Condition category
Circulatory System
Date applied
Date assigned
Last edited
Prospectively registered
Overall trial status
Recruitment status

Plain English Summary

Background and study aims
Stroke causes about 10% of all deaths worldwide, and much serious disability. Many strokes are caused by thick fatty deposits narrowing the carotid arteries, which are the main blood vessels in the neck that supply blood to the brain. People with this condition, called carotid artery stenosis, may have no symptoms from it (i.e., they are asymptomatic) until fragments of the deposits fall off, lodge in the brain and cause a major stroke. The standard operation to prevent this, carotid endarterectomy (CEA), involves surgical removal of the deposits before they cause a stroke. It involves some immediate risk but if successful, confers long-term protection. An alternative technique is carotid artery stenting (CAS), which involves placing a fine scaffolding (stent) inside the narrowed artery to hold it open indefinitely. The aim of this study is to compare the immediate risks and long-term benefits of CAS and CEA for the prevention of stroke.

Who can participate?
Asymptomatic carotid artery stenosis patients in need of some type of carotid artery treatment, but with substantial uncertainty about whether to treat with CEA or CAS.

What does the study involve?
Participants are randomly allocated to be treated with either CEA or CAS, and we compare the immediate hazards (mainly heart attack, stroke or death) and the stroke risks over the next few years. The type and severity of any strokes is also assessed.

What are the possible benefits and risks of participating?
Not provided at time of registration

Where is the study run from?
University of Oxford (UK)

When is the study starting and how long is it expected to run for?
April 2007 to December 2019

Who is funding the study?
Health Technology Assessment Programme (UK)

Who is the main contact?
Prof. Alison Halliday

Trial website

Contact information



Primary contact

Prof Alison Halliday


Contact details

University of Oxford
Richard Doll Building
Old Road Campus
Roosevelt Drive
United Kingdom
+44 (0)1865 617979

Additional identifiers

EudraCT number number


Protocol/serial number

HTA 06/301/233

Study information

Scientific title

Asymptomatic Carotid Surgery Trial 2: an international randomised trial to compare carotid endarterectomy with carotid artery stenting to prevent stroke



Study hypothesis

To compare:
1. The peri-procedural risks (within 30 days) of carotid endarterectomy (CEA) or carotid artery stenting (CAS)
2. The long-term (5-year) prevention of stroke and of disabling or fatal stroke

Ethics approval

Ethics approval for the lead centre (St George's, University of London): Hertfordshire 1 Ethics Committee, 11/10/2005, ref: 05/Q0201/66
All other centres have obtained ethics approval before recruitment of the first participant

Study design

International randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Patient information can be found at:


Stroke caused by stenosis in the carotid arteries


Carotid endarterectomy versus carotid artery stenting

Intervention type



Drug names

Primary outcome measure

1. Peri-procedural hazards (within 30 days) stroke, myocardial infarction and death
2. Long-term hazards (after 30 days) stroke and death

Secondary outcome measures

Cost-effectivness of CEA and CAS

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Patient in need of some type of carotid artery intervention, with substantial uncertainty about whether to treat with CEA or CAS
2. Carotid artery stenosis with no ipsilateral carotid territory symptoms within the last 6 months
3. Patient fit and willing for follow-up

Participant type


Age group




Target number of participants

At least 5000 patients

Participant exclusion criteria

1. Previous CEA or CAS in randomised artery
2. High risk of adverse events of trial treatment e.g. inaccessible stenosis
3. Small likelihood of worthwhile benefit e.g. low risk of stroke
4. Patient unable or unwilling to give informed consent

Recruitment start date


Recruitment end date



Countries of recruitment

Belgium, Bulgaria, Canada, China, Czech Republic, Egypt, Estonia, France, Germany, Greece, Hungary, Ireland, Israel, Italy, Japan, Kazakhstan, Netherlands, Norway, Poland, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom, United States of America

Trial participating centre

University of Oxford
United Kingdom

Sponsor information


University of Oxford (UK)

Sponsor details

Clinical Trials and Research Governance
Manor House
John Radcliffe Hospital
United Kingdom
+44 (0)1865 221 345

Sponsor type




Funder type


Funder name

Health Technology Assessment Programme

Alternative name(s)

NIHR Health Technology Assessment Programme, HTA

Funding Body Type

government organisation

Funding Body Subtype

National government


United Kingdom

Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

2009 protocol in:
2013 results in:

Publication citations

  1. Protocol

    Rudarakanchana N, Dialynas M, Halliday A, Asymptomatic Carotid Surgery Trial-2 (ACST-2): rationale for a randomised clinical trial comparing carotid endarterectomy with carotid artery stenting in patients with asymptomatic carotid artery stenosis., Eur J Vasc Endovasc Surg, 2009, 38, 2, 239-242, doi: 10.1016/j.ejvs.2009.05.010.

  2. Results

    , Halliday A, Bulbulia R, Gray W, Naughten A, den Hartog A, Delmestri A, Wallis C, le Conte S, Macdonald S, Status update and interim results from the asymptomatic carotid surgery trial-2 (ACST-2)., Eur J Vasc Endovasc Surg, 2013, 46, 5, 510-518, doi: 10.1016/j.ejvs.2013.07.020.

Additional files

Editorial Notes

16/03/2016: Plain English summary added. 09/12/2014: The overall trial end date was changed from 31/03/2012 to 31/12/2019. 02/09/2009: The sponsor was changed from St. George's University of London to University of Oxford.