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Pulmonary embolism

Background knowledge 🧠

Definition

  • Blockage of a pulmonary artery and/or its branches
  • Results in part of a lung being ventilated but not perfused
  • This is usually by a blood clot which has travelled from the deep veins of the legs (DVT)

Pathophysiology

  • Most commonly due to deep vein thrombosis (DVT) (thromboembolism)
    • Virchow’s triad: stasis, vessel wall injury, and hypercoagulability
  • Rarer causes of emboli: septic emboli (IE), fat (from fractures), air, amniotic fluid, or tumour

Risk factors

  • Recent surgery, especially orthopaedic procedures
  • Active cancer / malignancy
  • Oestrogen-containing contraception or hormone replacement therapy
  • Previous history of DVT or PE
  • Family history of DVT or PE
  • Pregnancy and postpartum
  • Extended travel (e.g., long-haul flights)
  • Thrombophilic conditions

Differentials for pleuritic chest pain

Cardiovascular Conditions

  • Pericarditis: pleuritic chest pain relieved by sitting fowards
  • Acute Myocardial Infarction (AMI): chest pain, dyspnoea, and elevated cardiac markers could suggest AMI
  • Congestive Heart Failure: shortness of breath and peripheral oedema may overlap with symptoms of PE

Pulmonary Conditions

  • Community-Acquired Pneumonia: features may include cough, fever, and focal chest signs on examination
  • Pneumothorax: sudden onset of unilateral chest pain and shortness of breath can mimic PE
  • COPD Exacerbation: chronic obstructive pulmonary disease patients may present with acute worsening of shortness of breath, which could be mistaken for PE

Gastrointestinal Causes

  • Gastro-oesophageal Reflux Disease (GERD): chest pain from GERD can be mistaken for the chest pain seen in PE
  • Gallbladder Disease: right upper quadrant pain and symptoms may mimic PE

Musculoskeletal Causes

  • Costochondritis: localised anterior chest pain that is reproducible on palpation can be confused with PE
  • Muscle Strain: musculoskeletal pain from strain or injury can occasionally mimic PE symptoms

Psychological Causes

  • Panic Attack/Anxiety Disorders: acute anxiety may cause symptoms like palpitations, chest pain, and shortness of breath, which overlap with PE symptoms

Other Conditions

  • Pleuritis: pain on respiration and pleuritic nature of the pain can sometimes be mistaken for PE
  • Aortic Dissection: acute onset of severe, tearing chest pain may be a clue to this life-threatening condition, which can mimic PE

Clinical Features 🌡️

Reduced oxygenation

  • Dyspnoea
  • Pale
  • Cyanosis
  • Tachypnoea, tachycardia
  • Decreased oxygen saturation

Infarction

  • Pleuritic chest pain
  • Haemoptysis (rare)
  • Pleural rub
  • Pleural effusion

Pulmonary hypertension and right ventricular strain

  • Increased JVP
  • Pulmonary oedema
  • RV heave
  • Gallop rhythm
  • Loud P2

Investigations 🧪

Initial investigations

  • D-dimer: sensitive but lacks specificity. Use to rule out the diagnosis if the two-level PE Wells score is low (<4).
  • Other bloods: FBC, U&E, CRP, troponin (to prognosticate)
  • ECG: possible patterns include: tachycardia; RV strain, i.e. T-wave inversion in right precordial and inferior leads; RBBB; right axis deviation; S1Q3T3; RA enlargement, i.e. P pulmonale; RV dilation, i.e. dominant R in V1
  • Chest radiograph: often normal, may show wedge infarcts, atelectasis or raised hemidiaphragm. Watermark sign is an area of reduced vascular markings. Important to exclude other causes for symptoms (e.g. pneumothorax, pneumonia).
  • ABG: characteristically shows type 1 respiratory failure with low CO2

Causes of a raised D-dimer

  • Pulmonary embolism / DVT (deep vein thrombosis)
  • Any infection (e.g pneumonia)
  • Myocardial infarction (MI)
  • Recent surgery
  • Sepsis
  • Pregnancy
  • Cancer: Certain malignancies can lead to a hypercoagulable state, raising D-dimer levels.
  • Liver Disease: As the liver plays a role in clotting, liver diseases can influence D-dimer levels.
  • Renal Disease: Impaired renal function can also lead to elevated D-dimer.
  • Inflammatory Conditions: Non-infectious inflammatory diseases like rheumatoid arthritis can also raise D-dimer levels.

The clinical context is essential in interpreting raised D-dimer levels to differentiate between various possible underlying conditions.

Diagnostic investigations

  • CT pulmonary angiography (CTPA) will show filling defects within the pulmonary vasculature (indicated by the red arrow above) with acute pulmonary emboli
  • V/Q (Ventilation/Perfusion) scan: used for patients with normal chest radiograph in whom it is preferable to avoid CT-related radiation (e.g. young patients, pregnancy)

Additional tests

If unprovoked, consider testing for:

  • Malignancy: undertake history, examination and basic blood tests (FBC, U&Es, LFTs, coagulation screen); further investigations only if relevant symptoms/signs
  • Antiphospholipid syndrome: check antiphospholipid antibodies if antiphospholipid syndrome suspected
  • Hereditary thrombophilia: consider testing if first-degree relative also has DVT or PE

Management 🥼

Initial management

  • Supportive measures where needed: oxygen, IV fluids
  • Anticoagulation: LMWH (e.g., enoxaparin), direct oral anticoagulants (DOACs) or warfarin
    • 3 months if provoked and provoking factor no longer present
    • Consider long-term anticoagulation if unprovoked or ongoing risk factor
  • Thrombolytic therapy: in high-risk PE (hemodynamic instability)
  • Insertion of an inferior vena cava (IVC) filter may be considered if anticoagulation is contraindicated

Thrombolysis indications, contraindications and risks

Indications

  • High-risk PE: PE with haemodynamic instability
  • Some guidelines also advocate for thrombolysis in high-risk patients who have not yet developed severe symptoms but display markers of right ventricular dysfunction or myocardial injury.

Contraindications

  • Active Bleeding: thrombolysis is contraindicated in patients with active bleeding or a high risk of uncontrollable haemorrhage
  • Recent Surgery: recent major surgery, particularly involving the central nervous system, eyes or spinal cord
  • History of haemorrhagic stroke: patients with a history of haemorrhagic stroke should not undergo thrombolysis for PE
  • Uncontrolled Hypertension: elevated blood pressure that is not adequately controlled is also a contraindication

Risks / Complications

  • Bleeding: the most significant risk associated with thrombolysis is bleeding, which could be systemic or localised. The risk is heightened in patients with contraindications.
  • Reperfusion Injury: rapid dissolution of the thrombus can lead to reperfusion injury, causing a cascade of inflammatory responses
  • Allergic Reactions: allergic reactions to the thrombolytic agent may occur, although they are rare
  • Arrhythmias: thrombolysis can also predispose to arrhythmias as a result of myocardial injury or reperfusion

Additional Notes

  • Post-thrombolysis, anticoagulation is essential to prevent recurrence. The patient is initially treated with unfractionated heparin before transitioning to warfarin, with regular monitoring of the International Normalised Ratio (INR).

Complications of pulmonary embolism

  • Chronic thromboembolic pulmonary hypertension
  • Recurrent VTE
  • Death, especially if high-risk PE or undiagnosed/untreated

Relevant guidelines…

NICE ‘NG158 Venous thromboembolic diseases: diagnosis, management and thrombophilia testing’ 2020

European Society of Cardiology ‘Guidelines for the diagnosis and management of acute pulmonary embolism’ 2019

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