Ann Thorac Surg 1996;62:733-736
© 1996 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Effects of Smaller Physical Size on Complex Arterial Grafting in Coronary Artery Operations
Hiroshi Nishida, MD,
Masato Nakajima, MD,
Kenji Ihashi, MD,
Motoki Sato, MD,
Akira Shiikawa, MD,
Masahiro Endo, MD,
Hitoshi Koyanagi, MD
Department of Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical College, Tokyo, Japan
Accepted for publication April 18, 1996.
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Abstract
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Background. The trend in coronary artery bypass grafting is for a gradual transition to the more extensive use of arterial grafts. This study was designed to investigate the effects of patient body size on complex arterial grafting in coronary artery bypass procedures.
Methods. Four hundred forty-five patients who underwent coronary artery bypass grafting with two or more distal anastomoses using arterial grafts were divided into two groups according to body surface area: group A (n = 114), 1.60 m2 or less; and group B (n = 331), greater than 1.60 m2. Preoperative patient characteristics and early and long-term results were compared between the groups.
Results. The prevalence of female sex (27% in group A versus 0.9% in group B; p < 0.0001) and age (62.7 ± 8.1 years in group A versus 58.9 ± 7.0 years in group B; p < 0.001) were significantly different. However, the prevalence of previous myocardial infarction and of left ventricular dysfunction and the extent of coronary artery disease were not significantly different. Three patients (2.6%) in group A and 3 patients (0.9%) in group B died within 30 days of operation (p = 0.18). The 1-month patency rate of arterial grafts was not significantly different (98.7% versus 96.7%; p = 0.16), but that of venous grafts was significantly lower in group A than in group B (88.9% versus 97.7%; p = 0.045). No significant difference was noted in the 3-year actuarial survival rate (93.8% versus 91.6%).
Conclusions. The extensive use of arterial grafts in patients with small body size was associated with excellent long-term results, with no significant increase in operative mortality or morbidity.
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Introduction
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Small body size is known to be an important risk factor in coronary artery bypass grafting (CABG) [1–3]. Suma and associates [4] reported that internal thoracic artery (ITA) grafting can be performed safely and effectively even in patients with small body stature, despite their low flow of the ITA and small diameter of the coronary arteries. However, the influence of body size on the outcome of CABG with extensive use of arterial grafts has not been investigated. The objective of this study was to determine the influence of patient body size on complex arterial grafting. The definition of complex arterial grafting in this study was CABG in which the patient received two or more distal anastomoses with arterial grafts.
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Patients and Methods
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From June 1970 to November 1994, 1,830 patients underwent isolated CABG. We have performed complex arterial grafting with two or more distal anastomoses using arterial grafts since August 1985. Since then, 1,240 patients underwent isolated CABG. Among them, the body surface area (BSA) was 1.60 m2 or less in 434 patients (35%) and greater than 1.60 m2 in the remaining 806 patients (65%). A total of 445 patients (36%) who underwent CABG with complex arterial grafting were investigated retrospectively. These patients were divided into two groups according to BSA: Group A included 114 patients (26%) whose BSA was 1.6 m2 or less, and group B comprised 331 patients (74%) whose BSA was greater than 1.6 m2. Values of BSA were 1.49 ± 0.14 m2 (range, 0.79 to 1.60 m2) in group A and 1.75 ± 0.10 m2 (range, 1.61 to 2.07 m2) in group B. Group A included 5 pediatric cases of Kawasaki disease. Patients were followed up for 1 to 112 months (mean, 35 months). The follow-up period was not significantly different between group A (35 months) and group B (36 months). Follow-up was complete in 99.3% (442 of 445) of the patients.
The operative technique used was essentially the same in both groups. The ITA was skeletonized using an ultrasonic surgical aspirator. The saphenous vein usually was harvested from below the knee. If the diameter was smaller than 4 mm, the vein was harvested from above the knee. The harvested vein was dilated gently with heparinized saline in a syringe and local application of pressure by finger tip. The vein was never dilated forcibly. Moderate hypothermia and cold crystalloid cardioplegia were used with pulmonary artery venting. All distal and proximal anastomoses of the vein grafts were carried out during a single period of aortic cross-clamping. Anastomosis of the ITA was performed with a continuous suture with stay sutures on each end using 8-0 polypropylene. Saphenous vein-coronary anastomosis was performed with a continuous suture with stay sutures on each end using 7-0 polypropylene, and saphenous vein-aortic anastomosis was performed with a continuous suture with four stay sutures using 6-0 polypropylene.
A postoperative angiographic study was performed in 110 patients (96.4%) in group A and 317 patients (95.7%) in group B, 3 to 4 weeks after the operation.
Student's t test, 
2 test, and Fisher's exact test were used for statistical analysis. For calculation of the long-term results, analysis was performed using the Kaplan-Meier method, and the two groups were compared by the Cox-Mantel method [5]. A probability value less than 0.05 was considered to indicate statistical significance. Data were expressed as mean ± standard deviation.
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Results
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The rate of complex arterial grafting was significantly lower in smaller patients (26%; 114 of 434) than in larger patients (41%; 331 of 475) (p < 0.0001).
Clinical Characteristics
The age in adult patients and the prevalence of female sex were significantly higher in group A (Table 1
). The prevalence of previous myocardial infarction, emergent operation (nonelective operation performed within 24 hours of request by a cardiologist), and the incidence of repeat CABG were not significantly different between the groups. Group A had a larger proportion of patients with chronic renal failure receiving dialysis.
Coronary Risk Factors
Smoking was less common in group A, probably because of the predominance of female patients (see Table 1
). Obese patients were more common in group B. No significant differences were noted in other risk factors.
Catheterization Data
The extent of coronary artery disease and the prevalence of left ventricular dysfunction, defined as left ventricular ejection fraction of 0.40 or less, were not significantly different between the groups (Table 2).
Operative Procedure
The mean number of distal anastomoses was 2.73 ± 0.84 in group A and 2.87 ± 0.94 in group B (see Table 2). The difference was not statistically significant. The type of arterial grafts used was comparable in group A and group B. The rates of sequential bypass with arterial grafts and use of additional saphenous vein grafts were also the same in the two groups.
Early Results
Three patients (2.6%) in group A and 3 patients (0.9%) in group B died within 30 days of operation (Table 3). Another 2 patients in group A and 1 patient in group B died in the hospital. Although the differences were not statistically significant, the hospital survival rate was slightly higher in group B, at 98.8%, than in group A, at 95.6%. However, only one of five in-hospital deaths in group A was a cardiac death. The causes of noncardiac deaths in the other 4 patients were as follows: rupture of a large abdominal aortic aneurysm in 1 patient, sepsis in 2 patients, and multiorgan failure in 1 patient. The latter 3 patients had been on hemodialysis for chronic renal failure preoperatively. We believe that these causes of death had nothing to do with the small body size of the patients. There was no significant difference in the incidence of perioperative myocardial infarction, defined as the appearance of a new Q wave or R/S ratio greater than 1 in lead V1 of the electrocardiogram associated with peak aspartate aminotransferase value greater than 200 KU. The prevalences of low output syndrome requiring intraaortic balloon pump support postoperatively, of cerebrovascular accident, and of reexploration for bleeding were not significantly different between the groups.
Although the patency rates of arterial grafts were not different, the patency rate of venous grafts was significantly lower in group A, at 88.9%, than in group B, at 97.7% (see Table 3). There was no significant difference in the patency of the left and right ITA and of the right gastroepiploic artery.
Long-Term Results
There was one late death in group A and 18 late death in group B (see Table 3). The difference was not statistically significant. The prevalence of cardiac events, such as repeat CABG, percutaneous transluminal coronary angioplasty, and myocardial infarction, was also not different between the groups. Myocardial infarction was defined as clinical evidence such as chest pain with elevated creatinine phosphate of twice the upper limit of normal. Figure 1 shows the actuarial survival curve including early deaths and all-cause deaths. At 3 years after operation, the actuarial survival rates were 93.8% in group A and 91.6% in group B; at 9 years, survival rates were 93.8% and 88.9%, respectively. The difference was not statistically significant. Figure 2 shows the cardiac death-free curve including early deaths. The cardiac death-free rates were 99.1% in group A and 97.4% in group B at 3 years after operation, and 99.1% in group A and 96.4% in group B at 7 years. Figure 3 shows the cardiac event-free curve including all cardiac deaths, repeat CABG, percutaneous transluminal coronary angioplasty, and acute myocardial infarction. Three-year cardiac event-free rates were 88.4% in group A and 89.2% in group B. No significant difference was noted between the groups.
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Comment
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The impact of female sex, smaller body size, and smaller diameter of the coronary arteries or arterial grafts on the clinical outcome of CABG has been investigated to determine whether these factors are significant predictors of operative mortality or morbidity.
Fisher and associates [1] and Loop and colleagues [2] reported higher operative mortality and morbidity after CABG in female patients. They attributed the poorer outcome in female patients to their smaller body size and coronary artery diameter. Fisher and associates [1] also reported that the coronary arteries were smaller in female patients, and operative mortality increased as the diameter of the coronary artery became smaller. O'Connor and associates [3], using logistic regression analysis, found that a smaller BSA was a significant risk factor for hospital death regardless of sex. They reported that an individual with a BSA of less than 1.6 m2 was approximately five times as likely to die as someone with a BSA of 2.0 m2 or greater. Christakis and associates [6] reported that female sex was a significant independent predictor of operative death and low output syndrome, whereas small body size itself did not increase the risk of operative death, but may have contributed to the risk of low output syndrome.
Because the mean BSA of American female patients is 1.66 m2, according to Loop and co-workers [2], Suma and associates [4] used the arbitrary cutoff of 1.6 m2 when they investigated the effectiveness of ITA grafting in patients with smaller body stature. Although this method uses BSA as a dichotomous variable and not as a continuous variable, we adopted the same cutoff point to be consistent with the previous report [4]. These data indicate that Japanese surgeons are operating on smaller patients than are American and European surgeons. We believe that a series of Japanese patients is a suitable cohort for studying the effects of small body size on the clinical outcome of CABG. Taking advantage of this situation, Suma and associates [4] reported comparable early results of ITA grafting in Japanese patients of small body size compared with large Japanese patients, regardless of their smaller coronary artery size and flow.
As in the report of Suma and associates [4], our results showed satisfactory early and long-term results of CABG with extensive usage of arterial grafts in smaller patients. In our study, the 1-month patency rate of arterial grafts in smaller patients was comparable to that in larger patients. However, the patency rate of vein grafts was significantly lower in smaller patients. We have previously reported a significantly (p < 0.05) higher patency rate of ITA grafts (94.3%) than of vein grafts (88.2%) in the left circumflex artery region even though the flow in ITA grafts, at 27.8 ± 12.8 mL/min, was significantly (p < 0.001) less than that in the vein grafts, at 60.0 ± 35.7 mL/min [7]. These results indicate that venous grafts are more prone to occlude than arterial grafts under low flow conditions during the early postoperative period. This higher patency rate of arterial grafts and the excellent long-term results indicate that technical difficulties in anastomosing a small arterial graft to a small coronary artery can be overcome with meticulous technique by well-trained surgeons. In contrast, the poor patency of vein grafts is not a technical matter, but an inherent disadvantage originating from the characteristics of this type of graft. Therefore, arterial grafting, which can be expected to yield a higher patency rate than venous grafting under low graft flow conditions, is beneficial in smaller patients, who generally have small coronary arteries with lower expected graft flow. These results can be achieved with no significant increases in operative mortality and morbidity. Although the rate of extensive use of arterial grafts was significantly lower in small patients, extensive usage of such grafts is justified and is the procedure of choice in small patients with small coronary arteries, as long as the arterial grafts are not excessively small.
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Acknowledgments
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We acknowledge Dr Wendy Ann Gray for her editorial assistance.
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Footnotes
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Presented at the Twenty-second World Congress of The International Society for Cardiovascular Surgery, Kyoto, Japan, Sep 10–15, 1995.
Address reprint requests to Dr Nishida, Department of Cardiovascular Surgery, The Heart Institute of Japan, Tokyo Women's Medical College, 8-1 Kawadacho, Shinjuku-ku, Tokyo 162, Japan.
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References
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- Fisher LD, Kennedy JW, Davis KB, et al. Association of sex, physical size, and operative mortality after coronary artery bypass in the Coronary Artery Surgery Study (CASS). J Thorac Cardiovasc Surg 1982;84:334–41.[Abstract]
- Loop FD, Golding LR, MacMillan JP, Cosgrove DM, Lytle BW, Sheldon WC. Coronary artery surgery in women compared with men: analysis of risks and long-term results. J Am Coll Cardiol 1983;1:383–90.[Abstract]
- O'Connor GT, Morton JR, Diehl MJ, et al. Differences between men and women in hospital mortality associated with coronary artery bypass graft surgery. Circulation 1993;88:2104–10.[Abstract/Free Full Text]
- Suma H, Takeuchi A, Kondo K, et al. Internal mammary artery grafting in patients with smaller body structure. J Thorac Cardiovasc Surg 1988;96:393–9.[Abstract]
- Cox DR. Regression models and life tables. J R Stat Soc [B] 1972;34:187–220.
- Christakis GT, Buth K, Weisel RD, et al. Is body size the cause for poor outcomes of coronary artery bypass operations in women? J Thorac Cardiovasc Surg 1995;110:1344–58.[Abstract/Free Full Text]
- Nishida H, Endo M, Koyanagi H, et al. Extensive use of arterial grafts for coronary artery bypass grafting in Japanese patients. Cardiovasc Surg 1994;2:93–6.[Medline]
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Abstract
Introduction
