Background Transient Ischaemic Attack (TIA) is a neurologic event with symptom resolution within 24 hours. Early specialist assessment of TIA reduces risk of stroke and death. NICE (2008) recommends patients with TIA are seen in specialist clinics within 24 hours (if high risk) and seven days (if low risk).

We aimed to develop a complex intervention for patients with low risk TIA presenting to the emergency ambulance service. The intervention was then to be used in the TIER feasibility trial, in line with the MRC guidance on staged development and evaluation of complex interventions.

Methods We conducted three interrelated activities to produce the TIER intervention:

• Survey of UK Ambulance Services (n=13) to gather information about TIA pathways already in use

• Scoping review of literature describing prehospital care of patients with TIA

• Synthesis of data and definition of the intervention by specialist panel of: paramedics; ED and stroke consultants; service users; ambulance service managers.

Results The panel defined the TIER intervention to include:

1. Protocol for paramedics to assess patients presenting with TIA and identify and refer low risk patients for prompt (<7 day) specialist review at TIA clinic

2. Patient Group Directive and information pack to allow paramedic administration of aspirin to patients left at home with referral to TIA clinic

3. Referral process via clinical desk in ambulance control room

4. Training package for paramedics

5. Agreement with TIA clinic service provider to ensure rapid review of referred patients

Conclusion We followed MRC guidance to develop a clinical intervention which assesses and refers low risk TIA patients requesting 999 care. We will test feasibility of implementing and evaluating this in the TIER feasibility trial. We will then develop a fully powered randomised multicentre trial, if findings indicate this is appropriate.