Eur J Cardiothorac Surg 1999;16:429-434
© 1999 Elsevier Science NL
Prospective evaluation of coronary arteries: influence on operative risk in coronary artery surgery
H. Corbineaua,
H. Lebretonb,
T. Langanaya,
Y. Logeaisa,
A. Leguerriera
a Department of Cardiovascular and Thoracic Surgery, University Hospital Center, Rennes, France
b Department of Cardiology, University Hospital Center, Rennes, France
Corresponding author. Chirurgie Cardiovasculaire, CHR, Centre Cardio-Pneumologique, 2, rue Henri Le Guilloux, 35000 Rennes, France. Tel.: +33-2-99-28-24-90; fax: +33-2-99-28-24-96
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Abstract
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Objective: Coronary angiography data included in the analysis of operative mortality after coronary artery surgery are generally limited to left main coronary artery stenosis and classification into one-, two- or three-vessel disease, but the role of stenoses and quality of distal runoff on each main coronary artery have never been analysed. The aim of this study was to assess the influence of coronary artery status (stenoses and distal runoff) on operative mortality in patients undergoing coronary artery surgery. Methods: Stenoses of the five main coronary arteries and their distal runoff were prospectively evaluated in a series of 2461 patients undergoing isolated coronary artery surgery. These angiographic variables were included in analysis of operative mortality in combination with conventional preoperative data. Results: Univariate analysis founded 21 preoperative variables being significant: age >70, body surface area <1.8 m2, arterial disease of lower limbs, history of peptic ulcer, CCS class IV angina, unstable angina, post-infarction unstable angina, congestive heart failure, left ventricular ejection fraction <50%, urgency, preoperative intra-aortic balloon pump, previous myocardial infarction, previous cardiac surgery, previous coronary bypass graft, presence of significant stenosis on the left main coronary artery or the circumflex marginal branch or the distal circumflex artery or the right coronary artery, absence of significant stenosis on the left anterior descending artery, impaired distal runoff on the left anterior descending artery or the circumflex marginal branch (for all, P<0.05). Multivariate analysis identified poor quality distal runoff in the left anterior descending artery and circumflex marginal branch as independent risk factor (P=0.0005 and P=0.04, respectively), while left main coronary artery stenosis was not. This lesion appears to be a significant risk factor only in a small subgroup of patients with CCS class IV angina. Other independent risk factors were CCS class IV angina, previous cardiac surgery, body surface area <1.8 m2, diabetes mellitus, age <70, history of peptic ulcer, left ventricular ejection fraction <50%. Impaired distal runoff or the presence of stenoses on the diagonal branch, right coronary artery, or distal circumflex artery does not significantly influence the operative mortality rate. Conclusions: The quality of distal runoff of the most frequently grafted vessels is a significant risk factor for operative mortality in coronary artery surgery. Left main coronary artery stenosis was not identified as a risk factor when these angiographic variables were included in the analysis. Functional status remains the most powerful predictive factor.
Key Words: Coronary artery surgery • Coronary angiography • Operative mortality
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1. Introduction
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Identification of predictive factors of operative mortality (OM) in patients undergoing coronary artery bypass grafts (CABG) has already been the subject of numerous studies. In earlier reports, data derived from selective coronary angiography and analysed as predictive factors of operative mortality were limited to the presence of significant stenosis of the left main coronary artery (LMCA) and classification into one, two- and three- vessel coronary artery disease.
Qualitative variables based on the quality of coronary arteries (stenoses and status of the distal vasculature), assessed on coronary angiography have never been integrated into these prospective analyses. Their influence on OM was previously considered when a higher operative risk was reported in women. One hypothesis proposed to explain this excess mortality was the smaller body surface area generally observed in women, associated with a smaller luminal coronary artery diameter [1,2]. Other studies analysing vein graft patency rates, postoperatively or at 1 year, have emphasised the importance of the diameter of grafted vessels [3–7]. Only three publications studied the relationship between internal diameter of the grafted vessels at the anastomotic site, always measured intraoperatively, and OM [1,2,8] and one retrospective analysis identified poor vessel quality as a predictive factor of OM in a specific subgroup of patients with ejection fraction <0.25 [9].
In the present report, we prospectively studied the relationships between hospital mortality and coronary artery status, based on the data of selective coronary angiography, including stenoses and distal runoff.
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2. Material and methods
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2.1. Patients
In our institution, preoperative clinical and complementary data as well as surgical procedure and postoperative data have been prospectively collected in a computerised database since 1981 for each patient undergoing a surgical procedure with cardiopulmonary bypass circulation. Only preoperative variables were used for this analysis and only patients who underwent isolated coronary artery bypass grafts were included. From January 1991 to March 1996, 2493 patients underwent coronary revascularisation. Coronary angiography data were missing for 32 patients, who were therefore excluded from the analysis. Two thousand four hundred and sixty-one patients were therefore included in this study. The patient's demographic data are summarised in Table 1. OM was defined by death occurring after cardiac surgery (0–30 days) or before discharge from hospital. Angina was graded according to the Canadian Cardiovascular Society (CCS) classification [10]. Unstable angina and postinfarction unstable angina were defined according to the Braunwald classification [11]. Urgent procedures were performed within 6 days of angiography [12].
2.2. Angiographic analysis
In addition to LMCA stenosis, stenosis of other coronary arteries was also noted. Five arteries were evaluated: left anterior descending artery (LAD) and its main diagonal branch, distal circumflex artery and the main obtuse marginal branch, and right coronary artery. Significant stenosis was defined as 
50% luminal coronary diameter stenosis for the LMCA, and 70% for the other coronary arteries. To assess the quality of distal runoff, all coronary angiographies were analysed preoperatively by the same examiner, not involved in the surgical procedure. Distal runoff of the five arteries evaluated was classified into four stages by visual estimation, based on the coronary artery diameter at the usual anastomotic sites (with reference to the diameter of the catheter used for coronary angiography) and the presence of parietal irregularities (Table 2). The distal runoff of the right coronary artery essentially corresponded to the posterior descending artery.
2.3. Coronary revascularisation
The LAD was usually revascularised with the left internal mammary artery. Other vessels were usually revascularised with saphenous vein grafts. In a few patients (2.7%), the right internal mammary artery was used to bypass the circumflex marginal branch or distal circumflex artery.
No revascularisation procedure was performed in patients with a history of extensive transmural myocardial infarction, even in the rare cases in which a vessel with good distal runoff was identified. This situation was particularly frequent for the inferior wall, with 774 patients presenting a history of inferior myocardial infarction, and only 303 revascularisations (39%) performed in this territory. For the lateral wall, 172 patients presented a history of lateral myocardial infarction and revascularisation was performed in this territory in 105 patients (61%). For the anterior wall, (413 patients with a history of anterior myocardial infarction), revascularisation was performed much more frequently, as 92% of these patients underwent revascularisation of this territory.
Our revascularisation strategy was largely based on the quality of the distal runoff. In the case of poor distal runoff, verified intraoperatively, and particularly in the case of vessels with a diameter less than 1.5 mm, the most frequent attitude was not to perform coronary artery bypass grafts on these narrow arteries, especially when they were associated with myocardial infarction. Consequently, the mean number of distal anastomoses per patient was 2.2. Details of coronary revascularisation procedures are summarised in Table 3.
2.4. Statistical methodology
Selected data were entered into a specific database and analysed using the Statistical Package for Social Sciences (SPSS/PC+). Subgroups for ordinal variables (Distal runoff, CCS class, ejection fraction at intervals of 10%, age per decade) were pooled after verifying the absence of any significant difference between subgroups (Distal runoff 1–2 vs. 3–4, CCS classes: I—II–III vs. IV, ejection fraction: <50% vs. 50%, body surface area: <1.8 m2 vs. 1.8 m2, age 
or >70 years). The patients’ clinical and angiographic characteristics were submitted to univariate screening using the Chi-square test. Fisher's exact test was used when the Chi-square test was inappropriate. The relative risk (RR) was computed for variables when the P-value associated with the Chi-square test or Fisher's exact test was found to be significant at the 0.05 level. Multivariate analysis was performed by forward stepwise logistic regression. Variables with an associated P-value <0.10 on univariate analysis were integrated into the logistic regression. The existence of interactions between the identified risk factors was investigated and adjusted odds ratios (OR) were calculated.
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3. Results
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3.1. Angiographic data
Angiographic data are presented in Table 4. Analysis of distal runoff for each vessel evaluated did not reveal any statistically significant difference between groups 1 and 2 or between groups 3 and 4. The probability of impaired distal runoff in the case of stenosis of a vessel was always significantly increased. No relationship was observed between LMCA lesions and distal runoff status of the left coronary arteries. This analysis also did not reveal any relationship between distal runoff and body surface area, sex, concomitant diabetes mellitus, or functional stage of angina. On the other hand, in the case of altered distal runoff, deterioration of left ventricular function was always observed regardless of the vessel considered. This relationship was very significant for the LAD, diagonal, distal circumflex, and right coronary arteries (for all, P (0.001), but was not significant for the left main coronary artery (P=0.26).
3.2. Operative mortality
Among the 2461 patients undergoing isolated CABG, 105 died during the postoperative period (4.3%). Variations of OM rates observed during the study period were not significant. Causes of death were: myocardial infarction (47); heart failure without myocardial infarction (25); ventricular arrhythmia (8); atrioventricular block (2); stroke (3); liver failure (1); sepsis (4); disseminated intravascular coagulation (1); respiratory failure (8); mesenteric infarction (5); gastrointestinal haemorrhage (1). A total of 70.5% of postoperative deaths were therefore cardiac-related. Variables listed in Tables 1 and 2 were submitted to univariate analysis for their association with OM. The results of this analysis are summarised in Table 5.
No significant difference was observed between the groups of patients with one-, two- or three-vessel disease (without LMCA stenosis) for whom the overall mortality was 3.6%. The OM was increased in the case of stenosis of the marginal branch of the circumflex, distal circumflex, diagonal branch and right coronary artery. Inversely, the OM was significantly decreased in the presence of LAD stenosis.
Impaired distal runoff on LAD and the marginal branch of the circumflex artery was associated with a significantly increased OM rate. These two vessels had the best distal runoff (77.4 and 71.0% of normal distal runoff, respectively) and were also the two vessels most frequently revascularised. The risk of postoperative infarction for the LAD was related to the quality of distal runoff. In the case of impaired quality of the distal runoff of the LAD, the RR of anterior myocardial infarction was 2.3-fold higher than in the case of satisfactory distal runoff (4.1% vs. 1.8%, P=0.0017). For the right coronary artery, the risk of inferior myocardial infarction was also increased in the case of poor distal runoff (4.7% vs. 3.4%, P=0.10), but this analysis did not demonstrate any increased risk of myocardial infarction in the case of poor distal runoff on the marginal artery of the left edge and the distal circumflex artery. Myocardial infarction and postoperative mortality rates as a function of distal runoff for each vessel are presented in Table 6.
Among the 23 variables selected for multivariate analysis, 10 were finally identified as independent predictive factors of OM (Table 7). Two of them were variables derived from selective coronary angiography (impaired distal runoff of LAD and marginal branch of the circumflex artery). Another four variables were concurrent diseases or morbidity factors (diabetes mellitus, history of peptic ulcer, previous cardiac surgery, age >70 years). An altered ejection fraction was associated with an increased risk of operative mortality, but the operative risk was decreased in the case of large body surface area. The most discriminant factor identified was functional status.
A statistically significant interaction was demonstrated between functional class and LAD stenosis. In the presence of LAD stenosis, the OR associated with CCS class IV was 2.5. In the absence of LAD stenosis, the OR associated with CCS class IV increased dramatically to 8.0. In this subgroup of patients, the LMCA stenosis rate was very high (81%), with an increased OM (20%). No other statistically significant interaction was observed. Three hundred and forty-three patients did not present any stenosis of the LAD, with an OM of 7.3%. Eighty patients did not present any stenosis of either the LAD or the LMCA, with an OM of 6.3% in this subgroup.
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4. Discussion
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This study emphasises the predominant role of the quality of distal runoff in the LAD and marginal branch of the circumflex artery. The risk of operative mortality in patients with impaired distal runoff of the LAD was 2.15-fold higher than in patients with satisfactory distal runoff of this vessel. This key role of the LAD has been previously reported by G. O'Connor and J. O'Connor [2,8], who studied the relationship between the intraoperative LAD diameter at the anastomotic site and operative mortality. We confirmed this major role of the LAD and its distal runoff which, even when it is associated with other classical preoperative risk factors for operative mortality, remained an independent predictive factor of mortality. This was confirmed by demonstration of an increased risk of anterior myocardial infarction in the case of impaired LAD distal runoff.
Our analysis also confirmed the relationship between the quality of distal runoff of the marginal branch of the circumflex artery and operative mortality. In this series, this artery was generally revascularised by a saphenous vein graft. The risk of occlusion of these vein grafts in the case of poor distal runoff has already been reported by Goldman and Paz [3,4,7], who analysed the risk of occlusion of these grafts as a function of the diameter of the grafted artery. Independently of antiplatelet therapy, either during the postoperative period or at 1 year, the probability of occlusion of a vein graft was inversely related to the diameter of the grafted vessel. The benefit of antiplatelet therapy on the graft patency rate has also been shown to be inversely proportional to the diameter of the grafted vessel, both postoperatively and at 1 year [3–7].
Body surface area, whose relationship with coronary artery diameter has already been emphasised, remained an independent predictive factor of operative mortality in our analysis with a lower risk as body surface area increased. Simultaneous identification of body surface area and quality of distal runoff of the LAD and circumflex marginal branch as independent risk factors for OM appears to be related to our scoring method of coronary artery distal runoff, as the presence of parietal irregularities was included in our score. These two variables associated in the analysis emphasise the dual aspect of coronary artery distal runoff. It therefore seemed essential to evaluate these vessels both in terms of their diameter and in terms of the presence or absence of parietal irregularities.
In our experience, a history of peptic ulcer has always been associated with an increased operative risk in all forms of adult heart surgery. This factor of comorbidity has already been identified as a risk factor for OM in coronary revascularisation surgery [13]. No link between this disease and an increased risk of postoperative gastrointestinal haemorrhage or mesenteric infarction has been demonstrated.
The main consequence of integration of these variables (distal runoff and coronary artery stenosis) was elimination of LMCA stenosis as an independent risk factor for operative mortality. The influence of LMCA stenosis on operative mortality appears to be mainly related to its functional repercussions. In the case of CCS class IV angina, the risk increases considerably when the LAD is not stenosed (OR: 8.0 vs. 2.1, P=0.005). The LMCA stenosis rate was 81% in this subgroup of CCS class IV patients without LAD stenosis (84 patients). Operative mortality was very high in these patients (17 patients, 20.2%) versus 3.6% in CCS functional class I–III patients with LMCA stenosis. Functional status therefore remains the most discriminant predictive factor of operative mortality. LMCA stenosis is associated with excess mortality only in the case of severe functional repercussions.
The main limitations of this study are related to the difficulties of analysis of the quality of distal runoff. The method used in this study took into account the arterial diameter as well as the presence of parietal irregularities, which are very difficult to quantify. Anatomical variants of the distribution of coronary arteries and dominant or equivalent contribution of the left and right coronary arteries must also be taken into account.
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5. Conclusion
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The quality of the distal runoff of the vessels most frequently grafted influences the immediate results of coronary artery surgery. LMCA stenosis must not be considered to be a particular risk factor. In the presence of LMCA stenosis, the immediate prognosis after coronary artery bypass graft is strongly correlated with functional class, which always remains the most important predictive factor of operative mortality in coronary artery surgery.
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Received April 12, 1999;
received in revised form July 26, 1999;
accepted August 4, 1999.
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Top
Abstract
1. Introduction
