Pulmonary Hypertension (Adult)

1. Overview

Pulmonary Hypertension (PH) is a haemodynamic and pathophysiological condition defined by an increase in mean pulmonary arterial pressure (mPAP) of > 20 mmHg at rest, as measured by right heart catheterisation (RHC). [1] This definition was updated from the previous threshold of 25 mmHg in the 2022 ESC/ERS Guidelines to enable earlier diagnosis and intervention, reflecting evolving understanding that even mildly elevated pulmonary pressures carry prognostic significance. [2]

The clinical significance of PH lies in its progressive nature and catastrophic impact on the right ventricle (RV). PH is not a single disease but a haemodynamic consequence of diverse pathophysiological processes spanning from primary vascular disorders (pulmonary arterial hypertension, PAH) to secondary complications of left heart disease (the most common cause worldwide), lung disease, chronic thromboembolic disease, and miscellaneous conditions. [3]

The Right Ventricle-Pulmonary Artery Unit

The fundamental problem in PH is ventricular-arterial uncoupling. The normal RV is a thin-walled, compliant chamber designed to pump against the low-resistance, high-capacitance pulmonary circulation. When pulmonary vascular resistance (PVR) rises, the RV must generate higher pressures to maintain cardiac output. Unlike the left ventricle, the RV poorly tolerates acute increases in afterload and rapidly decompensates. [4]

The transition from compensated RV hypertrophy to decompensated RV failure is the critical determinant of prognosis in PH. Death in PH is usually attributable to progressive right heart failure rather than respiratory failure. [5]

Modern Treatment Paradigm (2024)

Management has been revolutionised by several key developments:

1. Early combination therapy: The paradigm has shifted from sequential monotherapy to upfront combination therapy targeting multiple pathways simultaneously. [6]
2. Risk stratification: Contemporary algorithms employ validated risk scores to guide treatment intensity at diagnosis and follow-up. [7]
3. Sotatercept: The 2023 approval of sotatercept, an activin signalling inhibitor, represents the first "disease-modifying" therapy that addresses the proliferative vasculopathy underlying PAH, not merely vasodilation. [8]
4. CTEPH interventions: Advances in pulmonary endarterectomy (PEA) and balloon pulmonary angioplasty (BPA) offer potential cure or major improvement for appropriately selected patients. [9]

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2. Epidemiology & Classification

Prevalence

The true prevalence of PH varies dramatically by group:

• Overall PH (all causes): Approximately 1% of the global population, rising to 10% in those > 65 years. [10]
• Pulmonary Arterial Hypertension (Group 1): Rare, with incidence of 2-5 cases per million adults per year. [11]
• Left heart disease PH (Group 2): The most common form, present in approximately 60% of patients with HFpEF and 70% of those with severe mitral stenosis. [12]
• Lung disease-associated PH (Group 3): Affects 30-50% of patients with advanced COPD and up to 50% with severe ILD. [13]
• CTEPH (Group 4): Develops in 2-4% of patients following acute pulmonary embolism. [14]

The 6th World Symposium WHO Classification (Updated 2022)

The WHO classification system is foundational to clinical practice, as each group has distinct pathophysiology, investigation algorithms, and treatments. [15]

Group 1 PAH: Subclassification

Group 1 requires further categorization:

• 1.1 Idiopathic PAH (IPAH): Diagnosis of exclusion after screening for secondary causes
• 1.2 Heritable PAH: BMPR2 mutation (70% of familial cases), ALK1, ENG, SMAD9, others [16]
• 1.3 Drug/toxin-induced: Definite associations (methamphetamines, dasatinib) and possible associations (SSRIs, cocaine) [17]
• 1.4 Associated PAH (APAH): CTD (scleroderma has highest risk, 10-15% prevalence), HIV (0.5%), portal hypertension (2-6%), congenital heart disease
• 1.5 Long-term responders to CCB: Rare subset (less than 5% of IPAH) with positive acute vasoreactivity testing
• 1.6 PAH with features of venous/capillary involvement: Pulmonary veno-occlusive disease (PVOD), pulmonary capillary haemangiomatosis (PCH)

Mortality Risk

Prognosis has improved substantially but remains serious:

• Untreated IPAH: Historical median survival of 2.8 years from diagnosis. [18]
• Modern therapy: Median survival now exceeds 7 years with contemporary combination therapy, but 5-year mortality remains approximately 30%. [19]
• CTEPH: Untreated inoperable CTEPH has 5-year mortality of 30-40%; surgical PEA reduces this to less than 10% in operable disease. [20]
• Group 2 PH: Prognosis driven primarily by underlying left heart disease; presence of PH independently worsens outcomes.

Prognostic variables include WHO functional class, 6-minute walk distance, BNP/NT-proBNP, echocardiographic RV function, and haemodynamic parameters (cardiac index, right atrial pressure). [21]

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3. Aetiology & Pathophysiology

Molecular Pathophysiology of PAH

PAH (Group 1) provides the paradigm for understanding pulmonary vascular disease. The pathogenesis is characterized by endothelial dysfunction, smooth muscle proliferation, in-situ thrombosis, and inflammation converging on obliterative remodelling of small pulmonary arterioles (less than 500 μm diameter).

The 9-Step Molecular Cascade

1. Genetic Susceptibility/Environmental Trigger:

   • BMPR2 mutation (Bone Morphogenetic Protein Receptor 2): Present in 70% of heritable PAH and 10-40% of apparently "idiopathic" cases. BMPR2 normally inhibits smooth muscle proliferation. Loss-of-function mutations create a pro-proliferative state. [22]
   • Environmental insults: Drugs (fenfluramine, dasatinib), infections (HIV, schistosomiasis), toxins (dasatinib), inflammation (CTD) serve as "second hits" in genetically predisposed individuals.

2. Endothelial Dysfunction:

   • The pulmonary vascular endothelium shifts from a protective, antiproliferative, vasodilatory phenotype to a dysfunctional, procoagulant, proliferative state.
   • Prostacyclin (PGI2) and Nitric Oxide (NO) production falls dramatically.
   • Endothelin-1 (ET-1) and Thromboxane A2 production increases, causing vasoconstriction and smooth muscle mitogenesis. [23]

3. The TGF-β/Activin/BMPR2 Axis Imbalance:

   • Activin signalling (pro-proliferative) becomes dominant over BMPR2 signalling (anti-proliferative).
   • This drives hyperproliferation of pulmonary artery smooth muscle cells (PASMCs), adventitial fibroblasts, and endothelial cells.
   • Sotatercept, a fusion protein that acts as a ligand trap for activin, restores this balance and represents the first therapy targeting this fundamental mechanism. [8]

4. Smooth Muscle and Adventitial Remodelling:

   • Medial hypertrophy: PASMCs proliferate and migrate, thickening the vessel wall.
   • Adventitial fibrosis: Activated fibroblasts deposit extracellular matrix, making vessels rigid.
   • Muscularization of normally non-muscular arterioles: Arterioles that usually lack a smooth muscle layer acquire one, increasing tone and resistance.

5. Intimal Proliferation and the Plexiform Lesion:

   • Endothelial cells undergo "disordered angiogenesis," forming complex, glomeruloid-like tuft structures within the vessel lumen.
   • Plexiform lesions are pathognomonic of severe PAH and represent a point of near-irreversibility. They consist of endothelial cell clusters, smooth muscle, and inflammatory cells forming occluded vascular channels. [24]

6. In-Situ Thrombosis:

   • Slow pulmonary blood flow, endothelial damage, and a pro-coagulant endothelial surface promote microthrombus formation.
   • While not the primary cause, thrombosis contributes to progressive luminal obliteration.
   • Justifies the use of anticoagulation in some PAH patients, though evidence is mixed.

7. Inflammation and Immune Dysregulation:

   • Perivascular inflammatory infiltrates (T cells, B cells, macrophages) are common.
   • Cytokines (IL-1, IL-6, TNF-α) amplify vascular remodelling.
   • Particularly prominent in CTD-associated PAH and HIV-PAH. [25]

8. Vasoconstriction:

   • While proliferative remodelling is dominant, abnormal vasoconstriction also contributes.
   • Explains the benefit of acute vasodilator testing: a small subset (~5% of IPAH) have predominantly vasoconstrictive disease responsive to calcium channel blockers. [26]

9. Rising Pulmonary Vascular Resistance (PVR):

   • The cumulative effect of these processes is progressive increase in PVR.
   • Ohm's Law analogy: mPAP = (Cardiac Output × PVR) + PAWP
   • To maintain cardiac output, mPAP must rise proportionally to PVR elevation.

The Right Ventricle in PH: From Compensation to Failure

The RV response to elevated PVR determines patient outcomes.

Phase 1: Compensated RV Hypertrophy

• The RV wall thickens (concentric hypertrophy) to normalize wall stress per the Law of Laplace: Wall Stress = (Pressure × Radius) / (2 × Wall Thickness).
• RV systolic pressure increases to match elevated pulmonary artery pressure.
• Cardiac output is preserved at rest.
• Clinical correlate: Patients may be asymptomatic or have only mild exertional dyspnoea.

Phase 2: RV-PA Uncoupling

• As PVR continues to rise, the RV reaches its adaptive limit.
• Subendocardial ischaemia: RV wall tension exceeds coronary perfusion pressure, causing ischaemia even without epicardial coronary disease ("RV angina").
• Diastolic dysfunction: Hypertrophied RV becomes stiff, impairing filling.
• Clinical correlate: Progressive dyspnoea, reduced exercise capacity, BNP elevation.

Phase 3: Decompensated RV Failure ("The Death Spiral")

• The RV dilates (eccentric remodelling), increasing wall stress further.
• Tricuspid regurgitation (TR): Annular dilatation causes TR, which volume-overloads the failing RV.
• Interventricular septal bowing: The dilated RV compresses the LV, reducing LV preload and stroke volume (ventricular interdependence). [27]
• Reduced cardiac output: Initially during exercise, then at rest.
• Systemic congestion: Elevated right atrial pressure causes hepatic congestion, peripheral oedema, ascites.
• Clinical correlate: WHO functional class IV symptoms, hypotension, renal impairment, cachexia.

The Determinants of RV Failure

Not all patients with equivalent PVR have the same RV function. Key modulators:

• Chronicity: Gradual PVR increase (chronic PAH) permits more adaptation than acute increase (massive PE).
• Ischaemia: Coronary disease or anaemia worsen RV function.
• Arrhythmia: Atrial fibrillation eliminates atrial contribution to RV filling (~25% of stroke volume) and precipitates decompensation.
• Hypoxia and acidosis: Exacerbate pulmonary vasoconstriction.

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4. Clinical Presentation

Symptoms

PH is often diagnosed late because early symptoms are non-specific and attributed to other conditions (deconditioning, obesity, asthma).

Primary Symptoms

• Progressive Dyspnoea on Exertion: The cardinal symptom, present in > 90% of patients. Initially occurs with strenuous activity, gradually worsening to involve activities of daily living, and ultimately dyspnoea at rest. [28]
• Fatigue and Lethargy: Caused by low cardiac output, present in ~75% of patients. Often disproportionate to measured exercise capacity.
• Exertional Chest Pain: "RV angina" due to subendocardial ischaemia from high RV wall tension. Occurs in ~40% of PAH patients. May mimic angina pectoris.
• Exertional Syncope or Pre-syncope: Highly specific for severe PH. Occurs when fixed cardiac output cannot meet the demands of peripheral vasodilation during exertion. Near-syncope or syncope at rest indicates critically low cardiac output. [29]

Secondary Symptoms

• Palpitations: Atrial arrhythmias (atrial flutter, fibrillation) occur as the RA dilates. New-onset AF often precipitates acute decompensation.
• Haemoptysis: Rare, but concerning for pulmonary artery rupture or rupture of bronchial vessels. Also seen with PVOD.
• Hoarseness (Ortner's syndrome): Compression of the left recurrent laryngeal nerve by a dilated pulmonary artery.
• Abdominal distension: Ascites and hepatic congestion from elevated right atrial pressure.
• Peripheral oedema: Lower limb oedema from systemic venous congestion.

WHO Functional Classification

Used universally for symptom severity stratification and prognostic assessment:

Baseline WHO class and changes in class over time are powerful predictors of survival. [30]

Physical Signs

Physical examination is insensitive for early PH but provides critical clues in moderate-to-severe disease.

Cardiovascular Signs

1. Loud P2 (Pulmonary Component of S2):

   • Accentuated, often palpable at the left upper sternal border.
   • Results from forceful closure of the pulmonary valve against elevated PA pressure.
   • Sensitivity ~90% in severe PH but may be absent in mild disease.

2. Left Parasternal Heave (RV Lift):

   • Palpable RV impulse at the left sternal border.
   • Indicates RV hypertrophy or dilatation.

3. Pansystolic Murmur of Tricuspid Regurgitation:

   • Best heard at the left lower sternal border.
   • Increases with inspiration (Carvallo's sign).
   • May be accompanied by a pulsatile liver if TR is severe.

4. Right-Sided S3 or S4:

   • S3 indicates RV volume overload and decompensation.
   • S4 suggests RV hypertrophy with preserved systolic function but diastolic stiffness.

5. Elevated Jugular Venous Pressure (JVP):

   • Reflects elevated right atrial pressure.
   • Prominent v-wave if significant TR is present.
   • Kussmaul's sign (JVP rise with inspiration) may occur in severe RV failure.

6. Hypotension and Narrow Pulse Pressure:

   • Indicates severely reduced cardiac output.
   • Systolic BP less than 90 mmHg is a red flag for impending circulatory collapse.

Signs of RV Failure

• Peripheral oedema: Bilateral, pitting, typically starting at the ankles.
• Hepatomegaly: Tender, pulsatile liver edge (if TR present).
• Ascites: Large-volume fluid accumulation in decompensated RV failure.
• Cachexia: Muscle wasting in chronic, severe disease (cardiac cachexia).

Signs of Associated Conditions

• Scleroderma: Tight, shiny skin; digital ulcers; telangiectasia; Raynaud's phenomenon.
• Systemic sclerosis: Puffy fingers, sclerodactyly, calcinosis.
• Cirrhosis/portal hypertension: Stigmata of chronic liver disease (spider naevi, palmar erythema, splenomegaly).
• Eisenmenger syndrome: Central cyanosis, digital clubbing, differential cyanosis (cyanosis of lower but not upper extremities if PDA with reversed shunt).

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5. Investigations

The diagnostic pathway aims to:

1. Detect the presence of PH (screening).
2. Confirm PH haemodynamically (RHC).
3. Classify PH by WHO group (comprehensive workup).
4. Assess severity (functional class, exercise testing, biomarkers).
5. Risk-stratify for prognosis and treatment planning.

Step 1: Screening and Initial Assessment

Transthoracic Echocardiography (TTE)

The first-line screening tool for suspected PH. [31]

Parameters assessed:

• Tricuspid Regurgitation Velocity (TRV):

  • Derived from the velocity of the TR jet using continuous-wave Doppler.
  • "Simplified Bernoulli Equation: RVSP = 4 × (TRV)² + RAP"
  • "Interpretation:"
    • TRV ≤2.8 m/s: PH unlikely (unless additional signs present).
    • TRV 2.9-3.4 m/s: PH possible; consider if other echo/clinical signs present.
    • TRV > 3.4 m/s: PH likely; proceed to further workup.
  • "Limitation: TRV is not directly equal to mPAP. Assumes RAP and requires adequate TR jet quality."

• Additional Echocardiographic Signs of PH:

  • "RV/LV basal diameter ratio > 1.0: Indicates RV dilatation."
  • Flattening of the interventricular septum: "D-shaped" LV in systole (pressure overload) or diastole (volume overload).
  • "RV wall thickness > 5 mm: Suggests RV hypertrophy."
  • "Dilated inferior vena cava (IVC) > 21 mm with less than 50% inspiratory collapse: Elevated RA pressure."
  • "Pulmonary artery diameter > 25 mm: Enlarged main PA."
  • "Reduced tricuspid annular plane systolic excursion (TAPSE) less than 17 mm: RV systolic dysfunction."
  • "RV fractional area change (FAC) less than 35%: Impaired RV systolic function."
  • "Pulmonary artery acceleration time (PAAT) less than 105 ms: Suggests elevated PVR."

Echocardiographic probability of PH (2022 ESC/ERS criteria): Classified as high, intermediate, or low based on combination of TRV and presence/absence of additional signs.

Electrocardiogram (ECG)

Insensitive but may show:

• Right axis deviation: QRS axis > 90°.
• RV hypertrophy: R wave >S wave in V1; R wave in V1 > 7 mm; S wave in V5 or V6 > 7 mm.
• Right atrial enlargement: Peaked P waves in leads II, III, aVF (P pulmonale) > 2.5 mm.
• Right bundle branch block (RBBB): QRS > 120 ms with RSR' pattern in V1.
• RV strain pattern: T wave inversion in V1-V4.

Normal ECG does not exclude PH.

Chest X-Ray

Often normal in early disease. Findings in advanced PH:

• Enlarged pulmonary arteries: Prominent main and hilar pulmonary arteries.
• Peripheral vascular pruning: Reduced peripheral vascular markings.
• Enlarged cardiac silhouette: Mainly right-sided chambers.
• Signs of underlying lung disease: Hyperinflation (COPD), interstitial opacities (ILD).

Blood Tests

• Brain Natriuretic Peptide (BNP) or NT-proBNP: Elevated in RV strain; used for diagnosis, prognosis, and monitoring response. Levels > 300 pg/mL (NT-proBNP > 900 pg/mL) indicate worse prognosis. [32]
• Full blood count: Polycythaemia (chronic hypoxaemia), anaemia (may worsen RV function).
• Renal function and electrolytes: Renal impairment is common in advanced RV failure.
• Liver function tests: Elevated transaminases and bilirubin with hepatic congestion.
• Thyroid function: Screen for hypo- or hyperthyroidism (associated with PAH).
• HIV serology: Mandatory screening in all newly diagnosed PH.
• ANA, anti-Scl-70, anti-centromere, anti-RNA polymerase III: Screen for connective tissue disease, especially systemic sclerosis.
• Hepatitis serology and liver screen: If portal hypertension suspected.

Step 2: Confirming PH – Right Heart Catheterisation (RHC)

RHC is the gold standard for diagnosing PH and is mandatory before initiating PAH-specific therapy. [33]

Indications for RHC

• Intermediate or high echocardiographic probability of PH.
• Clinical suspicion despite low echo probability (e.g., CTD screening).
• Before starting PAH-specific medications.
• Assessment for vasoreactivity in PAH.

Haemodynamic Definitions (2022 Criteria)

• Normal: mPAP ≤20 mmHg at rest.
• Pulmonary Hypertension: mPAP > 20 mmHg at rest.

Distinguishing pre-capillary vs. post-capillary PH:

• Pre-capillary PH (Groups 1, 3, 4, 5):
  • mPAP > 20 mmHg
  • PAWP (Pulmonary Artery Wedge Pressure) ≤15 mmHg
  • PVR ≥2 Wood Units (or > 160 dyne·s·cm⁻⁵)
• Post-capillary PH (Group 2):
  • mPAP > 20 mmHg
  • PAWP > 15 mmHg
• Combined pre- and post-capillary PH (CpcPH):
  • mPAP > 20 mmHg, PAWP > 15 mmHg, and PVR ≥2 WU
  • Represents Group 2 with reactive pulmonary vascular changes.

Acute Vasoreactivity Testing (AVT)

Performed during RHC in Group 1 PAH only (not in Groups 2-5, where vasodilators are contraindicated).

Method: Inhaled nitric oxide (10-20 ppm) or IV epoprostenol or adenosine.

Positive response (defines "vasoreactive PAH"):

• Reduction in mPAP ≥10 mmHg and
• Absolute mPAP ≤40 mmHg and
• No reduction or increase in cardiac output.

Clinical significance: Only ~5% of IPAH patients are vasoreactive. These patients can be treated with high-dose oral calcium channel blockers (diltiazem 240-720 mg/day or nifedipine 120-240 mg/day) instead of PAH-specific drugs, with excellent long-term outcomes if response is sustained. [34]

Key Haemodynamic Parameters

• Mean right atrial pressure (RAP): Normal less than 5 mmHg; > 15 mmHg indicates severe RV failure.
• RV systolic/diastolic pressure: RV systolic pressure approximates PA systolic pressure in the absence of RVOT obstruction.
• Cardiac output (CO) and cardiac index (CI): Thermodilution or Fick method. CI less than 2.5 L/min/m² indicates low output.
• Pulmonary vascular resistance (PVR):
  • PVR (Wood Units) = (mPAP - PAWP) / Cardiac Output
  • Normal less than 2 WU; PVR ≥2 WU defines pre-capillary component.
• Transpulmonary gradient (TPG): mPAP - PAWP. Elevated in pre-capillary PH.
• Diastolic pressure gradient (DPG): PA diastolic pressure - PAWP. DPG ≥7 mmHg suggests intrinsic pulmonary vascular disease in patients with elevated PAWP.

Step 3: Determining the Cause – Group Classification Workup

After confirming PH, comprehensive evaluation determines the WHO group.

Ventilation-Perfusion (V/Q) Scan

• Mandatory in all newly diagnosed PH to screen for chronic thromboembolic disease (Group 4). [35]
• Interpretation:
  • "Normal or low-probability scan: Effectively excludes CTEPH."
  • "Mismatched segmental or larger perfusion defects: Highly suggestive of CTEPH → proceed to CT pulmonary angiography (CTPA) and invasive pulmonary angiography for surgical assessment."
• Sensitivity > 95% for CTEPH; superior to CTPA for screening.

High-Resolution CT Chest (HRCT)

• Identifies parenchymal lung disease (Group 3): COPD, ILD, combined pulmonary fibrosis and emphysema.
• Identifies signs of CTEPH: Mosaic attenuation, bronchial artery collaterals, organized thrombus.
• Identifies pulmonary veno-occlusive disease (PVOD): Smooth interlobular septal thickening, ground-glass opacities, mediastinal lymphadenopathy.

Pulmonary Function Tests (PFTs) and Arterial Blood Gas (ABG)

• Assess for obstructive (COPD) or restrictive (ILD) lung disease.
• DLCO typically reduced in PAH and ILD.
• ABG: Chronic hypoxaemia and hypercapnia suggest Group 3.

Nocturnal Oximetry or Polysomnography

• Screen for sleep-disordered breathing (obstructive sleep apnoea, obesity hypoventilation syndrome).

Contrast Echocardiography (Bubble Study)

• Identifies intracardiac shunt (ASD, VSD, PFO) or intrapulmonary shunt.

Abdominal Ultrasound or CT

• Assess for cirrhosis, portal hypertension, splenomegaly (portopulmonary hypertension).

Thrombophilia Screen

• Indicated in CTEPH to identify hereditary or acquired prothrombotic states (Factor V Leiden, Protein C/S deficiency, antiphospholipid syndrome).

Autoimmune Serology

• ANA, ENA, anti-Scl-70, anti-centromere, RF: Screen for CTD, especially systemic sclerosis (highest PAH risk among CTDs).

Step 4: Severity and Risk Assessment

6-Minute Walk Test (6MWT)

• Submaximal exercise test measuring distance walked in 6 minutes.
• Baseline distance and change over time are prognostic.
• Distance > 440 m is low-risk; less than 165 m is high-risk. [36]
• Simple, reproducible, widely used.

Cardiopulmonary Exercise Testing (CPET)

• Maximal exercise test with gas exchange analysis.
• Peak VO2 less than 12 mL/kg/min indicates poor prognosis.
• Identifies anaerobic threshold, VE/VCO2 slope (ventilatory efficiency).

Risk Stratification Scores

Multiple validated risk scores integrate clinical, functional, exercise, and haemodynamic data to classify patients as low, intermediate, or high risk. Treatment escalation is guided by risk category. [37]

REVEAL 2.0 Risk Score (Registry to Evaluate Early and Long-term PAH Disease Management): Assigns points based on:

• Aetiology (e.g., portopulmonary PAH higher risk than IPAH)
• Renal insufficiency
• WHO functional class
• Systolic blood pressure
• Heart rate
• BNP
• DLCO
• 6MWD
• RAP, PVR

Simplified Risk Stratification (ESC/ERS 2022):

• Assess at baseline and each follow-up (3-6 months).
• Three risk strata based on:
  • WHO functional class
  • 6MWD
  • BNP/NT-proBNP
  • Haemodynamics (RAP, CI)
  • Imaging (RV function, pericardial effusion)

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6. Management

Management is group-specific. Group 1 PAH has evidence-based drug therapies; other groups focus on treating the underlying cause.

General Measures (All Groups)

1. Oxygen Therapy: Target SpO2 > 90%. Reduces hypoxic pulmonary vasoconstriction.
2. Diuretics: Loop diuretics for volume overload. Titrate to euvolaemia; avoid excessive diuresis (RV is preload-dependent).
3. Digoxin: Consider in RV failure with atrial arrhythmias (rate control + mild inotropic effect). Evidence limited.
4. Anticoagulation:
   • Group 4 (CTEPH): Lifelong anticoagulation mandatory.
   • Group 1 (PAH): Controversial; historically recommended for IPAH but not supported by RCT evidence. Current guidelines suggest considering in IPAH, heritable PAH, and PAH due to anorexigens, but not routinely in APAH (especially CTD-PAH due to bleeding risk). [38]
5. Supervised Exercise Training: Improves 6MWD and QoL without adverse effects. Previously avoided due to syncope risk, but now endorsed based on RCT data. [39]
6. Vaccinations: Annual influenza, pneumococcal, COVID-19 vaccination to prevent respiratory infections.
7. Pregnancy Avoidance: Pregnancy carries 30-50% maternal mortality in PAH. Highly effective contraception mandatory. If pregnancy occurs, termination recommended.
8. Avoid Volume Depletion and Anaemia: Maintain adequate preload and oxygen-carrying capacity.

Group 1 (PAH): Pathway-Specific Drug Therapy

PAH-specific drugs target three key pathways: Endothelin, Nitric Oxide, and Prostacyclin.

The Three Pathways

1. Endothelin Pathway (Endothelin Receptor Antagonists, ERAs)

   • Mechanism: Block endothelin receptors (ETA and/or ETB) to reduce vasoconstriction and smooth muscle proliferation.
   • Agents:
     • Bosentan: Non-selective ETA/ETB antagonist. Requires monthly LFTs (hepatotoxicity risk).
     • Ambrisentan: Selective ETA antagonist. Lower hepatotoxicity.
     • Macitentan: Dual ETA/ETB antagonist with improved tissue penetration and fewer drug interactions.
   • Contraindication: Pregnancy (teratogenic).
   • Monitoring: LFTs monthly for first 6 months, then periodically.

2. Nitric Oxide-cGMP Pathway (PDE5 Inhibitors and sGC Stimulators)

   • Mechanism: PDE5 inhibitors prevent breakdown of cGMP, enhancing NO-mediated vasodilation.
   • Agents:
     • Sildenafil: 20 mg TDS (approved dose; higher doses did not improve outcomes).
     • Tadalafil: 40 mg OD (longer half-life, once-daily dosing).
   • Soluble guanylate cyclase (sGC) stimulator:
     • Riociguat: Directly stimulates sGC, increasing cGMP. Approved for Group 1 PAH and inoperable/recurrent CTEPH. Contraindication: Do not combine with PDE5 inhibitors (hypotension).

3. Prostacyclin Pathway (Prostacyclin Analogues and IP Receptor Agonists)

   • Mechanism: Mimic prostacyclin (PGI2) to induce vasodilation, inhibit platelet aggregation, and reduce smooth muscle proliferation.
   • Agents:
     • Epoprostenol (IV): Gold standard; requires continuous infusion via central line. Short half-life (~3 min); interruption can cause rebound PH crisis. Reserved for WHO FC IV or high-risk patients. Improves survival in severe PAH. [40]
     • Treprostinil: Available IV, SC, inhaled, or oral. SC route causes injection site pain. Less cumbersome than epoprostenol but similar efficacy.
     • Iloprost (inhaled): 6-9 inhalations per day (cumbersome). Useful in patients intolerant of systemic prostacyclins.
     • Selexipag (oral): Selective IP receptor agonist (not a true prostacyclin analogue). Oral route improves convenience. GRIPHON trial showed reduced morbidity/mortality. [41]

The Modern Treatment Algorithm (2022 ESC/ERS Guidelines)

Step 1: Perform acute vasoreactivity testing (AVT) at RHC

• If AVT positive (~5% of IPAH): Trial of high-dose oral CCB (diltiazem 240-720 mg/day or nifedipine 120-240 mg/day).
  • "Reassess after 3-6 months: if sustained response (WHO FC I/II, near-normal haemodynamics), continue CCB."
  • If no response or deterioration, start PAH-specific drugs.

Step 2: Initial risk stratification

• Low or intermediate risk at diagnosis:

  • "Start initial dual therapy: Ambrisentan (ERA) + Tadalafil (PDE5i). Based on AMBITION trial: dual therapy reduced clinical failure by 50% vs. monotherapy. [42]"
  • "Alternative: Macitentan + Tadalafil."

• High risk at diagnosis (WHO FC IV, CI less than 2.0, RAP > 15, severely reduced 6MWD):

  • "Start initial triple therapy: ERA + PDE5i + Prostacyclin (IV epoprostenol or SC/IV treprostinil)."
  • "Rationale: High-risk patients have unacceptably poor outcomes with dual therapy alone; early aggressive treatment improves survival. [43]"

Step 3: Reassess at 3-6 months

• Repeat risk stratification.
• If low risk achieved: Continue current therapy, monitor every 3-6 months.
• If intermediate or high risk: Escalate therapy.

Step 4: Sequential combination therapy

• Add third agent if not already on triple therapy:
  • If on ERA + PDE5i → add Selexipag (oral prostacyclin pathway agent) or parenteral prostacyclin.
  • If on dual therapy without ERA → add ERA.
• Consider Sotatercept (see below).

Sotatercept: The Disease-Modifying Agent (2024 Update)

Mechanism: Fusion protein (activin receptor IIA-Fc) that traps activin and other TGF-β superfamily ligands, restoring balance between pro-proliferative and anti-proliferative signalling in pulmonary vascular cells. [8]

Evidence: STELLAR trial (Phase 3 RCT, 2023):

• Patients on background dual/triple therapy randomized to Sotatercept vs. placebo.
• Primary endpoint: Change in 6MWD at 24 weeks.
• Results: Sotatercept significantly increased 6MWD (+40.8 m), reduced PVR (-235 dyne·s·cm⁻⁵), reduced NT-proBNP, and improved WHO FC. [8]
• First therapy to demonstrate vascular remodelling (reduced PVR beyond vasodilation).

Dosing: Subcutaneous injection every 3 weeks, starting 0.3 mg/kg, escalating to 0.7 mg/kg.

Indication: Add-on therapy for patients with PAH on background therapy who remain intermediate or high risk.

Monitoring: Haemoglobin (can increase Hb by ~2 g/dL; may require phlebotomy if Hb > 16 g/dL), platelet count, blood pressure.

Group 2 (Left Heart Disease): Treat the Left Heart

PAH-specific drugs are contraindicated in isolated post-capillary PH (Group 2). Vasodilating the pulmonary arteries without addressing the elevated left-sided filling pressures risks precipitating acute pulmonary oedema.

Management:

1. Optimize LV failure therapy:
   • HFrEF: GDMT (ACE-i/ARB/ARNI, beta-blocker, MRA, SGLT2i, diuretics).
   • HFpEF: SGLT2i, diuretics, treat comorbidities (hypertension, AF, obesity).
2. Valve intervention: Surgical or percutaneous repair/replacement for severe mitral or aortic valve disease.
3. Control atrial fibrillation: Rate or rhythm control.

Exception: If combined pre- and post-capillary PH (CpcPH) with significantly elevated PVR persists despite optimizing left heart disease, consider cautious trial of PAH drugs in specialist centres, though evidence is limited.

Group 3 (Lung Disease): Treat the Lung

Management:

1. Optimize treatment of underlying lung disease:
   • COPD: Bronchodilators, inhaled corticosteroids, smoking cessation, pulmonary rehabilitation.
   • ILD: Antifibrotics (nintedanib, pirfenidone for IPF), immunosuppression if inflammatory ILD.
   • OSA: CPAP or BiPAP.
2. Long-term oxygen therapy (LTOT): If resting hypoxaemia (PaO2 less than 55 mmHg or SpO2 less than 88%).
3. Pulmonary rehabilitation.

PAH-specific drugs: Not routinely recommended. May consider if severe PH out of proportion to lung disease in specialist centres, but evidence is weak and potential for harm (V/Q mismatch worsening).

Group 4 (CTEPH): Interventional or Surgical Cure

Surgery: Pulmonary Endarterectomy (PEA)

• Potentially curative for operable CTEPH. [44]
• Performed at specialist centres with expertise in PEA.
• Operability assessment: Multidisciplinary team review of imaging (CTPA, pulmonary angiography, V/Q), haemodynamics, and comorbidities.
• Criteria for operability: Thrombus accessible at surgery (segmental or more proximal), PVR significantly contributing to symptoms, absence of severe comorbidities.
• Outcomes: Perioperative mortality less than 5% at expert centres; majority have marked haemodynamic and symptomatic improvement; 5-year survival > 80%.

Balloon Pulmonary Angioplasty (BPA)

• Percutaneous intervention for distal, surgically inaccessible CTEPH or high surgical risk.
• Series of sessions dilating affected segmental/subsegmental arteries.
• Improves haemodynamics and symptoms in most patients. [45]
• Complications: Reperfusion pulmonary oedema, vascular injury.

Medical Therapy:

• Riociguat: Only drug approved for inoperable/recurrent CTEPH. CHEST-1 trial demonstrated improved 6MWD and PVR. [46]
• Lifelong anticoagulation: Mandatory to prevent recurrence.

Group 5 (Miscellaneous): Treat Underlying Condition

Heterogeneous group; management individualized:

• Sarcoidosis: Corticosteroids, immunosuppression.
• Sickle cell disease: Hydroxyurea, transfusion, treat vaso-occlusive crises.
• Chronic renal failure on dialysis: Optimize dialysis, consider transplantation.

PAH-specific drugs: Considered case-by-case in specialist centres if pre-capillary PH component is significant.

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7. Acute Pulmonary Hypertension Crisis (Emergency)

Definition: Acute RV decompensation in a patient with known or newly diagnosed PH, presenting with hypotension, hypoxia, and end-organ hypoperfusion (cardiogenic shock).

Triggers: Infection, arrhythmia (especially AF), PE, interruption of PAH therapy (especially IV prostacyclin), anaesthesia/surgery, pregnancy, sepsis.

Management Principles

1. Avoid Intubation if Possible:

   • Positive pressure ventilation reduces venous return (preload), worsening RV output.
   • Sedation and paralysis eliminate endogenous catecholamine support.
   • If intubation unavoidable, use low tidal volumes, avoid high PEEP, maintain permissive hypercapnia.

2. Optimize Preload:

   • RV is preload-dependent; hypovolaemia is catastrophic.
   • Give cautious fluid boluses (250 mL crystalloid), guided by response (BP, CO, CVP). Stop if CVP rises without BP improvement (excessive preload worsens TR and ventricular interdependence).

3. Reduce RV Afterload:

   • Inhaled nitric oxide (iNO): 10-40 ppm. Selectively vasodilates pulmonary circulation without systemic hypotension. Monitor for methaemoglobinaemia and rebound PH on withdrawal (taper gradually). [47]
   • Inhaled prostacyclin (epoprostenol, iloprost): Alternative to iNO if unavailable.

4. Improve RV Contractility:

   • Dobutamine: β1-agonist inotrope; increases RV contractility and mildly reduces PVR. Dose 2-10 mcg/kg/min. Risk: tachycardia, arrhythmia.
   • Milrinone: Phosphodiesterase-3 inhibitor; inotrope + pulmonary vasodilator. Dose 0.25-0.75 mcg/kg/min. Risk: systemic hypotension (requires concomitant vasopressor).
   • Avoid pure vasoconstrictors (norepinephrine, phenylephrine) unless severe systemic hypotension; they increase RV afterload.

5. Maintain Systemic Perfusion:

   • If hypotensive despite inotropes, add vasopressin (minimal effect on PVR) or low-dose norepinephrine to maintain MAP > 65 mmHg.

6. Treat Precipitant:

   • Antibiotics for infection.
   • Cardioversion for unstable atrial arrhythmias.
   • Anticoagulation if acute PE suspected.

7. Escalate to Mechanical Support if Refractory:

   • ECMO (VA-ECMO): Provides RV and LV support; bridge to recovery, transplantation, or LVAD implantation.
   • RV assist device (RVAD): Temporary support for isolated RV failure.

8. Consider Lung Transplantation Referral:

   • For patients with end-stage PAH refractory to maximal medical therapy.

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8. Prognosis and Monitoring

Prognosis

Modern combination therapy has transformed outcomes, but PH remains a serious disease:

• Low-risk PAH patients: 5-year survival > 90%.
• Intermediate-risk PAH: 5-year survival 70-80%.
• High-risk PAH: 5-year survival less than 50% despite therapy. [48]

Predictors of poor prognosis:

• WHO FC IV at diagnosis
• 6MWD less than 165 m
• NT-proBNP > 1400 ng/L
• RAP > 14 mmHg, CI less than 2.0 L/min/m²
• Pericardial effusion on echo
• Certain aetiologies: Portopulmonary HTN, scleroderma-PAH worse than IPAH

Follow-Up and Monitoring

Frequency: Every 3-6 months at specialist PH centre.

Assessments:

• Clinical status (WHO FC, symptoms, examination)
• 6MWT
• NT-proBNP
• Echocardiography (RV function, estimated PASP, pericardial effusion)
• Repeat RHC: Not routine; reserved for clinical deterioration, treatment escalation decisions, or transplant evaluation

Treatment adjustment: Guided by risk stratification. Goal is to achieve and maintain low-risk status.

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9. Evidence: Landmark Trials

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10. Clinical Vignettes and Exam Scenarios

Single Best Answer (SBA) Question 1

A 32-year-old female with limited cutaneous systemic sclerosis presents with progressive exertional dyspnoea over 6 months. She now experiences breathlessness walking up one flight of stairs. BP is 115/75 mmHg, HR 88 bpm, SpO2 94% on air. Examination reveals a loud P2, left parasternal heave, and pansystolic murmur increasing with inspiration. TTE shows TRV 3.8 m/s, dilated RV, and RV/LV basal diameter ratio 1.2. Which investigation is mandatory before initiating PAH-specific therapy?

A) CT pulmonary angiography
B) Ventilation-perfusion (V/Q) scan
C) Pulmonary function tests with DLCO
D) Right heart catheterisation
E) Exercise echocardiography

Answer: D. Right heart catheterisation is the gold standard for confirming the diagnosis of PH, determining haemodynamic subtype (pre-capillary vs. post-capillary), and performing acute vasoreactivity testing. It is mandatory before starting PAH-specific drugs. V/Q scan (option B) is also mandatory to exclude CTEPH but does not replace RHC for diagnosis and haemodynamic assessment.

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Single Best Answer (SBA) Question 2

A 45-year-old male with idiopathic PAH diagnosed 2 years ago presents for follow-up. He is on dual therapy with macitentan and tadalafil. He is WHO FC III with a 6MWD of 310 metres and NT-proBNP of 850 ng/L. Echocardiography shows moderate RV dysfunction. According to ESC/ERS risk stratification, he is classified as intermediate risk. What is the most appropriate next step?

A) Continue current therapy and reassess in 6 months
B) Add selexipag (oral prostacyclin pathway agent)
C) Discontinue macitentan and start riociguat
D) Reduce dose of tadalafil due to side effects
E) Refer for urgent lung transplantation assessment

Answer: B. The patient is at intermediate risk despite dual therapy. Current guidelines recommend escalation to triple therapy by adding a prostacyclin pathway agent (selexipag, or parenteral prostacyclin if higher risk). Sotatercept is another option for add-on therapy. Continuing dual therapy (option A) is inadequate for intermediate-risk patients. Riociguat (option C) is contraindicated with PDE5 inhibitors. Transplant assessment (option E) is premature; reserved for refractory high-risk patients despite maximal medical therapy.

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Single Best Answer (SBA) Question 3

Which molecular pathway is targeted by sotatercept, the novel agent recently approved for PAH?

A) Endothelin receptor A and B
B) Phosphodiesterase-5 enzyme
C) Activin signalling and TGF-β superfamily balance
D) Prostacyclin IP receptor
E) Voltage-gated calcium channels

Answer: C. Sotatercept is a fusion protein (activin receptor type IIA-Fc) that acts as a ligand trap for activins and other TGF-β superfamily members, restoring the balance between pro-proliferative (activin) and anti-proliferative (BMPR2) signalling in pulmonary vascular cells. It is the first therapy to target the underlying proliferative vasculopathy rather than providing symptomatic vasodilation.

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Viva Scenario 1: "The Group 2 Trap"

Examiner: "A 68-year-old woman with hypertension and atrial fibrillation presents with progressive dyspnoea. Echo shows LVEF 55%, E/e' ratio 18, and TRV 3.5 m/s. You perform RHC: mPAP 42 mmHg, PAWP 22 mmHg, cardiac output 4.0 L/min. The referring cardiologist asks if you can start sildenafil to help her breathlessness. What do you tell them?"

Model Answer:

1. Diagnosis: This is post-capillary pulmonary hypertension (Group 2) secondary to left heart disease, specifically heart failure with preserved ejection fraction (HFpEF). The elevated E/e' ratio and PAWP > 15 mmHg confirm elevated left-sided filling pressures.

2. Treatment decision: I would not start sildenafil or any PAH-specific vasodilator.

3. Rationale:

   • PAH-specific drugs vasodilate the pulmonary arteries, which increases pulmonary blood flow.
   • In the setting of high left-sided back-pressure (PAWP 22 mmHg), increased pulmonary flow cannot exit the lungs efficiently and will cause acute pulmonary oedema.
   • Group 2 PH is a marker of disease severity, not an independent treatment target.

4. Correct management: Optimize treatment of the left heart disease:

   • Diuretics to reduce volume overload and PAWP
   • SGLT2 inhibitor (evidence for benefit in HFpEF)
   • Antihypertensive therapy
   • Rate/rhythm control of atrial fibrillation
   • Lowering the PAWP will secondarily reduce the pulmonary pressures.

5. Exception: If she had combined pre- and post-capillary PH (CpcPH) with PVR ≥2 WU despite optimizing left heart treatment, there is limited evidence for cautious use of PAH drugs in specialist centres, but this is not standard practice.

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Viva Scenario 2: "Acute RV Failure During Anaesthesia"

Examiner: "A 50-year-old woman with known severe PAH is undergoing emergency laparotomy for perforated diverticulitis. Shortly after induction, her BP drops to 70/40 mmHg, HR rises to 130 bpm, and SpO2 falls to 85%. The anaesthetist asks for your help. What is happening and what do you advise?"

Model Answer:

1. Diagnosis: This is acute RV failure precipitated by anaesthesia induction. The combination of positive pressure ventilation (reducing preload), sedation (removing endogenous catecholamines), and vasodilatory anaesthetic agents has caused RV decompensation.

2. Immediate management priorities:

   • Maintain preload: Give cautious fluid boluses (250 mL crystalloid) while monitoring CVP. The RV is exquisitely preload-dependent.
   • Reduce RV afterload: Initiate inhaled nitric oxide (10-20 ppm) or inhaled prostacyclin. These selectively vasodilate the pulmonary circulation without causing systemic hypotension.
   • Support RV contractility: Start dobutamine (β1-agonist inotrope, 2-10 mcg/kg/min) to augment RV contractility. Milrinone is an alternative (inotrope + pulmonary vasodilator).
   • Maintain systemic perfusion: If systemic BP remains critically low, add vasopressin (minimal effect on PVR) or cautious low-dose norepinephrine.
   • Ventilation strategy: Use low tidal volumes (6 mL/kg), minimize PEEP, accept permissive hypercapnia. Avoid hyperventilation (alkalosis can paradoxically worsen RV function).

3. Avoid harmful interventions:

   • Do not give excessive fluid: Over-resuscitation worsens TR and ventricular interdependence.
   • Avoid pure vasoconstrictors (phenylephrine) as monotherapy; they increase RV afterload.

4. Escalation: If refractory, consider VA-ECMO as bridge to recovery or transplantation.

5. Prevention: Elective surgery in severe PAH should be performed in specialist centres with PH and cardiothoracic anaesthesia expertise. Regional anaesthesia is preferred when feasible.

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11. Patient Communication

Explaining PH to a Patient

"Pulmonary Hypertension means the blood pressure in the vessels between your heart and lungs—the pulmonary arteries—is too high. This is different from the blood pressure we measure on your arm.

Think of it like this: your heart has two sides. The right side pumps blood to your lungs to pick up oxygen. Normally, this is easy work because the blood vessels in the lungs are wide and flexible, like a large, soft garden hose. In Pulmonary Hypertension, those vessels become narrow and stiff, like trying to pump water through a very thin, rigid pipe.

Because of this, the right side of your heart has to work much harder. Over time, it can become tired and weakened, which is called right heart failure.

We treat this condition with medications that help relax and widen those blood vessels, reducing the pressure. We also have a newer medication that helps repair some of the damage to the vessels themselves, not just widening them.

Regular monitoring and sticking to your medications are essential to keep your heart working as well as possible."

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Discussing Prognosis

"Pulmonary Hypertension is a serious condition, but treatments have improved a lot in recent years. How well you do depends on several things: how severe the disease is when we catch it, what's causing it, and how well you respond to treatment.

We monitor you closely with tests like the 6-minute walk test, blood tests, and scans to see how you're responding. Our goal is to get you into what we call a 'low-risk' category, which means the disease is well-controlled and your risk of complications is much lower.

If you're in the low-risk group with treatment, the outlook is good, with most patients doing well for many years. If the disease is more advanced or doesn't respond as well, we have options to escalate treatment, including stronger medications and, in some cases, lung transplantation."

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12. Key Exam Pearls

1. Definition of PH changed in 2022: mPAP > 20 mmHg (previously > 25 mmHg).
2. RHC is mandatory for diagnosis and before starting PAH-specific drugs.
3. V/Q scan is mandatory in all new PH cases to screen for CTEPH.
4. Pre-capillary PH: mPAP > 20, PAWP ≤15, PVR ≥2 WU (Groups 1, 3, 4, 5).
5. Post-capillary PH: mPAP > 20, PAWP > 15 (Group 2).
6. Group 2 is the most common cause of PH worldwide; do not give PAH-specific vasodilators.
7. CTEPH is potentially curable with pulmonary endarterectomy (PEA).
8. Acute vasoreactivity testing identifies the ~5% of IPAH patients who respond to high-dose CCBs.
9. Initial dual therapy (ERA + PDE5i) is standard for low/intermediate-risk Group 1 PAH.
10. Initial triple therapy (ERA + PDE5i + prostacyclin) for high-risk Group 1 PAH.
11. Sotatercept is the first disease-modifying agent, targeting activin signalling.
12. Exertional syncope is a red flag for severe, fixed cardiac output.
13. Avoid intubation in acute RV failure if possible; use iNO, inotropes, cautious fluids.
14. BMPR2 mutation: Most common genetic cause of heritable PAH.
15. Plexiform lesions: Pathognomonic histologic finding in severe PAH.
16. 6MWD > 440 m, NT-proBNP less than 300 ng/L, WHO FC I-II: Low-risk criteria.
17. Do not combine riociguat with PDE5 inhibitors (risk of severe hypotension).
18. Pregnancy is contraindicated in PAH (30-50% maternal mortality).

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