Cardiovascular Imaging

Pulmonary arterial hypertension

(PAH), peak systolic and mean pressure exceeding 30 and 20 mmHg, respectively. Pulmonary arterial pressure can increase acutely and reversibly in response to hypoxia and excessive pulmonary blood flow. PAH is divided into primary (idiopathic) and secondary forms. Primary PAH occurs most frequently in young women; it may be intensified in the postpartum period and has been linked to oral contraceptives. It has also been linked to collagen vascular disease. Secondary PAH is due to a variety of aetiologies which can be classified into several types: increased resistance to pulmonary venous drainage such as increased left ventricular diastolic pressure, left atrial hypertension and pulmonary venous obstruction; increased resistance to flow through the pulmonary arterioles and capillaries such as in chronic lung disease, pulmonary arteritis and Eisenmengers syndrome; increased resistance to flow in the large pulmonary arteries such as in pulmonary thromboembolism, pulmonary arterial hypoplasia, and peripheral pulmonary arterial stenoses; and chronic hypoventilation such as occurs with Pickwickian syndrome.

Chest X-ray demonstrates enlargement of the main and central pulmonary arteries. Most severe pulmonary enlargement tends to occur in Eisenmenger's syndrome. Long-term PAH may be associated with calcification of the central pulmonary arteries (Fig.1). Right ventricular and atrial enlargement are frequently shown, especially with significant tricuspid regurgitation. Echocardiography demonstrates enlargement and hypertrophy of the right ventricle. Doppler echocardiography can estimate peak pulmonary artery pressure by measuring the peak velocity of the tricuspid regurgitant jet and using the modified Bernoulli equation. Perfusion nuclear scans of the lungs and contrast-enhanced spiral CT can be used to exclude chronic thromboembolism as the aetiology of PAH. Cardiac catheterization with oximetry, echocardiography and MRI are used to exclude Eisenmengers syndrome. MRI and electron beam CT depict the severity of right-sided chamber enlargement and right ventricular hypertrophy (Fig.2).

CBH

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Fig.1

Chest radiograph shows severe enlargement of the main and central pulmonary arterial segments with calcification (arrows) in the right and left pulmonary arteries in a patient with Eisenmenger atrial septal defect.
Pulmonary arterial hypertension, Fig.1
Pulmonary arterial hypertension, Fig.2