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Ann Thorac Surg 2001;71:549-554
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Effect of age on outcome of bilateral skeletonized internal thoracic artery grafting

^a Department of Thoracic and Cardiovascular Surgery, Tel Aviv Sourasky Medical Center and Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv, Israel

Accepted for publication August 24, 2000.

Address reprint requests to Dr Mohr, Department of Thoracic and Cardiovascular Surgery, Tel-Aviv Sourasky Medical Center, 6 Weizmann St, Tel Aviv 64239, Israel
e-mail: raphmohr{at}tasmc.health.gov.il

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. Elderly patients are considered to be at higher risk for coronary artery bypass grafting. Surgical techniques of arterial myocardial revascularization without vein grafts were primarily reserved for the young. This report evaluates the impact of age on the outcome of 634 consecutive patients who underwent double skeletonized internal thoracic artery grafting between April 1996 and December 1997.

Methods. Patients were stratified into five age groups: One hundred ninety-six were less than 60 years of age, 98 between 60 and 65 years, 132 between 65 and 70 years, 116 between 70 and 75 years, and 92 were older than 75 years. The groups did not differ with regard to preoperative risk factors.

Results. Hospital mortality was 2.5% (n = 16). Mortality of urgent and elective operations was 1.6%, and that of emergency operations was 9.7% (p < 0.001). There were 7 (1.1%) myocardial infarctions, 9 strokes (1.4%), and 10 deep sternal wound infections (1.6%). Using the Mantel-Haenszel test, there was no relation between age and hospital mortality, myocardial infarctions, strokes, or sternal infections. A correlation was found between advanced age and early unfavorable events (6.7%, 7.2%, 12.9%, 15.5%, and 15.2% in corresponding age groups, p < 0.003), and late mortality (0.6%, 1%, 1.5%, 4.3%, and 9.8%, respectively, p < 0.01). However, early return of angina was lower (2.6%, 1%, 0.8%, 0.9%, and 0%, p < 0.06).

Conclusions. This retrospective, nonrandomized study suggests that older age is not a risk factor for operative mortality in patients undergoing coronary artery bypass grafting with double skeletonized internal thoracic arteries. Apart from avoiding morbidity associated with leg incisions, older patients showed an interesting trend toward lower rates of angina return. Older patients, however, sustained increased perioperative morbidity and late mortality rates.

	Introduction

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With the expansion in life expectancy, an increasing number of elderly patients is referred for coronary artery bypass grafting (CABG), and the trend today is to use the internal thoracic artery (ITA) in all patients operated on, including the older ones. The current conventional and most commonly used operative procedure for myocardial revascularization includes one pedicled ITA together with one or more vein grafts [1, 2]. Vein graft exhaustion is a major drawback of CABG, and surgical techniques of complete arterial myocardial revascularization without veins have been attempted. Two popular techniques for achieving this goal are bilateral and sequential [3] ITA grafting.

When the ITA is dissected as a skeletonized artery [4] it becomes longer and its spontaneous blood flow is probably greater [5, 6] than that of the pedicled ITA, allowing the use of both ITAs to almost all coronary territories requiring bypass. In most patients, no additional vein grafts are required [7]. Another advantage of using ITA as a skeletonized artery is the preservation of collateral blood supply to the sternum [8], enabling more rapid healing, and decreasing the risk of infection [9, 10].

The bilateral skeletonized ITA technique was adapted in our service as the preferred method for myocardial revascularization. In this report we analyzed the impact of age on the outcome of the first 634 patients in whom we used this surgical technique.

	Material and methods

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Between April 1996 and December 1997, 634 consecutive patients (Table 1: preoperative data) underwent CABG using bilateral ITA. They comprised 71% of the 892 patients referred for CABG operation during this time period in our department. Other patients underwent either CABG with ITA as a single graft (6.3%), one ITA with right gastroepiploic artery (4%), and off-pump surgical revascularizations (6.6%). The conventional ITA and vein CABG was performed in 10.5%, and veins only were used in 1.4% of the patients.

We avoid excessive traction on the ITA, as these branches can tear easily, causing serious bleeding or hematomas. Throughout the dissection, the ITA is sprayed with warm diluted papaverine solution to minimize spasm and prevent dessication. To obtain maximal ITA length, diameter, and flow, it might be necessary to divide the internal mammary vein to obtain satisfactory exposure of these most proximal collateral branches.

Although the retractor is still in place and exposure is good, the superomedial pleural reflection is divided with cautery. The left ITA (LITA) is mobilized through this incision, and penetrates the pericardial cavity anterior to the phrenic nerve. This maneuver allows the ITA to lie medial and posterior to the lung, so that ventilation does not produce any notable stretch or distortion of the artery. In addition, the artery is somewhat protected from injury should resternotomy be required.

Heparin is administered before distal ITA division. The divided skeletonized artery is then put in a small syringe filled with 1:30 papaverine saline solution. This bath of warm papaverine ("jacuzzi") is good enough to relax any spasm produced during dissection without the risk of endothelial damage caused by other antispastic maneuvers, such as intraluminar papaverine injection or mechanical dilatation. Both ITA grafts are palpated after 5 to 10 minutes in the papaverine "jacuzzi." The pulse should be strong, and spontaneous free flow is almost always greater than 150 mL/min [3].

Operations were performed with cardiopulmonary bypass. Myocardial preservation technique was intermittent warm cardioplegia (30°C to 32°C). In 132 patients (21%), the right gastroepiploic artery was used as a third arterial conduit to bypass the posterior descending branch of the right coronary artery. In 397 patients (64%), a composite graft was prepared before connection to cardiopulmonary bypass. Most of the composite grafts included end-to-side anastomosis of free right ITA (RITA) on an in-situ LITA. When the proximal part of the LITA was damaged or when its spontaneous free flow was not sufficient, a free LITA was anastomosed end-to-side to an in-situ RITA. A third variation was the small Y graft, wherein a small distal section of an ITA was anastomosed end-to-side to a more proximal part of the same artery.

In 196 (32%) of the patients, the RITA was anastomosed to left anterior descending coronary artery, and LITA revascularized the circumflex territory ("cross" technique). Finally, when no graft to the posterior wall of the heart was necessary (the circumflex region), the LITA was grafted to the left anterior descending and the RITA to the right coronary artery or its posterior descending branch (in-situ technique). It should be noted that in most patients it is impossible to reach this branch with the right coronary artery graft when using the regular technique of isolating the pedicled ITA. The skeletonized RITA, however, is longer, and therefore, can usually easily reach the better quality distal posterior descending artery.

To decrease the risk of spasm of the arterial grafts in the early postoperative period, all patients were treated with high-dose intravenous infusion of isosorbide dinitrate (Isoket) (4 to 20 mg/hr) during the first 24 to 48 hours postoperatively. Isoket usually has a minimal effect on systemic blood pressure; however, when needed, either crystalloids, blood, or other volume expanders are used, as well as minimal doses of epinephrine (usually for a short period of time in the operating room, and rarely in the postoperative period) to maintain systolic blood pressure above 100 to 120 mm Hg.

Statistical analysis
Data are expressed as mean ± standard deviation or proportions. The ² test and two sample t tests were used to compare discrete and continuous variables, respectively. The linear association between age and the various outcome events was evaluated using the Mantel-Haenszel test for linear association. All 634 patients were stratified to five age groups according to their age (Table 2). Multivariate logistic regression analysis was used to predict unfavorable outcome events by various risk factors. Odds ratio (OR) and 95% confidence intervals (CI) are given. Postoperative survival is expressed by the Kaplan-Meier method and survival curves were compared by the log-rank test. All analyses were performed by SPSS 7.5 software (SPSS Inc, Chicago IL). All early and late mortality and morbidity events (stroke, perioperative and late myocardial infarction, wound infections, new onset of angina, and congestive heart failure) were defined as unfavorable outcome events for the purpose of statistical analysis.

	Results

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Follow-up was available in 605 of the 618 surviving patients (98%), up to 26 months postoperatively. There were 17 (2.7%) late deaths. Two were unrelated to the operation (abdominal aneurysm, gastrointestinal bleeding after gastrointestinal operation). Kaplan-Meier analysis of the entire cohort showed 1- and 2-year actuarial survival of 95.2% and 94.6%. There were 4 patients (0.6%) with late myocardial infarction and 10 (1.5%) new patients with congestive heart failure. There were five cases (0.8%) of sternal dehiscence (patients without sternal infection who underwent resternotomy late after discharge). Ten patients (1.5%) reported early return of angina. At the last follow-up, 571 of the surviving patients (92.4%) are well and angina-free. Twenty-seven patients underwent cardiac catheterization during the follow-up period (10 because of chest pain, and the remainder consented to elective catheterization within the framework of learning to use the composite graft). Eighty-four of the 89 distal anastomoses (94%) were patent.

Analysis of operative and late mortality
Univariate analysis (Table 1) indicated repeat operation, ejection fraction lower than 35%, emergency operation, and failure of preoperative percutaneous transluminal coronary angioplasty to be significant predictors of early mortality. Bypass time and cross-clamping time (not included in Table 1) were not significant predictors. After adjustment for previously identified demographic, clinical, and surgical predictors of outcome, only failed percutaneous transluminal coronary angioplasty (OR 8.4, 95% CI 2.4–29.3) and repeat operation (OR 10.3, 95% CI 2.1–51) emerged as independent risk factors for early mortality. Age older than 70 years and repeat operation were also found to be independent predictors of late mortality (Table 1) (OR 7.9, 95% CI 2.17–28.8 for old age, and OR 5.53, 95% CI 1.07–28.7 for repeat operation).

Independent predictors of overall (early + late) mortality were emergency surgery (OR 4.5, 95% CI 1.9–10.6), repeat coronary artery bypass grafting (OR 6.5, 95% CI 1.9–22), age older than 70 years (OR 4.1, 95% CI 1.9–8.9), and failed percutaneous transluminal coronary angioplasty (OR 3.5, 95% CI 1.4–9.2).

Analysis of deep sternal wound infection
Univariate analysis demonstrated chronic obstructive pulmonary disease and emergency operation to be associated with increased risk of sternal infection. Multivariate analysis adjusted all other demographic, clinical, and surgical predictors, and met both variables as significant risk factors. (chronic obstructive pulmonary disease: OR 22.0, 95% CI 2.1–227; emergency operation: OR 10.5, 95% CI 1.25–87.2).

Correlation between age and outcome events
There was no significant correlation between age and hospital mortality. However, older age was associated with increased risk for late and overall mortality, which were particularly high in the patients older than 75 years (9.8% and 13% for late and overall mortality, respectively). Two-year actuarial survival of patients older than 75 years was significantly lower than that of patients younger than 75 years (87% versus 96%, p < 0.001) (Fig 1).

View larger version (12K): [in this window] [in a new window]   Fig 1. Survival curves by patient’s age.

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
In the past few years, several important studies reported survival benefit after bilateral ITA (BITA) grafting when compared with single ITA grafting [11–13]. In the study by Lytle and colleagues [11] from the Cleveland Clinic, 10-year survival of BITA patients was higher (84% compared to 79%) for patients with single ITA (p < 0.001). Reoperative and angina-free survival, as well as freedom from additional revascularization procedures, were significantly higher in the BITA subset [11]. Buxton and colleagues [12] showed that besides late survival benefit, the use of BITA improved the rate of freedom from late myocardial infarction and reoperations. Schmidt and associates [13] suggested that survival benefit with BITA operations is achieved by grafting the ITA conduits to coronary arteries supplying the left ventricle rather than to the right coronary system.

In most studies patients were preselected for BITA according to their life expectancy, and few of the patients older than 65 years were offered this operation, probably because of concerns regarding sternal healing. The only large series (1,467 patients) comparing BITA with single ITA in the elderly (> 65 years) was reported by Galbut and colleagues [14]. In this study, patients with BITA had lower hospital mortality rates (3.1 versus 6.4), and late survival (mean, 43 months) was better (67.9% versus 60.7%).

Mortality of urgent and elective cases in our study was 1.6%, and older age was not associated with increased rate of hospital mortality. Mortality in patients older than 70 years was 2.6%, and in older than 75 years of age was 3.3%. Others reported operative mortality up to 24% in elderly patients (70 years and older) who received BITA [15]. In these reports the ITA was used as a pedicled conduit, and the fact that only 4% of the patients were grafted with BITAs might have explained higher rates of operative mortality and use of postoperative IABP in the BITA patients (16.2% versus 5.9%, p < 0.015). With a matched population cohort, Horneffer and colleagues [16] reported an increased operative mortality in patients older than 70 (9.3% versus 2.2, p < 0.0002). Weintraub and associates [17] portrayed increased mortality in every decade after the age of 40 years. For example, the mortality in patients aged 70 to 79 years was 5% and for those aged 80 to 89 years it was 8.3%. Interestingly BITAs were used in only 3.4% of the patients and in less than 1% of the patients more than 70 years of age. On the other hand, the results of Rahimtoola and Grunkemeier [18] compare favorably with our results. They concluded that the immediate results in patients aged 65 to 84 years were similar to those seen in younger patients.

In our series older age was associated with increased rate of early operative unfavorable events (6.9% in patients < 65 years compared to 14.4% in older patients, p < 0.01). Older age was also associated with increased late mortality. Two-year actuarial survival of patients older than 75 years was 87% compared to 96% in younger patients (Fig 1). In our study, no comparison was made with age-matched population. Gersh and colleagues [19] compared results of CABG with medical therapy alone in patients 65 years of age or older. The surgical group did better. Six-year survival was 79% versus 64% in the medical group (p < 0.0001).

Canver and associates [20] argued whether CABG is justified in older people with a reduced life expectancy, and documented that survival of the elderly surgical group (> 70 years) was similar to that of their age-matched population, but was diminished in younger patients undergoing CABG. This finding might be related to genetic factors, lipid metabolism abnormalities, malignant progression of coronary atherosclerosis, and less compliance of the young patients with measures designed to reduce cardiac risk factors, such as smoking cessation, weight reduction, and exercise. All the above correlate favorably with our study findings, that the rate of early return of angina was higher in the younger age groups (2.6% versus 0.8%, p < 0.05). It should be acknowledged that the higher incidence of late deaths observed in the older population might be a confounding factor, thus "reducing" their rates of recurrent chest pain.

In the study from the Cleveland Clinic, the number of patients older than 60 years operated on using BITA was relatively small [11]. However, BITA grafting improved survival in this subset of older patients. When compared to single ITA graft sternal wound complications were the only difference in reported morbidity between bilateral and single ITA grafted groups (2.5% and 1.4%, respectively). Harvesting the ITA as a wide musculofascial pedicle using electrocautery devascularizes sternal collateral blood supply and exposes the sternum to an increased risk of poor healing, dehiscence, and infection [5, 6, 8–10]. In a retrospective, nonrandomized study, Calafiore and colleagues [9] reported sternal infection rates of 4.5% in pedicled versus 1.7% in skeletonized BITA grafting.

Our report is retrospective, nonrandomized, and does not compare single ITA to BITA, and pedicled to skeletonized harvesting techniques. However, our series describes results in a large nonselected group of patients and it supports the hypothesis that the skeletonized ITA harvesting technique probably causes less damage to the sternal blood supply [8] and therefore, rates of sternal infections (1.6%) are low. Despite the fact that the sternum of elderly patients is sometimes more fragile and osteoporotic, with suboptimal blood supply, older age in this report was not found to be associated with increased rate of deep sternal infection (1.4% in older than 70 years versus 1.8% in younger patients). The only significant predictor of sternal infection in our study was chronic lung disease.

With the familiar limitations of being a retrospective and uncontrolled series with a relatively short follow-up period, this study suggests that older age is not a risk factor for operative mortality in patients undergoing CABG with double skeletonized ITA. Apart from the avoidance of morbidity associated with leg wound healing, older patients sustained lower rates of angina return. Older patients, however, sustained more perioperative complications, and their midterm mortality rates were higher.

	References

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