Long-term patency of as well as patient survival associated

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1 Angiographic Predictors of Graft Patency and Disease Progression After Coronary Artery Bypass Grafting With Arterial and Venous Grafts Hannu I. Manninen, MD, PhD, Pekka Jaakkola, MD, Matti Suhonen, MD, Sinikka Rehnberg, MD, PhD, Rauli Vuorenniemi, MD, and Pekka J. Matsi, MD Departments of Clinical Radiology, Surgery, and Medicine, Kuopio University Hospital, Kuopio, Finland Background. There are few data about angiographic determinants of functional graft patency and native artery disease progression after coronary artery bypass grafting operation with arterial grafts compared with venous grafts. Methods. Baseline and follow-up coronary angiograms at a mean of 2 years after operation in 91 patients with 194 arterial and 204 venous graft anastomoses were analyzed. Results. Ninety-two percent of the arterial and 87% of the venous graft anastomoses were patent at follow-up angiography (p 0.05, odds ratio 2.63). Unlike that of arterial grafts, the patency rate of venous graft anastomoses correlated negatively with decreasing severity of the bypassed lesion. In contrast to venous grafts, in which angiographic graft function was basically dichotomous (fully patent or occluded), compromised flow of the arterial graft anastomoses was registered in 12%. Progression of the disease was more common in segments bypassed with venous grafts than with arterial grafts (p 0.001, odds ratio 2.03). Conclusions. Angiographic determinants of functional graft patency and progression of occlusive changes in the bypassed artery segments are different for arterial and venous grafts. (Ann Thorac Surg 1998;66: ) 1998 by The Society of Thoracic Surgeons Long-term patency of as well as patient survival associated with in situ internal thoracic artery (ITA) grafts has been proved to be significantly better than that of saphenous vein grafts [1]. Long-term follow-up evaluation of patients with venous grafts has also revealed a greater incidence of disease progression in grafted than in nongrafted arteries, predominantly in the artery proximal to the anastomosis [2]. Data concerning the angiographic predictors of functional patency of arterial and venous coronary artery grafts, as well as the angiographic determinants of disease progression in the native coronary arteries after bypass graft operations using these two types of graft conduits, however, are scarce. Material and Methods Patients Between 1989 and 1992 a total of 1,558 coronary artery bypass graft operations were performed at our hospital. During this period 51 patients operated on by a single surgeon received sequential internal mammary artery grafts or right gastroepiploic artery grafts, or both (no operative mortality). Six of these patients were subsequently excluded from the trial because they refused follow-up angiography. For the remaining 45 patients Accepted for publication May 5, Address reprint requests to Dr Manninen, Department of Clinical Radiology, Kuopio University Hospital, SF Kuopio, Finland. and 46 control patients, selected to match the study group with respect to demographic and clinical data and operated on by the same surgeon, and who received conventional ITA and saphenous vein grafts, informed consent was obtained and control angiography was performed at a mean of 2 years (standard deviation [SD], 6.5 months; range, 13 to 31 months) after the operation. The study group consisted of 73 men and 18 women with a mean age of 56 years (range, 29 to 75 years). The patients routinely started taking acetosalicylic acid, 250 mg/day, on the day after operation and continued with that indefinitely with the exception of 6 patients who received warfarin medication. The following analyses combine all arterial grafts as one group and the saphenous vein grafts as another group. The study was approved by the ethics committee of the hospital. Coronary Operations The percentages of arterial grafts anastomosed to various vascular areas, eg, left anterior descending, circumflex, and right coronary artery, were 65%, 29%, and 6%, respectively, whereas the corresponding percentages for venous grafts were 15%, 38%, and 47%. The total number of arterial grafts was 144; the left ITA was used in 90 patients, the right ITA in 43 patients, and the right gastroepiploic artery in 9 patients. Forty-nine (34%) of the arterial grafts were sequential. Seventy-two patients received a total of 111 saphenous vein grafts, 75 (68%) of which were sequential. The number of arterial graft 1998 by The Society of Thoracic Surgeons /98/$19.00 Published by Elsevier Science Inc PII S (98)

2 1290 MANNINEN ET AL Ann Thorac Surg ANGIOGRAPHIC PREDICTORS OF GRAFT PATENCY 1998;66: anastomoses was 194 and of venous graft anastomoses 204, ie, a mean of 4.37 anastomoses per patient (range, 2 to 7). All analyses of the present study were performed per graft anastomosis, unless otherwise mentioned. Coronary Angiography In both preoperative and follow-up angiography the native coronary arteries were selectively imaged using biplane cineangiography in eight to ten identical projections. Analysis of the Angiograms Preoperative and follow-up arteriograms were analyzed independently by two experienced angiographers (H.I.M., M.S.) on two side-by-side cinefilm projectors (Tagarno 35 AX Xenon; Tagarno AS, Horsons, Denmark). The coronary vasculature was subdivided into 27 numbered anatomic segments using the standardized nomenclature of the Coronary Artery Surgery Study [1]. In the follow-up angiograms the vessel segments were further classified as (1) bypassed (segments immediately proximal to the graft anastomosis), (2) segments situated more proximally in the bypassed vessel, (3) nonbypassed arteries, and (4) segments situated distal to the graft anastomosis. Stenosis Determination The degree of the most severe stenosis within each segment was visually estimated as a percent diameter stenosis in relation to an appropriate adjacent reference diameter. The Pearson correlation coefficient between the two readers interpretations was 0.90 for the preoperative and 0.88 for the follow-up angiography for all segments with registered stenoses. The mean difference between the readers in the percent diameter stenoses of all 1,555 registered lesions (775 on preoperative and 780 on postoperative films) was 0.9% (SD, 20.9%; p 0.10 by t test for paired observations). For the statistical analyses, the means of the percent diameter stenoses from the two readers were used. The stenosis type was graded using a four-point scale: 1 short concentric; 2 short eccentric; 3 long tubular; and 4 diffusely diseased segment. Disease Progression Using side-by-side comparison of the cinefilms, the readers judged the individual stenoses as being (1) unchanged, (2) slightly progressed, (3) clearly progressed, or (4) totally occluded since the baseline angiogram. The kappa statistic for interobserver consistency of interpretation of lesion progression was In the statistical comparisons, progression was coded only when both of the observers registered progression. Lesion regression was registered in only five stenoses, and no further analyses of lesion regression were undertaken. Graft Patency The angiographic patency of the distal anastomoses was graded as (1) fully patent with good antegrade flow, (2) patent but with compromised flow, or (3) occluded. Anastomotic stenoses were registered. The slender sign, defined as flow dysfunction of the graft because of superior flow through the native artery [3] was also noted. The slender sign manifests as rapid dilution of the contrast media on entering the native coronary artery from the graft, together with considerable retrograde filling of the graft during contrast agent injection into the native coronary artery. In the statistical analyses compromised flow and the slender sign as well as anastomotic stenosis of the graft were coded only when both readers agreed. Side Branches of the ITA Grafts The unligated side branches of the ITA grafts were registered and classified into three categories: (1) one or several tiny side branches, (2) one major side branch of at least half the diameter of the distal ITA, or (3) several patent branches of considerable size. Diameter of the Graft and Native Coronary Artery The diameters of the distal graft and the native vessel immediately distal to the anastomosis were measured by one of the angiographers (H.I.M.) using a digital micrometer. The measurements were calibrated by using the diameter of the contrast-filled distal portion of the diagnostic catheter. The range of variability of the measurements was defined by performing 50 randomly selected readings twice. The standard deviation of the difference of the first and the second measurement was 6.8%. Statistical Analysis The primary aims of the statistical procedure were a proper analysis of angiographic predictors for patency and functional status of the arterial and venous grafts. The assumption that individual measurements are independent is not valid in cases like this in which vessels of the same individual tend to produce similar responses [4]. We took into account the correlation of outcomes within each patient by applying logistic regression analysis for distinguishable data (random-effects logistic regression, EGRET statistical software; Epidemiological Graphics). This method treats patency or occlusion of graft anastomoses within the same patient as dependent events. Besides statistical significance, the odds ratio and its 95% confidence limits (CL) are given. Results Graft Patency Eighty percent (156/194) of the arterial graft anastomoses were fully patent, 12% (23/194) were patent with compromised flow, and 8% (15/194) were occluded at follow-up angiography. The corresponding figures for the venous graft anastomoses were 85% (174/204), 2% (4/204), and 13% (26/204), respectively. Among 23 arterial anastomoses with compromised flow there were seven grafts less than 1 mm in diameter, four grafts with anastomotic stenoses, six grafts that were associated with presence of major side branches, and five grafts with stenoses in the native artery distal to the anastomosis. Among four

3 Ann Thorac Surg MANNINEN ET AL 1998;66: ANGIOGRAPHIC PREDICTORS OF GRAFT PATENCY 1291 venous anastomoses with compromised flow two anastomotic stenoses were registered and two grafts had a stenosis distal to the anastomosis. The 5% greater occlusion rate of the venous graft anastomoses is statistically significant (p 0.5; odds ratio 2.63; 95% CL, 1.01 and 6.86). Definite signs of atherosclerotic changes were not found in arterial grafts, but slight wall irregularities were observed in three venous grafts. The mean diameter of native coronary artery distal to the graft was 1.77 mm (SD, 0.71 mm); this was essentially the same in arteries anastomosed with venous or arterial grafts. The mean ratio of the diameter of the bypassed native arterial segment to that of the arterial graft was 0.96 (SD, 0.56); the corresponding ratio for venous grafts was 0.52 (SD, 0.32). Predictors of Graft Patency Factors showing no statistically significant correlation with the patency of either graft type included the ejection fraction, the vessel bypassed, and the morphology of the bypassed lesion. The mean degree of stenoses bypassed with arterial grafts was 81.5% (SD, 15.7%) and of those bypassed with venous grafts 78.2% (SD, 19.7%). The patency (dichotomized as fully patent or patent with compromised flow versus totally occluded) of venous graft anastomoses showed a positive correlation with the stenosis degree of the bypassed lesion at baseline angiography (p 0.05; odds ratio 0.94; 95% CI, 0.89, 1.00), whereas the patency of arterial graft anastomoses was essentially independent of the degree of the stenosis bypassed (p 0.85). This was especially evident when bypassed stenoses were grouped as moderate (ie, less than or equal to 75%) and severe (greater than 75%) (Fig 1). Up to 22.0% of venous graft anastomoses bypassing stenoses less than or equal to 75% were occluded at follow-up angiography, compared with a 7.7% occlusion rate in anastomoses bypassing narrower stenoses. For arterial conduits the proportion of totally occluded anastomoses was almost equal in both groups: 7.2% for grafts bypassing stenoses less than or equal to 75% and 6.4% for stenoses greater than 75%. Angiographic Predictors of Graft Function Slender sign was registered in 15.5% (30/194) of arterial graft anastomoses but in only 1.0% (2/204) of venous graft anastomoses. Because patency of venous graft anastomoses was basically dichotomous, ie, fully patent or totally occluded, further analyses of graft function were performed only for arterial conduits. The slender sign was more common as the ratio between the diameters of the native artery and graft increased (p 0.001; odds ratio 16.7; 95% CL, 4.54 and 50.0) and correlated negatively with increased severity of the bypassed stenosis in follow-up angiography (p 0.001; odds ratio 1.07; 95% CL, 1.02 and 1.12). Internal thoracic artery grafts included 20 cases with tiny side branches, 9 cases with one branch of at least half the diameter of the ITA, and 3 cases with several side branches of considerable size. Fig 1. Patency rates of the arterial (A) and saphenous vein graft anastomoses (B) according to the percent diameter stenosis of the bypassed lesion. The difference between the moderate and severe bypassed lesions for the vein grafts is statistically significant. (p 0.03; odds ratio 0.12; 95% confidence limits, 0.02 and 0.83.) Progression of the Disease Table 1 shows progression of the disease registered in three types of vessel segments of the native coronary arteries. Because the results of the arterial and venous grafts were similar, all grafts are combined. Stenoses distal to the anastomosis were detected in only 11 patients, and this category was not included in the analyses. Progression was less commonly registered in lesions situated in nonbypassed arteries than in bypassed segments or segments situated more proximal in the grafted artery. Follow-up angiography revealed progression in 33.0% (256/775) of the coronary artery stenoses: 17.6% of the lesions showed slight progression, 4.1% of the lesions showed marked progression, and 12.1% of the stenoses had progressed to total occlusions. Progression to total Table 1. Proportion of Lesions Showing Progression Between Baseline and Follow-up Angiographies in Various Coronary Artery Segments Segment Percentage of Lesions Progressed Progression to Occlusion Bypassed 39.6% (156/394) 46.8% (73/156) Proximal to the graft 33.1% (54/163) 22.2% (12/54) Nonbypassed 20.2% (44/218) a 20.4% (9/44) a Nonbypassed segment was significantly different from other segments by Kruskal-Wallis one-way analysis of variance.

4 1292 MANNINEN ET AL Ann Thorac Surg ANGIOGRAPHIC PREDICTORS OF GRAFT PATENCY 1998;66: Table 2. Disease Progression in Coronary Artery Segments Bypassed With Arterial and Venous Grafts Stenosis Location occlusion was more common in bypassed segments than in nonbypassed arteries or vessel segments situated more proximally to the graft (see Table 1). Sixty-five of the 91 patients had encountered native vessel progression in at least one segment during the follow-up time. Predictors of Disease Progression in the Bypassed Arterial Segments Disease progression in the bypassed segments proved to be equally frequent in cases of patent and occluded grafts, and showed no association with the severity and morphology of the original stenoses. Progression was less frequently seen in stenoses in vessel segments bypassed with arterial grafts than those bypassed with saphenous veins (Table 2). Comment Percentage of Lesions Progressed Arterial Grafts Venous Grafts p Value Odds Ratio (95% CL) Bypassed segment 32.6% 46.1% (62/190) (94/204) (1.31, 3.13) More proximal 25.6% 44.9% segment (24/94) (31/61) (1.32, 6.36) CL confidence limits. The type of coronary artery graft, the lumen diameter of the grafted artery, and the location of the distal anastomosis are proven to be predictors of graft patency in follow-up studies. Improved long-term patency has been found in ITA grafts (versus saphenous vein grafts), with larger grafted arteries, and in the left anterior descending coronary artery (versus other grafted arteries) [4 6]. Our material contained three types of arterial grafts with both single and sequential types, as was the case with the venous grafts, which is why our primary objective was not to compare patency rates between various surgical subtypes of grafts, but rather to find angiographic predictors of graft patency and native artery disease progression for the two basically different types of grafts: in situ arterial and saphenous vein grafts. Although the arterial graft group of the present study was surgically heterogeneous, the group was a reasonably homogeneous entity angiographically: all were in situ conduits of similar caliber, and the patency rates of the arterial grafts were similar. On the other hand, the arterial and venous graft groups were angiographically comparable: both groups contained a significant number of sequential grafts, and the lumen diameters of the native arteries distal to the anastomoses were practically equal, as were the mean diameters of the stenoses of the bypassed lesions. Our patients were not prospectively randomized to receive arterial versus venous grafts and the decision to place the type of graft might have included some patient characteristics that were possibly not matched by demographic and clinical data. This could not cause significant bias in the present study concentrating on angiographic predictors of graft patency because most patients (72/91) received both types of grafts. Various vascular areas were unequally represented as recipients of the arterial and venous anastomoses. When performing comparisons between the arterial and venous grafts, care was taken to analyze only factors that were basically independent of the anatomic location of the anastomosis. The occlusion rate of 13% after a mean follow-up of 2 years for the venous graft anastomoses in the present study is comparable with the 13% to 15.8% rate at 1 year reported by others [5, 7]. Similarly, the occlusion rate of 8% of the arterial graft anastomoses in the present study is similar to the 5% to 7.8% occlusion rates at 12 to 24 months for ITA grafts reported by others [8 10], as well as the 5% to 23% occlusion rates reported for right gastroepiploic artery grafts [11]. Quantitative stenosis measurement was not used in the present study. We selected visual estimation of percent diameter stenosis as this method is generally used in clinical work as well as in angiographic follow-up studies of coronary artery disease [12]. The standard deviation of the mean variability of the visually determined percent diameter stenoses of the two readers was 20.9%, which is comparable with the 14.6% to 18% variability reported in other studies [13, 14]. Although the variability in visual stenosis evaluation is considerably greater than the 9.4% SD of the mean variability reported for quantitative stenosis determination [15], the use of two independent readers increases the confidence of stenosis evaluation [14]. Functional graft patency was evaluated in this work in two ways. First, we classified anastomotic patency. Basically, venous graft anastomoses were fully open or occluded, whereas in arterial graft anastomoses compromised flow was seen in a considerable number of grafts, especially when the bypassed stenosis was less than or equal to 75% (see Fig 1). Second, we recorded the presence of the slender sign. This phenomenon was found in a considerable number of arterial graft anastomoses (15.5%) but in only 1.0% of saphenous vein graft anastomoses. We registered the slender sign more frequently than Nakao and Kawaue [3] in right gastroepiploic artery grafts (7.8%). The slender sign was associated significantly with less severe bypassed stenoses and was more common when the ratio of the diameter of the native artery to that of the distal graft was increased. The clinical impact of this phenomenon is unclear, but it might arise when sufficient native blood flow is present in the coronary artery trunk and, consequently, the competitive graft flow is unnecessary. The slender sign is useful as it can reveal the probable reason for the graft dysfunction: the bypassed stenosis is too mild. We registered one or more side branches of considerable size in 9% of ITA grafts, and half of these cases were associated with angiographically compromised graft flow. The clinical significance of the steal effect of the hypertrophied side branches is poorly understood, but

5 Ann Thorac Surg MANNINEN ET AL 1998;66: ANGIOGRAPHIC PREDICTORS OF GRAFT PATENCY 1293 Singh and Sosa [16] and Singh and Magovern [17] reported 5 symptomatic patients with unusually enlarged side branches and a case in which the lumen of the distal part of the ITA showed 50% enlargement when a prominent side branch was surgically occluded. The occlusion rate of the saphenous vein graft anastomoses correlated significantly with the percent diameter stenosis of the bypassed lesion. Twenty-two percent of venous graft anastomoses to arteries with a stenosis of less than or equal to 75% at baseline angiogram were occluded, in comparison with a 7.7% occlusion rate for narrower lesions (see Fig 1). Also, Kroncke and associates [2] reported that 5 years after operation there was a tendency, although not statistically significant, for higher closure rates in saphenous vein grafts anastomosed to arteries with minimal disease than to arteries with severe disease at baseline. In the present study, the occlusion rate of arterial grafts showed no correlation with the stenosis severity. There are reports of the ability of ITA grafts to stay open even in no-flow situations and to hypertrophy in association with progression of the native artery disease [18, 19]. Better patency of in situ arterial grafts in mild stenoses may exist because in situ grafts function as a live conduit, with functioning smooth muscle that can adapt to the demands of flow [16, 17]. It should be pointed out, however, that frequency of the slender sign correlated with decreased stenosis severity. If these dysfunctional grafts are added to the occluded grafts, a moderate lesion in the native circulation appears to have about the same likelihood of being associated with a bad graft with either an arterial or a venous graft. Similarly, in the whole material, our finding about the better patency rate of the arterial grafts compared with venous grafts would disappear if grafts with compromised flow were classified as occluded. The result of the present study that disease progression of the native coronary arteries is more common in lesions that have been bypassed than in nonbypassed lesions (39.7% versus 20.2%) is not new, and this was verified for saphenous vein grafts as early as the 1970s [20]. Data concerning the association of disease progression in the bypassed artery with patency of the graft are conflicting. Some authors reported results similar to ours for venous grafts, namely that progression is not associated with patency of the graft [20]. On the other hand, Kroncke and coworkers [2] reported a tendency for greater progression in arteries with patent venous grafts 5 years after operation, whereas Hwang and colleagues [21] found significantly more progression in arterial segments with occluded grafts compared with segments with patent grafts. An interesting result in our study was that progression of stenotic changes was more common in segments immediately proximal to the graft anastomoses than in more proximal segments of the same artery (see Table 1). This result is logical and gives support for the hypothesis of competing flows between the native and bypass conduits as an accelerating factor for vasoocclusive disease. The proportion of progression up to total occlusion was also greater in lesions of bypassed segments, a result obtained also by others [2]. We found that disease progression was more common in segments bypassed with saphenous vein than with arterial grafts (46.0% versus 32.8%). This is in accordance with the result of Cosgrove and associates [22], who found that in the first 2 years after a bypass operation, the proximal coronary arterial lesion progressed in 39% of patients with patent ITA grafts, as compared with 67% of those whose coronary arteries had been grafted with saphenous veins. It has been suggested that arterial grafts may permit more antegrade flow through the proximal stenosis than do the larger diameter saphenous vein grafts [23]. This is supported by our finding that the slender sign was seen almost exclusively in arterial grafts. Consequently, the effect of competitive graft flow to increase vasoocclusive changes in the native artery might be less with arterial grafts. The present study does not provide information about the functional patency of the grafts long term (after approximately 2 years). However, it is firmly established by several studies that between 1 and 5 years postoperatively, the rate of attrition of both ITA and saphenous vein grafts is low [24]. We are grateful to Mrs Pirjo Halonen, MSc, for statistical consultation. References 1. Cameron A, Davis KB, Green G, Schaff HV. Coronary bypass surgery with internal-thoracic-artery grafts effects on survival over 15-year period. N Engl J Med 1996;334: Kroncke GM, Kosolcharon P, Clayman JA, Peduzzi PN, Detre K, Takaro T. Five-year changes in coronary arteries of medical and surgical patients of the Veterans Administration randomized study of bypass surgery. Circulation 1988; 78(Suppl 1): Nakao T, Kawaue Y. Effect of coronary revascularization with the right gastroepiploic artery. Comparative examination of angiographic findings in the early postoperative period. J Thorac Cardiovasc Surg 1993;106: Van der Meer J, Hillege HL, van Gilst WH, et al. A comparison of internal mammary artery and saphenous vein grafts after coronary artery bypass surgery. No differences in 1-year occlusion rates and clinical outcome. Circulation 1994; 90: Fitzgibbon GM, Leach AJ, Kafka HP, Keon WJ. Coronary bypass graft fate: long-term angiographic study. J Am Coll Cardiol 1991;17: Chow MST, Sim E, Orszulak TA, Schaff HV. Patency of internal thoracic artery grafts: comparison of right versus left and importance of vessel grafted. Circulation 1994;90(Suppl 2): Goldman S, Copeland J, Moritz T, et al. Saphenous vein graft patency 1 year after coronary artery bypass surgery and effects of antiplatelet therapy. Results of a Veterans Administration cooperative study. Circulation 1989;80: Huddleston CB, Stoney WS, Alford WC Jr, et al. Internal mammary artery grafts: technical factors influencing patency. Ann Thorac Surg 1986;42: Dion R, Verhelst R, Rousseau M, Goenen M, et al. Sequential mammary grafting. Clinical, functional, and angiographic assessment 6 months postoperatively in 231 consecutive patients. J Thorac Cardiovasc Surg 1989;98: Van Stergenburg SMM, Ernst SMPG, de la Riviére AB, et al. Triple sequential grafts using the internal mammary artery. An angiographic and short term follow-up study. J Thorac Cardiovasc Surg 1992;104:60 5.

6 1294 MANNINEN ET AL Ann Thorac Surg ANGIOGRAPHIC PREDICTORS OF GRAFT PATENCY 1998;66: Grandjean JG, Boonstra PW, den Heyer P, Ebels T. Arterial revascularization with the right gastroepiploic artery and internal mammary arteries in 300 patients. J Thorac Cardiovasc Surg 1994;107: Alderman EL, Corley SD, Fisher LD, et al. Five-year angiographic follow-up of factors associated with progression of coronary artery disease in the Coronary Artery Surgery Study (CASS). J Am Coll Cardiol 1993;22: DeRouen TA, Murray JA, Owen W. Variability in the analysis of coronary angiograms. Circulation 1977;55: Beauman GJ, Vogel RA. Accuracy of individual and panel visual interpretations of coronary arteriograms: implications for clinical decisions. J Am Coll Cardiol 1990;16: Folland ED, Vogel RA, Hartigan P, et al. Relation between coronary artery stenosis assessed by visual, caliber, and computer methods and exercise capacity in patients with single vessel coronary artery disease. Circulation 1994;89: Singh RM, Sosa JA. Internal mammary artery coronary artery anastomosis. Influence of the side branches on surgical results. J Thorac Cardiovasc Surg 1981;82: Singh RM, Magovern GJ. Internal mammary graft: improved flow resulting from correction of steal phenomenon. J Thorac Cardiovasc Surg 1982;84: Dincer B, Barner HB. The occluded internal mammary artery graft. Restoration of patency after apparent occlusion associated with progression of coronary disease. J Thorac Cardiovasc Surg 1983;85: Aris A, Borras X, Ramio J. Patency of internal mammary artery grafts in no-flow situations. J Thorac Cardiovasc Surg 1987;93: Frick MH, Valle M, Harjola P-T, Korhola O. Changes in native coronary arteries after coronary bypass surgery. Role of graft patency, serum lipids and hypertension. Am J Cardiol 1975;36: Hwang MG, Meadows WR, Palac RT, et al. Progression of native coronary artery disease at 10 years: insights from a randomized study of medical versus surgical therapy for angina. J Am Coll Cardiol 1990;16: Cosgrove DM, Loop FD, Saunders CL, Lytle BW, Kramer JR. Should coronary arteries with less than fifty percent stenosis be bypassed? J Thorac Cardiovasc Surg 1981;82: Loop FD. Internal-thoracic-artery grafts. Biologically better coronary arteries. N Engl J Med 1996;334: Lawrie GM, Morris GC Jr, Chapman DW, Winters WL, Lie JT. Patterns of 596 vein grafts up to seven years after aorto-coronary bypass. J Thorac Cardiovasc Surg 1977;73: Notice From the Southern Thoracic Surgical Association The Forty-fifth Annual Meeting of the Southern Thoracic Surgical Association will be held at the Disney s Yacht & Beach Club Resort in Orlando, Florida, November 12 14, The Postgraduate Course will be held the morning of Thursday, November 12, 1998, and will provide in-depth coverage of thoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. D. Glenn Pennington, MD Secretary/Treasurer Southern Thoracic Surgical Association 401 North Michigan Avenue Chicago, IL (800) 685-STSA or (312) fax: (312) stsa@sba.com by The Society of Thoracic Surgeons Ann Thorac Surg 1998;66: /98/$19.00 Published by Elsevier Science Inc