This is a prospective, international, multicenter outcome cohort study. This study starts at the moment patients visit the outpatient clinic 3 to 6 months after a diagnosis of acute PE as part of routine medical care. If patients consent to study participation, the CTEPH clinical prediction score will be calculated. CTEPH is considered to be not present in patients with a low probability (≤6 points) and no symptoms suggestive of CTEPH, i.e. dyspnea on exertion, edema, newly developed palpitations, syncope or chest pains.The remaining patients with either high probability (>6 points) or who report symptoms that may be associated with CTEPH will be subjected to the 'rule-out criteria'. CTEPH will be assumed not present in patients with an age- and gender dependent normal NT-proBNP level (as defined by the assay's manufacturer), in the absence of any of the 3 ECG criteria. Patients who have an abnormal result from the 'rule-out criteria' will be referred for transthoracic echocardiography. All echocardiograms will be performed according to a predefined standardized protocol.

In case of echocardiographic intermediate or high probability of PH, patients will be referred for further diagnostic work-up of suspected CTEPH starting with perfusion lung scan or VQ-scan and right heart catheterization, of which the results will be discussed by an independent interdisciplinary working group of PH specialists, to ensure optimal diagnostic management. This latter diagnostic work-up of an abnormal echocardiograph lies within the setting of standard medical care.

All patients who were not diagnosed with pulmonary hypertension of any origin, or with NYHA class III or IV heart failure due to left ventricular systolic dysfunction, left ventricular diastolic dysfunction or significant valvular lesions, will be followed for a total of 2 years from the index PE diagnosis. During that period, the study protocol will not interfere with standard patient care, allowing diagnostic tests as deemed indicated by the treating physician including echocardiography in case of new respiratory symptoms. At the end of the follow-up period, all patients will be subjected to a second echocardiography that will be handled according to the above stated procedures to evaluate the presence of CTEPH.

This is a prospective, international, multicenter outcome cohort study. This study starts at the moment patients visit the outpatient clinic 3 to 6 months after a diagnosis of acute PE as part of routine medical care. If patients consent to study participation, the CTEPH clinical prediction score will be calculated. This score consists of 6 variables that should be assessed at the time of PE diagnosis: unprovoked PE (+6 points), known hypothyroidism (+3 points), diagnostic delay >2 weeks (+3 points), right ventricular dysfunction on computed tomography pulmonary angiography (CTPA) or echocardiography (+2 points), known diabetes mellitus (-3 points) and thrombolytic therapy or embolectomy for the acute PE event (-3 points) CTEPH is considered to be not present in patients with a low probability (≤6 points) and no symptoms suggestive of CTEPH, i.e. dyspnea on exertion, edema, newly developed palpitations, syncope or chest pains. The remaining patients with either high probability (>6 points) or who report symptoms that may be associated with CTEPH will be subjected to the 'rule-out criteria'. CTEPH will be assumed not present in patients with an age- and gender dependent normal NT-proBNP level (as defined by the assay's manufacturer), in the absence of these 3 ECG criteria: 1) rSR' or rSr' pattern in lead V1, 2) R:S >1 in lead V1 with R >0.5mV and 3) QRS axis >90o. Patients who have an abnormal result from the 'rule-out criteria' will be referred for transthoracic echocardiography. All echocardiograms will be judged by the echocardiographic criteria for suspected PH according to the 2015 ESC guidelines.

In case of echocardiographic intermediate or high probability of PH, patients will be referred for further diagnostic work-up of suspected CTEPH starting with perfusion lung scan or VQ-scan and right heart catheterization, of which the results will be discussed by an independent interdisciplinary working group of PH specialists, to ensure optimal diagnostic management. This latter diagnostic work-up of an abnormal echocardiograph lies within the setting of standard medical care.

All patients who were not diagnosed with pulmonary hypertension of any origin, or with NYHA class III or IV heart failure due to left ventricular systolic dysfunction, left ventricular diastolic dysfunction or significant valvular lesions, will be followed for a total of 2 years from the index PE diagnosis. During that period, the study protocol will not interfere with standard patient care, allowing diagnostic tests as deemed indicated by the treating physician including echocardiography in case of new respiratory symptoms. At the end of the follow-up period, all patients will be subjected to a second echocardiography that will be handled according to the above stated procedures to evaluate the presence of CTEPH.

Inclusion Criteria:

• All patients with an objectivated first or recurrent diagnosis of symptomatic acute PE, who have been treated for at least three months with therapeutically dosed anticoagulant therapy according to current guidelines;
• Signed and dated informed consent of the subject available before the start of any specific study procedures;
• Age ≥18 years;

Exclusion criteria:

• Known CTEPH or PH;
• Known (i.e. echocardiographic confirmed) NYHA class III or IV chronic heart failure due to left ventricular systolic dysfunction, left ventricular diastolic dysfunction or significant valvular lesions;
• Severe renal failure (eGFR <15 ml/min) or renal replacement therapy;
• Medical or psychological condition that would not permit completion of the study or signing of informed consent, including life expectancy less than six months, or unwillingness to sign informed consent;
• Non-compliance or inability to adhere to treatment or to the follow-up visits.

Consecutive patients treated for objectivated symptomatic acute PE