Pulmonary embolism (PE) is a common cardiovascular condition with an estimated incidence of 0.60 to 1.12 per 1000 inhabitants in the United States of America, and the diagnosis is challenging as patients with PE present with a wide array of symptoms.

Computed tomography pulmonary angriography (CTPA) and lung ventilation-perfusion scintigraphy (VQ) are considered the gold-standards in PE-diagnostics but may not always be feasible. CTPA is contraindicated by contrast allergy or renal failure and both modalities require involvement of multiple staff-members and transport of the patient. Lung scintigraphy cannot be performed in an emergency situation, with unstable patients and patients unable to comply to the examination.

Ultrasound represent a possible tool in confirming or dismissing clinical PE suspicion. Ultrasound is non-invasive and can be performed bedside by the clinician, an approach known as point-of-care ultrasound (PoCUS), reducing both time, radiation-exposure and costs.

The aim of this study is to investigate whether integrating cardiac, lung and deep venous ultrasound in the clinical evaluation of suspected PE reduces the need for referral to CTPA or lung scintigraphy, during emergency department work up, while maintaining safety standards.

All ultrasound examinations will be performed by a physician certified in ultrasound by the Danish Society for Emergency Physicians in accordance with the Danish Health Agency.

Based on ultrasonographic findings, PE suspicion is allocated to one of three categories:

1. Clinical suspicion of PE confirmed if ≥1 of the following ultrasound findings:

1. Visible proximal deep venous thrombus
2. ≥2 hypoechoic subpleural lung consolidations with a diameter of ≥0,5cm
3. Visible right ventricular thrombus
4. McConnell's sign if no known pulmonary hypertension, interstitial lung disease, COPD or pulmonary valve disease
5. D-sign present in both systole and diastole if no known pulmonary hypertension, interstitial lung disease, COPD or pulmonary valve disease

If PE is confirmed by ultrasound, the physician will apply the simplified pulmonary embolism severity index score (sPESI) and estimate risk of mortality within 30 days based on clinical signs and symptoms, cardiac troponin level and RV dysfunction. Patients with intermediate-high or high risk, requiring admission to a cardiology department will be referred for CTPA. Patients with low or intermediate-low risk, not requiring admission, will be discharged with anticoagulative treatment.

A thorough presentation of the sPESI-score and early mortality risk assessment is available in the 2019 collaborative guidelines by the ERS and ESC on the diagnosis and management of PE.

2. Further diagnostic imaging (CTPA or V/Q) required if ≥1 of the following ultrasound findings:

1. 1 hypoechoic subpleural lung consolidation with a diameter of ≥0,5cm
2. Pleural effusion not explained by other cause
3. Basal RVEDD/LVEDD >1.0 or an RV visibly larger than the LV
4. TAPSE <17 mm
5. No deep venous thrombus, no lung consolidation or effusion, no signs of RV strain or thrombus but strong clinical suspicion.
6. McConnell's or D-sign in the presence of known pulmonary hypertension, interstitial lung disease, COPD or pulmonary valve disease

If PE suspicion can be neither dismissed nor confirmed after ultrasound investigation, the patient will be referred to further investigation as usual with CTPA or lung scintigraphy. Subsequent plan will be in accordance with department guidelines.

3. Clinical suspicion of PE dismissed if ≥1 of the following ultrasound findings:

1. No deep venous thrombus, no lung consolidation or effusion, no signs of RV strain or thrombus and a plausible differential diagnosis or low clinical suspicion
2. Obvious differential diagnosis demonstrated on ultrasound (i.e., pneumonia, pneumothorax, interstitial syndrome, left sided heart failure)

If PE suspicion is dismissed by ultrasound investigation, the patient will be either discharged or subject to further investigations in accordance with department guidelines if indicated.

Inclusion Criteria:

• Referred or Admitted to an emergency department
• Clinical suspicion of PE raised by physician requiring further diagnostic imaging (Well's score 0-6 with elevated age-adjusted D-dimer or Wells score >6 regardless of D-dimer)

Exclusion Criteria:

• Refusal of informed consent
• Pregnancy
• Permanent mental disability
• Age <18 years
• Diagnosis of PE within the last 6 months
• Hemodynamic instability (systolic blood pressure <90 mmHg for at least two consecutive measurements)
• Ultrasound of heart, lungs or deep veins performed prior to enrollment