Pulmonary Vascular Diseases

Pulmonary Embolism - Clot Commotion

Obstruction of pulmonary artery/branches, often by dislodged thrombus from deep veins (DVT).

• Risk Factors: 📌 Virchow's Triad: SHE

  • Stasis (e.g., immobilization, surgery)
  • Hypercoagulability (e.g., OCPs, malignancy, genetic)
  • Endothelial injury (e.g., trauma, surgery)

• Types of Emboli: Thrombus (>95%), fat, air, amniotic fluid, tumor cells, septic emboli.

• Pathophysiology: ↑Dead space → V/Q mismatch; hypoxemia; ↑Pulmonary Vascular Resistance (PVR) → right ventricular strain.

• Clinical Features: Sudden onset dyspnea, pleuritic chest pain, hemoptysis, tachypnea, tachycardia, syncope (massive PE).

• Diagnosis:

  • Clinical probability: Wells score, PERC rule.
  • D-dimer: High sensitivity, low specificity.
  • CT Pulmonary Angiography (CTPA): Gold standard.
  • V/Q Scan: If CTPA contraindicated/inconclusive.
  • ECG: S1Q3T3 pattern (classic but uncommon), sinus tachycardia, RBBB.
  • Echocardiogram: RV dysfunction, McConnell's sign.

• Management:

  • Anticoagulation: LMWH/UFH, then DOACs/Warfarin.
  • Thrombolysis (e.g., alteplase): For massive PE (hypotension).
  • Embolectomy (catheter/surgical): For massive PE if thrombolysis fails/contraindicated.

• Complications: Chronic Thromboembolic Pulmonary Hypertension (CTEPH), right heart failure, death.

⭐ A normal D-dimer has a high negative predictive value to rule out PE in low-probability patients.

Pulmonary Hypertension - Pressure Overload

• Definition: Mean Pulmonary Arterial Pressure (mPAP) >20 mmHg at rest (2022 ESC/ERS).
• Pathophysiology: Vasoconstriction, vascular remodeling (e.g., intimal fibrosis, medial hypertrophy, plexiform lesions), microthrombosis, inflammation.
• WHO Classification (📌 Mnemonic: PAH, Left heart, Lung disease, CTEPH, Others - PLLCO)

  Group	Type	Examples
  1	PAH	Idiopathic, heritable, drug, CTD
  2	PH due to Left Heart Disease	LHD (LV dysfxn, valvular)
  3	PH due to Lung Diseases/Hypoxia	Lung disease/hypoxia (COPD, ILD, sleep apnea)
  4	CTEPH	CTEPH
  5	PH with Unclear Multifactorial Mechanisms	Unclear (hematologic, systemic, metabolic)

• Clinical Features: Dyspnea, fatigue, chest pain, syncope; RHF signs (edema, JVD, loud P2, RV heave).
• Investigations:
  • Echocardiography: Initial screening (estimates PASP, RV size/function).
  • Right Heart Catheterization (RHC): Gold standard (diagnosis, severity: mPAP, PVR >3 Wood units for pre-capillary PH; vasoreactivity testing).
• Management Principles:
  • Treat underlying cause.
  • General measures: Diuretics, oxygen, anticoagulation (select groups).
  • Targeted (Group 1 PAH): Prostanoids (epoprostenol), ERAs (bosentan), PDE5 inhibitors (sildenafil), sGC stimulators (riociguat).

⭐ Plexiform lesions are characteristic histopathological findings in advanced Group 1 Pulmonary Arterial Hypertension (PAH), indicating severe vascular remodeling.

Pulmonary Edema - Fluid Fiasco

• Definition: Abnormal accumulation of excess extravascular fluid in lung interstitium & alveoli.
• Pathophysiology: Imbalance in Starling forces: $J_v = L_p S ([P_c - P_i] - \sigma[\pi_c - \pi_i])$.
• Clinical Features: Dyspnea, orthopnea (esp. cardiogenic), pink frothy sputum.

High‑Yield Points - ⚡ Biggest Takeaways

• Pulmonary embolism (PE): Most commonly from DVT; Lines of Zahn indicate pre-mortem clot formation.
• Pulmonary hypertension (PHTN): Defined as mean pulmonary arterial pressure >20 mmHg; BMPR2 gene mutation is often implicated in primary PHTN.
• Common causes of secondary PHTN include COPD, mitral stenosis, recurrent PEs, and connective tissue diseases.
• Plexiform lesions in pulmonary arteries are pathognomonic for severe, irreversible PHTN.
• Fat embolism syndrome: Classic triad of respiratory distress, neurological symptoms, and petechial rash, typically after long bone fractures.
• Amniotic fluid embolism: Characterized by sudden DIC, profound shock, and severe hypoxia during or immediately post-delivery; high mortality rate.