PH is a condition characterized by high blood pressure in the arteries of the lungs. This elevated pressure forces the right side of the heart, which pumps blood into the lungs, to work harder against increased resistance. Because the symptoms of PH, such as shortness of breath and fatigue, are often vague, initial testing is crucial. Echocardiography, or “echo,” is the primary non-invasive imaging method utilized by clinicians to screen for and monitor this condition. Echo findings guide the next steps in the diagnostic process, identifying individuals who require more definitive evaluation.
The Primary Role of Echocardiography in Screening
Echocardiography is the initial test for suspected PH because it is widely available, inexpensive, and easily repeatable. The technique provides a structural assessment using two-dimensional (2D) imaging and a functional assessment using Doppler technology to measure blood flow velocities. The main purpose of this initial screening is not to provide a final diagnosis, but to estimate the likelihood of PH being present. This estimation relies on detecting the hemodynamic and structural consequences high pressure imposes on the heart, helping determine which patients warrant invasive confirmation.
Estimating Pulmonary Artery Pressure Using Doppler
The most direct method for estimating pulmonary pressure involves analyzing blood flow across the tricuspid valve during systole, known as tricuspid regurgitation (TR). When TR occurs, a jet of blood flows backward from the high-pressure right ventricle into the right atrium. Continuous-wave Doppler measures the peak velocity (\(v\)) of this TR jet in meters per second.
This velocity is mathematically converted into a pressure gradient using the simplified Bernoulli equation (\(4v^2\)). This calculation yields the pressure difference between the right ventricle and the right atrium. To find the estimated Right Ventricular Systolic Pressure (RVSP), which serves as a proxy for the Pulmonary Artery Systolic Pressure (PASP), the estimated Right Atrial Pressure (RAP) is added to the gradient. RAP is estimated non-invasively by observing the size and collapsibility of the inferior vena cava.
A peak TR velocity of \(2.8\) meters per second or less suggests a low probability of PH. A velocity ranging from \(2.9\) to \(3.4\) meters per second indicates an intermediate probability. A TR velocity greater than \(3.4\) meters per second, corresponding to a pressure gradient over \(47\) mmHg, strongly suggests a high probability of PH. This process provides a non-invasive estimation of pressure, relying on an adequate TR signal and an estimated RAP.
Assessing Right Ventricular Structure and Function
Echocardiography provides detailed insight into how the right side of the heart is coping with the increased afterload imposed by PH. Because the right ventricle (RV) is designed for a low-pressure system, sustained high pressure causes structural changes. Early signs include thickening of the RV free wall (hypertrophy), followed by dilation or enlargement of the RV chamber as the pressure overload persists.
Chronic strain is often visible in the shape of the interventricular septum, the wall separating the right and left ventricles. High RV pressure can cause the septum to flatten or bulge into the left ventricle, known as “D-shaping.” Clinicians also use quantitative metrics to assess RV functional capacity, such as the Tricuspid Annular Plane Systolic Excursion (TAPSE). TAPSE measures the longitudinal movement of the tricuspid valve annulus during contraction, and a reduced value indicates impaired RV systolic function.
Speckle-Tracking Echocardiography measures RV longitudinal strain, quantifying the deformation in the heart muscle fibers. Strain values that are less negative indicate reduced myocardial shortening and are a sensitive marker of subtle RV dysfunction. These markers often provide prognostic information even when conventional measures like TAPSE are normal. The capacity of the RV to maintain its function is a major determinant of patient outcome in PH.
Moving Beyond Estimation: The Need for Definitive Diagnosis
Despite its utility in screening and monitoring, echocardiography cannot provide a definitive diagnosis of PH. The accuracy of the pressure estimate depends on obtaining a clear, measurable TR jet, which is not always possible due to poor acoustic windows or absent tricuspid regurgitation. Furthermore, the non-invasive estimation of right atrial pressure can be imprecise, introducing variability. Echo findings establish a probability of PH rather than a precise pressure measurement.
When the echocardiogram suggests a high probability of PH, or clinical suspicion remains strong, the next step is typically Right Heart Catheterization (RHC). RHC is the gold standard for diagnosis because it is an invasive procedure that directly measures pressures within the right heart chambers and pulmonary artery. This direct measurement of mean pulmonary artery pressure (mPAP) is required to formally confirm PH before treatment begins. RHC also allows calculation of hemodynamic variables, such as pulmonary vascular resistance, necessary to classify the type and severity of PH.