Monitoring of Carotid Artery Surgery

Correspondence Monitoring of Carotid Artery Surgery To the Editor: In 1999, two major prospective reports of symptomatic stenosis and a metaanalysis of asymptomatic stenosis firmly established the risk of conservative management of carotid stenosis.1-3 The crucial question that every clinician will now raise is: what is the operative risk in my surgical unit? The chances are great that the answer is unknown, leaving clinicians embarassed at not being able to provide adequate counseling for their patients. To prove statistically that the performance of a surgeon or unit falls below the range of good practice, when the risk of a deleterious event is only 5%, requires study of an excessively large number of patients. The analysis may be further flawed by an unfavorable case mix, as may occur in community or referral hospitals where a greater proportion of serious cases are seen. A schema that displays cumulative risk-adjusted scores can, however, rapidly show trends diverging from standard results,

irrespective of the case mix.4 Figure 1 represents our cumulative results from a 10-year series (from 1989 to 1998) of 272 isolated carotid artery endarterectomies. This figure incorporates success and failure in chronological order and takes into account previously estimated risk.5 The table (upper left panel) shows the magnitude of the increase (positive increment) or decrease (negative increment) for each patient as determined by preoperative risk. The increase is small for a patient with a low risk and large for another patient with a high risk who survives the operation without deficit. Should these two patients die or suffer a stroke, the decrease would be large for the first (low-risk) and small for the second (highrisk) patient. The graph (upper right panel) compares the cumulative score achieved in our series with the predicted one (calculated from the number of patients in each group and their respective predicted risk) and also shows the limit (called the alarm curve) that the curve should never cross. Finally, the figure (lower panel) plots the increment above (neurologic events saved) or below (neurologic events in excess) the zero-line (which represents the predicted line). Units that persistently stay below or diverge from this line should take action before excessive damage to patients occurs, and those that per-

Fig. 1. Cumulative scores and neurological events saved. Group A, asymptomatic; B, reversible neurologic deficit; C, partially reversible neurologic deficit; D, crescendo attacks and stroke in evolution. 540

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sistently stay above the line should offer surgery to patients with reduced spontaneous risk of stroke as defined in recent reports.1-3 DOI: 10.1007/s100169910069 Rene´ Preˆtre, MD Peter Benedikt, MD Mark I. Turina, MD Cardiovascular Surgery University Hospital 100 Ramistrasse 8091 Zurich, Switzerland

REFERENCES 1. European Carotid Surgery Trialists Collaborative Group. Randomised trial of endarterectomy for recently symptomatic ca-

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rotid stenosis: final results of the MRC European Carotid Surgery Trial (ECST). Lancet 1998;351:1379-1387. 2. Barnett HJM, Taylor DW, Eliasziw M, et al. Benefit of carotid endarterectomy in patients with symptomatic moderate or severe stenosis. N Engl J Med 1998;339:1415-1425. 3. Benavente O, Mohler D, Pham B. Carotid endarterectomy for asymptomatic carotid stenosis: a meta-analysis. BMJ 1998;317:1477-1480. 4. Lovegrove J, Valencia O, Treasure T, Sherlaw Johnson C, Gallivan S. Monitoring the results of cardiac surgery by variable life-adjusted display. Lancet 1997;350:1128-1130. 5. Moore WS, Mohr JP, Najafi H, Robertson JT, Stoney RJ, Toole JF. Carotid endarterectomy: practice guidelines. Report of the Ad Hoc Committee to the Joint Council of the Society for Vascular Surgery and the North American Chapter of the International Society for Cardiovascular Surgery. J Vasc Surg 1992;15:469-479.