Carotid stenosis intervention

External validity can also be affected if trials have protocols that differ from usual clinical practice. For example, prior to randomization in the trials of endarterectomy for symptomatic carotid stenosis patients had to be diagnosed by a neurologist and to have conventional arterial angiography, neither of which are routine in many centers. The trial intervention itself may also differ from that used in current practice, such as in the formulation and bioavailability of a drug, or the type of anesthetic used for an operation. The same can be true of the treatment in the control group in a trial, which may use a particularly low dose of the comparator drug or fall short of best current practice in some... 

In patients with known chronic cerebral ischemia related to underlying carotid artery stenotic lesions, CBF is usually preserved, at least initially, because of the cerebrovascular reserve. The cerebrovascular reserve represents the vasodilatation ability of cerebral arteries to compensate for a CBF tending to decrease and maintain this CBF at a normal level. In patients with chronic cerebral vascular disorders, it is necessary to quantify the residual cerebrovascular reserve and to distinguish tissue that has used only a limited fraction of its vasodilatation ability and still has cerebrovascular reserve available as a bulfer from tissue that has exhausted its vasodilatation ability and cerebrovascular reserve. The latter is at risk of ischemia, which can be triggered by any hemodynamic stress, and requires intervention to increased CBF, usually through carotid stenosis surgery or endovascular treatment, or extracranial-intracranial artery bypass (Nariai et al. 1995). 

Due to the very low event rates in patients with asymptomatic lesions of moderate severity (<60% diameter stenosis), it is unknown whether currently available interventional techniques can improve long-term outcomes over those achievable with optimal medical management. Also unresolved are the indications for carotid stenting in asymptomatic individuals with contralateral carotid occlusion (53) and those undergoing major cardiac or vascular surgery (54). 

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