Carotid endarterectomy: does it work?

Carotid endarterectomy. Who needs it?

Although carotid endarterectomy is one of the most frequently performed operations in this country, recent evidence casts doubt on its advisability, particularly for patients with ocular manifestations of cerebral ischemia. The following evidence is that: the risk of future stroke in untreated patients with amaurosis fugax, retinal plaques, and infarcts is less than 3% per year, far lower than that expected for cerebral (hemispheric) transient ischemic attacks (TIAs); the perioperative risk of stroke and death after endarterectomy may be much higher than previously suspected; and aspirin is a comparatively risk-free and moderately effective alternative to endarterectomy. Because of the questions raised about the risk-to-benefit ratio of endarterectomy, patients with ocular manifestations of cerebral ischemia should be considered for this operation only as part of a proposed randomized collaborative study.

Cerebral haemodynamic changes after extracranial-intracranial bypass surgery

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in twelve patients with carotid artery occlusion. Follow-up studies were carried out at a mean interval of eleven weeks after extracranial-intracranial bypass surgery. Clinical improvement was observed in three patients who had presented with frequent transient ischaemic attacks. One patient with multiple vascular occlusions suffered a stroke at the time of surgery. Follow-up studies showed an increase of regional cerebral blood flow in only two of the twelve patients. In the group as a whole, there was no significant change of cerebral blood flow, oxygen consumption or fractional oxygen extraction after bypass surgery. The most consistent post-operative change, observed in eleven of the twelve patients, was a fall of cerebral blood volume in the cortical territory of the bypassed carotid artery (p less than 0.01). This effect was most marked in patients with bilateral carotid occlusion, in whom there was often an accompanying fall of blood volume in the contralateral hemisphere. The post-operative findings were consistent with an increase of regional cerebral perfusion pressure as a result of the bypass procedure. Although this effect is potentially of value, those patients with most to gain from bypass surgery may also run the highest risk of peri-operative cerebral ischaemia.

Derivation of clinical indications for carotid endarterectomy by an expert panel

We used a two-round consensus panel method to derive and rate the appropriateness of comprehensive sets of detailed clinical indications for performing carotid endarterectomy. Before meeting, nine nationally influential physicians rated 675 indications; after review and discussion, they rated 864. The method did not force unanimity; our purposes were not only to encourage agreement but also to uncover areas of disagreement concerning the procedure's appropriate use. The panelists agreed on the level of appropriateness for 54 per cent of the final 864 indications and disagreed on 18 per cent. Ratings were reliably reproduced six to eight months after the completion of the process. The physicians' indications and ratings were consistent with those in the literature, and statistical analysis demonstrated that they followed logical clinical rationale. We conclude that consensus methods that do not force agreement can be used with panels of physicians to produce detailed, reliable, and valid indications. They can also identify medically controversial reasons for using a procedure that can serve as a starting point for a research agenda.

IMPS (intact months of patient survival): an analysis of the results of carotid endarterectomy

The literature on carotid surgery for lesions appropriate to prior episodes of ischemia has been reviewed. Only one randomized study and six non-controlled reports give useful data (this despite more than thirty years of surgical activity in this field). When analyzed by the IMPS (intact months of patient survival) criterion, the randomized study failed to show benefit from surgery. This failure can be attributed to a high (35%) operative stroke and death rate. That sufficiently low operative stroke and death rates are readily achievable is not clear, however, only two of six relevant non-controlled series reported in the literature had operative stroke and death rates below the 10.4% level calculated as necessary for a "break-even" situation. Three of the six non-controlled series contain sufficient follow-up data to permit IMPS comparison against the "standard" of the control group of the randomized study. Against this "standard" only one of the three non-controlled studies would have "shown benefit" from surgery. Barnett, Plum, and Walton have called for audits of endarterectomy results in institutions in which such surgery is performed. It is suggested that such audits be done by the IMPS method, which gives appropriate weight to the effects of operative, as well as of long-term follow-up, strokes and deaths.

Carotid endarterectomy in Great Britain and Ireland

A survey of the practice of carotid surgery by 245 vascular and neurological surgeons in Great Britain and Ireland was conducted with a 96 per cent response. Ninety-six surgeons (41 per cent) performed at least one carotid endarterectomy in 1984 and a total of 1374 such operations were carried out in that year. The indications for carotid endarterectomy in order of frequency were transient ischaemic attack, minor stroke and stroke. Operation was hardly ever undertaken for asymptomatic carotid bruit. Eighty-six per cent of surgeons who performed carotid endarterectomy generally assessed patients in the first instance using techniques less invasive than conventional angiography, principally Doppler ultrasonography or digital subtraction angiography. Nevertheless, conventional angiograms were usually performed before surgery by 89 per cent of surgeons. Almost all surgeons operated only under general anaesthesia, while opinion on the use of an intraluminal shunt during carotid endarterectomy was divided. Despite an increase in the number of carotid endarterectomies in recent years, this operation is currently performed nineteen times less frequently in Great Britain and Ireland than in the USA. The reasons for this are explored and certain controversies surrounding carotid endarterectomy are discussed.

Risks of carotid endarterectomy. Toronto Cerebrovascular Study Group

An objective, retrospective review of 358 carotid endarterectomies performed in the neurosurgical teaching units of the University of Toronto in the year 1982 demonstrated a perioperative stroke rate of 3.9% and a death rate of 1.5%. Most (82%) surgical neurological complications occurred after the immediate post-operative period (24 hours). This high incidence of delayed stroke suggests that most perioperative strokes are embolic rather than hemodynamic. Careful operative technique and the use of anticoagulants and antiplatelet agents may be more important in preventing postoperative deficits than intraoperative monitoring and intraluminal shunting. Our figures and those of current published data indicate that a 5-6% combined morbidity and mortality should be expected in carotid endarterectomy. These data are critical both to decision making with the individual patient as well as in the planning of future carotid surgery trials.

Surgical versus nonoperative treatment of asymptomatic carotid stenosis. 290 patients documented by intravenous angiography

From 1980 through 1982, intravenous extracranial digital subtraction angiography (DSA) was performed in 6684 patients at the Cleveland Clinic. Of these, 290 previously unoperated patients had asymptomatic carotid stenosis exceeding 50% of lumen diameter on unequivocal DSA studies. Either the presence or the absence of carotid bruits substantially misrepresented the severity of angiographic stenosis on approximately 30% of sides. Nonoperative management was employed in 195 patients, including 104 (53%) who received antiplatelet therapy, while another group of 95 patients underwent prophylactic carotid endarterectomy. During mean follow-up intervals of 33-38 months, surgical treatment significantly reduced the cumulative incidence of subsequent neurologic events in men (p = 0.05). Statistically unconfirmed trends also suggested that carotid endarterectomy tended to prevent late strokes in subsets of patients with greater than 70% stenosis or bilateral carotid lesions. The overall stroke rate for women was higher in the surgical group (p = 0.03), in part because of their unusual risk for perioperative complications (9%) in this particular series.

Surgical versus nonoperative treatment of symptomatic carotid stenosis. 211 patients documented by intravenous angiography

From 1980 through 1982, intravenous extracranial digital subtraction angiography (DSA) was performed in 6684 patients at the Cleveland Clinic. Of these, 211 previously unoperated patients had prior transient ischemic attacks (TIA) or strokes in conjunction with greater than 50% carotid stenosis on unequivocal DSA studies. Nonoperative management was employed in 126 patients, including 120 (84%) who received antiplatelet therapy or formal anticoagulation. The remaining 85 patients underwent carotid endarterectomy. During a mean follow-up interval of 36 months, there was no overall difference in survival, late TIA, or stroke between the nonoperated and surgical cohorts. However, parity was maintained in these groups only because of the prevalence of intermediate (50-69%) stenotic lesions and stable internal carotid occlusions in the nonoperated group. Carotid endarterectomy provided superior stroke prevention for patients with greater than 70% unilateral stenosis (p = 0.04), for those with greater than 50% bilateral stenosis (p = 0.004), and for those with internal carotid occlusions associated with greater than 50% contralateral stenosis (p = 0.03). The special risk of such discrete subsets should be recognized in order to plan appropriate treatment at the present time, as well as to conduct safe clinical trials in the future.

Does treatment of hypertension explain the decline in mortality from stroke?

Mortality from stroke has been declining in New Zealand since 1950 and at an accelerating rate since the early 1970s. Hypertension is the single most important risk factor for stroke. The temporal association between the recent decline in mortality and an increase in the proportion of patients with hypertension detected and treated led to the assumption of a cause and effect relation. Data from studies of the prevalence of blood pressure carried out in the community and from therapeutic trials of the treatment of hypertension were used to estimate the proportion of the decline in mortality from stroke that could be accounted for by increased treatment of hypertension during 1973-82 in New Zealand. Treatment of hypertension was estimated to account for roughly 10% of the observed reduction in deaths from stroke. Greater understanding of the reasons for the decline in mortality from stroke is required.

Effect of perioperative platelet inhibition on postcarotid endarterectomy mural thrombus formation. Results of a prospective randomized controlled trial using aspirin and dipyridamole in humans

A prospective randomized double-blind trial was conducted to study the effect of platelet-inhibiting drugs on mural thrombus formation after carotid endarterectomy. Twenty-two patients undergoing carotid endarterectomy were randomly assigned to perioperative administration of an aspirin/dipyridamole combination or a placebo, and the postoperative results were compared. Autologous indium-111-labeled platelets were injected postoperatively, and platelet deposition was measured at the endarterectomy site. It was found that the treated group had a significant reduction in platelet accumulation compared with the placebo group. The results suggest that the perioperative use of aspirin/dipyridamole may reduce the risk of operative stroke and the long-term risk of repeat carotid stenosis.

The causes of stroke in the young

In a group of 75 patients under the age of 45 years with stroke, ischaemic cerebral infarction was diagnosed in 60 patients and primary intracerebral haemorrhage in 15. Trauma was found to be the commonest identifiable predisposing factor to cerebral infarction, being present in 13 cases (22%). Migraine was the second most commonly identified predisposing factor while atheroma and hypertension were infrequent. Such a high frequency of preceding trauma has not previously been described, perhaps because it is not generally appreciated that the delay between the traumatic event and subsequent stroke may be considerable. The diagnostic management of young stroke patients is considered with particular reference to the indications for specialized cardiac and neuroradiological investigations.

Decreased incidence and mortality of stroke

Dr. Whisnant argues persuasively that control of hypertension has played a major role in the decline of stroke. He offers a cohesive and logical overview on this decline and does so with data from his own vast experience and with the advantages of the Mayo Clinic system which includes a centralized population-based diagnostic index, neurological expertise and a high autopsy rate. However, neither Dr. Whisnant's arguments nor the Mayo Clinic data justify the conclusion that "treatment of hypertension is the only significant contributor to the decline of stroke."