| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ann Thorac Surg 2004;78:142-148
© 2004 The Society of Thoracic Surgeons
a Cardiothoracic Surgery, Liverpool, United Kingdom
b Research and Development, The Cardiothoracic Centre-Liverpool, Liverpool, United Kingdom
Accepted for publication February 6, 2004.
* Address reprint requests to Dr Karthik, Yorkshire Heart Centre, Leeds General Infirmary, Great George St, Leeds LS17 8AP, UK
e-mail: suchkats{at}yahoo.com
 |
Abstract |
|---|
 Top Abstract IntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
METHODS: Between April 1997 and September 2001 a total of 4406 consecutive patients underwent coronary artery bypass grafting with revascularization to the left anterior descending artery. All data were collected prospectively except reasons for nonusage of the left internal mammary artery. Logistic regression and Cox proportional hazards analyses were used to adjust in-hospital and medium-term outcomes, respectively. Selection bias was controlled by constructing a propensity score. A case note review was carried out to determine reasons for nonusage.
RESULTS: A total of 4047 patients (91.8%) received the left internal mammary artery to the left anterior descending artery leaving 359 patients (8.2%) who did not. We found no difference in hospital mortality or morbidity, however, patients receiving the left internal mammary artery had a survival advantage at 4 years. Reasons for not using the left internal mammary artery were damage to the conduit (n = 44), poor flow (n = 43), poor lung function (n = 45), unstable symptoms (n = 24), vascular problems (n = 12), and 19 patients with "other" reasons (previous radiotherapy, chest wall deformity, and obese patients). Case notes had no reason stated for 146 patients and reasons for 26 patients were unobtainable.
CONCLUSIONS: Left internal mammary artery usage is not associated with any increase in hospital mortality and morbidity, but these patients have better medium-term survival. Injury on harvesting, poor flow, and poor lung function were the most common reasons for not using this conduit.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
In the past, some doubts have been raised about the in-hospital outcomes and morbidity in patients who received LIMA compared with those who have received vein grafts. However, there have been several reports illustrating that the early outcomes are as good as, if not better, in patients who received LIMA [5–7].
In view of the short- and long-term benefits revealed in various studies [2–7], it would be appropriate to consider LIMA to be the "gold standard" conduit of choice for surgical revascularization of the left anterior descending artery (LAD) [8]. Whereas the worldwide trend in the last two decades has been a steady increase in the usage of LIMA, not much is documented about the reasons for not using LIMA. Hence, we have designed a study to look at the experiences at our center with regard to LIMA usage. Although we looked at the patient characteristics and early and midterm outcomes of those having LIMA versus those in whom it was not used, the main focus of this project was to look into the case notes of those patients in whom the LAD was grafted, but LIMA was not used, to determine reasons for nonusage of LIMA.
|
Material and methods |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Data collection methods and definitions have been published previously [9]. Data collected prospectively included variables listed in Table 1 (preoperative) and Table 2 (in-hospital outcomes). A retrospective case note review was carried out to identify reasons for not using LIMA to LAD.
|
|
Patient follow-up
Patient records were linked to the National Strategic Tracing Service (NSTS), which records all causes of mortality in the United Kingdom to establish current vital statistics (as of July 31, 2002). Patients were matched to the NSTS based on patient name, National Health Service number, date of birth, gender, and postcode.
Statistical analysis
Categorical variables are shown as a percentage with 95% confidence intervals (CI). Comparisons were made with 
2 tests as appropriate. Standard statistical tests were used to calculate odds ratios (OR) and 95% CI. Parsonnet scores were calculated, modified to a regional standard [9] to assess differences in patient case mix, and are shown as a median with 25th and 75th percentiles. Logistic regression was used to examine the impact of LIMA usage on in-hospital mortality and morbidity, while adjusting for differences in patient characteristics (treatment selection bias) [11]. Deaths occurring as a function of time were described actuarially using the product-limit methodology of Kaplan–Meier [12]. To control for treatment selection bias, we used Cox proportional hazards analysis to calculate adjusted relative risk and to risk adjust the Kaplan–Meier survival curve [13].
Treatment selection bias was controlled for by constructing a propensity score [14]. The propensity score was the probability that a patient would receive LIMA and was constructed from the variables listed in Table 1 (C statistic = 0.75). Once the propensity score is constructed for each patient, there are three ways of using the score for comparisons: matching, stratification, and multivariable adjustment. Because of the small sample size available to us for this study, we have decided to use multivariable adjustment as matching would have reduced the study size even further and stratification can be difficult to interpret. The propensity score is then included along with the comparison variable (LIMA vs no LIMA) in multivariable analyses of outcome producing adjusted OR as shown in Table 2. The propensity score adjusts for the treatment selection bias, which is evident in Table 1, between the two groups [14]. In all cases a p value less than 0.05 was considered significant. All statistical analysis was performed retrospectively with SAS for Windows Version 8.2 (SAS Institute, Inc., Chicago, IL).
|
Results |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Table 1 lists study characteristics and the rate of LIMA use by patient subgroup. Clinical factors associated with low LIMA use included older age, females, smaller body mass index (BMI), increased severity of angina and dyspnea, poor left ventricular ejection fraction, emergency surgery, on-pump surgery, and patients with comorbid disease (history of diabetes, congestive cardiac failure, respiratory disease, cerebrovascular disease, and renal dysfunction). The median Parsonnet score for the LIMA group was 2.1 (25th and 75th percentiles: 1.0–4.2) compared with 4.2 (25th and 75th percentiles: 2.1–7.3) in the non-LIMA group (p < 0.001).
Reasons for nonusage of LIMA
Of the 4406 patients in our study, 5 patients received alternate arterial grafts to the LAD. In all cases, the radial artery was the conduit used. The reasons for not using the LIMA were documented in the patients' medical records in 187 cases (52.1%). These included 44 patient cases of damage/injury to LIMA on harvesting, 43 patient cases with poor flow in LIMA, 45 patient cases with poor lung function, 24 patient cases with unstable symptoms, 12 patient cases with vascular complications, and 19 patient cases with other reasons (previous radiotherapy to the chest wall, chest wall deformity, and obese patients with a short sternum). No apparent reason was stated for nonusage of LIMA in 146 patient cases (40.7%), whereas 26 patient case notes were unobtainable (7.2%).
In-hospital outcomes
Crude and adjusted OR for in-hospital outcomes (LIMA vs no LIMA) are shown in Table 2. In-hospital outcomes were adjusted for the propensity score which included emergency surgery, age at operation, off-pump surgery, sex, ejection fraction, cerebrovascular disease, respiratory disease, unstable angina, congestive cardiac failure, and body mass index.
Hospital mortality after CABG was 2.0% (95% CI 1.6–2.5) in patients receiving LIMA (n = 4047) and 4.5% (95% CI 2.6–7.3) in patients not receiving LIMA (n = 359) (p = 0.003; Table 3). After multivariate adjustment was made with the propensity score, patients receiving LIMA compared with patients not receiving LIMA were no longer associated with a lower incidence of in-hospital mortality (Table 4).
|
|
After multivariate adjustment with the propensity score, there was no association between LIMA use and postoperative stroke, myocardial infarction, reexploration for bleeding, renal failure, deep and superficial SWI, need for inotrope and IABP support, duration of mechanical ventilation, ICU length of stay and postoperative length of stay (Table 4).
Follow-up mortality
Three-hundred thirty-nine deaths (7.4% [95% CI 6.7–8.2]) occurred during the study period, with a mean follow-up of 2.9 years (standard deviation 1.4 years). The crude relative risk of long-term mortality for LIMA patients was 0.47 (p < 0.001; Fig 1).
Freedom from death in LIMA patients at 30 days, 1 year, 2 years, 3 years, and 4 years was 98.1%, 96.3%, 94.8%, 93.4%, and 92.0%, respectively, compared with 95.2%, 91.1%, 88.9%, 86.9%, and 83.4% for the non-LIMA patients.
|
|
|
Comment |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
An analysis of our database revealed several variations in patient characteristics in the LIMA and the non-LIMA groups. Women were less likely to receive LIMA compared with men. This was illustrated in several previous studies [15–17]. Elderly patients were also less likely to receive LIMA to LAD compared with younger patients. The longer patency of LIMA and its attendant benefits are probably less likely to benefit older patients.
Obese patients (BMI > 35 kg/m2) were less likely to receive LIMA than nonobese individuals. However, patients with a BMI less than 25 kg/m2 were also less likely to receive LIMA to the LAD. A previous study has shown a similar relationship with body surface area [16]. Although the reason for this is unclear, a possible reason could be the smaller sizes of LIMA in this subgroup.
The rates for LIMA usage were 61.5% in patient cases requiring emergency revascularization compared with 92.5% in the nonemergent group. The case note review revealed this to be a fairly common reason for nonusage of LIMA (0.54% of the total study group). The lower rate of LIMA usage in this group of patients is likely to be due to hemodynamic instability or a greater bleeding risk as these patients are often on antithrombotic and anticoagulant therapy. The perceived prognostic benefits of LIMA may not be as obvious in this group.
Upon further analysis of the preoperative variables by multivariate logistic regression, we found elderly patients (> 70years), patients with respiratory diseases, females, diabetics, patients with ejection fraction (EF) less than 30%, and patients undergoing emergency CABG were less likely to receive LIMA to LAD.
In the last two decades, LIMA usage has improved worldwide. Several patients, who would have been denied LIMA in the past because of the perceived early risks associated with LIMA usage, are now receiving it more often. There have been several observational studies in the last 10 years demonstrating not only the long-term benefits of LIMA usage, but also illustrating the protective effect of LIMA in the early postoperative period [5, 7].
In our study, there was a considerable difference in the crude mortality rates between the two groups with the patients receiving LIMA doing better. However, after adjusting for propensity score, this favorable effect was no longer evident. This also seems to be the case with the various measures of postoperative morbidity.
Although the overall trend is toward a better outcome in the LIMA group, none of the differences were statistically significant after adjusting for the various factors enumerated in Table 1. The reason for this becomes apparent on analyzing the modified Parsonnet scores (0.51 of the calculated Parsonnet score) [9]. Although the median score of the LIMA group was 2.1, that of the non-LIMA group was 4.2. This indicates that the patients not receiving LIMA were higher risk patients. Hence, on accounting for these differences, there is no marked advantage with regard to in-hospital outcomes. What is quite apparent is that there is certainly no disadvantage in terms of early outcomes in the LIMA group.
Several studies have shown some early benefits in patients with LIMA usage; however, no sound mechanism responsible for this advantage has been proposed. Among the reasons advanced for this early benefit are the early higher patency rates of LIMA. This however is debatable. Although Grondin and associates [18] have shown a 1-month occlusion rate of 10.9% for saphenous vein grafts versus 2.6% for IMA grafts, Sethi and associates [19] did not find any difference in the 7–10-day or 1-year patency rates of these two conduits. Dabal and associates [20] have recently shown that LIMA use is associated with better short-term outcomes in all patients including lower mortality rates, lower incidence of ventricular arrhythmias, shorter duration of ventilation and transfusion requirements, and shorter length of stay. They were able to demonstrate these benefits in certain high-risk groups such as women, diabetics, and elderly patients.
Another possible reason for the improved operative survival in the LIMA group, especially when the other proximal anastomosis is performed with a side-biting clamp, is the perfusion of this vital territory by LIMA as soon as the cross-clamp is removed [5]. However, this remains speculative and is essentially unproven.
Although the early benefits arising out of LIMA usage may be debatable, there have been several studies in the literature showing the long-term survival benefits of LIMA [3, 4]. In our study, we have been able to show a definite survival advantage for patients in whom LIMA was used and this advantage seems to be increasing with the passage of time. At 4 years, the adjusted freedom from death for the LIMA patients was 92%, whereas for patients without LIMA usage it was 88.2%. This is in accordance with most of the studies published.
To identify practices with regard to LIMA usage, we carried out a case note review of the patients who did not have LIMA used. In 1% of the study population, the cause was injury to LIMA while harvesting. In another 1%, the LIMA was discarded after harvesting as it was deemed to have poor flow. In another 1% of the patient cases, LIMA was not harvested either because of poor lung function, chronic obstructive airways disease (COAD), or emphysematous lungs. Patients who were too unstable before surgery and those who needed inotropic agents/IABP on induction of anesthesia or had cardiac arrest before sternotomy were the other major group of patients not receiving LIMA (0.54%). Arteriopaths and patients with extensive peripheral vascular diseases and arch vessel diseases were another subset of patients who did not receive LIMA to LAD. Among the other reasons for not using the LIMA were previous radiotherapy to the chest wall, chest wall deformity, and obese patients with a short sternum.
We acknowledge that often reasons mentioned in patient case notes represent the judgment of an individual surgeon to a given clinical situation. This study has definitely made us aware of a variety of reasons that may prevent LIMA usage in specific cases. One of the positive outcomes of this study has been a change in our data collection so that we can now collect reasons for not using the LIMA in individual cases. We anticipate that this will provide us with valuable information in the future which might help in regulating our practice further. A recent study of the Society of Thoracic Surgeons database reveals a LIMA usage of 81% across all coronary revascularization procedures in the United States [21]. We believe that a better awareness of reasons for nonusage of LIMA will probably lead to a gradual increase in this figure. We accept that LIMA usage will never be 100%; our aim during CABG should be to reach as close to that figure as possible with valid reasons for not using it in selected cases.
As results of CABG are improving, surgeons are taking up more challenging patient cases and operating on high-risk patients. At the same time, the results of individual surgeons and institutes are coming under greater scrutiny. As most units now conduct regular audits, it is inevitable that LIMA usage will be perceived as a measure of quality.
There are some limitations which may affect the conclusions drawn from our study. These include the retrospective observational design of the study. We have used propensity score adjustment to account for this, however this is no substitute for a properly designed randomized controlled trial. On the other hand, retrospective comparisons with propensity score adjustment are more versatile and may be more widely acceptable than randomized control trials [14]. A further limitation is that we have only assessed all-cause mortality rates, which means that cardiac related deaths are potentially overpredicted; however, we do not expect this to considerably affect our conclusions as the chances of a noncardiac related death are equal in both groups. This study also does not assess other long-term outcomes for these patients (eg, graft patency, reintervention rates, and quality of life). Such outcomes will be of interest as our experience grows. A final limitation of the study is the fact that we were only able to obtain a reason for nonusage in 52.1% of patient cases where the LIMA was not used. A more complete picture will become available to us in the next year or two with prospectively collected reasons for nonusage of LIMA.
In conclusion, there has been a steady increase in LIMA to LAD grafting at our center during the study period. LIMA was not associated with in-hospital mortality and morbidity; however, there is a notable mortality advantage in LIMA patients over a period of 4 years after surgery.
This study looks at reasons for nonusage of LIMA. The common reasons for not using the LIMA are damage during harvesting, poor flow in the LIMA after harvesting, and patients with poor lung functions/COAD—each of these being seen in at least 1% of the patient population. This study has also helped us identify patient groups in whom LIMA to LAD usage could be increased further. These groups include females, the obese, patients older than 70 years, and those undergoing emergency revascularization. We believe that maximizing LIMA to LAD usage is important, as it is quite likely to become a quality improvement marker for coronary artery bypass surgery.
|
Acknowledgments |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
|
References |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. Karthik, A. K. Srinivasan, A. D. Grayson, T. Friede, and B. M. Fabri Effect of the Left Internal Mammary Artery to the Left Anterior Descending Artery on Mortality and Morbidity After Combined Coronary and Valve Operations Ann. Thorac. Surg., July 1, 2005; 80(1): 163 - 169. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
