The course of both pulmonary embolism (PE) and one of its more relevant late complications, i.e. chronic thromboembolic pulmonary hypertension (CTEPH) is still substantially unknown.

Recent evidence has shown that the incidence of CTEPH is higher than previously believed, but this has not been confirmed by other studies. A clear link between PE and CTEPH has been questioned by some experts. A great number of patients affected by PE persistently have residual chronic thromboembolic material the meaning of which is a matter of debate. The evidence sustaining a link between chronic residual PE and subsequent PE recurrences or CTEPH is insufficient.

Thus, a nationwide, multicentre, prospective cohort study was designed with the following aims:

1. to ascertain the incidence of symptomatic CTEPH after a first episode of acute PE;
2. to ascertain the incidence of venous thromboembolic (VTE) recurrences after a first episode of acute PE;
3. to evaluate whether a relation exists between chronic residual PE and CTEPH
4. to evaluate whether a relation exists between chronic residual PE and VTE recurrences;
5. to evaluate whether a relation exists between persistent right ventricular dysfunction and CTEPH;
6. to evaluate whether a relation exists between persistent right ventricular dysfunction and PE recurrences.

For each enrolling centre, consecutive outpatients or inpatients with an objectively diagnosed first acute PE episode are considered eligible.

All patients enrolled in the study received a diagnosis of PE by means of chest CT scan, lung scanning or pulmonary angiography. All patients should undergo an echocardiographic examination during the acute phase of PE, when this is possible. All patients will be treated according to current international guidelines and local protocols. All surviving patients will receive an echocardiographic examination after 6 weeks and 6 months. All surviving patients will receive a perfusional pulmonary scintigraphy at 6 months and be subsequently followed up every 6 months for at least 3 years.

In case of clinical suspicion of VTE recurrence a diagnostic procedure will be performed in order to confirm the recurrent VTE episode ( Chest CT scan, lung scan, Pulmonary angiography, compressive ultrasound, phlebography, vein CT scan).

In case of clinical suspicion of CTEPH, a further diagnostic workup will be performed, consisting in echocardiography, ventilation/perfusion lung scanning, multidetector chest CT scanning, and pulmonary angiography, with direct measurement of the pulmonary-artery pressure.

The extension of pulmonary embolism during the acute phase will be graded according to a standardized scoring system by local investigators while the extension of chronic residual pulmonary embolism will be graded according to a standardized scoring system ( Meyer score) by both local investigators and an independent committee. All outcome events will be centrally adjudicated by an independent committee.

All clinical data ( initial data on medical history, clinical symptoms, presence of risk factors, diagnoses, diagnostic tests results, treatment type and duration, outcome events and other) will be collected by the local investigators in an electronic medical database. Related data will be sent to the coordinating centre on a regular basis. All recruiting centres will be regularly monitored by the coordinating Centre.

Inclusion Criteria:

• Consecutive Outpatients/Inpatients with acute first episode of acute pulmonary embolism

Exclusion Criteria:

• Pregnancy
• Age < 18 years
• expected survival < 2 years
• previous episodes of VTE
• need for anticoagulation for reasons other than VTE
• preexisting severe cardiac or pulmonary diseases
• preexisting diseases that could cause non thromboembolic pulmonary hypertension
• Patients geographically inaccessible for follow up
• Low compliance to anticoagulant therapy and planned diagnostic work-up
• Refusal to give written informed consent

Consecutive outpatients or inpatients with an objective diagnosis of first acute PE episode.