I thoracic artery (LITA) anastomosed to the anterior

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1 Similar Hospital Morbidity With the Use of One or Two Internal Thoracic Arteries Eric Berreklouw, MD, Jacques P. A. M. Schonberger, MD, PhD, Johannus H. Bavinck, MD, Victor J. Verwaal, MD, Evert L. Koldewijn, MD, Frits van der Linden, MD, Ingeborg van der Tweel, PhD, and Johan J. Bredee, MD, PhD Department of Cardio-pulmonary Surgery, Catharina Hospital, Eindhoven, The Netherlands The hospital morbidity and mortality of patients operated with two internal thoracic arteries with or without additional vein grafts (BITA group) were compared with a matched group of patients operated with one left internal thoracic artery (ITA) on the anterior descending artery with additional vein grafts (LITA control group). In each study group, % of the patients had diabetes mellitus. There was no statistical significant difference in hospital mortality (% versus O%), perioperative myocardial infarction (% versus %), low cardiac output (% versus %), rethoracotomy (% versus O%), lung complications (% versus % ), wound complications (8% versus 8%), other cardiac complications (6% versus 6%), other noncardiac complications (% versus 4%), median duration of stay in the intensive care unit ( versus day), and mean duration of stay in the hospital (.4 versus.8 days) between the groups. Logistic regression analysis showed that the number of ITAs used was not a predictor of complications. Thus, there is no difference between the BITA and LITA control group in hospital mortality and morbidity (in patients with a low incidence of diabetes). If an improvement in cardiac event-free and reoperation-free survival is to be expected, the use of both ITAs can be continued in similar patients. ( 994;7:6&7) t has been proved that the use of the left internal I thoracic artery (LITA) anastomosed to the anterior descending artery (LAD) results in a better cardiac eventfree and reoperation-free survival than the use of the saphenous vein as conduit [l]. Few studies demonstrate that the use of bilateral internal thoracic arteries (BITA) results in a better cardiac event-free survival than the use of the LITA only [4]. For patients aged 6 years or younger this incremental improvement might be more pronounced [4]. In achieving such an improvement in cardiac event-free and reoperation-free survival one should question at what price this can be reached in terms of hospital mortality and morbidity and at what postoperative interval the expected improvement occurs. The first question is the topic of this study. Material and Methods Data were collected retrospectively from consecutive patients operated between January 99 and July 99 (Appendix ). For this study, patients operated with BITA as single or sequential grafts with or without additional vein grafts (BITA group) were matched with similar patients operated with a LITA as a single or sequential graft on the left anterior descending artery and its branches, with additional vein grafts (LITA control group). The patients were matched to the following Accepted for publication Oct, 99 Address reprint requests to Dr Berreklouw, Department of Cardiopulmonary Surgery, Catharina Hospital, Michelangelolaan, 6 ZA Eindhoven, The Netherlands. 994 by The Society of Thoracic Surgeons criteria: time of operation (next consecutive patient), age, sex, and extent of coronary artery disease. In a few cases, when a patient matching all criteria could not be found, one was selected that met the matching criteria the most. During the operation, the choice to use the LITA with vein grafts or the BITA was made depending on preference of the surgeon. All patients were operated with pedicled ITAs or reversed saphenous vein grafts as single or sequential grafts. Patients treated with free ITAs, gastroepiploic arteries, reoperations, or combined procedures were excluded from the study, as well as patients who were operated for an acute myocardial infarction. Diabetes was defined as any diabetes treated with insulin or oral antidiabetic medication. To evaluate the effect of obesity, the body mass or Quetelet index (body weight [kglheight [m ]) was used. At a Quetelet index of kg/m or more, obesity and overweight are synonymous. The quality of the coronary arteries at angiography was determined by the surgeon using a four-scale grading system. During the operation the quality of the coronary arteries was determined again by the surgeon using the same four-scale grading system as at angiography. Completeness of revascularization was determined by computer analysis of the total number of distal anastomoses divided by the number of all coronary vessels that were narrowed by more than %. Data Collect ion and Stat is t ical Methods All data were compiled in a computerized databank and analyzed with the Number Cruncher Statistical System (Hintze, Kaysville, UT). In the statistical analysis of the study groups no consideration was given to the matching -497/94/$7.

2 994:7: 647 BERREKLOUW ET AL 6 process. Statistical analysis of categorical variables was performed using cross-tables with the Pearson test. If the expected values were small, the Fisher exact test was used. Continuous variables were analyzed with the twosample t test, if the variances of the groups were equal; otherwise the Mann-Whitney U test was used. If continuous variables were not normally distributed, they were logarithmically transformed. To determine the best subset of predictors for the development of perioperative infarction, low cardiac output, lung complications, wound complications, other cardiac complications, and stay of more than day in the intensive care unit (ICU) and duration of stay in hospital, a selection of variables was made from 6 variables (Appendix ) by McHenry s algorithm []. For this analysis the respective complications were grouped according to the Postoperative variables of Appendix. The predictors for the binarydependent variables were analyzed using a linear logistic regression model, and for the analysis of the duration of stay in the hospital the Cox s proportional hazards regression model was used. The regression analysis was performed with backward elimination and was continued until all nonsignificant predictors were removed. The odds ratios and relative risks are calculated from the beta estimates, with 9% confidence limits using the standard errors of the beta estimates (see Table 4). In all statistical tests a p value less than. was considered to be significant. Results Patient Matching Patients were matched by preoperative characteristics and catheterization and angiographic data (Table ). There were no significant differences in age, sex, height, weight, body mass, preoperative angina class, history of heart failure, previous infarction, smoking, diabetes, chronic obstructive lung disease, or year of operation between both study groups. There was no significant difference in extent of coronary disease or quality of the coronary arteries at angiography between both study groups. More than half of the patients had two-vessel disease, about 4% had three-vessel disease, and a few patients had a lesion of the left main only. Left ventricular function was comparable for both study groups. Operative Procedures The ITAs were harvested using a modified Favaloro retractor and low-dose electrocautery. The pleural space at the side of the ITA was intentionally opened and drained. All operations were performed by one of four surgeons. Although one of the four surgeons was less experienced with extensive revascularization with arterial grafts, all operations during that surgeon s learning period are included in the study. A routine blood-saving program was applied in all patients, including the addition of million KIU of aprotinin to the prime solution of the extracorporeal circuit [6]. If the free blood flow from the arterial conduit was poor (less than ml/min), the flow was improved by hydrostatic intraluminal dilatation Table. Preoperative Characteristics of the BITA and LITA Groups V a r i a b e Age (Y) Age range (Y) 6 years 6 years Men Height (cm) Weight (kg) Quetelet index (kg/m) Quetelet index (kglm) Angina class History of heart failure Previous infarction Smoking Diabetes mellitus Insulin-dependent Oral antidiabetics COPD No. of diseased coronary arteries No. of diseased coronary systems Left main only Two Three Quality of coronary arteries LVEDP Total CASS score Year of operation BITA LITA (n = ) (n = ) p Value. (7.) (6.8) 78.8 (9.8) 6. (.). (.8) 4 7. (.).4 (.6) 6 4. (.8).6 (7.). (4.9) (6.) (7.6) 79.6 (.) 6. (.) 7. (.6) (.).4 (.) 9 4. (.7).4 (.8). (6.) a Categorical data are presented as the actual numbers. Continuous data are presented as the mean with the standard deviation within parentheses. BITA = bilateral internal thoracic artery with or without vein grafts; CASS = Coronary Artery Surgery Study; COPD = chronic obstructive pulmonary disease; LITA = left internal thoracic artery with or without vein grafts; LVEDP = left ventricular end-diastolic pressure. by injection of a papaverine solution or with a dilating balloon catheter. Distal single or sequential anastomoses were performed using a running suture technique with to. times magnification loops under ischemic arrest with moderate hypothermia using antegrade St. Thomas or blood cardioplegia. Most frequently, the left ITA was anastomosed to the anterior descending artery with the right ITA on the right or circumflex coronary artery (Fig ). Or, the left ITA was anastomosed to the branches of the circumflex artery with the right ITA to the anterior descending artery (Fig ) or right coronary artery (Fig ). In some cases, the left or right pedicled thoracic artery could reach the posterior descending coronary artery (Fig 4). Patients were rewarmed adequately to prevent spasm of the arterial conduits postoperatively. To provide the myocardium with adequate flow through the ITAs at the

3 66 BERREKLOUW ET AL 994;7647 end of cardiopulmonary bypass, the mean arterial pressure was maintained above 6 mm Hg, with phenylephrine if necessary. Opera f ive Da fa Operative data are presented in Table. The number of BITA and LITA procedures was not equally (p <.) distributed among the different surgeons. Although St. Thomas cardioplegia was used most often in LITA procedures, there was no significant difference in the method of myocardial protection. The mean total number of distal anastomoses was. in both groups. The number of distal anastomoses with both ITAs was two in 67 patients, three in 9 patients, and four in patients. Because of the study design, there were more (p <.) distal ITA anastomoses in the BITA than in the LITA group. In LITA patients a mean of. ITA anastomosis was performed with the left ITA, whereas in BITA patients a mean of.4 ITA anastomoses were performed with both ITAs. The distribution of distal vein anastomoses in the BITA group was significantly different (p <.) from the one in the LITA group. There was no significant difference in the quality of the coronary arteries at operation, the number of endarterectomies, and the percentage of complete revascularization. In judging the relative low numbers of complete revascularization one has to consider that this was a computer calculation in which the diameter of the vessels at operation or the presence of scar tissue was not computed. Fig. Left internal thoracic artery () anastomosed to obtuse marginal branch (4) and posterolateral branch () of the circumflex artery and right internal thoracic artery () anastomosed to the anterior descending artery (). Clinical Res u ts There were no statistically significant differences in any of the clinical results of both treatment modalities between the two study groups (Table ), therefore, in the analysis of the predictors for the different complications, the two patient groups were grouped together. MORTALITY. One patient in the BITA group died in the hospital; no patient died in the control group. One 7- year-old man received an LITA on the left anterior descending artery and a right ITA on the obtuse marginal branch. Because of an allergy to protamine, none was given. On arrival at the ICU the patient was hemodynamically unstable, developed an atrioventricular block, had to be resuscitated and subsequently died. No autopsy was undertaken. The cause of death was probably related to irreversible excessive blood loss. Fig. Retroaortic right internal thoracic artery () anastomosed with the obtuse marginal branch of the circumflex artery () and left internal thoracic artery () anastomosed to diagonal branch (4) and anterior descending artery (). PERIOPERATIVE MYOCARDIAL INFARCTION. One patient in the LITA group and patients in the BITA group sustained a perioperative myocardial infarction (MI). All infarctions were confirmed by echography. Four of the 6 patients were women and in 4 no vein grafts were used. In 4 of the BITA patients with a perioperative MI a complete arterial revascularization was performed (p = NS). It was striking that in of the 6 perioperative MI patients poor quality, small (< mm) diameter, or intramural coronary vessels were noticed, leading to an incomplete revascularization in patients and additional throm-

4 994;76&7 BERREKLOUW ET AL 67 Fig. Left internal thoracic artery () anastomosed to obtuse marginal branch (4) and posterolateral branch () of the circumflex arte ry and right internal thoracic artery () anastomosed to right coronary artery (). boendarterectomy in patients. Linear logistic regression analysis showed sex ( p =.), BITA without vein grafts (p =.), and surgeon's experience (p =.) as Table. Operative Data of the BITA and LlTA Groups" Variable Surgeon A B C D Myocardial protection St. Thomas cardioplegia Blood cardioplegia Other No. distal anastomoses Two Three Four Five Six No. ITA anastomoses One Two Three Four No. vein anastomoses Zero One Two Three Quality of coronary arteries Endarterectomy Complete revascularization BITA LITA (n = ) (n = ) p Value (.9) (.6) (.7) (.8) (.8) (.4) < (.8) < (.8) a Categorical data are presented as the actual numbers. Continuous data are presented as the mean with the standard deviation within parentheses. BITA = bilateral internal thoracic artery with or without vein grafts; LITA = left internal thoracic artery with vein grafts. predictors for perioperative MI, with relatively high odds ratios (Table 4). LOW CARDIAC OUTPUT. Three patients in both groups needed inotropic support and in LITA patients an intraaortic balloon pump was used. Five of 8 patients needing support for low cardiac output had a perioperative MI (p <.) and were women (p <.). Logistic regression analysis confirmed that these two variables, perioperative MI (p =.8) and sex (p =.7), were predictors for low cardiac output (Table 4). RETHORACOTOMY. Only in BITA patient a rethoracotomy was performed for excessive bleeding that was not related to the use of the ITAs or vein grafts. Fig 4. Right internal thoracic artery () anastomosed to posterior descending branch of the right coronary artery (). LUNG COMPLICATIONS. Thirteen patients in each study group sustained a variety of lung complications. Logistic regression analysis showed that postoperative low cardiac output was the most important predictor for the occurrence of lung complications (p =.9) (Table 4). Smoking or preoperative lung disease did not appear to be related to postoperative lung complications.

5 68 BERREKLOUW ET AL 994;7647 Table. Clinical Results of the BITA and LITA Groupsa Variable Hospital mortality Low cardiac output Inotropics Intraaortic balloon pump Rethoracotomy for nongraft bleeding Lung complications Pneumothorax More than 48 hr ventilation Pleural effusion Pneumonia Phrenic nerve lesion Wound complications Subcutaneous chest infection Sternum dehiscence Mediastinitis Other Other cardiac complications Atrial fibrillation Atrioventricular block Ventricular tachycardia fibrillation Postcardiotomy syndrome Other noncardiac complications Urinary tract infection Ulnar nerve lesion Cerebral infarction Stay in intensive care unit Median days (range) day ICU > day ICU Stay in hospital Median days (range) BITA LITA (n = ) (n = ) p Value 8 6 l(-) 67 8 (-6) l(-8) (-8) a Categorical data are presented as the actual numbers. Continuous data are presented as the median with the range within parentheses. BITA = bilateral internal thoracic artery with or without vein grafts; ICU = intensive care unit; LITA = left internal thoracic artery with vein grafts. WOUND COMPLICATIONS. Eight patients in each study group experienced wound complications from the sternal wound. Mediastinitis was observed only in LITA patients, but in no BITA patients. Logistic regression analysis showed a Quetelet index greater or equal than kg/m (p =.) and year of operation (p =.4) as the main predictors for sternal wound complications (Table 4). Diabetes or the number of ITAs were not predictors of wound complications. OTHER CARDIAC COMPLICATIONS. Cardiac complications, other than perioperative MI or low cardiac output, being mainly atrial fibrillation or (temporary) atrioventricular conduction abnormalities, were noticed in 6 BITA and 6 LITA patients. Logistic regression analysis showed that the occurrence of a perioperative infarction (p =.4) and (a higher) age (p =.48) were the predictors for these cardiac complications (Table 4). OTHER NONCARDIAC COMPLICATIONS. Other noncardiac complications (mainly urinary tract infections) occurred in BITA and 4 LITA patients. DURATION OF STAY IN THE INTENSIVE CARE UNIT. The median stay in the ICU was day for both study groups. About one third of the patients in both study groups stayed longer than day in the ICU. Logistic regression analysis showed that age above or equal to 6 years was the most important ( p =.4) predictor for a longer stay at the ICU. There also was a correlation with blood cardioplegia (p =.), a higher left ventricular enddiastolic pressure ( p =.8), and low cardiac output (p =.) (Table 4). DURATION OF STAY IN THE HOSPITAL. The median stay in the hospital was 8 days for BITA and 8. days for LITA patients. Cox s proportional hazards regression analysis showed that (sternal) wound complications (p <.) and the duration of stay at the ICU (p =.) were the most important predictors for the duration of stay in the hospital (Table 4). (A negative beta estimate for predicting hospital stay means a smaller risk to be dismissed from the hospital and thus a longer stay in the hospital.) Comment In this study we could not demonstrate any statistically significant difference in the clinical results with the use of one or two ITAs. The use of one or two ITAs had no predictive value for the occurrence of the studied hospital complications. A hospital mortality of % in the BITA group and % in the LITA group is low in comparison with the.9% to 9% and % to.8% observed by other studies [,, 7-]. Our study confirms that there is no significant difference in hospital mortality between BITA or LITA operations, as reported before [,, 7, 8,. The incidence of perioperative infarction was not significantly different: % in the BITA and % in the LITA group. In a recent study, Kouchoukos and colleagues [8] found a perioperative MI rate of % in both groups. Our higher infarction rate in the BITA group might be attributed to the high percentage of poor-quality vessels, incomplete revascularization, and endarteriectomy in these patients, factors that have been recognized to increase the risk of perioperative MI [ll]. Logistic regression analysis of perioperative MI was performed with only a very small number of incidents and therefore, should be interpreted only as indicative. There was an association between the occurrence of an perioperative infarction and female sex, BITA without vein grafts, and with the experience of the surgeon. Also Suma and colleagues [] found a two times higher but not significantly different incidence of perioperative MI in ITA patients with a small body surface area. Female sex has been identified to increase the risk

6 994;7: -7 BERREKLOUW ET AL 69 Table 4. Predictors for Cornalications Predictor Predictors for perioperative infarction (6 patients, %) Sex BITA without vein grafts Surgeon's experience Predictors for low cardiac output (8 patients, 4%) Sex Predictors for lung complications (6 patients, %) Low cardiac output Age 6 y Predictors for wound complications (6 patients, 8%) Quetelet index Year of operation Log (LVEDP) Predictors for other cardiac complications (4 patients, %) Age (Y) Predictors for stay at ICU for more than day (7 patients, %) Age 6 Myocardial protection Log (LVEDP) Low cardiac output Predictors for duration of hospital stay ( patients) Wound complications Duration stay ICU Surgeon's experience Confidence Beta Standard J p Value Odds Limits Estimate Error (Beta = ) (Beta = ) Ratio (9%) E E (NS).8.7. (NS) (NS) (NS) (NS) (NS) < (NS) ICU = intensive care unit; ITA = internal thoracic artery; NS = not significant. for operative mortality in ITA operations [,. Gender, physical size, and size of the coronary arteries have been identified as risk factors for operative mortality with the use of venous bypass grafts [4] and it appears that these factors form a higher risk for perioperative MI in ITA operations as well. In this study it appears that complete arterial revascularization with BITAs is a risk factor for perioperative MI, although this was not confirmed comparing only the BITA patients with or without additional vein grafts with each other. It is suggested that with a complete arterial revascularization there could be a discrepancy in ITA flow and myocardial demand []. We found no difference in the frequency of support for low cardiac output in the study groups, as recognized by other investigators [8]. The regression analysis of low cardiac output was performed for only a small number of these incidents. The strong association of low cardiac output with the occurrence of perioperative MI is logical and well known and the number of ITAs used has no influence on this relation. Because there is an association between sex and perioperative MI, sex has an influence on low cardiac output as well. It is remarkable that preoperative left ventricular function does not appear to be a predictor of low cardiac output. In this study there was only one rethoracotomy for bleeding. This low incidence might be attributed to our blood-saving program, including low-dose aprotinin. Previously, we and others [6--8 have shown that BITA operations do not lead to more reoperations for bleeding. The number of pulmonary complications was not different in both study groups. In most studies, only respiratory insufficiency is noted, varying from.% to 8.% for BITA operations [7-9. In our study, however, minor complications, such as pleural effusions, were noted as

7 7 BERREKLOUW ET AL 994;764-7 pulmonary complications. It has been shown that the use of one ITA, independent of whether the pleural space is opened or not, may lead to more pulmonary complications than with the use of saphenous vein grafts only [6, 7. In our patients, in which we always opened and drained the pleural space, one might expect more pulmonary complications in BITA patients, but we found no difference related to the number of ITAs used. Surprisingly, we could not demonstrate a correlation between postoperative pulmonary complications and preoperatively known lung diseases or smoking habits. We found no significant difference in the incidence of sternal wound complications between both treatment modalities. If we consider mediastinitis and sternal dehiscence together as serious wound complications, then there were BITA and 4 LITA patients with these complications. Kouchoukos and colleagues [8] could demonstrate a significant difference in the incidence of sternal infection (6.9% versus.9%) and superficial chest wound infections, sterile dehiscence, or delayed healing (.% versus.9%) in their BITA versus LITA patients. We could confirm the findings of Kouchoukos and associates that a Quetelet index equal or above highly correlates with the occurrence of wound complications, even if one considers that in our study adipositas was present in only % of the BITA patients versus % in the study of Kouchoukos and colleagues. That we could not confirm diabetes as a predictor for wound infection might be explained by the fact that only % of our patients and % of Kouchoukos s BITA patients had diabetes. Cosgrove and colleagues [7] found significantly more wound complications (.4% versus.%) in their BITA patients and showed that diabetes mellitus and advanced age were the only significant risk factors for these wound complications. The fact that we could not confirm the influence of diabetes mellitus or age on these complications might be attributed to our patient selection, as demonstrated by the relatively low percentage of our BITA patients with diabetes mellitus, % versus.7% in the Cleveland Clinic study. If in this study bias would have been involved in selecting patients for BITA operation, then one has to admit that, considering the not significant difference in preoperative variables, the surgeons have selected their patients carefully not only for BITA operation, but for LITA operation as well. The reason that not more perioperative variables, known for their predictive value for postoperative complications [ 8, were included, had to do with the aim of this study, which was not to examine all the possible predictors of hospital outcome, but to study the difference in hospital outcome between BITA and LITA operation. One has to be cautious in the interpretation of the multivariate analysis of the hospital outcome and especially the analyses performed with small numbers of events. In conclusion, it appears that there is no difference in hospital mortality and morbidity between BITA and LITA operation in well selected patients. Therefore, if an improvement in cardiac event-free and reoperation-free survival is to be expected, as is the case in patients younger than 6 years, one should not withhold an operation using both ITAs. We thank Mrs Joyce Wetselaar-Whittaker for her fine hand drawings and Bertjan Arends, BSc, for his help with the statistical analysis. References. Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery on -year survival and other cardiac events. N Engl J Med 986;4-6.. Cameron A, Kemp HG, Green GE. Bypass surgery with the internal mammary artery graft: year follow-up. Circulation 986;74(suppl ):M.. Fiore AC, Naunheim KS, Dean P, et al. Results of internal thoracic artery grafting over years: single versus double grafts. 99;49: Cosgrove DM, Hill A, Lytle BW, et al. Are two internal thoracic arteries better than one? Am Assoc Thorac Surg McHenry CE. Computation of a best subset in multivariate analysis. J Roy Stat SOC, Series C 978; Schonberger JP, Everts PA, Ercan H, et al. Low-dose aprotinin in internal mammary artery bypass operations contributes to important blood saving. 99;4: Cosgrove DM, Lytle BW, Loop FD, et al. Does bilateral internal mammary artery grafting increase surgical risk? J Thorac Cardiovasc Surg 988;9: Kouchoukos NT, Wareing TH, Murphy SF, Pelate C, Marshall WG. Risks of bilateral internal mammary artery bypass grafting. 99;49: Galbut DL, Traad EA, Dorman MJ, et al. Seventeen-year experience with bilateral internal mammary artery grafts. Ann Thor Surg 99;49:9-.. Naunheim KS, Barner HB, Fiore AC. Results of internal thoracic artery grafting over years: single versus double grafts [update]. 99;:764. Burton JR, FitzGibbon GM, Keon WJ, et al. Perioperative myocardial infarction complicating coronary bypass. J Thorac Cardiovasc Surg 98;8:7&64.. Suma S, Takeuchi A, Kondo K, et al. Internal mammary artery grafting in patients with smaller body structure. J Thorac Cardiovasc Surg 988;96:9%9.. Cosgrove DM, Loop FD, Lytle BW, et al. Does mammary artery grafting increase surgical risk? Circulation 98; ~~(SUPP~ ): 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 98;84:4-4. Jones EL, Lattouf OM, Weintraub WS. Catastrophic consequences of internal mammary artery hypoperfusion. J Thorac Cardiovasc Surg 989;98:9-7. Hurlbut D, Myers ML, Lefcoe M, et al. Pleuropulmonary morbidity: internal thoracic artery versus saphenous vein graft. 99;: Landymore RW, Howell F. Pulmonary complications following myocardial revascularization with the internal mammary artery graft. Eur J Cardiothorac Surg 99;4:6-6. Hammermeister KE, Burchfiel C, Johnson R, et al. Identification of patients at great risk for developing major complications at cardiac surgery. Circulation 99;8(suppl4):9(L9.

8 ~~~~~ 994;76&7 BERREKLOUW ET AL 7 Appendix. Listing of Coded Variables Sex = male = female Age years Age number number number Height cm Weight kg Quetelet index Angina class 4 (Canadian classification) Heart failure = none = yes Previous myocardial = none infarction = yes Smoking = none = yes Diabetes mellitus = none = yes, insulin = yes, oral medication COPD = none = COPD = lung emphysema = other active lung disease No. of diseased coronary = main stem systems = two systems, other than main stem = three systems, other than main stem No. of diseased coronary number arteries Quality of diseased = normal caliber, no distal disease coronaries = normal caliber, distal disease = small caliber, no distal disease 4 = small caliber, distal disease LVEDP mm Hg CASS score cumulative CASS score Year of operation 9 = 99 9 = 99 Surgeon -4 Surgeon s experience = experienced = inexperienced Myocardial protection = no cardioplegia = St. Thomas cardioplegia = blood cardioplegia = one = two -6 Total no. of distal anastomoses No. of ITA anastomoses No. of vein anastomoses Quality of coronary arteries Endarterectomy Complete revasculariza tion Maximum ASAT on ECG on echocardiogram 4-4 = no = yes percentage (G) U/L = no = yes = not done = yes = none Appendix. Continued ~ Low cardiac output Rethoracotomy Lung complications Wound complications Sternum Other cardiac complications Other noncardiac complications Stay intensive care Stay hospital = none = yes with inotropics = yes with IABP = yes with cardiac assist = none = yes, ITA bleeding = yes, vein bleeding = yes, other bleeding 4 = yes, no bleeding = none = effusion with punction = paralysis diaphragm = pneumonia 4 = pneumothorax with drainage 48 h on ventilator = none = subcutaneous infection wound = sternum dehiscence = mediastinitis 4 = infection wound leg = none = atrial fibrillation = postcardiotomy syndrome = atrioventricular block 4 = ventricular tachycardiaifibrilla tion = none = urinary tract infection = ulnar nerve lesion = cerebral infarction d d ASAT = aspartate aminotransferase enzyme; CASS = Coronary Artery Surgery Study; COPD = chronic obstructive lung disease; ECG = electrocardiography; ITA = internal thoracic artery; LVEDP = left ventricular end-diastolic pressure.

9 7 BERREKLOUW ET AL 994;764-7 Appendix. Variables Considered as Independent Variables in the Linear Logistic and Cox Proportional Regression Analysis Preoperative clinical variables Age all years Age 6 y Age 6 y Sex Height Weight Obesity (Quetelet) index Quetelet index Angina class History of heart failure Previous myocardial infarction Smoking Diabetes Chronic obstructive lung disease Number diseased coronary vessels Number diseased coronary systems Left ventricular end-diastolic pressure (LVEDP) Left ventricular motion score (CASS) Operation-related variables Year of operation Surgeon Surgeon s experience No vein grafts (BITA only) Total no. of distal anastomoses No. of ITA anastomoses No. of vein anastomoses Endarterectomy Myocardial protection Complete revascularization Postoperative variables Perioperative myocardial infarction Low cardiac outputazb Rethoracotomy, Lung complications, Wound complications,b Other cardiac complicationsa,b Duration of stay in intensive care = none = yes = none = yes = none = yes = none = yes = none = yes = none = yes no. of days a Not used to analyze perioperative infarction. Not used to analyze low cardiac output. Only used to analyze duration of stay in the hospital. BITA = bilateral internal thoracic arteries; CASS = Coronary Artery Surgery Study; ITA = internal thoracic artery; LVEDP = left ventricular end-diastolic pressure.