Classification: What Is High-Risk Pulmonary Embolism?
The 2019 ESC guideline defines high-risk pulmonary embolism by haemodynamic instability. This includes three clinical presentations:
- cardiac arrest
- obstructive shock
- persistent hypotension
The thresholds for blood pressure and duration are set out in the current ESC guideline.
Pathophysiologically, the central problem is acute pressure overload of the right ventricle. The right ventricle dilates, and the septum shifts to the left. This impairs left ventricular filling and reduces cardiac output. As systemic pressure falls, coronary perfusion of the right ventricle also deteriorates. This creates a downward spiral that, without rapid reperfusion, often leads to cardiac arrest.
In the emergency setting, high-risk pulmonary embolism typically presents with:
- acute dyspnoea and tachypnoea
- hypoxaemia
- syncope
- distended neck veins
- signs of shock, often with unremarkable lung auscultation
None of these signs is specific on its own.
Emergency Diagnosis
Diagnostic Pathway in Unstable Patients
In haemodynamically stable patients, the first step is assessment of clinical probability, for example using scores and D-dimer. When high-risk pulmonary embolism is suspected, the 2019 ESC guideline provides a separate, shortened pathway:
- CT pulmonary angiography immediately available and transfer feasible: confirmation by CT.
- CT not immediately available or patient too unstable: bedside echocardiography is the first diagnostic step.
- Unequivocal right ventricular dysfunction with a compatible clinical picture: treatment as high-risk pulmonary embolism is justified without waiting for further imaging.
- No signs of right ventricular strain: according to the ESC, pulmonary embolism as the cause of shock becomes very unlikely. Other causes of shock then move to the forefront.
Assessing Right Ventricular Strain with Ultrasound
The following ultrasound findings suggest acute right ventricular strain:
- Dilated right ventricle: enlarged relative to the left ventricle in the apical four-chamber view.
- Flattened septum: "D sign" in the parasternal short-axis view, often with paradoxical septal motion.
- McConnell's sign: hypokinetic right ventricular free wall with preserved apical contraction.
- Impaired longitudinal function: reduced tricuspid annular plane systolic excursion (TAPSE).
- Distended inferior vena cava: dilated and showing little respiratory collapse.
- Direct thrombus detection: free-floating thrombus in the right heart ("thrombus in transit") or deep vein thrombosis on compression ultrasound of the leg veins.
Pitfalls:
- Chronic pressure overload: a hypertrophied right ventricular wall suggests chronic pulmonary hypertension. An acutely dilated, thin-walled ventricle suggests an acute event.
- Differential diagnoses: pericardial tamponade, hypovolaemia, left ventricular pump failure, tension pneumothorax and aortic dissection must be considered.
- Aortic dissection: it is also a contraindication to thrombolysis. If the clinical picture fits, the aortic root and pericardium should therefore be included in the same examination.
Ultrasound During Ongoing Resuscitation
The ERC Guidelines 2025 support point-of-care ultrasound during resuscitation under two conditions:
- It is performed only by experienced operators.
- It does not prolong interruptions to chest compressions.
A proven approach is to perform the examination during the rhythm-check pause and to record video clips for subsequent review.
Important for interpretation: a dilated right ventricle also develops during cardiac arrest in the absence of pulmonary embolism. During resuscitation, this finding alone is therefore not diagnostic. It must be assessed together with the history and circumstances.
Systemic Thrombolysis in Shock
The 2019 ESC guideline recommends systemic thrombolysis as the first-line reperfusion therapy in high-risk pulmonary embolism. Anticoagulation with unfractionated heparin should be started without delay. Dosing and coordination with thrombolysis follow the summary of product characteristics and the ESC guideline.
Alteplase Dosing
| Regimen | Dose | Status |
|---|---|---|
| Licensed regimen (summary of product characteristics) | 100 mg i.v.: 10 mg bolus over 1–2 min, then 90 mg over 2 h | licensed |
| Body weight < 65 kg | Total dose max. 1.5 mg/kg (summary of product characteristics) | licensed |
| Accelerated regimen (ESC 2019) | 0.6 mg/kg i.v. over 15 min, max. 50 mg | off-label, not licensed |
Practical notes:
- Preparation: after reconstitution, the concentration is 1 mg/ml, e.g. 50 mg in 50 ml. The licensed regimen therefore corresponds to 100 ml.
- Accelerated regimen: it is mentioned in the 2019 ESC guideline but is explicitly not licensed. It may be considered, for example, in extreme instability. The maximum dose of 50 mg is reached at a body weight of 84 kg, e.g. 42 mg at 70 kg.
- Weight-based dosing: body weight and the calculated dose are stated aloud within the team and cross-checked.
Contraindications
According to the summary of product characteristics, contraindications include:
- previous intracranial haemorrhage or stroke of unknown origin
- central nervous system damage, central nervous system tumour or arteriovenous malformation
- recent major trauma, surgery or head injury
- active bleeding or known bleeding diathesis
- aortic dissection
In high-risk pulmonary embolism and during resuscitation, these contraindications should be regarded as relative. Benefit and bleeding risk must be weighed individually. The decision should be documented in a traceable manner.
When Thrombolysis Is Not Possible or Fails
For situations with contraindications or lack of response, the 2019 ESC guideline lists the following alternatives:
- surgical embolectomy
- catheter-directed treatment
- extracorporeal circulatory support (ECMO) in refractory circulatory failure, only in combination with one of these reperfusion procedures
The evidence for these procedures is limited. Their availability depends heavily on the site. Early contact with a specialist centre is therefore advisable, ideally before thrombolysis has been completed.
Circulatory Support Until Reperfusion
The 2019 ESC guideline emphasises the particular features of the failing right ventricle:
- Fluids: administer fluids cautiously only. Further right ventricular dilatation can additionally impair left ventricular filling.
- Vasopressor: noradrenaline is established for stabilising systemic pressure and thus right ventricular coronary perfusion.
- Oxygenation: give oxygen liberally as needed; consider non-invasive options first.
- Induction of anaesthesia and intubation: anaesthetic agents and positive pressure ventilation can trigger circulatory collapse through vasodilatation and reduced venous return. If airway management is unavoidable, the following are required:
- an experienced team
- haemodynamically gentle induction
- a vasopressor running or drawn up
- readiness for resuscitation and thrombolysis
Pulmonary Embolism and Resuscitation
Pulmonary embolism is one of the reversible causes of cardiac arrest (Hs and Ts). The ERC Guidelines 2025 recommend considering fibrinolysis when pulmonary embolism is the suspected or confirmed cause.
Indications that pulmonary embolism may be the cause:
- known thrombosis or immobilisation
- recent surgery
- dyspnoea or syncope before collapse
- pulseless electrical activity (PEA) as the initial rhythm
None of these indications is conclusive. The decision remains a matter of clinical judgement.
Dosing During Resuscitation
- The ERC Guidelines 2025 do not specify a dosing regimen.
- The accelerated ESC regimen of 0.6 mg/kg i.v., maximum 50 mg (off-label), is frequently used.
- The ESC describes this regimen for administration over 15 min. An immediate bolus is to be distinguished from this.
- The local protocol is decisive. It should ideally be established in advance.
After Thrombolysis
- Resuscitation is continued for 60–90 min after thrombolysis, because the drug needs time to take effect.
- The decision to give thrombolysis should therefore be made early and not only at the end of a resuscitation attempt.
- For prolonged resuscitation, for example during transport, mechanical chest compression may be considered.
- Extracorporeal cardiopulmonary resuscitation (eCPR) is an option for selected patients in suitable settings.
- After return of spontaneous circulation, three points take priority:
- monitoring for bleeding complications
- continuation of anticoagulation
- prompt handover to a centre with interventional expertise
Key Points for Practice
- Definition: high-risk pulmonary embolism is defined by haemodynamic instability (ESC 2019).
- Imaging: in unstable patients, bedside echocardiography is the first step if CT is not immediately possible. Absence of right ventricular strain makes pulmonary embolism unlikely as the cause of shock.
- Ultrasound during resuscitation: it is helpful, but a dilated right ventricle is non-specific in this setting.
- Thrombolysis: the licensed regimen is 100 mg alteplase over 2 h; for < 65 kg max. 1.5 mg/kg. The accelerated regimen of 0.6 mg/kg (max. 50 mg) is off-label.
- Pulmonary embolism and resuscitation: consider fibrinolysis, follow the local protocol, continue resuscitation for 60–90 min after thrombolysis.
- Alternatives: in case of contraindication or failed thrombolysis, involve surgical or catheter-directed options early.
References
- Konstantinides SV, Meyer G, Becattini C et al. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism developed in collaboration with the European Respiratory Society (ERS). Eur Heart J 2020;41:543–603.
- Soar J, Böttiger BW et al. European Resuscitation Council Guidelines 2025 Adult Advanced Life Support. Resuscitation 2025;215 Suppl 1:110769 (Korrigendum 2026).
- Kurzfassung der Leitlinien des European Resuscitation Council 2025. Notfall Rettungsmed 2025.
- Fachinformation Alteplase (Boehringer Ingelheim) – aktuelle Fassung.
This article does not replace clinical judgement in the individual case or the current summary of product characteristics and guidelines.
