Transthoracic doppler-echocardiography (TTE)
TTE is a non-invasive screening test for patients with suspected PH. TTE estimates pulmonary artery systolic pressure (sPAP) and may provide additional information about the cause and consequences of PH. The estimation of PAP is based on the peak velocity of the jet of tricuspid regurgitation. The simplified Bernoulli equation describes the relationship of tricuspid regurgitation velocity and the peak pressure gradient of tricuspid regurgitation = 4 x (tricuspid regurgitation velocity). Estimation of PA systolic pressure require to take into account right atrial pressure (PA systolic pressure = tricuspid regurgitation pressure gradient + estimated right atrial pressure). Right atrial pressure cannot be measured and is estimated based on the diameter and respiratory variation of the inferior vena cava [15]. An alternative approach to echocardiographic diagnosis of PH is based on the comparison of tricuspid regurgitation velocity with values reported in a healthy population. Ideally, the influence of age, sex and body mass should be taken into consideration [187]. This method avoids cumulative error but is less directly linked to the accepted hemodynamic definition of PH based on mPAP [15].
Other echocardiographic variables that might raise or reinforce suspicion of PH independently of tricuspid regurgitation velocity should always be considered. They include an increased velocity of pulmonary valve regurgitation and a short acceleration time of RV ejection into the PA. Increased dimensions of right heart chambers, abnormal shape and function of the interventricular septum, increased RV wall thickness, pericardial effusion and dilated main PA are also suggestive of PH, but these signs are considered to be related to the hemodynamic severity [15].
Besides identification of PH, TTE also allows a differential diagnosis of the possible causes of pulmonary hypertension. TTE can recognize left heart valvular diseases and myocardial diseases responsible for post-capillary PH, and congenital heart diseases with systemic-to-pulmonary shunts. The venous injection of agitated saline can help to identify patent foramen ovale or small sinus venosus type atrial septal defects. Transesophageal echocardiography is rarely required in the setting of PH.