Patients undergoing electrophysiology studies (EPS) and cardiac ablation procedure for the treatment of cardiac arrhythmias may be at increased risk of deep vein thrombosis (DVT) during or after the procedure, which may lead to pulmonary embolus which can be life threatening. The study will use Doppler ultrasound scanning at 24h and between 10-14 days post EPS and cardiac ablation to assess the incidence of undiagnosed DVT. A positive finding may provide support for a larger clinical trial to assess the benefit of prophylactic anticoagulation post EPS procedure.

Electrophysiological study (EPS) and catheter ablation is an established method for the assessment and treatment of many patients with cardiac arrhythmias (altered heart rhythm). It is generally carried out in patients who are usually otherwise fairly fit and healthy. In the UK many patients undergo this procedure and the numbers are increasing. The procedure involves a number of catheters (tubes) being inserted into the femoral vein over a period of up to 2 ½ hours. Presence of the catheter in the vein increases the risk of blood clot formation, if a clot blocks a deep vein in the leg (deep vein thrombosis), it can lead to pain and chronic leg swelling as well as the need for blood thinning (anticoagulant) medications. In some patients, fragments of the blood clot can break off and travel to the lungs which can be life-threatening. It is important to detect the presence of a clot as soon as possible, so that treatment may be given. The investigators hope to establish if the condition is more common than originally thought.

The investigators plan to recruit 100 patients who are due to undergo EPS or catheter ablation. Prior to the participant's clinical procedure, the investigators will perform an additional blood test to check blood clotting function. After the cardiac procedure, the participants will then undergo Doppler ultrasound scans at 24 hours and a second scan between 10-14 days to check for the presence of blood clots.

The aim of the study is to increase understanding of how often these blood clots occur and confirm if blood tests or current gold-standard imaging is best at showing the early stages of blood clot formation. The results of the study will help decide if a clinical trial is needed to test whether giving preventative blood thinning treatment after cardiac procedures would be beneficial.

Inclusion Criteria:

• Patients aged 18 - 80 undergoing elective EP study and catheter ablation
• Procedure duration between 30 minutes - 4 hours from the time of venous puncture to sheath removal
• 3-5 sheaths in a femoral vein

Exclusion Criteria (pre-procedure):

• Under 18
• Electrophysiology study only (no ablation performed)
• Inadequate understanding of spoken English
• Intubated/ventilated patients
• Unwilling to give consent to participation OR advised by consultee that this would be against the patient's wishes.
• Recently treated infection
• Intravascular implanted cardiac device
• Prior pacemaker extraction
• Prior cardiac surgery
• Previous cardiac ablation within 6 months
• Documented atrial flutter or atrial fibrillation within 1 year prior to ablation procedure.
• Participation in a clinical trial of an investigational medicinal product (CTIMP)
• Documented previous venous thrombosis or pulmonary embolism
• Known coagulopathy or anticoagulant use
• Known use of anti-platelet agent
• Known concurrent clinical problem likely to interfere with participation or completion of the study

Exclusion criteria (post-procedure):

• EPS carried out without ablation
• Left sided ablation or other clinical mandate for perioperative anticoagulation
• Complications during procedure (including arterial puncture or failure to advance venous wires)
• Peri-procedural complications that would, in the opinion of the PI/designee preclude further participation in the study
• Post-procedure bleeding or haematoma formation requiring prolonged (>30 minutes) pressure

Patients referred for elective EP study and catheter ablation.