How is pulmonary hypertension diagnosed?

Diagnosis of Pulmonary Hypertension

Pulmonary hypertension is definitively diagnosed by right heart catheterization showing mean pulmonary arterial pressure ≥25 mmHg at rest, but the diagnostic pathway begins with echocardiography as the first-line screening tool when PH is clinically suspected. 1

Initial Clinical Suspicion

Suspect PH in patients presenting with:

• Unexplained dyspnea on exertion (most common symptom) that is disproportionate to underlying disease 1, 2
• Syncope, particularly with exertion, indicating severely compromised cardiac output 2
• Rapidly progressive symptoms including fatigue, weakness, and abdominal distension 2

Physical examination findings that raise suspicion include:

• Accentuated pulmonary component of S2 (loud P2) - most consistently associated sign with PAH 2
• Left parasternal lift (RV heave) indicating right ventricular hypertrophy 2
• Pansystolic murmur of tricuspid regurgitation 2

Diagnostic Algorithm

Step 1: Echocardiography (First-Line Test)

Transthoracic Doppler echocardiography is recommended as the first-line non-invasive diagnostic investigation when PH is suspected 1, with sensitivity of 79-100% and specificity of 68-98% for detecting moderate PH 2.

Echocardiography assesses:

• Estimated pulmonary artery systolic pressure
• Right ventricular size and function
• Structural left heart abnormalities (valvular disease, left atrial enlargement, left ventricular dysfunction) 1
• Signs suggesting specific PH etiologies 1

Step 2: Identify the Underlying Cause

Once echocardiography shows high or intermediate probability of PH, perform comprehensive evaluation to determine PH group:

Essential baseline investigations include: 1

• Clinical history, symptoms, signs, ECG
• Chest radiograph
• Pulmonary function tests with DLCO 1
• Arterial blood gas analysis 1
• High-resolution CT of the chest 1

Mandatory screening tests: 1

• Ventilation/perfusion (V/Q) or perfusion lung scan is recommended in all patients with unexplained PH to exclude chronic thromboembolic PH (CTEPH) 1
• Routine biochemistry, hematology, immunology, HIV testing, and thyroid function tests 1
• Abdominal ultrasound for screening of portal hypertension 1

Step 3: Specialized Imaging When Indicated

Contrast CT angiography of the pulmonary artery is recommended in the workup of patients with CTEPH 1, as it can delineate complete obstruction, bands, webs, and intimal irregularities 1.

High-resolution CT provides critical information for:

• Identifying interstitial lung disease or emphysema (Group 3 PH) 1
• Detecting pulmonary veno-occlusive disease (PVOD) - look for diffuse central ground-glass opacification, thickening of interlobular septa, lymphadenopathy 1, 3
• Assessing pulmonary artery diameter (≥29 mm suggests PH) 1

Pulmonary angiography should be considered in the workup of patients with CTEPH 1 to identify those who may benefit from pulmonary endarterectomy 1.

Step 4: Right Heart Catheterization (Definitive Diagnosis)

Right heart catheterization is mandatory to confirm the diagnosis of PH and define hemodynamic characteristics 1, 4.

Hemodynamic criteria for PH diagnosis:

• Mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest 1, 4
• Pre-capillary PH: PAWP ≤15 mmHg AND PVR >3 Wood units 1
• Isolated post-capillary PH: PAWP >15 mmHg AND PVR ≤2 Wood units 4
• Combined post- and pre-capillary PH: PAWP >15 mmHg AND PVR >2 Wood units 4

RHC also measures cardiac output, pulmonary vascular resistance, and allows vasoreactivity testing when indicated 1.

Clinical Classification After Diagnosis

Once PH is confirmed hemodynamically, classify into one of five clinical groups 1:

1. Pulmonary arterial hypertension (PAH) - requires pre-capillary PH with PVR >3 Wood units, excluding other causes 1
2. PH due to left heart disease - most common cause in the United States 5
3. PH due to lung diseases and/or hypoxia - including COPD, interstitial lung disease 1
4. Chronic thromboembolic PH (CTEPH) - identified by V/Q scan and CT angiography 1
5. PH with unclear/multifactorial mechanisms 1

Critical Pitfalls to Avoid

Open or thoracoscopic lung biopsy is not recommended in patients with PAH 1 due to high risk and lack of diagnostic benefit.

Do not rely on chest radiograph or ECG alone for diagnosis - while they may show suggestive findings (central pulmonary arterial dilatation, right ventricular hypertrophy), they have inadequate sensitivity and specificity as screening tools 2.

When PVOD is suspected (ground-glass opacities on CT, pulmonary edema in apparent PAH patient), immediately discontinue pulmonary vasodilators as they worsen pulmonary edema 3 and refer urgently for lung transplantation evaluation.

Referral Timing

Immediate referral to a PH center is indicated for: 2

• Syncope
• Rapidly progressing symptoms
• Signs of right heart failure
• Clinical or echocardiographic signs of severe PH and/or severe RV dysfunction