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Randomized controlled trials: still the backbone of vascular surgery?

Prior to the introduction of evidence-based medicine, decision-making was largely based upon ‘intuitive reasoning’, whereby senior clinicians dictated practice based upon personal dogma, personal experience and (often) biased observational studies. This era began to end (in vascular surgery) following completion of the landmark randomized trials in carotid disease, which recruited patients throughout the 1980s. Despite scepticism amongst some surgeons of the time these particular randomized trials have stood the test of time and remain the cornerstone of virtually every guideline of practice to this day. The carotid randomized trials became a beacon for using ‘evidence’ rather than ‘intuitive reasoning’ and randomized trials have now been used to determine optimal practice in a plethora of carotid surgery and stenting trials, lower limb revascularization and numerous aortic aneurysm based studies.

The literature abounds with situations where practice (previously based on observational study data) was changed overnight following publication of a well-designed randomized trial. However, while observational studies are prone to selection bias, randomized trials bring their own unique limitations including problems with external validity, they take too long to complete, they are very expensive, they are notorious for problems with recruitment and they can frequently become obsolete. This has led to a (not unreasonable) call for more observational studies to be used in the development of practice guidelines. Unfortunately, the principle guideline bodies around the world, e.g. National Institute for Health and Care Excellence (NICE) and the American Heart Association (AHA), prioritize randomized trial evidence above all else. Until that changes, guideline makers will find it very difficult to deviate from using historical randomized trial evidence, even when high quality observational data suggest that ‘real world’ practice bears little comparison to that reported in the randomized trials. Nowhere is that more evident than in developing contemporary guidelines for the management of asymptomatic carotid disease.

Why is the management of asymptomatic carotid disease so controversial?

BACKGROUND

Despite level I evidence supporting a role for carotid endarterectomy (CEA) in the management of patients with asymptomatic carotid disease, there is surprisingly little international consensus regarding the optimal way to manage these patients.

METHODS

Review of current strategies for managing asymptomatic carotid disease

MAIN FINDINGS

Those favouring a pro-interventional approach argue that: (i) until new randomised trials demonstrate that best medical therapy (BMT) is better than CEA or carotid artery stenting (CAS) in preventing stroke, guidelines of practice should remain unchanged; (ii) strokes secondary to carotid thromboembolism harboured a potentially treatable asymptomatic lesion prior to the event. Because 80% of strokes are not preceded by a TIA/minor stroke, CEA/CAS is the only way of preventing these strokes; (iii) screening for carotid disease could identify patients with significant asymptomatic stenoses who could undergo prophylactic CEA/CAS in order to prevent avoidable stroke; (iv) international guidelines already advise that only 'highly-selected' patients should undergo CEA/CAS; (v) the 30-day risks of death/stroke after CEA/CAS are diminishing and this will increase long-term stroke prevention and (vi) the alleged decline in annualized stroke rates in medically treated patients is based upon flawed data.

CONCLUSIONS

The inescapable conclusion is that only a relatively small proportion of asymptomatic patients benefit from prophylactic CEA/CAS. The key question, therefore, remains; is society prepared to invest sufficient resources in identifying these 'high risk for stroke' patients so that they can benefit from aggressive BMT and CEA or CAS, leaving the majority of lower risk patients to be treated medically?