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Risk prediction of outcome following carotid endarterectomy
Copyright
Cardiovascular Surgery, Vol. 4, No. 3, pp. 338-339, 1996 Q 1996 The International Society for Cardiovascular Surgery Published by Elsevier Science Ltd. Printed in Great Britain 0967~2lW96 $15.00 + 0.00
0967-2109(95)00108-S
Risk prediction of outcome following endarterectomy
carotid
A. H. Davies, J. K. Hayward, I. Currie, S. E. A. Cole, A. Lopatazidis*, f? M. Lamont and R. N. Baird Department UK
of Vascular Studies and *Department
of Anaesthesia,
Bristol Royal Infirmary; Bristol,
The quoted combined mortality and morbidity following carotid endarterectomy is about S-7%. In an attempt to identify a subgroup of high risk patients, a review has been undertaken of 404 carotid endarterectomies performed between January 1985 and March 1994. The perioperative mortality rate was 2%. with 3.4% of patients experiencing transient neurological deficits and 4% permanent strokes. Multiple logistic regression analysis was used to estimate the influence on outcome of age, gender, indication for surgery, bilateral internal carotid artery disease, hypertension and smoking. No significant explanators were identified. Copyright 0 1996 The International Society for Cardiovasular Surgery. Keywords:
carotid endarterectomy.
stroke. death
The publication of the interim reports of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the MRC European Carotid Surgery Trial1,2 have not only defined the indications for surgery more clearly but have quoted figures of 5-7% for combined mortality and morbidity following carotid endarterectomy for transient ischaemic attacks. However, stroke rates of between 1.6% and 24% have also been quoted4-6. It has been stated that the indication for surgery and the presence of bilateral disease may be factors that affect the early outcome of carotid surgery 5,7-11. This study was aimed at assessing the effect of certain variables on the early outcome of carotid endarterectomy.
Method and patients Between January 1985 and March 1994, 404 carotid endarterectomies were carried out on 275 men and 129 women aged between 31 and 84 with a mean age of 66 years. The first 5-year experience of 203 carotid endarterectomies has been previously audited and published12. The procedures were all performed with systemic heparinization under general anaesthesia with a policy of non-selective shunting and with transcranial Correspondence Surgery, Charing
338
to: Mr A. H. Cross Hospital,
Davies, London
University Department W6 8RF, UK
of
Doppler monitoring in recent years. Data on the procedures were stored prospectively on a computerized data base. Multiple logistic regression was performed using the LOGIST procedure in the SAS package. Three outcome models were examined: (i) whether or not the patient had a ‘permament neurological deficit within the 30 days postoperatively; (ii) whether or not the patient had died by 30 days; and (iii) whether or not the patient had suffered either of the above outcomes. The potential explanators were all offered as binary (yes or no) variables: age less than 60, age more than 70, male gender, previous stroke, more than 50% internal carotid artery stenosison the contralateral side, receiving treatment for hypertension, and smoking. The logistic regression models estimated the logic of the probability (p) of a bad outcome, fitting an equation of the form log.{pl(l - p)} = I + A.EZ + B.E.2 + C.E3 +. . . etc., where I is the log.(odds ratio) for a bad outcome in the absence of any of the explanatory factors; El, E2, E3 etc. are the values (0 or 1) of the explanatory variables and A, B, C etc. are the log.(odds ratios) of the presence of the explanatory variables. A variable that has no significant effect will have a log.(odds ratio) that is not significantly different from zero. The regression process estimates the probability that the estimated log.(odds ratio) could have differed only randomly from zero (a log odds ratio of zero means an odds ratio of 1, which indicates no effect).
CARDIOVASCULAR
SURGERY
JUNE 1996 VOL 4 NO 3
Risk mble 1 Probablities that log odds ratios associated variables differed only randomly from zero Independent
variable
Dependent
with
explanatory
variable
Stroke (p value)
Death (p value)
Combined* (p value)
Younger than 60 years Older than 70 years Male gender Previous stroke Bilateral disease Hypertension Smoking
0.11 0.93 0.65 0.26 0.28 0.36 0.17
0.52 0.54 0.17 0.76 0.59 0.18 0.59
0.31 0.83 0.93 0.30 0.24 0.33 0.29
*Combined
stroke
= death and/or
factors
in carotid
endartefectomy:
A. N. Davies
et al.
with respect to bilateral disease were similar in both groups; however, it should be noted that the unit policy is now to shunt all cases. The benefits ol shunting are still the focus of ongoing debate4i9. I-Iowever, these results confirm those of Moore et aLx and Jansen et ~1.‘. In the former study the majority of patients were shunted’ and in the latter very intensive intraoperative monitoring was undertaken in order to select cases for shunting’. Naylor et al. have shown that age is an imporrant factor in determining outcome”, but jansen et LZ/.“ found no such significant effect in their logistic regression analysis, a fact confirmed by the presenr authors.
References 1.
Results The indications for surgery were stroke in 67 cases, transient ischaemic attack/amaurosis fugax in 3 IO, global in 12 and asymptomatic in 15. One hundred and seventy-one patients had bilateral disease. The mortality rate was 2%, the rate of transient neurological deficits was 3.4% and the permanent stroke rate was 4%. Sixteen patients had a permanent stroke, only three of whom had suffered a preoperative stroke, and nine occurred in the 171 patients who had bilateral carotid disease. In none of the outcome models did logistic regression identify any significant explanator (Table 1).
2.
3.
4. 5.
6.
7.
Discussion This study represents one unit’s experience with carotid endarterectomy for a range of clinical indications. The data from other studies have suggested that this procedure carries a higher risk in certain groups, especially those who have had a previous stroke Opl* or have significant bilateral disease7,13. The overall conclusions about risk factors are, however, contradictory5y8. Moore et aL8 found no difference in outcome with contralateral disease, though both Jansen’ and Naylor et al.” have all stated that indication for surgery is a determinant of outcome. This study, however, has not confirmed that a previous stroke makes any difference to outcome. This may well be because of the authors’ policy of waiting 6 weeks after a major stroke before performing a carotid endarterectomy, a policy also used by other centres’4p15. It has been previously shown that patients with bilateral carotid disease have a poorer outcome from surgery’. The importance of contralateral disease is also reflected in the fait that the CHAT classification takes into account the extent of vascular disease when used as an evaluator of outcome 13. In this series, the findings CARDWWSC!ULAR
SlJffiERV
JUNE 1996 VOL 4 NO 3
8.
9.
10.
11.
12.
13. 14.
1.5.
Paper
Clinical alert: benefit of carotid endarterectomc for patients with high grade stenosis of the internal carotid artery. National Institute of Neurological Disorder and Stroke. February 1991. European Carotid Surgery Trialists’ Collaborative Group. MR(: European Carotid Surgery Trial: interim resufta for symptomatic patients with severe (70-99%) or with mild
25 July 1995
339
Cardiovascular Surgery, Vol. 4, No. 3, pp. 338-339, 1996 Q 1996 The International Society for Cardiovascular Surgery Published by Elsevier Science Ltd. Printed in Great Britain 0967~2lW96 $15.00 + 0.00
0967-2109(95)00108-S
Risk prediction of outcome following endarterectomy
carotid
A. H. Davies, J. K. Hayward, I. Currie, S. E. A. Cole, A. Lopatazidis*, f? M. Lamont and R. N. Baird Department UK
of Vascular Studies and *Department
of Anaesthesia,
Bristol Royal Infirmary; Bristol,
The quoted combined mortality and morbidity following carotid endarterectomy is about S-7%. In an attempt to identify a subgroup of high risk patients, a review has been undertaken of 404 carotid endarterectomies performed between January 1985 and March 1994. The perioperative mortality rate was 2%. with 3.4% of patients experiencing transient neurological deficits and 4% permanent strokes. Multiple logistic regression analysis was used to estimate the influence on outcome of age, gender, indication for surgery, bilateral internal carotid artery disease, hypertension and smoking. No significant explanators were identified. Copyright 0 1996 The International Society for Cardiovasular Surgery. Keywords:
carotid endarterectomy.
stroke. death
The publication of the interim reports of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the MRC European Carotid Surgery Trial1,2 have not only defined the indications for surgery more clearly but have quoted figures of 5-7% for combined mortality and morbidity following carotid endarterectomy for transient ischaemic attacks. However, stroke rates of between 1.6% and 24% have also been quoted4-6. It has been stated that the indication for surgery and the presence of bilateral disease may be factors that affect the early outcome of carotid surgery 5,7-11. This study was aimed at assessing the effect of certain variables on the early outcome of carotid endarterectomy.
Method and patients Between January 1985 and March 1994, 404 carotid endarterectomies were carried out on 275 men and 129 women aged between 31 and 84 with a mean age of 66 years. The first 5-year experience of 203 carotid endarterectomies has been previously audited and published12. The procedures were all performed with systemic heparinization under general anaesthesia with a policy of non-selective shunting and with transcranial Correspondence Surgery, Charing
338
to: Mr A. H. Cross Hospital,
Davies, London
University Department W6 8RF, UK
of
Doppler monitoring in recent years. Data on the procedures were stored prospectively on a computerized data base. Multiple logistic regression was performed using the LOGIST procedure in the SAS package. Three outcome models were examined: (i) whether or not the patient had a ‘permament neurological deficit within the 30 days postoperatively; (ii) whether or not the patient had died by 30 days; and (iii) whether or not the patient had suffered either of the above outcomes. The potential explanators were all offered as binary (yes or no) variables: age less than 60, age more than 70, male gender, previous stroke, more than 50% internal carotid artery stenosison the contralateral side, receiving treatment for hypertension, and smoking. The logistic regression models estimated the logic of the probability (p) of a bad outcome, fitting an equation of the form log.{pl(l - p)} = I + A.EZ + B.E.2 + C.E3 +. . . etc., where I is the log.(odds ratio) for a bad outcome in the absence of any of the explanatory factors; El, E2, E3 etc. are the values (0 or 1) of the explanatory variables and A, B, C etc. are the log.(odds ratios) of the presence of the explanatory variables. A variable that has no significant effect will have a log.(odds ratio) that is not significantly different from zero. The regression process estimates the probability that the estimated log.(odds ratio) could have differed only randomly from zero (a log odds ratio of zero means an odds ratio of 1, which indicates no effect).
CARDIOVASCULAR
SURGERY
JUNE 1996 VOL 4 NO 3
Risk mble 1 Probablities that log odds ratios associated variables differed only randomly from zero Independent
variable
Dependent
with
explanatory
variable
Stroke (p value)
Death (p value)
Combined* (p value)
Younger than 60 years Older than 70 years Male gender Previous stroke Bilateral disease Hypertension Smoking
0.11 0.93 0.65 0.26 0.28 0.36 0.17
0.52 0.54 0.17 0.76 0.59 0.18 0.59
0.31 0.83 0.93 0.30 0.24 0.33 0.29
*Combined
stroke
= death and/or
factors
in carotid
endartefectomy:
A. N. Davies
et al.
with respect to bilateral disease were similar in both groups; however, it should be noted that the unit policy is now to shunt all cases. The benefits ol shunting are still the focus of ongoing debate4i9. I-Iowever, these results confirm those of Moore et aLx and Jansen et ~1.‘. In the former study the majority of patients were shunted’ and in the latter very intensive intraoperative monitoring was undertaken in order to select cases for shunting’. Naylor et al. have shown that age is an imporrant factor in determining outcome”, but jansen et LZ/.“ found no such significant effect in their logistic regression analysis, a fact confirmed by the presenr authors.
References 1.
Results The indications for surgery were stroke in 67 cases, transient ischaemic attack/amaurosis fugax in 3 IO, global in 12 and asymptomatic in 15. One hundred and seventy-one patients had bilateral disease. The mortality rate was 2%, the rate of transient neurological deficits was 3.4% and the permanent stroke rate was 4%. Sixteen patients had a permanent stroke, only three of whom had suffered a preoperative stroke, and nine occurred in the 171 patients who had bilateral carotid disease. In none of the outcome models did logistic regression identify any significant explanator (Table 1).
2.
3.
4. 5.
6.
7.
Discussion This study represents one unit’s experience with carotid endarterectomy for a range of clinical indications. The data from other studies have suggested that this procedure carries a higher risk in certain groups, especially those who have had a previous stroke Opl* or have significant bilateral disease7,13. The overall conclusions about risk factors are, however, contradictory5y8. Moore et aL8 found no difference in outcome with contralateral disease, though both Jansen’ and Naylor et al.” have all stated that indication for surgery is a determinant of outcome. This study, however, has not confirmed that a previous stroke makes any difference to outcome. This may well be because of the authors’ policy of waiting 6 weeks after a major stroke before performing a carotid endarterectomy, a policy also used by other centres’4p15. It has been previously shown that patients with bilateral carotid disease have a poorer outcome from surgery’. The importance of contralateral disease is also reflected in the fait that the CHAT classification takes into account the extent of vascular disease when used as an evaluator of outcome 13. In this series, the findings CARDWWSC!ULAR
SlJffiERV
JUNE 1996 VOL 4 NO 3
8.
9.
10.
11.
12.
13. 14.
1.5.
Paper
Clinical alert: benefit of carotid endarterectomc for patients with high grade stenosis of the internal carotid artery. National Institute of Neurological Disorder and Stroke. February 1991. European Carotid Surgery Trialists’ Collaborative Group. MR(: European Carotid Surgery Trial: interim resufta for symptomatic patients with severe (70-99%) or with mild
25 July 1995
339