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Determining Whether Acute Myocardial Infarction inPatients With Previous Coronary Bypass Grafting Is the

Result of Narrowing of a Bypass Conduit or ofa Native Coronary Artery

Raul Moreno, MD, Esteban Lopez de Sa, MD, Jose Lopez-Sendon, MD, Rafael Rubio, MD,Jaime F. Bobadilla, MD, Eulogio J. MD, and Juan L. Delcan, MDGarc Bıa,

TABLE I Characteristics of Patients According to the IRCA

IRCA

Graft Native p Value

Number of patients 32 (48%) 35 (52%)Age (yr) 63.9 { 8.1 64.1 { 9.0 NSMale gender (%) 84 89 NSPrevious AMI (%) 66 71 NSMonths between CABG and AMI 79 { 47 76 { 49 NSNumber of narrowed coronary arteries 2.5 { 0.6 1.9 { 0.8 0.002Number of grafts/patient 2.4 { 0.7 1.6 { 0.7 0.001Reperfusion (TRL or direct PTCA) (%) 28 40 NSST elevation on admission (%) 28 83 õ0.001New Q wave (%) 25 77 õ0.001Peak CK value (UI) 649 { 308 1,297 { 813 0.001Peak CK-MB value (UI) 88 { 51 178 { 102 õ0.001Killip class other than I (%) 19 6 0.09In-hospital mortality (%) 18.8 2.9 0.03

CKÅ creatine kinase; IRCAÅ infarct-related coronary artery; PTCAÅ primary percutaneous transluminalcoronary angioplasty; TRL Å thrombolysis.

In patients with acute myocardialinfarction (AMI) and previous

coronary artery bypass grafting(CABG), the infarct-related coro-nary artery (IRCA) may be a graftor a native coronary artery (a non-grafted artery or a native artery dis-tally to the bypass). The clinical orelectrocardiographic characteristicsrelated to the type of IRCA (graft ornative artery) as well as the prog-nosis in relation with the IRCAwere investigated.

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From January 1987 to May1996, 86 patients with previousCABG (ú1 month from interven-tion) were admitted in the coronarycare unit because of 101 episodes ofAMI. The diagnosis of AMI wasmade in presence of at least 2 of the 3 common cri-teria (clinical, electrocardiographic, and laboratorydata). Catheterization was performed in 76 patients,who constitute the object of our study. Angiogramswere evaluated to determine if the IRCA was a nativecoronary artery (nongrafted native artery or a graftedone distally to the anastomosis) or a graft accordingto electrocardiographic changes related to AMI. Thefollowing variables were retrospectively studied:age, gender, previous coronary disease, time fromCABG, main arteries grafted, electrocardiogram atadmission (ST elevation, ST depression, or othercharacteristics), development of new Q waves, Killipclass, creatine kinase and creatine kinase-MB peakvalues, and in-hospital survival.

The mean age was 64 { 8 years and 67 patients(88%) were men. Fifty-five patients (72%) had pre-vious myocardial infarction. The average time fromCABG was 77 { 49 months (range 1 to 168). Thenumber of grafts per patient was 2.5 { 1.0 (range 1to 5). There was only 1 main artery grafted in 21cases (27%), 2 in 30 (39%), and 3 in 25 (35%). Theright coronary artery was grafted in 43 patients withsaphenous vein graft, the left anterior descending in

From the Cardiology Department, Hospital Universitario GregorioMaranon, Madrid, Spain. Manuscript received July 8, 1996; revisedmanuscript received and accepted September 17, 1996. Addressfor reprints: Esteban Lopez de Sa, MD, Coronary Care Unit, Cardi-ology Department, Hospital Universitario ‘‘Gregorio Maranon,’’Calle Doctor Esquerdo 46, 28007 Madrid Spain.

69 patients, 40 of them with saphena (59%), and thecircumflex artery in 43 patients, 40 of them with veingraft (93%).

The electrocardiogram at admission showed STelevation as the main alteration in 40 cases (53%),ST depression in 24 (32%), and other manifestations(left bundle branch block, pacemaker, negative Twaves, or normal electrocardiogram) in 12 (16%).The AMI was anterior in 12 cases (16%), inferior in24 (32%), posterior in 1 (1%), non–Q wave in 37(49%), and undetermined in 2 (3%). The mean peakcreatine kinase value was 968 { 706 IU/L and cre-atine kinase-MB 133{ 92 IU/L. Nine patients (12%)died before discharge. Twelve patients (16%) re-ceived thrombolytic therapy and primary angioplastywas performed in 12 (16%).

The IRCA was a graft in 32 (42%), a native arteryin 35 (46%), and it could not be determined in 9(12%) patients. Table I lists the characteristics of pa-tients with graft or native IRCA. Patients in whom agraft was the IRCA, versus those in whom it was anative vessel, had a lower frequency of ST elevationat admission (28% vs 83%, p õ0.001), a lower fre-quency of development of new Q waves (25% vs77%, p õ0.001), a lower peak creatine kinase (649{ 308 vs 1,297 { 813 IU, p õ0.001), and creatinekinase-MB value (88 { 51 vs 178 { 102 IU, põ0.001), a higher number of principal vessels dis-eased (2.5 { 0.6 vs 1.9 { 0.8, p Å 0.002), a highernumber of principal vessels grafted (2.4 { 0.7 vs 1.6{ 0.7, p õ0.001), and a higher in-hospital mortality

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(18.8% vs 2.9%, p Å 0.030). In the presence of STelevation, the IRCA was unknown in 2 (5%), a graftin 9 (23%), and a native artery in 28 (72%); con-versely, in the absence of ST elevation, it was 7(19%), 23 (62%), and 7 (19%), respectively (põ0.001).

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It has been demonstrated that AMI in patientswith previous CABG is different from that in pa-tients without previous surgical revascularization,perhaps because of a different pathogenesis, withlower creatine kinase values and a lower frequencyof development of new Q waves, although AMI isnot associated with a better prognosis.1–3 To ourknowledge, there have been no investigations onwhether the manifestations of AMI in patients withprevious CABG depend on the type of IRCA. In thepresent series, in patients with known IRCA, the pro-portion of native artery or graft occlusion was sim-ilar. This divergence with previous reports, in whicha graft was most frequently the IRCA, could prob-ably be due to a higher proportion of patients withan internal mammary graft in the present series.4–6

The results of this study suggest that AMI maybe different when the IRCA is a graft or a nativevessel: the infarct size is smaller (lower creatine ki-nase and creatine kinase-MB values) and ST eleva-tion on admission and the development of new Qwaves occur less often. These findings, not previ-ously reported, could be explained by a differentpathogenesis of AMI according to the type of IRCA.When the IRCA is a native vessel, the mechanismof occlusion should be a plaque rupture with acuteand complete thrombotic occlusion of a vessel as inpatients without previous CABG. The graft occlu-sion probably occurs less abruptly because of pro-gressive intimal hyperplasia and thrombus formationdue to blood stasis,7,8 causing a prolonged suben-docardial rather than transmural ischemia.

In this series, the AMI patients with graft occlu-sion, despite having smaller infarcts, presented withhigher in-hospital mortality than patients with a na-tive vessel occlusion. This finding could be relatedto: (1) a greater extent of the disease in patients with

graft occlusion because they have more arteriesgrafted; (2) a higher proportion of these patients be-ing treated conservatively (less utilization of reper-fusion strategies) because of absence of ST elevation;and (3) a trend toward worse Killip classification inpatients with graft occlusion.

Otherwise, electrocardiographic changes help toidentify the type of IRCA; in patients with ST ele-vation on admission, a native vessel is more fre-quently the IRCA. These differences may contributeto the management of AMI in patients with previousCABG, not only in the acute phase, but also in therisk stratification.

In conclusion, in patients with AMI and previ-ous CABG, when the IRCA is a coronary graft, theelectrocardiogram shows ST elevation on admis-sion and development of new Qwaves less oftenthan when the IRCA is a native coronary artery,and this is probably related to a different pathologyof AMI. When the IRCA is a graft, the infarctionis smaller but presents a worse in-hospital prog-nosis.

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