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Ann Thorac Surg 1999;67:466-470
© 1999 The Society of Thoracic Surgeons

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Original Articles

Comparison of long-term clinical results of double versus single internal mammary artery bypass grafting

^a Department of Surgery, Montreal Heart Institute, Montreal, Quebec, Canada

Accepted for publication July 10, 1998.

Address reprint requests to Dr Carrier, Montreal Heart Institute, 5000 Bélanger St E, Montreal, PQ H1T 1C8, Canada
e-mail: carrier{at}icm.umontreal.ca

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. The long-term benefits of double versus single internal mammary artery (IMA) coronary bypass grafting have not yet been established.

Methods. Six hundred patients were studied retrospectively 10 years after coronary revascularization using saphenous vein grafts (SVGs) only or single or double IMA grafts.

Results. Patients with double IMA grafts were younger and were more likely to have diabetes, left main coronary stenosis, and three-vessel coronary artery disease than patients with SVGs or single IMA grafts. Patients with SVGs and double IMA grafts had a greater number of diseased coronary vessels and a greater number of coronary bypass grafts per patient than patients with single IMA grafts (mean ± SEM, 2.8 ± 1.0, 2.8 ± 0.7, 2.1 ± 0.8 grafts per patient, respectively, p < 0.0001). Actuarial survival rates 10 years after placement of SVGs and single and double IMA grafts averaged 83% ± 6%, 90% ± 4%, and 87% ± 8%, respectively (p = 0.03). Cox regression analysis showed that diabetes (relative risk, 2.03; 95% confidence interval, 1.55 to 2.66) and chronic pulmonary obstructive disease (relative risk, 2.20; 95% confidence interval, 1.58 to 3.80) increased, whereas an IMA graft on the left anterior descending coronary artery significantly decreased, the risk of death after operation (relative risk, 0.45; 95% confidence interval, 0.36 to 0.57) throughout the follow-up period.

Conclusions. Use of an IMA graft on the left anterior descending coronary artery improves survival compared with use of an SVG. Although patients with double IMA grafts had a greater number of poor prognosis risk factors before operation, their 10-year survival rate was similar to that of patients with a single IMA graft.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Coronary artery bypass grafting (CABG) is an established treatment for relieving symptoms of myocardial ischemia and, in certain subgroups of patients, prolonging survival [1, 2]. Surgical treatment is particularly beneficial for patients with triple-vessel coronary artery disease, left main coronary stenosis, and left ventricular dysfunction [3, 4]. The use of internal mammary artery (IMA) grafts to the left anterior descending coronary artery provides better long-term patency, survival, and freedom from cardiac events than saphenous vein grafts (SVGs) only [5, 6] because of the absence of neointimal hyperplasia [7], the relative resistance to atherosclerosis, and the preserved endothelial function of IMA grafts [8].

Although the benefit of single IMA grafts to the left anterior descending coronary artery is established, the advantage of double IMA grafts with regard to survival and event-free survival remains unproved [9–12]. Moreover, double IMA grafts are associated with a higher rate of sternal wound infections, which may limit the overall beefit of multiple arterial grafting using IMAs in some patients [13].

The present study was designed to compare the long-term clinical results of single and double IMA grafts with those of SVGs. We studied retrospectively the late clinical outcome of 600 patients who underwent CABG at the Montreal Heart Institute between 1982 and 1986. The main hypothesis was that double IMA grafting improves patient survival at long-term follow-up compared with SVGs and with single IMA grafting.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Between 1982 and 1986, 200 consecutive patients who underwent CABG with SVGs only, 200 consecutive patients who underwent single IMA grafting, and 200 consecutive patients with bilateral IMA grafting were recruited for the present study of clinical events during long-term follow-up. Patients recruited for the study were operated on by the same group of seven surgeons at the Montreal Heart Institute.

Demographic variables (gender and age) and risk factors for coronary artery disease (arterial hypertension, chronic obstructive pulmonary disease [COPD], diabetes, reoperation for CABG) were recorded. The following angiographic variables were analyzed: number of diseased coronary vessels; presence of significant left main coronary artery stenosis (greater than 50%); presence of significant left anterior descending, circumflex, or right coronary artery stenosis (greater than 50%); and left ventricular ejection fraction. The operative variables studied were the number of IMA grafts and SVGs and the target coronary vessels for left and right IMA grafts.

Patient survival during follow-up, the need for reoperation or percutaneous transluminal coronary angioplasty, occurrence of acute myocardial infarction, and recurrence of angina were recorded. All patients were evaluated at the outpatient clinic, by phone interview, or by contact with their physician. Follow-up was complete except for 3 patients (597 [99%] of 600). Mean length of follow-up for the three groups combined was 10 ± 3 years (10 ± 5 years for patients with SVGs only, 10 ± 2 years for patients with single IMA grafts, and 8 ± 2 years for patients with double IMA grafts).

Patient survival, occurrence of myocardial infarction, reoperation for CABG, percutaneous transluminal coronary angioplasty, and recurrence of angina were analyzed. Deaths of unknown cause were attributed to a cardiovascular etiology. Statistical analysis was done using the NCSS 6.0 software package (Kaysville, UT). Univariate analysis was performed using ² tests and analysis of variance methods. Survival analysis was performed by the Kaplan-Meier method and the log-rank test for statistical significance. Cox proportional hazard regression models were used to determine the influence of demographic, angiographic, and operative covariates on survival and on recurrence of angina at long-term follow-up. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated to determine the magnitude of effect of the covariates on survival and on recurrence of angina. Results are expressed as mean value and standard error of the mean.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Patient characteristics
Patients who underwent CABG with double IMA grafts were younger and had a higher incidence of diabetes than those with single IMA grafts and SVGs. Arterial hypertension and COPD were evenly distributed among the three groups. Patients with double IMA grafts had a greater number of diseased coronary vessels and a lower left ventricular ejection fraction than those in the other two groups. The number of patients with previous CABG was higher among those with SVGs and double IMA grafts than in those with single IMA grafts (Table 1).

View larger version (21K): [in this window] [in a new window]   Fig 1. Actuarial survival comparing patients with saphenous vein (SVG) and single (SIMA) and double internal mammary artery (DIMA) grafts (log-rank, p = 0.004).

View larger version (18K): [in this window] [in a new window]   Fig 2. Actuarial analysis comparing freedom from myocardial infarction during follow-up between the three groups (log-rank, p = 0.48). (Abbreviations as in Fig 1.)

View larger version (15K): [in this window] [in a new window]   Fig 3. Actuarial analysis comparing freedom from reoperation during follow-up between the three groups of patients (log-rank, p = 0.35). (Abbreviations as in Fig 1.)

View larger version (18K): [in this window] [in a new window]   Fig 4. Actuarial analysis comparing freedom from percutaneous transluminal coronary angioplasty during follow-up between the three groups of patients (log-rank, p = 0.003). (Abbreviations as in Fig 1.)

After adjustment for patient population differences at baseline, including age, gender, arterial hypertension, diabetes, number of diseased coronary vessels, and previous operations, long-term survival was not significantly different between the patients with single IMA grafts and those with double IMA grafts (p > 0.05).

A multivariate model assessing risk factors for recurrence of angina in patients with single and double IMA grafts showed that arterial hypertension (RR, 1.57; 95% CI, 1.16 to 2.12, p = 0.05) and reoperation for CABG (RR, 2.46; 95% CI, 1.38 to 4.39, p = 0.002) were associated with a higher risk of recurrence of symptoms during follow-up.

Of the 200 patients with double IMA grafts, 107 (53%) had both IMAs grafted to left coronary arteries, and 93 (47%) had the right IMA grafted to the right coronary artery and the left IMA grafted to the left anterior descending coronary artery. The former group had a higher survival rate 7 and 10 years after operation than the latter group, although the difference was not statistically significant (Fig 5).

View larger version (18K): [in this window] [in a new window]   Fig 5. Actuarial survival rates between patients with double internal mammary artery grafts to the right and left coronary arteries and those with both internal mammary artery grafts to the left coronary arteries only (log-rank, p = 0.22).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

Coronary artery bypass grafting with both IMAs is still considered hazardous in some situations and has been associated with higher rates of sternal wound infection [13]. However, several studies have shown that when patients with severe obesity, COPD, or diabetes are excluded, double IMA grafting does not increase surgical risk [12, 13, 15]. Naunheim and colleagues [16] reported that patient survival 15 years after CABG averaged 65% for double IMA grafts compared with 58% for single IMA grafts, although this difference was not statistically significant. Other investigators have reported similar survival rates ranging from 80% at 10 years to 60% after 15 years [17]. In patients with complete revascularization using only arterial grafts, some investigators have reported a 5-year survival rate of 95% after operation [18]. These reports suggest that the clinical outcome in terms of incidence of cardiac events is improved with the use of double IMA grafting. In contrast, other investigators have found similar survival rates and no advantage after CABG with single versus double IMA grafts [10, 12, 19–21].

In the present study, patients with double IMA grafts were younger and had a higher incidence of diabetes and a greater number of diseased coronary arteries than patients with single IMA grafts. Moreover, patients with double IMA grafts had a greater number of previous CABG operations than patients with single IMA grafts. Clearly, in the present study patients with double IMA grafts had more extensive and severe coronary artery disease than patients treated with SVG or single IMA grafts. Although late survival was similar in the two groups with IMA grafts, recurrence of angina and the need for percutaneous transluminal coronary angioplasty were more frequent in patients with double IMA grafts, but myocardial infarction and reoperation rates were similar. The higher recurrence rate of angina in patients with double IMA grafts may be related to the presence of more severe coronary artery disease and higher rates of diabetes and reoperation for CABG, three significant risk factors for a poorer prognosis [22]. Pick and colleagues [23] showed a significant decrease in the incidence of angina recurrence with the use of bilateral compared with single IMA grafts, but diabetes was more prevalent among patients with single IMA grafts and may have affected the results.

According to Cameron and associates [14], the survival benefit of an IMA graft is maintained over time. Because of the continuous progression of atherosclerosis in SVGs, IMA grafts have improved late patient survival, the main determinant being an arterial graft on the left anterior descending coronary artery [24]. Some investigators have reported excellent results with double IMA revascularization to the left coronary territory. Schmidt and colleagues [18] showed that bilateral IMA operations led to longer patient survival when arterial conduits were used to graft the left anterior descending and circumflex coronary arteries than grafting the right and left coronary arteries. In the present study, analysis of the subgroup with double IMA grafts showed better survival for grafts on the left coronary arteries than on the right and left coronary vessels, although the difference was not statistically significant 10 years after operation. A larger group of patients with a longer follow-up period would be necessary to confirm the latter observation.

Limitations and inferences of the present study
The present study represents the 10-year follow-up of 600 consecutive patients who underwent CABG with three accepted technical approaches between 1982 and 1986. Although SVGs alone are now seldom used, single and double IMA grafting remain our routine approaches. A single IMA graft to the left anterior descending coronary artery associated with SVGs is used in the elderly population, and double IMA grafts to left anterior descending and circumflex coronary arteries is preferred in younger patients. Morbid obesity, diabetes, and COPD are the main contraindications to the latter approach.

The selection of consecutive patients for retrospective cohorts reduced the selection bias but resulted in significant differences in the characteristics of the patient populations. Differences in preoperative characteristics may be partly responsible for the similar survival rates in patients who underwent single and double IMA grafting and the higher recurrence rate of angina at long-term follow-up in the latter group because patients with double IMA grafts had a greater number of poor prognostic factors than patients with single IMA grafts. A prospective randomized trial with a larger group of patients and a longer follow-up period would be necessary to reach a definitive answer, although the logistics of such a study may be arduous.

The present results stress the deleterious effect of diabetes on patient survival after CABG. Although, several investigators have suggested that diabetes is a major factor of poor prognosis, preventive approaches need to be developed [25]. Finally, hyperlipidemia was not systematically monitored or treated in the present patient cohort. In a recent clinical trial, aggressive lowering of low-density lipoprotein cholesterol levels to below 100 mg/dL not only reduced the progression of atherosclerosis in SVGs, but also decreased the need for percutaneous transluminal coronary angioplasty and reoperation for CABG after initial surgical revascularization with at least two SVGs [26]. Thus, it appears that several nonsurgical factors have a significant influence on long-term results after CABG.

Conclusions
Ten-year survival after CABG was similar in patients with single or double IMA grafts, although patients with double IMA grafts had a greater number of poor prognostic factors. The presence of an IMA graft to the left anterior descending coronary artery prolonged survival but did not prevent progression of atherosclerosis in other segments of the coronary tree. Secondary prevention with lipid-lowering treatment and better control of diabetes mellitus may be key factors for improving the long-term outcome after CABG [26] rather than multiplication of arterial grafts other than the IMA to the left anterior descending coronary artery.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Jean-Marc Farinas Michel Carrier Raymond Cartier Michel Pellerin Louis P. Perrault Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Farinas, J.-M. Articles by Pelletier, L. C. Search for Related Content PubMed PubMed Citation Articles by Farinas, J.-M. Articles by Pelletier, L. C.