3.4 Pulmonary Embolism, Pulmonary Hypertension & Sleep Apnoea

Pulmonary Embolism (PE): Risk Stratification, Diagnostic Algorithms & ECG Features

Pulmonary Embolism (PE) is a life-threatening pulmonary vascular emergency resulting from occlusion of the pulmonary arterial bed by thromboemboli, originating primarily from deep vein thrombosis (DVT) of the lower limbs.

Clinical Risk Stratification: The Wells Score

In patients with suspected PE, clinical probability assessment dictates the initial diagnostic path.

Diagnostic Decision Algorithm

• Wells Score >4.0 ("PE Likely"): Proceed directly to CT Pulmonary Angiography (CTPA). If CTPA is contraindicated (severe renal impairment e.g., eGFR <30 mL/min, contrast anaphylaxis, pregnancy), perform a Ventilation-Perfusion (V/Q) SPECT scan. Therapeutic anticoagulation (e.g., LMWH) should be initiated while awaiting imaging unless contraindicated.
• Wells Score ≤4.0 ("PE Unlikely"): Perform a high-sensitivity D-dimer assay.
  • Negative D-dimer: PE is safely ruled out without imaging.
  • Positive D-dimer: Proceed to CTPA.

Pulmonary Embolism Rule-out Criteria (PERC)

In patients with a low pre-test probability of PE, the PERC rule can avoid unnecessary D-dimer testing. If ALL 8 criteria are satisfied, PE is ruled out without blood testing:

1. Age <50 years,
2. Heart rate <100 beats/min,
3. SpO2 ≥95% on room air,
4. No prior DVT or PE,
5. No recent trauma or surgery (<4 weeks),
6. No haemoptysis,
7. No exogenous estrogen use,
8. No unilateral leg swelling.

Electrocardiographic (ECG) Manifestations

• Sinus Tachycardia: Most common ECG finding (~40% of cases).
• Classic S1Q3T3 Pattern: Prominent S wave in lead I, Q wave in lead III, and inverted T wave in lead III (reflects acute cor pulmonale; present in <20% of cases).
• Right Ventricular Strain: Right axis deviation, right bundle branch block (RBBB), and T-wave inversions in leads V1–V4 and inferior leads (II, III, aVF).

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PE Severity Classification & Emergency Management

PE is classified by hemodynamic stability and mortality risk to guide escalation of therapeutic intervention.

Thrombolysis Protocol: In massive PE with cardiogenic shock, Alteplase 100 mg IV over 2 hours (or 0.6 mg/kg bolus over 15 minutes during cardiac arrest) is administered alongside Unfractionated Heparin (UFH). UFH is preferred over LMWH due to its short half-life and complete reversibility with protamine sulphate.

Anticoagulation Duration

• Provoked PE (transient major risk factor e.g., surgery, trauma, immobilisation): 3 months of anticoagulation.
• Unprovoked PE or ongoing persistent risk factor (active cancer, antiphospholipid syndrome): Indefinite (long-term) anticoagulation.

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Pulmonary Hypertension (PH): Definition, Classification & Targeted Therapies

Pulmonary Hypertension is defined hemodynamically via Right Heart Catheterisation (RHC) as a Mean Pulmonary Arterial Pressure (mPAP) >20 mmHg at rest.

Clinical Classification (5 ESC/ERS Groups)

1. Group 1: Pulmonary Arterial Hypertension (PAH): Precapillary PH defined by mPAP >20 mmHg, Pulmonary Artery Wedge Pressure (PAWP ≤15 mmHg), and Pulmonary Vascular Resistance (PVR >2 Wood units).
   • Etiologies: Idiopathic PAH, heritable (BMPR2 mutation), drug/toxin-induced (methamphetamine, appetite suppressants), connective tissue disease (Systemic Sclerosis), HIV infection, portal hypertension.
2. Group 2: PH Secondary to Left Heart Disease: Postcapillary PH (PAWP >15 mmHg). Most common overall cause (HFpEF, HFrEF, mitral/aortic valve disease).
3. Group 3: PH Secondary to Lung Disease / Hypoxia: Precapillary PH due to COPD, ILD, or OSA.
4. Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH): Precapillary PH caused by non-resolving organized thromboemboli. Diagnosed via V/Q scan showing unmatched perfusion defects. Potentially cured by Pulmonary Endarterectomy (PEA).
5. Group 5: PH with Unclear / Multifactorial Mechanisms: Hematologic, systemic, or metabolic disorders.

Targeted PAH Pharmacotherapy (Group 1 Only)

• Endothelin Receptor Antagonists (ERAs): Bosentan (dual ET-A/ET-B antagonist; requires monthly LFT monitoring due to hepatotoxicity), Ambrisentan (selective ET-A), Macitentan.
• Phosphodiesterase-5 (PDE-5) Inhibitors: Sildenafil, Tadalafil (increase cGMP to promote pulmonary vasodilation).
• Soluble Guanylate Cyclase (sGC) Stimulators: Riociguat (directly stimulates sGC to produce cGMP; approved for Group 1 PAH and inoperable Group 4 CTEPH; contraindicated with PDE-5 inhibitors).
• Prostacyclin Analogues & Receptor Agonists: Epoprostenol (continuous IV infusion), Iloprost (inhaled), Treprostinil, Selexipag (oral IP receptor agonist).

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Obstructive Sleep Apnoea (OSA) & Obesity Hypoventilation Syndrome (OHS)

Obstructive Sleep Apnoea (OSA) involves recurrent upper airway collapse during sleep, causing apnoeas (airflow cessation ≥10 sec) and hypopnoeas (≥30% airflow reduction with ≥3% oxygen desaturation or arousal).

Clinical Features & Diagnostic Grading

• Symptoms: Excessive daytime sleepiness (evaluated using the Epworth Sleepiness Scale [ESS], score >10 indicates excessive sleepiness), loud snoring, witnessed apnoeic pauses, morning headaches, nocturia, and impaired concentration.
• Polysomnography (PSG): Evaluates the Apnoea-Hypopnoea Index (AHI) (number of apnoeas and hypopnoeas per hour of sleep):
  • Normal: AHI <5 events/hour
  • Mild OSA: AHI 5–14 events/hour
  • Moderate OSA: AHI 15–29 events/hour
  • Severe OSA: AHI ≥30 events/hour

Management & Regulatory Driving Standards

• Continuous Positive Airway Pressure (CPAP): First-line gold standard therapy for moderate-to-severe OSA or symptomatic mild OSA. Pneumatically splints the pharyngeal airway open.
• Mandibular Advancement Devices (MAD): Custom oral appliances that advance the mandible, indicated for mild-to-moderate OSA or CPAP-intolerant patients.
• Obesity Hypoventilation Syndrome (OHS / Pickwickian Syndrome): Defined by the triad of:
  1. BMI ≥30 kg/m²,
  2. Daytime hypercapnia (PaCO2 >6.0 kPa / 45 mmHg), and
  3. Sleep-disordered breathing in the absence of alternative hypoventilatory causes. Treatment: Non-Invasive Ventilation (NIV / BiPAP) and targeted weight reduction.

Driver Licensing Regulations (DVLA / Irish RSA Rules): Patients diagnosed with OSA associated with excessive daytime sleepiness MUST cease driving immediately and notify the national driver licensing authority. Driving may resume only when sleepiness is fully controlled with documented CPAP adherence and medical confirmation.