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Ann Thorac Surg 2001;71:1949-1958
© 2001 The Society of Thoracic Surgeons
a Miami Heart Research Institute, Miami Beach, Florida, USA
Address reprint requests to Dr Kurlansky, Miami Heart Research Institute, 801 Arthur Godfrey Rd, 5 Fl, Miami Beach, FL 33140
Presented at the Forty-seventh Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 9–11, 2000.
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Abstract |
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Methods. A retrospective analysis was performed comparing 261 consecutive women from a single surgical practice receiving BIMA and supplemental vein grafts between January 1972 and October 1994 with a computer-matched cohort of 261 women receiving single internal mammary artery (SIMA) and vein grafts during the same period. Univariate analysis confirmed the homogeneity of the two groups based on nine preoperative variables.
Results. Operative mortality was comparable in the two groups, 3.8% (10 of 261 patients) in the SIMA and 3.4% (9 of 261 patients) in the BIMA group, with a markedly reduced mortality in both groups since 1990, 2.3% (2 of 86 patients) in the SIMA and 1.3% (1 of 78 patients) in the BIMA group. The mean number of distal grafts (2.78, SIMA; 3.14, BIMA), perfusion time (104 minutes, SIMA; 108 minutes, BIMA), and cross-clamp time (58 minutes, SIMA; 66 minutes, BIMA) were all comparable. There was no significant difference in the incidence of postoperative complications, including sternal wound infection. Patient follow-up ranged from 1 month to 27 years, with a mean of 10.0 years in the SIMA group and 9.1 years in the BIMA group. Clinical results were excellent, with 100% (136 of 136 patients) of the SIMA and 100% (167 of 167 patients) of the BIMA patients in Canadian Cardiovascular Society class I or II at follow-up. Rates of late myocardial infarction, percutaneous transluminal coronary angioplasty, and reoperation were similarly low in both groups: 3.7% (5 of 136 patients) versus 1.8% (3 of 166 patients), 5.4% (7 of 136 patients) versus 4.8% (8 of 166 patients), and 3.7% (5 of 136 patients) versus 1.8% (3 of 166 patients), for SIMA versus BIMA survivors, respectively. No significant difference was found in the long-term and event-free survival or in any of the eight subscales of the SF-36 quality of life survey for the two groups.
Conclusions. Excellent short- and long-term results have been demonstrated with internal mammary artery grafting in women. However, the addition of a second internal mammary artery graft does not appear to confer any additional clinical benefits in a comparably matched cohort of patients.
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsCommentAcknowledgmentsDiscussionReferences |
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These findings have been attributed to numerous risk factors in women including the incidence of diabetes [4, 5], smaller body habitus [6], coronary artery size [7], and functional status [8]. Analyses of these factors have failed to generate a therapeutic solution to the problem. The internal mammary artery (IMA) has become the conduit of choice for coronary artery bypass grafting. Long-term patency rates are superior to those achieved with saphenous vein grafts. Patient survival and freedom from reoperation and the occurrence of late cardiac events have also clearly improved with the use of the IMA [9]. Moreover, the IMA has been shown to ameliorate the influence of gender on operative and long-term mortality [10, 11].
Bilateral internal mammary artery (BIMA) grafting has demonstrated excellent perioperative and long-term clinical results in women [12]. However, the incremental benefits of a second IMA graft remains controversial in patients undergoing surgical revascularization [13, 14]. In female patients, this issue remains unexplored.
The purpose of this report is to review the long-term clinical outcomes in a computer-matched cohort of women receiving single or BIMA grafting. Furthermore, perioperative morbidity and mortality rates, freedom from recurrent angina and major adverse late cardiac events, as well as patient long-term survival and quality of life are examined.
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Patients and methods |
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Patients in the SIMA group ranged in age from 36 to 81 years (mean, 65.1 ± 8.8 years) and in the BIMA group, 32 to 84 years (mean, 65.1 ± 9.5 years). There were 154 patients (59.0%) in the SIMA group who had a family history of coronary artery disease and 159 (60.9%) in the BIMA group. One hundred twelve patients (42.9%) in the SIMA group had hypertension and 110 patients (42.1%) in the BIMA group. In the SIMA group, 41 patients (15.7%) had hypercholesteremia and 41 (15.7%) in the BIMA group. There were 72 patients (27.6%) in the SIMA group with diabetes mellitus and 71 (27.2%) in the BIMA group.
There were 4 patients (1.5%) in the SIMA group who had renal dysfunction (creatinine level, 2.0 mg/dL) and 4 (1.5%) in the BIMA group. Eleven patients (4.2%) in the SIMA group had peripheral vascular disease and 11 (4.2%) in the BIMA group. In the SIMA group, 126 (48.3%) had at least one myocardial infarction before operation. The timing of the myocardial infarction revealed that 36 patients (13.8%) in the SIMA group had a history of a recent myocardial infarction (< 3 weeks) and 76 patients (29.1%) had a remote myocardial infarction (> 3 weeks). In 14 patients (5.4%), the timing of the myocardial infarction was not documented. In the BIMA group, 129 patients (49.4%) had at least one myocardial infarction before operation. Thirty-nine patients (14.9%) had a history of a recent myocardial infarction (< 3 weeks) and 80 patients (30.7%) had a remote myocardial infarction (> 3 weeks). In 10 patients (3.8%), the timing of the myocardial infarction was unknown.
The patient’s preoperative angina status was ranked according to the Canadian Cardiovascular Society classification system. In the SIMA group, 4 patients (1.5%) were in class II, 118 patients (45.2%) in class III, and 139 patients (53.2%) in class IV. In the BIMA group, 6 patients (2.3%) were in class II, 117 patients (45.2%) in class III, and 138 patients (52.9%) in class IV. Patients in unstable condition constituted the group with class III or IV symptomatology. There were 37 patients (14.1%) in the SIMA group and 34 patients (13.0%) in the BIMA group who had a history of congestive heart failure.
There were 40 patients (15.3%) in the SIMA group and 24 patients (9.2%) in the BIMA group who had previously undergone percutaneous transluminal coronary angioplasty. Twelve patients (4.6%) in each of the groups had previously undergone coronary artery bypass grafting.
Preoperative angiographic findings
All patients in the study had selective coronary angiography before operation. Significant coronary artery disease was defined as an estimated reduction in luminal diameter of 50% or more. Preoperative angiographic findings in the SIMA group revealed that 32 patients (12.3%) had single-vessel disease, 57 patients (21.2%) double-vessel disease and 172 patients (65.9%) triple-vessel disease. In the BIMA group, 50 patients (19.2%) had double-vessel disease, and 211 patients (80.8%) triple-vessel disease. A greater proportion of the BIMA patients had triple-vessel disease (p = 0.001). There were 54 patients (12.7%) in both the SIMA and BIMA groups with left main disease greater than 0.50.
Ejection fraction determination from left ventriculography was available in all patients (100%) in both groups. In the SIMA group, the ejection fraction was greater than 0.50 in 200 patients (76.6%), between 0.30 and 0.50 in 54 patients (20.7%), and less than 0.30 in 7 patients (2.7%). In the BIMA group, the ejection fraction was greater than 0.50 in 203 patients (77.8%), between 0.30 and 0.50 in 51 patients (19.5%), and less than 0.30 in 7 patients (2.7%). The clinical characteristics of the patient population are summarized in Table 1.
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Operative data
The types of conduit and corresponding recipient arteries by patient group are presented in Table 2. In the SIMA group, there were 22 sequential IMA grafts and 100 sequential vein grafts. There were 4 left IMA and 17 right IMA free grafts.
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A total of 726 coronary artery grafts were performed in the SIMA group (mean, 2.78 per patient; range, 1 to 6). In the BIMA group, a total of 820 grafts (mean, 3.14 per patient; range, 2 to 6) were done. The BIMA group had a significantly higher number of grafts than the SIMA group (p = 0.001).
The mean cardiopulmonary bypass time for SIMA patients was 104.1 ± 48.5 minutes (range, 15 to 371 minutes) and 108.1 ± 43.5 minutes (range, 40 to 351 minutes) for BIMA patients. The mean duration of aortic cross-clamping for the SIMA group was 58.7 ± 24.4 minutes (range, 8 to 180 minutes) and for the BIMA group 66.4 ± 20.6 minutes (range, 20 to 200 minutes). Between-group comparisons revealed that BIMA patients experienced an increased duration of aortic cross-clamping times (p = 0.001).
Operative urgency
The operation was performed in the SIMA group electively in 86 patients (33.0%), urgently in 145 patients (55.6%), and emergently in 30 patients (11.5%). In the BIMA group, the operation was performed electively in 95 patients (36.4%), urgently in 157 patients (60.2%), and emergently in 9 patients (3.4%). An urgent operation was defined as being required within 48 hours in an effort to prevent further clinical deterioration. Emergency operation referred to those instances when a patient had intractable angina that did not respond to aggressive clinical measures or had impending infarction, or when decompensation occurred in the cardiac catheterization laboratory and measures such as defibrillation, extended cardiac massage, balloon counterpulsation, or inotropic support were required. All other patients in the series were considered to have had elective operations.
Data sources
Perioperative data were obtained by retrospective review of the patient’s hospital record, catheterization reports, and cine angiograms. Follow-up information was obtained through comprehensive questionnaires and by telephone interview with surviving patients, family members, or the patient’s personal physician. Follow-up data included activity level, current symptoms, diagnostic tests, occurrence of major adverse late cardiac events, and medications being taken. Patients were asked to describe their functional capacity and were ranked according to the Canadian Cardiovascular Society classification system. The National Death Index and the Office of Vital Statistics were contacted when necessary to obtain death certificates and cause of death. Autopsy reports, when available, furnished additional information.
A Patient Registration Form and a Patient Follow-Up Form were completed for each participant in the study. These data collection instruments provided standardized reporting of each patient’s clinical status before and after the operation. Quality of life assessment was conducted with the Short Form (SF)-36 developed by Ware and associates [16]. The SF-36 is a standardized instrument comprised of 36 items designed to measure eight dimensions of overall health. These include physical functioning, social functioning, role limitations attributed to emotional problems, mental health, vitality (energy/fatigue), bodily pain, and general health perception. For each dimension, item scores are computed, totaled, and converted into a scale, which ranges from 0 for worst health to 100 representing best health.
Two summary components—a physical and mental health score—are also computed. A high score in the Physical Health Summary component indicates no physical limitations, disabilities, decrements in well-being, or high energy levels. A low score indicates substantial limitations in self-care, physical, social, and role activities, severe bodily pain, or persistent tiredness. In the Mental Health Summary component, a high score demonstrates recurring positive affect, absence of psychological distress, and a sense of emotional well-being. A low score is indicative of the presence of psychological disturbance and substantial social and role dysfunction due to emotional instability [17].
The instrument has been used in a number of public health studies. It is generally completed in approximately 10 to 15 minutes and may be administered in person, by telephone or mail.
A 96.0% follow-up was obtained for SIMA patients and 97.6% for BIMA patients in the present study.
Statistical analysis
Data are presented as frequency distributions and simple percentages. Values of continuous variables are expressed as mean ± standard deviation. Univariate analysis of selected preoperative and postoperative discrete variables was accomplished by 
2, the continuity-adjusted 2 analysis, or a two-tailed Fisher’s exact test with the appropriate degrees of freedom to test for the equality of proportions in the case of categorical variables. Comparison of means for continuous variables was conducted by an unpaired Student’s t test.
Patient survival for those discharged from the hospital was expressed by actuarial analysis according to the method of Cutler and Ederer [18] using time zero as the date of operation and late death as the end point (with variability expressed as the standard error of the mean) and by linearized occurrence rates with standard errors. The algorithm of Lee and Desu [19] was used to test the equality of survival distribution for the two patient groups. Data collected were subjected to both quantitative and qualitative analysis using the biostatistical capabilities of the Patient Analysis and Tracking Systems (PATS; Axis Clinical Software, Inc, Portland, OR) and the Number Cruncher Statistical Systems (NCSS, Kaysville, UT).
A significant difference between measurements was defined as p less than or equal to 0.05.
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Results |
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Patients with deep sternal infection included those with instability of the sternum with positive wound cultures necessitating an additional surgical procedure, such as incision and drainage, debridement, or secondary closure. Pulmonary insufficiency included patients who required intubation for more than 48 hours or tracheostomy (or both). Cerebrovascular accident referred to a neurologic deficit that remained unresolved and presented for more than 24 hours, and renal dysfunction was defined as a creatinine level greater than or equal to 2.0 mg/dL.
Myocardial infarction was defined as a new onset of Q waves with or without elevation of myocardial enzymes, or a substantial elevation of myocardial enzymes alone. Low cardiac output referred to clinical evidence of hypotension, oliguria, and peripheral vascular constriction with normal or supranormal left ventricular filling pressure or a measured cardiac index of less than 2 L · min-1 · m-2, necessitating the administration of catecholamines or use of the intraaortic balloon pump, or both.
Placement of the intraaortic balloon pump was required in 41 patients (15.7%) in the SIMA group. Thirty-three patients (12.6%) had an intraaortic balloon pump placed preoperatively, 7 (2.7%) intraoperatively, and 1 (0.4%) postoperatively. In the BIMA group, 38 patients (14.6%) required placement of an intraaortic balloon pump. Seventeen patients (6.5%) had an intraaortic balloon pump placed preoperatively, 18 (6.9%) intraoperatively, and 3 (1.1%) postoperatively. There was no significant difference in the use of the intraaortic balloon pump between the groups. None of the patients requiring the use of the intraaortic balloon pump in either group experienced a major complication.
The overall incidence of postoperative morbidity for the two groups was low with most patients in the SIMA group (83.9%; n = 219) and 82.8% (n = 212) in the BIMA group experiencing no hospital complications. The average postoperative length of stay for SIMA patients was 13.9 ± 11.6 days and 13.4 ± 11.8 days for BIMA patients. This difference did not achieve statistical significance.
Hospital mortality rate
Hospital mortality was defined as death occurring during the operation or the hospitalization in which the procedure was performed or death occurring after discharge from the hospital but within 30 days of the surgical procedure, unless the cause was unrelated to the operation. The overall hospital mortality rate for SIMA patients was 3.8% (10 of 261) and 3.4% (9 of 261) for BIMA patients. Since 1990, the hospital mortality rate for both groups has been markedly reduced, 2.3% (2 of 86) in SIMA patients and 1.3% (1 of 78) in BIMA patients. These differences in mortality rate before 1990 and those after were not found to be significant.
The elective mortality rate for SIMA patients was 1.2% (1 of 86) and 2.1% (2 of 95) for BIMA; the urgent mortality rate for SIMA patients was 3.4% (5 of 145) and 3.8% (6 of 157) for BIMA; and the emergent mortality rate for SIMA patients was 13.3% (4 of 30) and 11.1% (1 of 9) for BIMA patients. A between-group comparison of the mortality rates for various urgency categories did not achieve statistical significance.
The mortality rate for first operation for SIMA patients was 3.6% (9 of 249) and 2.8% (7 of 249) for BIMA patients. The mortality rate for reoperation in SIMA patients was 8.3% (1 of 12) and in BIMA patients, 16.7% (2 of 12). A comparison of the influence of surgical history on hospital mortality rates revealed no significant difference.
Long-term follow-up
Follow-up data were collected for 241 SIMA patients (96.0%) and 246 BIMA patients (97.6%) discharged from the hospital. The follow-up for SIMA ranged from 2 months to 27.0 years (mean, 10.0 years) and for BIMA from 2 months to 24.8 years (mean, 9.1 years). The cumulative follow-up for SIMA patients was 2,516.1 patient-years and for BIMA, 2,289.6 patient-years. The linearized late mortality rate for SIMA patients was 4.17% ± 0.20% per patient-year (105 events) and 3.45% ± 0.19% for BIMA patients (79 events).
At the completion of the follow-up, 136 (54.2%) of the 251 SIMA hospital survivors were alive and 167 (66.3%) of the 252 BIMA hospital survivors were alive. Information concerning the causes of late death for the two groups is presented in Table 3. The actuarial survival data for 251 SIMA patients and 252 BIMA patients discharged from the hospital are shown in Figure 1. At 7 years, survival for SIMA patients (± standard error of the mean) was 79.7% ± 2.6% and 84.9% ± 2.3% for BIMA patients. At 15 years it was 49.3% ± 4.0% for SIMA patients and 53.7% ± 4.8% for BIMA patients. The equality of survival distribution for the two groups of patients was tested, and no significant difference was noted.
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Comment |
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TopAbstractIntroductionPatients and methodsResultsCommentAcknowledgmentsDiscussionReferences |
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The use of the IMA graft with its well-documented superior patency has been shown to ameliorate the influence of gender on short- and long-term outcomes after coronary artery bypass grafting [10, 11]. Despite nearly three decades of collective surgical experience with the use of BIMA grafting, the efficacy of single versus double IMA grafting in women has not been clearly defined. In a recent study with a median follow-up of 10.1 years, the Cleveland Clinic demonstrated a decreased risk of death, reoperation, and percutaneous transluminal coronary angioplasty in 10,124 patients receiving IMA grafts. There were only 215 female BIMA patients in the series, but the incremental benefits of a second IMA graft in women were not specifically addressed [14]. In a similar long-term study, with a median follow-up of 6.4 years, Sergeant and colleagues [13] reported that the use of more than a single arterial graft did not appear to reduce early or late myocardial infarction after coronary artery bypass grafting. This study included 202 female patients who underwent BIMA grafting.
The retrospective nature of the present study is limited by the lack of uniformity in the selection of the surgical treatment (SIMA versus BIMA). It should be noted that even in prospective randomized trials, selection bias may influence the results. Often, the selection of the treatment alternative occurs at the point of entry into the study rather than at the time of the delivery of therapy. Carefully performed observational studies may actually be more representative of the entire population at risk as well as the treatment being studied and thus, may be equally as effective as randomized controlled trials in evaluating treatment alternatives [21].
In the present study, the focus was to obtain comparable computer-matched groups of female patients to discern the efficacy of single versus bilateral IMA grafting. Patient groups were initially matched on nine preoperative variables resulting in a total of 15 preoperative variables being similar for the two study cohorts (see Table 1). The application of these comparative measures ensured the homogeneity of the two study groups. However, the extent of coronary artery disease was greater in BIMA than SIMA patients (p = 0.001). As may have been anticipated, there was a significantly greater number of mean grafts per patient in the BIMA group (3.14 versus 2.78; p = 0.001).
As with all retrospective studies, there are a series of inherent practical and theoretical limitations, which influence the ability to draw definitive conclusions from the findings. In the present study, the 261 patients in each cohort provide sufficient statistical power to detect a moderate effect size for selected statistical comparisons [22].
Postoperative hospital morbidity was low in both groups with most patients in the SIMA group 83.9% (219 of 261) and 82.8% (212 of 261) in the BIMA group experiencing no hospital complication. There was no significant difference in the occurrence of hospital complications between the two groups. However, the incidence of pulmonary insufficiency was greater in BIMA (8.0%) than in SIMA patients (3.8%). This difference represents a trend and begins to approach statistical significance (p = 0.0640). This finding may be attributed to the technique of dissecting and dividing the highest intercostal branch, thus potentially temporarily impairing phrenic function. This approach, however, has not resulted in any long-term impairment of pulmonary function for patients in the two cohorts.
In the present series, there was a low incidence of deep sternal infection in BIMA patients (1.4%). Moreover, in BIMA patients with diabetes mellitus the rate was 2.8% and in elderly patients 65 years of age and older it was 2.1%. This is in contrast with other reports where patients undergoing BIMA grafting experienced a higher incidence of deep sternal infection [23]. Between-group comparison of the occurrence rate of deep sternal infection in the present series found no significant difference.
The low occurrence rate of deep sternal infection in the present study may be a function of the surgical technique used, which included harvesting an isolated or skeletonized mammary rather than removing a pedicle from the chest wall. This approach results in less devascularization of the sternum than when the IMA is harvested as a pedicle [24]. The application of this technique increases graft length and provides the surgeon with a greater degree of versatility [25].
The operative mortality rates for the series in both groups is consistent with that reported in the literature [2]. Improvements in anesthesia, myocardial preservation, and perioperative care during the past decade have decreased hospital mortality rates. As may have been anticipated, surgical urgency and history of previous coronary artery bypass grafting increased the hospital mortality rate for both cohorts of patients. However, these differences did not achieve statistical significance.
The long-term patient survival in the present study was comparable to that found in an age-matched group in the Coronary Artery Surgical Study registry [3]. Moreover, the equality of survival distribution revealed no significant difference between the two study groups (Fig 1). The freedom from major adverse late cardiac events—nonfatal myocardial infarction, percutaneous transluminal coronary angioplasty, and reoperation for coronary artery bypass grafting—was similar for both groups (Fig 4). SIMA-treated patients had greater freedom from angina than BIMA-treated patients in the study. However, this difference did not achieve statistical significance (p = 0.1283).
It has been suggested that to derive the full benefits from BIMA grafting, both IMAs must be grafted to major branches of the left coronary artery system [26]. It might further be stated that a right IMA grafted to the diagonal branch of the left coronary system does not provide comparable clinical benefits to one grafted to the left anterior descending coronary artery or to a major branch of the circumflex coronary artery. To further explore this hypothesis, a within-group analysis of the long-term survival of patients in whom the right IMA was grafted to either the left anterior descending coronary artery or the circumflex were compared with those receiving a right IMA graft to either the right coronary artery or a branch of the diagonal coronary artery. This analysis demonstrated significantly improved long-term survival in patients where the right IMA was placed to the right coronary artery or a branch of the diagonal coronary artery (p = 0.0188). However, there was no significant difference in the occurrence rate of major adverse late cardiac events between these two cohorts of patients. Moreover, there was no significant difference between these groups when compared with SIMA patients in the study. On the basis of these findings, it cannot be inferred that the absence of incremental clinical benefits from a second IMA graft is a function of the site grafted.
In the present study, as may have been anticipated, the more extensive degree of coronary artery disease was found in the BIMA group. This may have influenced patient selection for the choice of surgical treatment. Such a group with increased coronary artery disease would be expected to have a higher late mortality rate and decreased long-term clinical outcome. However, an analysis of those patients with triple vessel disease failed to demonstrate any significant difference in long-term survival between SIMA and BIMA patients. In addition, no difference was found in the occurrence of major adverse late cardiac events.
There is increased recognition that the patient’s quality of life after operation is of paramount importance [11, 27]. We are entering an era of intense scrutiny by health care providers to develop specific quality of life measurement tools for patients undergoing cardiac operations. Systematic quality of life studies in cardiac surgery are just emerging and expanded research is urgently needed to better define the outcomes of various treatment strategies.
Quality of life is a multidimensional construct, which refers to the psychosocial, emotional, and physical outcomes of treatment as perceived by the patient. The importance of considering quality of life and sense of well-being issues throughout the treatment of the patient undergoing cardiac operation is evident. The goal for all patients should be restoration of optimal physical, social, and psychological function. The SF-36 can serve as a viable assessment tool in the measurement of quality of life in patients undergoing cardiac operations. It can provide increased sensitivity in assessing various treatment alternatives.
In the present study, a comparison of health status using the SF-36 demonstrated no significant differences in any of the eight health scale scores for SIMA- and BIMA-treated patients. Moreover, when compared to an age-adjusted control group (41.0 ± 11.5), neither SIMA (41.7 ± 13.1) nor BIMA (42.2 ± 13.6) patients demonstrated any significant differences in the physical health summary score. These results document excellent self-reported functional outcomes in both cohorts of patients. These findings further corroborate the clinical results found at follow-up that 95.6% of the SIMA and 97.0% of the BIMA patients were in Canadian Cardiovascular Society class I.
With reference to the mental health summary score, SIMA patients were found to be comparable to age-adjusted controls (52.9 ± 8.0 versus 51.4 ± 10.5). However, BIMA patients achieved a significantly higher score than their controls (53.5 ± 8.2 versus 51.4 ± 10.5; p = 0.011). The results generated by the SF-36 are impressive and when compared with the clinical outcomes documented in the study provide further evidence that this quality of life assessment tool can provide increased sensitivity in assessing treatment alternatives.
The findings in the current study do not support the notion or the hypothesis that BIMA grafting in women is a clinically superior treatment alternative. Despite the multiple analyses of various clinical variables, the findings in the present study were unable to demonstrate any incremental benefits from the addition of a second IMA graft in women. This is difficult to explain in light of a large and impressive study conducted by the Cleveland Clinic that demonstrated two IMAs were better than one [14]. Perhaps, the sample size in the current study was too small to detect the influence of the second IMA. Although this may be the case, this series represents the largest and longest term study of BIMA grafting in women currently available. The absence of any trends suggesting a difference in the multiple measurements evaluated certainly casts uncertainty on the possibility of any clinically significant differences that may not in some way be apparent with the measurement techniques used.
If in fact there is no evidence of incremental benefit using a second IMA graft in women, how can this be accounted for in the present study? The improved patency of the IMA graft has long been recognized as the physiologic basis for the superior clinical results when this conduit is compared to saphenous vein grafting. Why then would not a second IMA confer additional clinical benefits in female patients?
It must be recognized that coronary arteriosclerosis is a chronic disease, which has reached an advanced stage by the time the patient presents for operation. At this point, the availability of surgical choices to influence long-term clinical outcomes will be circumscribed by the underlying patient substrate. The constellation of presenting risk factors, comorbidities, and age-related limitations of life expectancy all may have a more powerful affect on long-term outcomes than the choice of a second IMA [13]. Women may constitute such a group. Although BIMA grafting remains an excellent surgical option for selected patients, the greatest long-term clinical benefits for women may be realized by focusing attention on risk factors and lifestyle modification, rather than BIMA grafting [1].
The results of this longitudinal study are impressive and provide substantial evidence that SIMA and BIMA grafting in women can be performed with low operative risk and hospital morbidity. Furthermore, it has demonstrated a decreased occurrence rate of major adverse late cardiac events, excellent functional improvement, freedom from recurrent angina, enhanced long-term survival, and improved quality of life in both patient groups. The IMA is clearly the conduit of choice in coronary revascularization. However, in this long-term study the application of a second IMA in women does not appear to confer any additional benefits in the multiple clinical variables measured.
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Discussion |
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Another factor that I think you should consider is that if you are having such good results with your single mammary group, that is, about a 4% adverse event, and you wish to improve that even by 50%, the power of having 261 cohort samples is going to be very poor. It needs to be 1 to 0.8 to have a relevance, and your figures are, by my calculations, to be 0.092. I think to show a difference with that good a result you need at least 2,743 patients in each cohort. Thank you.
DR KURLANSKY: Thank you very much for your comments. Actually I am glad you asked the question, because personally this study was very difficult for me; it was a learning experience in doing research. I began this study convinced that the bilateral internal mammary artery patients should do better than the single internal mammary artery patients, and I was very concerned that they did not. One of the first things I noticed was that there was more extensive disease in the bilateral internal mammary artery patients. I do not have slides to this effect but I do have the results of some studies that we did do. And we therefore looked at the patients with three-vessel disease in the single internal mammary artery group and the patients with three-vessel disease in the bilateral internal mammary artery group, and we did these same set of analyses, we did the actuarial survival and we did the freedom from major adverse effects, and there was absolutely no difference between the groups. One could argue that if there is more extensive disease in the bilateral internal mammary artery patients and they do just as well, then the bilateral internal mammary artery operation must be better. Our subset analysis does not bear that out, because the comparable groups of patients, both with triple-vessel disease, did equally well in the bilateral internal mammary artery and the single internal mammary artery group.
As to your second comment, it is extremely pertinent, and one of the many things that concerned me is that I am sitting here with 261 patients in each group and Bruce Lytle and Gene Blackstone are sitting up in Cleveland reporting on 10,000 patients. However, if you look at their study, the number of women who received bilateral internal mammary artery grafting in that study was only 215. Therefore, we are better powered with this study to detect a difference than any other study in the literature to date. Unfortunately, that still remains a statistical constraint.
What came up in your question was the number of patients that would be required to detect a difference, and I think there is something very important and probably it is the take-home message of this study. The take-home message of this study is not that bilateral internal mammary artery grafting is not a good operation. It is an excellent operation. And in fact Dr Traad, who was unable to make it today, wanted me to comment that you should understand that many of the patients in the bilateral internal mammary artery group would not have been capable of having saphenous vein grafts because they did not have them or that the saphenous vein grafts were varicose or for other reasons. That along with problems with the aorta, off-pump bypass, there are many reasons for bilateral internal mammary artery grafting. However, we as surgeons become very focused on what we do, which is a good thing; however, you must understand that women by the time they come to coronary bypass surgery already have extensive disease. They have coronary artery disease that is a chronic, inflammatory, and debilitating disease. This operation does absolutely nothing to change the pathophysiology of the disease that brought them to operation. It merely treats the mechanical side effects of the disease. Therefore, the long-term prognosis of these patients can only be partially determined by the choice of the operation, and it may be that in the case of women, the incremental benefit of a second mammary is so small that it pales in the face of the other determinants of their long-term outcome.
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