Pulmonary Arterial Hypertension (PAH)

Several imaging tests are available to help complete an initial diagnostic evaluation of patients with pulmonary arterial hypertension (PAH). PAH testing tools include chest radiography, computed tomography (CT), electrocardiography (ECG), and transthoracic echocardiography.

Chest Radiography

Chest radiography, which uses electromagnetic waves to create images of the structures around the chest, reveals abnormalities at the time of diagnosis in about 90% of patients with idiopathic PAH. Abnormalities include central pulmonary arterial dilatation and loss of the peripheral blood vessels. Enlargement of the right atrium (RA) or right ventricle (RV), particularly in advanced cases, can also be observed on the chest radiograph. It may assist in differential diagnosis by revealing alterations suggestive of lung disease or left heart disease (pulmonary venous congestion). It may also help in differentiating between arterial and venous pulmonary hypertension (PH) by showing increased artery to vein ratio in arterial PH while decreased artery to vein ratio in venous PH; however, a normal chest radiograph does not exclude PAH. Further, the extent of abnormalities revealed by the chest radiograph does not correlate with the degree of PAH.^1,2

Computed Tomography

Computed tomography of the chest is an easy, reproducible and widely available procedure that provides important information about abnormalities in the lung parenchyma, blood vessels, heart, and mediastinum. If the CT imaging shows enlargement of the pulmonary artery (PA) or RV or RA, it is suggestive of PH. Computed tomography may also assist in differentiating PH because of lung disease that is indicated by the concomitant presence of lung parenchymal disease. In specialized centers, CT angiography may be used for the evaluation of chronic thromboembolic pulmonary hypertension. It can also provide clues about the form of PAH, such as the presence of esophageal dilation in systemic sclerosis, or congenital cardiac defects, such as anomalous pulmonary venous drainage.

Pulmonary hypertension is suggested by CT imaging if PA diameter is increased (≥29 mm) and ratio of PA diameter to aortic diameter is increased (≥1). A high ratio of segmental artery to bronchus >1:1 in 3 or 4 lobes is considered highly specific for PH. High-resolution CT is useful when pulmonary veno-occlusive disease is clinically suspected. Findings on CT are interstitial edema with diffuse central ground-glass opacity and thickened interlobular septa, along with lymphadenopathy or pleural effusions in some cases. Diffuse bilateral thickening of the interlobular septa and the presence of small, centrilobular, poorly circumscribed nodular opacities on the CT scan are suggestive of pulmonary capillary hemangiomatosis. Ground-glass abnormalities are observed in more than one-third of patients with PAH.^1,3

Electrocardiography

Electrocardiography, measurement of the electrical impulses generated by the heart muscle using electrodes attached to the patient’s skin, may provide supportive evidence of PH; however, a normal ECG does not exclude the diagnosis, and an abnormal ECG is more probable in severe PAH. Electrocardiography may reveal abnormalities such as right bundle branch block, right axis deviation, RV hypertrophy, RV strain, P pulmonale, and QTc prolongation. Right ventricular strain has been found to be more sensitive as a screening tool than RV hypertrophy. Severe disease is suggested by prolongation of the QRS complex and QTc. It may also assist in differential diagnosis of anterolateral myocardial ischemia, which is indicated by changes in the lateral and inferior leads. Supraventricular arrhythmias, such as atrial flutter and atrial fibrillation, can occur in advanced disease.^1,3

Transthoracic Echocardiography

Transthoracic echocardiography, a procedure that takes an ultrasound of the heart using a probe placed on the patient’s chest, is used to assess effects of PH on the heart function and estimate the pressure in the right heart. Peak tricuspid regurgitation velocity (TRV) is one of the most important parameters of echocardiography that allows an estimate of the pulmonary artery systolic pressure (PASP). Even mild elevations in PASP have been found to be associated with poor outcomes.

The sixth World Symposium on Pulmonary Hypertension recommends the use of TRV together with additional echocardiographic variables to assess the presence or absence of PH.

These additional echocardiographic parameters include measurements from the pulmonary artery (eg, reduced RV outflow tract acceleration time, elevated early diastolic pulmonary regurgitation velocity), ventricles (eg, RV/left ventricle basal diameter ratio >1, flattening of the interventricular septum), or increase in inferior vena cava diameter or RA area. These additional signs provide an assessment of the RV size and pressure overload, the pattern of blood flow velocity out of the RV, the diameter of the PA, and an estimate of RA pressure.^1,3

Pulmonary Arterial Hypertension Staging

The clinical staging of PAH is classified according to the revised World Health Organization functional classification (FC) system that was adapted from the New York Heart Association FC system. Patients with PAH are classified into 4 FCs according to the severity of symptoms and impact on day-to-day activities.⁴

Class I

In this FC, patients have no limitation of physical activity. Symptoms such as dyspnea, fatigue, chest pain, or near-syncope do not occur because of ordinary physical activity.

Class II

In this FC, patients have slight limitations of physical activity. They are comfortable at rest, but ordinary physical activity (such as climbing stairs or making a bed) causes undue dyspnea or fatigue, chest pain, or near-syncope.

Class III

The patients in this FC have marked limitations of physical activity. They are comfortable at rest, but even less-than-ordinary activity causes undue dyspnea, fatigue, chest pain, or near-syncope.

Class IV

In this FC, patients are unable to perform any physical activity without symptoms. These patients manifest signs of right heart failure. Symptoms such as dyspnea or fatigue may be present even at rest. Any physical activity can lead to increased discomfort.

References

1. Galiè N, Humbert M, Vachiery J-L, et al. 2015 ESC/ERS guidelines for the diagnosis and treatment of pulmonary hypertension. Eur Heart J. 2016;37(1):67-119. doi:10.1093/eurheartj/ehv317
2. Milne EN. Forgotten gold in diagnosing pulmonary hypertension: the plain chest radiograph. Radiographics. 2012;32(4):1085-1087. doi:10.1148/rg.324125021
3. Sahay S. Evaluation and classification of pulmonary arterial hypertension. J Thorac Dis. 2019;11(Suppl 14):S1789-S1799. doi:10.21037/jtd.2019.08.54
4. Galiè N, Hoeper MM, Humbert M, et al. Guidelines for the diagnosis and treatment of pulmonary hypertension. Eur Respir J. 2009;34(6):1219-1263. doi:10.1183/09031936.00139009

Reviewed by Harshi Dhingra, MD, on 7/1/2021.

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Erum Naqvi, PhD

Erum Naqvi obtained her Ph.D. in Molecular Medicine from Hannover Medical School (Germany) after completing her Masters in Biomedical Science and Bachelors in Microbiology from University of Delhi (India). She has several years of experience as a science writer.