Deep vein thrombosis (DVT) can cause long-term scarring and narrowing of veins. When there is extensive damage to the veins in the legs, groin or abdomen it can affect the way that blood is able to flow back up to the heart. Some patients are left with severe symptoms such as pain, leg swelling and ulcers, and have surgical treatment with nitinol stents to re-open the veins and relieve symptoms. The primary aim of this study is to investigate venous blood flow to the heart during exercise in patients with extensive damage to the veins in the groin and abdomen after DVT, and changes that happen after stenting.

Participants will have cardiopulmonary exercise testing, 6 minute walk test and basic blood tests to establish exercise tolerance and rule out other heart and lung conditions. Exercise cardiac MRI will be used to evaluate cardiac function during exercise. All participants will complete generic and disease specific quality of life questionnaires.

Participants who are having a stenting procedure will repeat assessments 6-8 weeks after surgery.

Inclusion Criteria:

All groups:

->16 years of age

- Consent to participate in the research study and be willing to commit to study requirements, including completion of questionnaires and follow up visits.

Group 1:

• Venous thrombosis/obstruction involving the inferior vena cava >12 months ago.
• Symptoms of exertional dyspnoea reported by patient.
• Judged by the chief investigator as suitable for surgical intervention before recruitment to the study.
• Agree to adhere to therapeutic anticoagulation after surgical intervention.

Group 2:

• Venous thrombosis/obstruction involving the inferior vena cava >12 months ago.
• Under the clinical care of the deep venous service for surveillance of symptoms.

Group 3:

• Unilateral Iliofemoral venous thrombosis /obstruction >12 months ago.
• Judged by the chief investigator as suitable for surgical intervention before recruitment to the study.
• Agree to adhere to therapeutic anticoagulation after surgical intervention.

Exclusion Criteria:

All groups:

• DVT or PE in last 12 months
• Significant or untreated left sided heart disease (eg coronary artery disease, LV dysfunction, valvular abnormalities, congenital heart disease, chronic or paroxysmal arrhythmias)
• Significant or untreated chronic lung disease (eg asthma, COPD, ILD)
• Moderate to severe renal disease
• Moderate to severe liver disease
• Peripheral arterial disease
• Significant neurological or musculoskeletal disease
• Cognitive impairment or learning disabilities
• Pregnant or planning to become pregnant in next 12 months
• Active cancer (primary, metastatic or treated within last 6 months)
• Life expectancy < 2 years or chronic non-ambulatory status.
• Any other contraindication to exercise.
• Any contraindications to MRI scanning
• Inability to provide informed consent or comply with study assessments (e.g. due to cognitive impairment, physical limitations or geographic distance).

Group 4:

All of the above, plus:

• Previous DVT or PE
• Known, or clinical signs of chronic venous disease as judged by the chief investigator e.g. varicose veins, leg ulcers.

Participants with previous deep vein thrombosis /chronic outflow obstruction in the iliofemoral veins and inferior vena cava.