ACST-2 (Second asymptomatic carotid surgery trial): stenting vs. surgery for tight carotid stenosis

Reported from the European Society of Cardiology ESC Congress 2021

Why this study/ The rationale-objective

In patients with severe carotid stenosis, carotid artery stenting (CAS) and carotid endarterectomy (CEA) have been shown to reduce recurrent strokes in symptomatic patients and have provided primary stroke prevention in asymptomatic patients by restoring patency. Both open and endovascular treatment modalities come with the risk of procedure-related disabling or non-disabling stroke, non-fatal myocardial infarction and death, all of which are halved in asymptomatic patients compared to symptomatic ones. 

Considering the shortage of related randomized data, the ACST-2 trial, the largest trial of carotid revascularization yet completed, aimed to compare short- and long-term outcomes between the two revascularization procedures in patients with asymptomatic carotid artery disease.

How was it executed? – the methodology

The ACST-2 is an international, multicentre and randomized trial, which included patients with severe unilateral or bilateral carotid stenosis (≥ 60 % stenosis on ultrasound) with no recent ipsilateral stroke or other symptoms from it. After further assessment with CT or MRI to confirm the eligibility for both treatments, the patients were randomized to either CAS or CEA. Patients with stroke or transient ischemic attack within the previous six months, previous ipsilateral intervention, unsuitable anatomy for CAS or CEA, recent acute myocardial infarction, high risk of cardiac emboli, or any major life-threatening condition were excluded from the study. 

The primary outcomes were procedural risks including death, MI, stroke at 30 days and non-procedural strokes during 5-year follow up.

What is the main result?

A total of 3,625 patients (CAS=1,811 and CEA=1,814) were included in the study. Nearly 90% of patients got good medical therapy consisting of lipid-lowering, antithrombotic, and antihypertensive medications. 

During the periprocedural period (30 days), death or disabling stroke (0.9% vs 1.0%, p=0.77) the rate of death, MI, or any stroke (3.9% vs 3.2%, p=0.26) were not different between the groups. However, in line with previous studies, the rate of periprocedural non-disabling stroke was higher in the stenting arm (2.7% vs 1.6%; P = 0.03).

At 5-year follow-up, death or disabling stroke rates (3.4% vs 3.5%, p=0.86) and the rate of fatal or disabling strokes  (2.5% in each arm, p=0.91) were basically identical between the groups. Neither was there a significant difference in the rate of any non-procedural stroke , although it was numerically slightly higher after CAS (5.2% vs 4.5%), driven mainly by non-disabling (mRS:0-2) strokes. This difference was not statistically significant.

Critical reading and the relevance for clinical practice

The ACST-2, the largest CAS versus CEA trial conducted, revealed that in asymptomatic patients with severe carotid stenosis, CAS was found to be as safe and effective as open surgery, with comparable short- and long term results. Nonetheless, there was a slightly increased rate of periprocedural minor strokes in the cas group, which were reversible and asymptomatic at six months. These strokes may be avoided by using technologies such as proximal occlusion embolic protection and double-layer stents that were used very rarely in this study. 

Reassuringly, the ACST-2 trial shows that regarding disabling and fatal stroke, CAS and CEA have comparable effects and risks and CAS is a reasonable alternative to CEA in  asymptomatic patients with severe carotid stenosis. However, the slightly increased periprocedural risk of minor strokes for CAS needs to be taken into account.

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