to identify the condition, but also to detect any underlying contributing pathology. As well as playing a crucial role in diagnosis, echo can assess the severity of right ventricular (RV) dysfunction, provide prognostic information and act as a non-invasive means of evaluating disease progression.

"Echocardiography raises the suspicion of PH and may help to identify its underlying cause, such as left heart or congenital heart disease"

Dr Athanasios Charalampopoulos, Sheffield Pulmonary Vascular Disease Unit

The criteria form guides, not rules, and the Echocardiographer should use their judgement in whether further assessment is required. While echo can estimate pressures in the heart and lungs, the final diagnosis of PH can only be made by right heart catheterisation, since this provides an accurate measurement of pulmonary arterial and wedge pressures.

Measuring the RV

In PH, the RV becomes dilated, hypertrophied and there is impairment in its contractile function.

In response to the pressure loading from the increased pulmonary artery pressure, one of the first changes in the RV is progressive dilatation. This can be assessed in the parasternal long axis view, where normally the RV would be one-third of the size of the left ventricle (LV). Chronically raised RV afterload results in hypertrophy of the RV walls. The free wall thickness, normally <0.5 cm, can be measured in the subcostal view. The interventricular septum can also be seen to flatten or bow into the LV. This is demonstrated in image B below. 

Figure 1. The normal configuration of the RV and LV (A) and the changes seen in PH (B)

Measuring pressures

Right atrial (RA) pressure can be estimated from the size and motion of the inferior vena cava (IVC) during respiration. 

The normal diameter of the IVC at end-expiration is 1.5 to <2.1 cm; this should collapse by at least 50% with a sniff or 20% with quiet inspiration. Dilatation of the IVC or failure of the IVC to collapse with respiration is associated with higher RA pressures. 

Video 1. Subcostal view of the IVC

The tricuspid regurgitant velocity (TRV) can be used to estimate the RV systolic pressure (RVSP).

The peak TRV is derived from the measurement of the tricuspid regurgitant jet using continuous-wave Doppler. The velocity reflects the difference in pressure between the RV and the RA, and provides an estimate of the RVSP. As long as there is no pulmonary valve stenosis, the RVSP reflects the pressure in the pulmonary arteries. When TRV cannot be measured, the pulmonary artery end-diastolic pressure and mean pressure can be estimated instead. 

Measuring volumes

The RA and RV areas can be measured to determine the volume of the chambers.

The RA area is measured in the apical four-chamber view or from the subcostal view. RA area should be measured at end-systole, when the maximal volume is reached. 

The RV fractional area change, measured in the apical four-chamber view, is a way of assessing RV systolic function. It is calculated as the difference in end-diastolic area and end-systolic area divided by the end-diastolic area. This measure has been shown to correlate with prognosis and response to treatment in PH. 

Measuring function

There are several ways of assessing the severity of RV dysfunction.

The RV function can be evaluated with different echo measures. The methods of obtaining these are explained in detail in the full protocol.

> Myocardial performance index (MPI) – a combination of systolic and diastolic measurements
> S’ wave velocity – tissue Doppler imaging of the S’ waveform
> Isovolumic relaxation time – time from pulmonary valve closure to tricuspid valve opening
> Tricuspid annular plane systolic excursion (TAPSE) – movement reflecting base to apex shortening of the RV in systole
> RV dP/dt – index of RV contractility and systolic function

Video 2. Measurement of RV dP/dt

Echo combined with pulsed-wave Doppler imaging can be used to measure cardiac output, stroke volume and pulmonary vascular resistance. These measurements can also provide information on function, but are not considered mandatory in the protocol.

ASSESSING PROGNOSIS AND SEVERITY WITH ECHO

Studies have shown that increasing RA area, TAPSE and the presence of pericardial effusion are associated with poor prognosis. While echo can provide valuable information on prognosis, it should always be combined with the presence of other clinical indicators such as functional class, haemodynamics and exercise capacity. Click here to read more about the assessment of prognosis in PAH.

"Echocardiography can provide a non-invasive assessment of cardiopulmonary haemodynamics and right ventricular function, making it an essential tool in the follow up of PH"

Dr Luke Howard, National Pulmonary Hypertension Service (London)

Table 1. Normal and abnormal values for the RV and pulmonary circulation

This table shows the full list of normal and abnormal reference values for the RV and pulmonary circulation that are described in the full protocol. The online e-book also contains images, videos and patient case studies to support your learning. To view the full protocol please click here.

The lead author of the 2018 British Society of Echocardiography guidelines on pulmonary hypertension, Dr Daniel Augustine, has also provided a summary of the latest advice on the echocardiographic assessment of patients. Click here to learn more.

References

  1. Imperial College Healthcare NHS Trust (2018). Echocardiographic Assessment of Pulmonary Hypertension: Standard Operating Procedure. Available from: http://www.echoprotocol.co.uk

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