Everything You Need to Know About Pulmonary hypertension for Step 1

Pulmonary hypertension (PH) is one of those Step 1 topics that feels “cardio + pulm + pharm” all at once—and it loves showing up as a vignette with loud P2, exertional dyspnea, and a right heart that’s slowly losing the battle. If you can confidently define PH, explain why the pulmonary vasculature remodels, and pick the right drug class (and contraindication), you’ll pick up a lot of easy points.

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Big-Picture Definition (Know the Numbers)

Pulmonary hypertension = elevated pressure in the pulmonary arterial system.

• Modern hemodynamic definition (tested conceptually even if the exact cutoff varies by resource):
  Mean pulmonary arterial pressure (mPAP) elevated at rest on right heart catheterization.
• Practical board framing:
  • Think elevated pulmonary artery pressure → increased RV afterload → RV hypertrophy/dilation → right heart failure (cor pulmonale).

Key equation (high yield)

Pulmonary vascular resistance:

$PVR = \frac{mPAP - PCWP}{CO}$

• Precapillary PH: elevated PVR with normal PCWP
• Postcapillary PH (left-sided heart disease): elevated PCWP (pulmonary venous hypertension)

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Classification: The 5 WHO Groups (Step-Friendly)

First Aid cross-reference (where this lives conceptually): Pulmonary HTN, cor pulmonale, hypoxic vasoconstriction, V/Q mismatch, and pulmonary pharmacology (PDE-5 inhibitors, endothelin antagonists, prostacyclin analogs).

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Pathophysiology: What Actually Raises the Pressure?

The “core triad” in PAH (Group 1)

1. Vasoconstriction (imbalance: ↓NO and prostacyclin; ↑endothelin)
2. Vascular remodeling (smooth muscle proliferation, fibrosis)
3. In situ thrombosis (endothelial dysfunction → prothrombotic state)

Classic histology: plexogenic arteriopathy

• Plexiform lesions (classically associated with severe PAH)
• Think: proliferation and complex vascular channels in small pulmonary arteries/arterioles.

Why the right ventricle suffers

• Pulmonary circulation is normally a low-pressure system
• PH → chronically increased RV afterload
• RV adapts via hypertrophy, then decompensates → RV dilation, tricuspid regurg, decreased CO, syncope, and right-sided congestion

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High-Yield Etiologies & Associations (Memorize These)

Idiopathic / Heritable PAH

• BMPR2 mutation (TGF-β family signaling) → unchecked vascular smooth muscle proliferation
  Step clue: young patient, progressive dyspnea, signs of RV strain; no lung disease.

Drugs and toxins

• Amphetamines (and historically appetite suppressants) are classic board associations.

Connective tissue disease

• Systemic sclerosis (scleroderma/CREST) is a top association
  Step move: patient with Raynaud + skin thickening + dyspnea → think PAH.

Congenital heart disease (late)

• Unrepaired L→R shunts can progress to Eisenmenger syndrome:
  • Chronic increased pulmonary flow → vascular remodeling → pulmonary HTN
  • Eventually shunt reverses (R→L) → cyanosis + clubbing
  • Polycythemia may develop due to chronic hypoxemia

Chronic hypoxia

• Hypoxic pulmonary vasoconstriction is adaptive short-term but pathologic long-term
• Seen in COPD, OSA, ILD, high altitude → Group 3 PH

Chronic thromboembolism (CTEPH)

• Underrecognized and very testable because it’s potentially curable (pulmonary endarterectomy in select patients).

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Clinical Presentation: How It Shows Up on Exams

Symptoms (often subtle early)

• Progressive exertional dyspnea
• Fatigue, weakness
• Chest pain (RV ischemia)
• Exertional syncope/presyncope (fixed CO with exertion)

Physical exam (classic Step findings)

• Loud P2 (accentuated pulmonic component of S2)
• RV heave (parasternal lift)
• Tricuspid regurgitation murmur (holosystolic at LLSB)
• Signs of right heart failure:
  • JVD, hepatomegaly, ascites, peripheral edema

Complications to recognize

• Cor pulmonale: RV failure secondary to pulmonary disease/PH
• Hemoptysis can occur (vessel rupture in severe disease)
• Arrhythmias in advanced disease

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Diagnosis: The Board-Style Workup (Know the “Gold Standard”)

Stepwise approach (how vignettes are built)

1. Echocardiography (screening)
   • Estimates pulmonary artery systolic pressure (via TR jet)
   • Assesses RV size/function
2. Right heart catheterization (RHC) = gold standard
   • Confirms PH and distinguishes:
     • Precapillary vs postcapillary via PCWP
3. Identify the cause
   • PFTs and imaging for lung disease
   • V/Q scan (often preferred screening test for CTEPH)
     • CTEPH classically has segmental perfusion defects
   • Consider HIV, connective tissue disease labs when appropriate

Key hemodynamic patterns you should be able to match

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Treatment: Match the Therapy to the PH Type

The “big rule”

• Treat the underlying cause first (especially Groups 2–4).
• Targeted PAH drugs are mainly for Group 1 (PAH) (and select other cases under specialist guidance).

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PAH (Group 1) Targeted Therapies (Most Testable Pharm)

1) Endothelin receptor antagonists

• Bosentan, Ambrisentan
• Mechanism: block endothelin-1 → ↓vasoconstriction, ↓smooth muscle proliferation
• High-yield adverse effects:
  • Hepatotoxicity (check LFTs)
  • Teratogenicity (pregnancy contraindication)

2) PDE-5 inhibitors

• Sildenafil, Tadalafil
• Mechanism: inhibit PDE-5 → ↑cGMP → potentiates NO → vasodilation
• High-yield adverse effects:
  • Headache, flushing, hypotension
• Contraindication: nitrates (profound hypotension)

3) Prostacyclin (PGI₂) analogs / prostacyclin pathway agonism

• Epoprostenol, Iloprost, Treprostinil
• Mechanism: ↑cAMP → vasodilation + ↓platelet aggregation + antiproliferative
• High-yield note: Epoprostenol is classically used in severe PAH and can improve survival.

4) Soluble guanylate cyclase stimulator

• Riociguat
• Mechanism: ↑cGMP (NO pathway enhancement)
• High-yield caution: avoid with PDE-5 inhibitors (hypotension risk)

Supportive measures (often vignette-relevant)

• Oxygen (especially hypoxic patients—critical in Group 3)
• Diuretics for right-sided volume overload
• Anticoagulation may be considered in select PAH/CTEPH contexts (exam questions often emphasize CTEPH requires anticoagulation)
• Lung transplant in refractory severe disease

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Group-Specific Pearls (Step 1/2 Favorite Traps)

Group 2 (left heart disease)

• Primary issue is elevated left atrial pressure → high PCWP
• Management: treat HF/valvular disease (not PAH-targeted meds as first-line)

Group 3 (lung disease/hypoxia)

• Oxygen is therapy (reduces hypoxic vasoconstriction)
• Treat COPD/ILD/OSA (CPAP for OSA)

Group 4 (CTEPH)

• Think: persistent dyspnea after PE
• Workup: V/Q scan
• Management:
  • Lifelong anticoagulation
  • Pulmonary endarterectomy (potentially curative in selected patients)
  • Riociguat can be used in inoperable CTEPH (classically tested)

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Classic USMLE-Style Vignettes (Recognize Quickly)

Vignette 1: Young woman + progressive dyspnea + loud P2

• Suspect idiopathic/heritable PAH
• Confirm with RHC
• Treat with endothelin antagonist / PDE-5 inhibitor / prostacyclin

Vignette 2: Scleroderma patient with exertional syncope

• Suspect PAH due to connective tissue disease
• Same PAH-targeted therapies (plus disease management)

Vignette 3: COPD patient with edema + JVD + loud P2

• Cor pulmonale (Group 3 mechanism)
• Key therapy: Oxygen, treat COPD; diuretics for volume overload

Vignette 4: Months after PE, still dyspneic

• CTEPH
• Screen with V/Q scan
• Treat with anticoagulation ± endarterectomy

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High-Yield Summary (What to Burn In)

• Gold standard diagnosis: Right heart catheterization
• Key sound: Loud P2
• Key consequence: RV hypertrophy → RV failure (cor pulmonale)
• Group 1 PAH pathogenesis: endothelial dysfunction → ↑endothelin, ↓NO/PGI₂ → vasoconstriction + remodeling
• BMPR2 = classic genetic association
• PAH drugs to know cold:
  Bosentan, Ambrisentan, Sildenafil/Tadalafil, Epoprostenol/Iloprost, Riociguat
• CTEPH: think V/Q scan, anticoagulation, possible endarterectomy
• Hypoxia-induced PH: treat with oxygen

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First Aid Cross-References (Concept Map)

Use these as “anchors” while you review:

• Pulmonary HTN & cor pulmonale (RV failure due to lung disease/PH)
• Hypoxic pulmonary vasoconstriction (Group 3 mechanism)
• Eisenmenger syndrome (late complication of congenital L→R shunts)
• Pulmonary pharmacology: PDE-5 inhibitors, endothelin antagonists, prostacyclin analogs
• Cardiac physiology: RV heave, split S2 physiology, JVP findings