Degree of stenosis: this refers to the maximum degree of linear stenosis at or around the symptomatic carotid bifurcation by method of measurement used in the NASCET trial and the Carotid Endarterectomy Trialists’ Collaboration.7,9 Accepted values for this variable are limited to between 50% and 99% stenosis. There is no evidence of benefit from endarterectomy in patients with <50% stenosis. It is important in cases where stenosis has been measured using non-invasive methods of imaging that users ensure that measurement of the degree of stenosis has been calibrated against the NASCET method of measurement on angiography, or that they transform the result using the previously determined formulae.10
Near-occlusion: The degree of stenosis by the NASCET method of measurement is invalid in patients with near-occlusion i.e. narrowing or collapse of post-stenotic internal carotid artery.9 The program will not therefore accept a specific degree of stenosis if the patient is also entered as a near-occlusion. However, the program automatically assumes that a near-occlusion is a severe stenosis.
Time since last event: refers to the most recent ipsilateral vascular symptomatic event. As outlined above accepted values for this variable are limited to between 7 days and 180 days. It should also be noted that the majority of patients in the ECST had only one or two events prior to presentation. The risk predictions will not apply to patients who have had many recurrent TIAs over months or years without having a stroke.
Primary symptomatic event: refers to the most “severe” ipsilateral vascular event during the previous 6 months (major stroke > minor stroke > multiple cerebral TIAs > single cerebral TIA > monocular TIA or retinal artery occlusion).
Major stroke is defined as a non-disabling stroke with residual neurological symptoms after 7 days.
Minor stroke is defined as a stroke with symptoms lasting between 24 hours and 7 days.
TIA is defined as an event with symptoms lasting up to 24 hours.
Diabetes (type 1 or 2), previous myocardial infarction, peripheral vascular disease: these variables refer to recent or previous confirmed clinical diagnoses irrespective of whether these conditions are currently symptomatic.
Treated hypertension: reflects a past history (i.e. prior to the current presentation with TIA or stroke) of hypertension that was considered to merit blood pressure lowering drugs. It should be noted that when the ECST was performed “hypertension” was usually defined as a BP of 160/90 or higher.
Irregular or ulcerated plaque surface: This definition was based on the surface morphology of the symptomatic carotid plaque as visualised on conventional arterial angiography, which was the imaging investigation of choice in the ECST. More detailed definitions are given elsewhere.11,12 If the patient has not undergone conventional angiography then please enter “Don’t know” and the program will give you the results for both ulcerated/irregular plaque and for smooth plaque separately. Angiographically irregular and ulcerated plaque have been shown to be highly correlated with lipid-rich unstable or ruptured plaques on histology.12
A patient with strong evidence of lipid rich or unstable/ruptured/ulcerated plaque on non-invasive imaging could therefore be entered as having irregular or ulcerated plaque.