Effect of Coronary Artery Diameter in Patients Undergoing Coronary Bypass Surgery
Background Coronary artery diameter is known to be inversely associated with perioperative mortality related to coronary artery bypass grafting (CABG). This association is believed to be responsible for increased risk among women and smaller people. However, the associations between sex, body size, and coronary size have not been carefully examined because direct information about coronary size is rarely available. Also, whether sex has an independent effect on vessel size is largely unknown.
Methods and Results Height, weight, sex, age, status at hospital discharge, and luminal diameter of the midleft anterior descending coronary artery (mid-LAD) were recorded prospectively in 1325 patients undergoing CABG. Small vessel size was associated with substantially increased risk of in-hospital mortality (15.8% for 1.0-mm vessels, 4.6% for 1.5- to 2.0-mm vessels, and 1.5% for 2.5- to 3.5-mm vessels, P[trend]<.001). Vessel size was strongly related to both sex and measures of body size. In multiple linear regression analysis, vessel size was positively correlated with body surface area (P[trend]<.01), body mass index (P[trend]=.004), height (P[trend]=.001), and weight (P[trend]=.001). After controlling for differences in age and body size, sex remained an important predictor of coronary size. Within each quartile of each body-size measure, mid-LAD diameter in men was greater than that in women (mean difference [range], 0.14 to 0.23 mm).
Conclusions Small mid-LAD diameter is associated with substantially increased risk of in-hospital mortality with CABG. Although body size is correlated with mid-LAD diameter, women have smaller coronary arteries than men after controlling for differences in body size. These findings further support the hypothesis that smaller coronary arteries explain higher perioperative mortality with CABG in women and smaller people.
Coronary artery diameter is known to be inversely associated with perioperative mortality related to CABG. This association is believed to be responsible for increased risk among women and smaller people.1 2 3 In a previous study by our group, female patients remained 75% more likely to experience in-hospital mortality than male patients after adjusting for age, comorbidity, and a wide range of variables associated with coronary disease severity.3 The CASS study1 found that physical size predicted operative mortality after adjustment for sex and other clinical predictors. Increased risk among those with small arteries may be related to increased risk of thrombosis in smaller vessels, technical difficulties of operating on smaller vessels, and decreased short-term patency in bypass conduits grafted to coronary vessels of small diameter.4 5 6 7 8 9 10
Despite the fact that others have described the effect of coronary vessel size on in-hospital mortality, the associations between coronary size and sex and body size have not been carefully examined. Although several studies showed that women have smaller coronary arteries than men,11 12 13 most studies of coronary disease outcomes lacked direct measurements of coronary artery size, relying instead on body-size measures such as height, weight, BSA, or BMI as proxies for vessel size.14 15 16 17 18 The appropriateness and relative predictive value of these body-size measures have not been explored. Furthermore, few studies have carefully examined whether women have smaller coronary arteries than men after accounting for differences in body size.
In the present study, we report in-hospital mortality rates by mid-LAD diameter. In addition, we explore the relationships between various measures of body size, sex, and mid-LAD diameter among 1325 patients undergoing CABG in northern New England.
The NNECDSG is a voluntary research consortium representing all five medical centers in Maine, New Hampshire, and Vermont in which heart surgery is performed. Since its inception in July 1987, the NNECDSG has maintained registries that contain information regarding patients undergoing CABG, heart valve replacement, or percutaneous transluminal coronary angioplasty at each of these institutions. For the current study, data were obtained from 1325 consecutive patients from one center who underwent CABG between July 1987 and April 1989. Only patients who received a bypass graft to the mid-LAD were included in these analyses.
Mid-LAD luminal diameter at the site of the distal anastomosis was measured with a set of graduated (0.5-mm increments) 1.0- to 3.5-mm probes. In addition, data were obtained on patient height, weight, age, and status at hospital discharge (dead or alive). BSA, a measure of overall body size, was calculated with the method of DuBois and DuBois,19 in which BSA=W0.425×H0.725×C, where W is weight (in kilograms), H is height (in centimeters), and C is a constant (C=71.84). BMI, a measure of obesity, was calculated from Quetelet’s formula20 as weight (kilograms) divided by height (meters) squared. Patients were divided into quartiles for each body-size measure to facilitate analysis and comparison between body-size measures.
A nonparametric test for trend across ordered groups, which was developed by Cuzick,21 was used to assess the statistical significance of observed differences in percent in-hospital mortality by vessel-size category. Multiple linear regression was used to assess associations between height, weight, BSA, BMI, and mid-LAD diameter while controlling for age and sex differences. All statistical analyses were performed with the STATA computer program (Stata Corp), and all probability values were two-tailed.
Mid-LAD diameter was inversely related to in-hospital mortality (Fig 1⇓). Percent in-hospital mortality was substantially higher in the smallest vessel-size category (1.0 mm: 15.8%) compared with those in the middle (1.5 to 2.0 mm: 4.6%) and largest (2.5 to 3.5 mm: 1.5%) categories (P[trend]<.001).
Overall, mean mid-LAD diameter was 2.04 mm for men (n=963) and 1.81 mm for women (n=362) (P<.001). Median vessel size was 2.0 mm for both groups. However, women were much more likely to have the smallest (1.0 to 1.5 mm) mid-LAD diameters, whereas there were significantly more men in the bigger (2.5 to 3.5 mm) vessel-size categories (Fig 2⇓).
In multivariate analysis, both sex and body size were significant, independent predictors of mid-LAD diameter (Table⇓). Because women were on average 2.5 years older than men, these results are age adjusted. Among patients of the same body size, mean mid-LAD diameter in men was significantly greater than that in women (mean difference ranged from 0.14 to 0.23 mm). For example, among patients in the second height quartile, mean mid-LAD diameter in men was 0.16 mm greater than that in women.
Similarly, there were significant trends for increasing vessel size with each of the body-size variables after adjustment for sex (Table⇑). For example, mid-LAD diameter was significantly greater in patients with BSA in the largest quartile than in those in the smallest (mean difference in women, 0.18 mm; in men, 0.14 mm; P[trend]<.001). Of the body-size measures, BMI was the least predictive of mid-LAD diameter (mean difference in women, 0.10 mm; in men, 0.09 mm; P[trend]=.004).
In the present study, small coronary artery diameter was associated with substantially increased risk of in-hospital mortality. Those in the smallest vessel-size category were 3.4 and 10.5 times more likely to die before discharge from the hospital than those in the middle and largest vessel-size categories, respectively. Both body size and sex were strong, independent predictors of age-adjusted mid-LAD diameter. As expected, mid-LAD diameter increased linearly with measures of increasing body size assessed by height, weight, BSA, or BMI. Among patients of the same body size, mid-LAD diameter in men remained 0.14 to 0.23 mm bigger than that in women.
Others1 3 have observed increased CABG mortality in patients with small coronary arteries. The CASS study1 found that operative mortality decreased with increasing average vessel diameter among men and women and that both vessel size and body size provided additional predictive power after controlling for clinical predictors of operative mortality. Our findings also confirm earlier work based on coronary arteriograms by Dodge et al,22 which demonstrated smaller coronary vessels in women after adjustment for BSA. In the present study, the magnitude of the effect of sex on mid-LAD diameter was similar to the effect of the extremes of body size on vessel size.
Heart size is known to vary both by sex and by body size,23 but it is not known whether these effects are independent. Furthermore, conditions known to be correlated with left ventricular mass, such as exercise, hypertension, and congestive heart failure, may have effects on vessel diameter and may differ in prevalence by sex. For example, left ventricular hypertrophy and dilated cardiomyopathy have been shown to be associated with increased luminal diameter of the coronary arteries22 and may be conditions that are differentially distributed among men and women. Although we believe that these factors are likely related to coronary artery diameter, the issue is difficult to address analytically. First, primary data reflecting heart size were not available for this analysis. Factors such as hypertension, previous myocardial infarction, exercise, and mitral valve disease are too heterogeneous to serve as reasonable proxies for heart size. Second, if these factors are in the same causal pathway between sex, body size, and vessel size, it would be inappropriate to control for them analytically as confounders of that relationship.
It is important to consider other potential limitations of this study. First, mid-LAD diameter was assessed with probes that were graduated in 0.5-mm increments. Although suitable for identifying patients at the extremes of vessel size, the measuring probe lacks the precision to make finer distinctions among patients near the mean size (1.5 to 2.5 mm). The likely effect of this classification error would be to underestimate the true predictive effect of sex and body size on vessel size. Second, coronary artery size may be related as much to body composition (eg, muscle mass ratios) as measures of body size. Differences in body composition that were not assessed in the present study could underlie the apparent independent effect of sex on coronary size. Third, our study assessed only mid-LAD diameter. Although it is possible that sex and body size are related differently to other coronary arteries, the previous study by Dodge et al22 found the effect of sex on vessel size to be generalizable to the entire coronary circulation.
Small mid-LAD diameter is associated with substantially increased risk of in-hospital mortality with CABG. Although coronary artery diameter is highly related to body size, women have smaller coronary arteries than men after accounting for differences in body size. These findings further support the hypothesis that smaller coronary arteries explain higher perioperative mortality with CABG and poorer outcomes with other treatments for coronary disease in women and smaller people.
Selected Abbreviations and Acronyms
|BMI||=||body mass index|
|BSA||=||body surface area|
|CABG||=||coronary artery bypass grafting|
|mid-LAD||=||mid–left anterior descending coronary artery|
|NNECDSG||=||Northern New England Cardiovascular Disease Study Group|
This study was supported by a FIRST award (No. R29-LM-04667) to Dr O’Connor and by grants from the Agency for Health Care Policy and Research (Nos. HS-06503 and HS-05745).
Reprint requests to Nancy J. O’Connor, MS, Clinical Research Section, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756.
↵1 Participating centers: Optima Health Care (Manchester, NH), Dartmouth-Hitchcock Medical Center (Lebanon, NH), Eastern Maine Medical Center (Bangor), Maine Medical Center (Portland), and Fletcher Allen Health Care (Burlington, Vt).
- Received October 31, 1995.
- Revision received December 12, 1995.
- Accepted December 19, 1995.
- Copyright © 1996 by American Heart Association
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