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Diagnostic Evaluation

A high index of suspicion, a meticulous history and a careful physical examination are paramount to the diagnosis of pulmonary hypertension. Particular attention should be given to previous medical conditions, drug use (legal and illegal) and family history. In addition, all systems should be carefully reviewed. Commonly, suspicion is increased by the presence of increasing dyspnea on exertion in a patient with a known cause of pulmonary hypertension.

FIGURE 1. Electrocardiogram demonstrating the changes of right ventricular hypertrophy (long arrow) with strain in a patient with primary pulmonary hypertension. Right axis deviation (short arrow), increased P-wave amplitude in lead II (black arrowhead), and incomplete right bundle branch block (white arrowhead) are highly specific but lack sensitivity for the detection of right ventricular hypertrophy.12

In pulmonary hypertension, the electrocardiogram (ECG) may demonstrate signs of right ventricular hypertrophy, such as tall right precordial R waves, right axis deviation and right ventricular strain (Figure 1). The higher the pulmonary artery pressure, the more sensitive is the ECG.¹² The chest radiograph is inferior to the ECG in detecting pulmonary hypertension, but it may show evidence of underlying lung disease¹² (Figure 2). Not infrequently, recognition of pulmonary hypertension begins with the discovery of right ventricular hypertrophy on the ECG or prominent pulmonary arteries on the chest radiograph.

Patients with signs, symptoms or electrocardiographic or radiographic findings suggestive of pulmonary hypertension

In addition to arterial blood gas analysis, exercise and overnight oximetry should be used to determine if supplemental oxygen might benefit a patient with pulmonary hypertension.

should undergo two-dimensional echocardiography with Doppler flow studies. Echocardiography is the most useful imaging modality for detecting pulmonary hypertension¹³ and excluding underlying cardiac disease. Confirmation of pulmonary hypertension is based on identification of tricuspid regurgitation. The addition of mean right atrial pressure to the peak tricuspid jet velocity gives an accurate noninvasive estimate of peak pulmonary pressure. Right ventricular dilatation and hypertrophy are late findings.

All patients with documented pulmonary hypertension should undergo a comprehensive laboratory evaluation to clarify the etiology. The goal is to identify or exclude treatable causes. Initial tests include complete blood count, prothrombin time, partial thromboplastin time, hepatic profile and autoimmune panel (if this panel is suggested based on the history or physical examination). HIV testing should be considered in all patients, especially those with a compatible history or risk factors.

Arterial blood gas analysis should be performed to exclude hypoxia and acidosis as contributors to pulmonary hypertension. It is important to note that normal resting oxygenation does not exclude exertional or nocturnal oxygen desaturation. Approximately 20 percent of patients with COPD and normal awake arterial oxygen tensions have nocturnal nonapneic oxygen desaturation.¹⁴ Elevations of pulmonary artery pressure during transient oxygen desaturation are due to increases in pulmonary vascular resistance and cardiac output. These episodes are ameliorated with supplemental oxygen. Therefore, exercise and overnight oximetry should also be performed in all patients with pulmonary hypertension.

FIGURE 2. Anatomy of the thorax, along with indication of the upper limits of normal pulmonary vascular dimensions. A right interlobar pulmonary diameter of greater than 16 mm or a hilar-to-thoracic ratio of greater than 0.44 is specific but not sensitive for the diagnosis of pulmonary hypertension.12

Pulmonary function tests are necessary to establish airflow obstruction or restrictive pulmonary pathology. Unless hypoxia is present, pulmonary hypertension cannot be attributed to these disorders until pulmonary function is severely reduced. Computed tomographic (CT) scanning of the chest with high-resolution images is useful for excluding occult interstitial lung disease and mediastinal fibrosis when the pulmonary function tests and chest radiograph are nondiagnostic.

If the cause of the pulmonary hypertension remains unexplained, chronic thromboembolism should be excluded before the diagnosis of primary pulmonary hypertension is accepted. Fortunately, ventilation-perfusion lung scanning is a reliable method for differentiating chronic thromboembolism from primary pulmonary hypertension. The finding of one or more segmental or larger perfusion defects is a sensitive marker of embolic obstruction. In primary pulmonary hypertension, the ventilation-perfusion scan is normal or demonstrates patchy subsegmental abnormalities.¹⁵

If the ventilation-perfusion scan suggests the presence of chronic thromboembolism, pulmonary angiography can be performed safely to confirm the diagnosis, define the extent of disease and evaluate the need for surgical thromboendarterectomy.¹⁶ The role of helical CT scanning of the pulmonary arteries remains unclear. This imaging technique has high specificity but undefined sensitivity for the diagnosis of pulmonary embolism.¹⁷

Cardiac catheterization should be performed in patients with unexplained pulmonary hypertension, and remains the gold standard for its diagnosis and quantification. Catheterization is particularly useful in diagnosing occult shunts, congenital heart disease and distal pulmonary artery stenosis.

An algorithm for the evaluation of suspected pulmonary hypertension is provided in Figure 3.

Evaluation of Suspected Pulmonary Hypertension FIGURE 3. Algorithm for the evaluation of a patient with suspected pulmonary hypertension.