Dr Daniel Augustine is Consultant Cardiologist at Royal United Hospital, Bath and Honorary Consultant Cardiologist at The Bristol Heart Institute. He is the current national guideline lead for the British Society of Echocardiography (BSE). Dr Augustine is also part of the regional pulmonary hypertension (PH) service in Bath, which runs in collaboration with the Royal Free Hospital, London, and he was recently lead author of the 2018 BSE guidelines on PH.
PH is defined as a mean arterial pressure of ≥25 mmHg at rest, as confirmed by right heart catheterisation. PH can complicate many diseases affecting different systems in the body, for example, cardiovascular (e.g. heart valve disease), respiratory (e.g. airways disease or pulmonary emboli) and connective tissue disease (e.g. systemic sclerosis).1 If left untreated, morbidity and mortality levels are high,2 therefore accurate and prompt diagnosis is crucial.
The diagnosis of PH requires a clinical suspicion based on symptoms, medical history, physical examination and review of a rigorous set of investigations. Echocardiography is a key imaging modality in the assessment of patients with suspected or known PH.3
The right side of the heart has two valves: the tricuspid valve, allowing blood to flow between the right atrium and right ventricle, and the pulmonary valve, allowing blood to flow between the right ventricle and the pulmonary arteries to the lungs.
Traditionally, the pulmonary arterial systolic pressure (PASP) has been estimated by echocardiography. If there is no obstruction to the pulmonary valve then, in theory, the pressure in the pulmonary arteries should be equivalent to the right ventricular systolic pressure (RVSP).4
With each contraction of the heart, there will be some blood flow back across the tricuspid valve, from the right ventricle to the right atrium. This is called tricuspid regurgitation. The speed and pressure of tricuspid regurgitation can be estimated with continuous-wave Doppler echocardiography and is called the peak tricuspid regurgitation velocity (TRV).4
Left image: Tricuspid regurgitation on echocardiography; Right image: Measuring the peak TRV on continuous-wave Doppler echocardiography. Reproduced with permission from Augustine, Echo Res Pract. 20183. Click to access the full guidelines
When peak TRV is added to right atrial pressure, as shown in the Bernoulli equation, this gives an approximate RVSP, which is equivalent to the PASP.4
RVSP = 4(TRV)2 + right atrial pressure
When assessing the probability of PH, the measurement of TRV should be used in conjunction with other echocardiographic markers of PH.3
Over time, we have seen that estimating the PASP using the Bernoulli equation, which combines peak TRV and right atrial pressure, may not be the most accurate way to assess the presence and severity of PH.
Previous studies have demonstrated good correlation across patient populations, but only moderate precision of absolute pulmonary artery systolic pressure values calculated from tricuspid regurgitation.5,6 This is important since, in an individual patient, significant under or over estimation of the TRV can occur, leading to misdiagnosis and inappropriate treatment.7
Potential errors may occur if the Doppler signal is poor or there is only a small amount of regurgitation present. There can also be errors when assessing right atrial pressure.3 Studies have shown that PH can be present even with the absence of tricuspid regurgitation.8
Figure 1: Flow chart to assess the probability of PH using parameters identified from ≥2 categories (the ventricles, pulmonary artery or the inferior vena cava and right atrium)
The flow chart, depicted in Figure 1, demonstrates how the echocardiographic probability of PH is assessed. This method, described by the joint European Society of Cardiology and European Respiratory Society (ESC/ERS) guidelines, is endorsed by the BSE.1,3 The first step in assessing the probability of PH is to measure peak TRV. If this is a good quality signal and is greater than 3.4 m/s, there is a high probability that PH is present. If the peak TRV is below 3.4 m/s, the probability of PH is assessed by evaluating for the presence of other echocardiographic markers. These markers fall into three categories. Echocardiographic markers from at least two different categories are needed to help assign the probability of PH.
Table 1: Echocardiographic signs used to help grade the probability of PH. Adapted from Galiè, Eur Heart J 2016.1 (aEchocardiographic parameters from at least two different categories (A/B/C) from the list should be present to alter the level of echocardiographic probability of PH.)
This animation, based on the joint ESC/ERS guidelines, explains how to determine the probability of PH in a patient and describes the different echo signs above in more detail.
While echocardiography can be used as a screening tool to estimate the probability of PH in a patient, confirmation with right heart catheterisation is needed for a definitive diagnosis of PH, particularly if pre-capillary PH specific therapies may be indicated.3
Right heart catheterisation may be associated with complications and patients should be referred to a specialist PH centre to have this procedure.1
Click here (link is external) to view the full BSE guidelines for the assessment of PH. The protocol aims to outline a practical approach to assessing the probability of PH and should be used in conjunction with the previously published minimum dataset for a standard echo.
October 2020 | EM-42933