Treatment of severe carotid artery stenosis to prevent stroke is arguably the most significant and perhaps the best vascular reconstructive operation in the speciality as a whole. It is nothing short of an icon for evidence-based medicine, but it is not without challenges. An estimated 20% of carotid endarterectomy (CEA) procedures are done on so-called 'high-risk' patients, mostly related to unfavourable vascular or neck anatomy. Medical co-morbidities - cardiac mainly - can also increase risk or even preclude performance of CEA, although only infrequently.
Another challenge focuses on the question of whether community-based and low-volume operators can reproduce the results achieved at centres of excellence. In addition, CEA, as good as it may be, is a 'standard open operation' and, as such, is viewed with suspicion and increasing disdain by those who glorify all things less invasive and endovascular simply for being so. This is the setting in which carotid angioplasty stenting (CAS) evolved over a 25-year period. However, it has been over the past six to seven years that this procedure has come of age, due largely to the development and now routine utilisation of embolic protection technologies. Further refinements in techniques and equipment will undoubtedly occur, but they are likely to be evolutionary - not revolutionary - and gradual over time. It can be stated with some confidence today that the degree of technical standardisation and device development that has been achieved are here to stay, providing a good foundation for a discussion of the topic at hand.
Those who are strong proponents of CAS are not shy to advance their opinion that the procedure may be equivalent to CEA and that it offers patients a valuable and potentially better treatment alternative when high-risk factors for CEA exist. Furthermore, it is unmistakable that CAS champions - of a non-surgical background - want to advance the concept that carotid stent intervention is a procedure that can replace CEA for the majority of patients. The key question is whether this will ever happen, and if so, how soon and under what circumstances.
This brings us to our assignment for this article, that is, a discussion on the current status of CAS and a perspective on future projections for the next five years and beyond.
Current Status of Coronary Angioplasty Stenting
A summary of what is known today about CAS is detailed as follows (see Table 1):
- CAS has been proven to be non-inferior to CEA in the treatment of high-risk patients. The non-inferiority concept is one that sounds obscure and somewhat foreign to most clinicians. However, it is a well-accepted term in clinical research and statistical circles. The underlying thought is that a non-surgical percutaneous procedure need not be superior to an open surgical operation to be accepted and embraced, but it does need to be reasonably comparable and generally safe. Most of the medical world can agree on this.
- Distal filter embolic protection seems effective in preventing CAS-related major ipsilateral stroke, resulting in an incidence of less than 2%. On the downside, these filters do allow the passage of small particles. The clinical consequences of such microembolisation to the brain are still unclear and many well-respected investigators remain concerned. While the majority of individuals might be able to tolerate limited ischaemic injuries, the elderly and others with diminished cerebral reserve may not fare as well.
- Symptomatic patients, with a history of recent transient ischaemic attacks or stroke undergoing CAS are at increased risk when compared with those who are asymptomatic. This is likely related to both the nature of their stenosing carotid plaque and the status of the brain itself.
- The jury is still out on whether CAS is safe or appropriate for elderly patients. Stroke and mortality rates would appear to be significantly higher on octogenarians, and it would not be surprising if general consensus is reached soon on advising against CAS for such patients, especially those with asymptomatic carotid stenosis. These, in fact, may do better without any intervention at all.
- Incidence of peri-procedural myocardial infarction (MI) events, mostly non-Q wave, is definitely lower after CAS than after CEA surgery.
- CAS avoids cranial nerve injury altogether.
- Occurrence of post-CAS re-stenosis - requiring re-intervention - appears to be infrequent, with an incidence that may be lower than that following CEA. However, little, if any, meaningful data exist after two years.
- Long-term - greater than five years - stroke prevention after CAS remains largely unknown.
Future Projections for Coronary Angioplasty Stenting - The Next Five Years
Data from several on-going and future clinical trials will hopefully clarify the role of CAS in the management of patients who are not high risk for CEA. The non-high-risk patient population holds the key, perhaps, to the future of CAS since the largest 'market' for carotid revascularisation resides with this group, especially those who are asymptomatic. Approximately 70% of CEA operations performed in the US today are conducted on patients without symptoms.
One important piece missing in many of the trials and registries conducted over the past several years is the study of modern-day pharmacological treatment, especially the use of statins that may well make a significant difference. These will undoubtedly form part of all future trials, and are likely to be compared with surgical and/or interventional approaches in the management of asymptomatic patients. Much of this will be completed and their results disseminated within the next five years.
It is likely that asymptomatic patients with carotid stenosis may be treated increasingly without intervention in the future. This is in fact already happening in some European countries and worldwide.
It could also be predicted that, within the next five years, the issue of cerebral microembolisation - with use of distal filter protection - is going to be elucidated once and for all, allowing treating physicians to make better informed decisions on appropriateness and safety of CAS intervention for patients over the age of 80 and others who might have diminished reserve.
The relative merits of proximal occlusion devices will be studied on one or more clinical trials. It would appear that such devices may offer benefits in several situations where distal filters cannot or should not be used.
The nature of the plaque itself, as characterised by ultrasound, is something of great theoretical and practical importance. The impact on the CAS procedure itself and its outcome may be significant. It may even have influence on equipment choice in the future, i.e. the choice of open versus closed cell stent designs.
The concept that CAS should be offered almost exclusively to patients who are at high risk for CEA should be revisited. The result of such policy is that most patients undergoing stent intervention have one or more high-risk factors and unfavourable features. This carries significant potential for less-than- optimal outcomes. Some leading investigators are beginning to look at this paradigm in a different manner. In future, patients who are at low risk for CAS, as opposed to high risk for CEA should probably be sought. It may well be the best way to optimise interventional outcomes.
Lastly, what if any will be the future for CEA? While it is essentially impossible to predict with any degree of accuracy at this time, it would be safe to state that CEA will undoubtedly 'survive' in the foreseeable future, and its role - while somewhat diminished - will continue to be a most important one.