Clinical and Investigative Medicine

 

Management of unstable coronary syndromes in patients with previous coronary artery bypass grafts following coronary angiography

Albert W. Chan, MD
John Ross, MD

Clin Invest Med 1997;20(5):320-326

[résumé]

Dr. Chan was with the Department of Medicine, The Toronto Hospital, Toronto, Ont., and is now with St. Paul's Hospital, Vancouver, BC; and Dr. Ross is with the Division of Cardiology, Department of Medicine, The Toronto Hospital, Toronto, Ont.

Original manuscript submitted November 25, 1996; received in revised form July 15, 1997; accepted July 16, 1997)

Reprint requests to: Dr. Albert W. Chan, St. Paul's Hospital, 1081 Burrard St., Rm. 170, Vancouver BC V6Z 1Y6; fax 604 231-7603; awwchan@interchange.ubc.ca

Contents
[ Top of document ]

Abstract

 Objective:To characterize patients who had undergone previous coronary artery bypass grafting (CABG) and who were admitted for coronary angiography for unstable coronary syndromes, to determine the long-term therapy selected for these patients and to assess the outcomes of the intervention.

Design: Descriptive retrospective study.

Setting: A university-affiliated tertiary care institution.

Patients: A total of 129 patients with 1 previous CABG who underwent coronary angiography for myocardial infarction or unstable angina in 1991.

Outcome measures: Information regarding initial CABG, indications for cardiac angiography, cardiovascular risk factors, ultimate treatment selected and outcomes at 1 year were abstracted from patients' charts, and outcomes at 1 year were also determined by a patient survey.

Results: Seventy-six patients (59%) were given drug therapy, 28 patients (22%) were treated with angioplasty, and 25 (19%) underwent repeat surgery. During their index admissions, of patients given drug therapy, 4 (5.3%) died from myocardial infarction (MI) and 42 (55%) were discharged without complications; of those undergoing angioplasty, all except 2 were treated successfully (major procedural complications included nonfatal MI in 1 patient [4%] and nonfatal ventricular arrhythmia in 1 patient [4%], as well, reocclusion of the lesions occurred before discharge in 2 patients [7%]); of those undergoing repeat surgery, almost all patients (96%) were discharged, except 1 who died from MI during the postoperative period (there were no procedural complications, but early complications included nonfatal MI in 2 patients [8%], angina in 2 [8%] and nonfatal arrhythmias in 11 [44%]). Eighty-seven patients (67%) were available for follow-up at 1 year. Of the patients given drug therapy, 3 (6.4%) had died, 14 (30%) had recurrent anginal episodes and 5 (11%) required either angioplasty or CABG. Of the patients who initially received angioplasty, 15 (63%) had recurrent angina but none died, 12 (50%) underwent repeat angioplasty and 2 (8.3%) required repeat CABG. No patients who received repeat surgery died or required further surgery or angioplasty. Three of these patients (19%) had recurrent angina within the first year. Patients in this category also enjoyed a greater degree of symptomatic improvement of coronary artery disease.

Conclusions: Patients who had a previous CABG and subsequently presented with MI were more likely to be given conservative drug therapy than those who presented with unstable angina. At 1-year follow-up, recurrent angina occurred more often in the patients treated by angioplasty, less often in patients given drug therapy and least in those who underwent repeat bypass grafting. Restenosis remained a problem, and about 50% of patients treated with angioplasty (without intracoronary stenting) required a second angioplasty within the first year. Patients who were candidates for repeat CABG enjoyed greater symptomatic improvement within the first year.

[ Top of document ]

Résumé

Objectif : Caractériser les patients qui avaient déjà subi un pontage aortocoronarien (PAC) et qui ont été admis pour subir une angiographie coronarienne à cause de syndromes coronariens instables, déterminer le traitement à long terme choisi pour ces patients et évaluer les résultats de l'intervention.

Conception : Étude rétrospective descriptive.

Contexte : Établissement de soins tertiaires affilié à une université.

Patients : Au total, 129 patients qui avaient déjà subi un PAC et ont subi une angiographie coronarienne à cause d'un infarctus du myocarde ou d'un angor instable en 1991.

Mesures des résultats : On a résumé, à partir des dossiers des patients, les renseignements sur le PAC initial, les indications relatives à l'angiographie cardiaque, les facteurs de risque cardiovasculaire, le traitement final choisi et les résultats à 1 an, et déterminé aussi les résultats à 1 an par sondage auprès des patients.

Résultats : Soixante-seize patients (59 %) ont été traités par des médicaments, 28 (22 %), par angioplastie, et 25 (19 %) ont subi une autre intervention chirurgicale. Au cours de leur admission repère, parmi les patients qui ont été traités avec des médicaments, 4 (5,3 %) sont morts d'un infarctus du myocade (IM) et 42 (55 %) ont été libérés sans complications. Parmi ceux qui ont subi une angioplastie, tous sauf 2 ont été traités avec succès (les principales complications liées à l'intervention ont inclus un IM non mortel chez un patient [4 %] et une arythmie ventriculaire non mortelle chez un autre [4 %]; les lésions se sont refermées avant la libération chez 2 patients [7 %]); parmi ceux qui ont subi une nouvelle intervention chirurgicale, presque tous les patients (96 %) ont été libérés, sauf 1 qui est mort d'un IM après l'intervention (il n'y aucune complication liée à l'intervention, mais les complications précoces ont inclus un IM non mortel chez 2 patients [8 %], de l'angor chez 2 autres [8 %] et des arythmies non mortelles chez 11 [44 %]). Quatre-vingt-six patients (67 %) étaient disponibles pour le suivi à 1 an. Parmi les patients traités avec des médicaments, 3 (6,4 %) étaient morts, 14 (30 %) avaient eu des épisodes d'angor récurrent et 5 (11 %) avaient eu besoin d'une angioplastie ou d'un PAC. Parmi le patients qui ont subi une première angioplastie, 15 (63 %) souffraient d'angor récurrent, mais aucun n'était mort, 12 (50 %) ont subi une nouvelle angioplastie et 2 (8,3 %) ont eu besoin d'un autre PAC. Aucun des patients qui ont subi une autre intervention chirurgicale n'est mort ou n'a eu besoin d'une autre intervention chirurgicale ou d'une angioplastie. Trois de ces patients (19 %) ont souffert d'angor récurrent au cours de la première année. Les patients de cette catégorie ont aussi vu leurs symptômes coronariens s'améliorer davantage.

Conclusion : Les patients qui avaient déjà subi un PAC et se sont présentés par la suite souffrant d'un IM étaient plus susceptibles d'être traités de façon conservatrice par des médicaments que ceux qui se présentaient avec un angor instable. Au suivi à 1 an, l'angor récurrent était plus fréquent chez les patients traités par angioplastie, moins fréquent chez ceux qui avaient été traités par des médicaments et moins fréquent chez ceux qui ont subi un autre pontage aortocoronairien. La resténose est demeurée un problème et environ 50 % des patients traités par angioplastie (sans port de stents intracoronariens) ont dû subir une autre angioplastie au cours de la première année. Les patients candidats à un autre PAC sont ceux qui ont vu leurs symptômes s'améliorer le plus au cours de la première année.

[ Top of document ]

Introduction

 Since the advent of aortocoronary bypass grafting a quarter of a century ago, physicians have dealt with increasing numbers of patients with previous coronary artery bypass grafting (CABG) seeking medical attention for unstable angina or myocardial infarction (MI). These patients are a heterogeneous group, in which coronary artery disease may involve both native vessels and grafts and in which myocardial damage may be more severe than in those without a previous CABG. Consequently, the natural history and treatment of such patients may differ from those of patients who have not had a previous CABG. Patients with an acute transmural MI generally receive thrombolytic therapy at presentation. However, treatment decisions for patients who are not candidates for thrombolysis are often delayed until better visualization of the coronary anatomy is obtained through angiography. Treatment of symptomatic post-CABG patients with drug therapy alone, percutaneous transluminal coronary angioplasty (PTCA) or repeat CABG has not been studied in a randomized clinical trial. Although we suspected that most post-CABG patients were being treated with drug therapy alone, the exact proportion receiving each of these treatments was unknown.

We describe our experience with this group of patients at our institution. The objectives of this study were (1) to better characterize the post-CABG patients who received coronary angiography for symptomatic coronary artery disease; (2) to determine which long-term therapy was selected for these patients; and (3) to document the outcomes of each of the 3 treatments.

[ Top of document ]

Methods

Patient selection

All patients with previous CABG who underwent diagnostic coronary angiography at The Toronto Hospital­General Division between Jan. 1, 1991, and Dec. 31, 1991, were identified. The Toronto Hospital is an university-affiliated tertiary care institution in Toronto, Ont.

Patients were eligible for study if they had had either an acute MI or unstable angina at the index admission for coronary angiography. Patients who had more than 1 previous CABG or had had PTCA after their first CABG were excluded.

The diagnosis of acute MI required evidence of myocardial damage on electrocardiograms (ECGs) (new Q waves, or new, persistent ST-segment depression or T-wave inversion) that was associated either with chest pain typical of myocardial ischemia or with elevations of serum levels of total creatine kinase (greater than 220 IU/L for men or 170 IU/L for women) and creatine kinase isoenzymes (greater than 15 IU/L). Patients with unstable angina exhibited at least 1 of the following: new-onset angina, rapidly progressing angina, angina at rest, angina refractory to medications, variant angina, acute coronary insufficiency with ECG changes but no significant enzyme changes, or post-MI angina.

Classification of the patients

After information was obtained from angiography, these patients were treated by 1 of the 3 aforementioned methods. They were classified into 3 groups according to the treatment selected at the index admission.

Group A consisted of patients for whom drug therapy alone was considered the best treatment before discharge. For these patients, PTCA or repeat CABG was rejected either because they were considered high-risk in light of the anatomy of the lesions, or because the benefit obtained would not outweigh the risk involved.

Group B consisted of patients judged to be most suitable for PTCA, based on the anatomy and the accessibility of the guide-wire to the lesion(s). These patients all consented to urgent CABG in case of emergency complications during the procedure. Angiograms were taken immediately after the procedures, and the residual stenoses were documented. A procedure was considered successful if the residual stenosis was less than 50% and the degree of stenosis was reduced by 40%. These patients may have also received other adjuvant therapies (atherectomy and stenting) during the procedure.

Group C consisted of patients who underwent urgent repeat CABG during the index admission.

To further characterize the lesions in the vessels, the native vessels and the vein grafts were divided into 2 and 3 anatomical sites, respectively. The native vessels were divided into proximal and distal: the section proximal to the posterolateral branch of right coronary artery (RCA) was the proximal RCA, the section proximal to the first diagonal branch of left anterior descending artery (LAD) was the proximal LAD, and the portion proximal to first obtuse marginal branch of circumflex artery (Cx) was the proximal Cx. All the vein grafts were divided into proximal, body and distal anastomoses, according to the sites where the grafts were attached to the native vessels.

Patients were followed for 1 year. Information was obtained by reviewing hospital and clinic charts and by sending out a questionnaire to each patient at the end of the 1-year period. Information regarding symptoms, additional investigations and outcomes was requested in the questionnaire. The end points at 1 year included death, readmission for symptomatic coronary artery disease, repeat CABG or PTCA, and improvement of symptoms of angina greater than 2 classes in the Canadian Cardiovascular Society (CCS) Classification system.

[ Top of document ]

Results

A total of 221 patients who had had previous CABG and received cardiac angiography in 1991 were screened. Twenty-two patients had had more than 1 CABG and another 23 patients had had at least 1 angioplasty after their first CABG but before 1991. Of the remaining 176 patients, 2 (1.1%) presented with arrhythmia, 4 presented with congestive heart failure and no evidence of myocardial injury, 25 (14%) had chronic stable angina and 16 underwent angiography for other cardiac or noncardiac problems. All of these patients were excluded from the study. Thus, 129 patients were included.

Of these 129 patients, 27 (21%) presented with acute MI, and 102 (79%) were diagnosed with unstable angina at the index admission. The clinical characteristics and the results of coronary angiography are shown in Table 1. It should be noted that 15% of all internal mammary grafts had greater than 69% stenosis, whereas 30% to 50% of saphenous vein grafts in each patient had a similar degree of disease.

Patients were subsequently treated with drugs alone, PTCA or repeat CABG, according to the clinical decision of the attending physicians (Table 2). Seventy-six patients (59%) received drug therapy alone, 28 (22%) underwent PTCA, and 25 (19%) underwent repeat CABG. Patients presenting with acute MI were more likely to be treated with drug therapy alone, possibly because of irreversible myocardial damage.

Outcomes

Group A: drug therapy

During their index admissions, 4 patients (5.3%) died from MI, 1 patient (1.3%) suffered a nonfatal MI, 21 patients (28%) had recurrent angina and 8 patients (11%) had nonfatal ventricular arrhythmias. A comparison of the drugs these patients were taking at admission and at discharge is shown in Table 3. Forty-two patients (57%) were discharged without having had any complications. Forty-seven (65%) of these patients were available at the end of 1 year, and the outcomes for them are shown in Table 4.

Group B: PTCA

PTCA was initially performed in 28 patients (22% of the 129 patients). Angioplasty of 27 lesions in 25 native vessels and 14 lesions in 13 saphenous vein grafts was attempted. Twenty-two patients (79%) had only 1 dilatation attempt, 4 patients (14%) had 2 attempts and 2 patients (7%) had 3 attempts. The mean stenosis of lesions was reduced from 80% to 24%. One attempt failed because the lesion was located just distal to the bifurcation of the circumflex artery from the left main coronary artery, which formed a sharp turn and was too difficult for the guiding wire to pass through. In the other attempt, reocclusion occurred at the dilated site shortly after PTCA. All attempts performed on saphenous vein grafts achieved initial success. Adjuvant therapy was employed in some patients: 3 patients had coronary atherectomy, 2 patients had coronary stenting and 1 patient required intra-aortic balloon pump. None received thrombolytic therapy.

Adverse outcomes in patients who received PTCA are shown in Table 4. All early complications were managed conservatively with drug therapy, and all patients were discharged from the hospital. The 1-year follow-up results are shown in the same table.

Group C: repeat CABG

On the basis of clinical factors including age, previous myocardial damage, age of the grafts, left ventricular function and angiographic findings, 25 patients (19%) were selected for repeat CABG. Twelve (48%) of these procedures were done on emergency basis, and the rest were performed semi-urgently. A total of 53 saphenous vein grafts (3 to LAD, 12 to diagonal branches of LAD, 18 to obtuse marginal branches of Cx, and 20 to RCA) and 18 internal mammary arterial grafts (to LAD) were implanted. Each patient received a mean 2.8 (standard deviation 1.0) grafts. Complications during admission are shown in Table 4. During the 1-year follow-up period (Table 4), 3 patients (19%) were readmitted within a mean 7.1 (standard deviation 3.6) months for recurrent angina. All 3 patients were discharged without requiring any invasive therapy, and there were no deaths.

[ Top of document ]

Discussion

Patients who have had a previous CABG and experience recurrent symptomatic coronary artery disease are distinct from patients who have not had previous bypass surgery. Decision-making regarding management of these patients is more complex, and the conventional guidelines1 may not be suitable. Symptoms may originate from progressively diseased native vessels, from vein grafts undergoing stenosis, or both. Management depends not only on the anatomy of the lesions, but also on the age of the grafts, size of the viable myocardium in jeopardy, left ventricular function, age of the patient, and many other clinical variables.2

Since the current medical literature provides little information about the management of this subset of patients, we report the clinical characteristics and the outcomes in 1 such group who were treated with drug therapy, PTCA or CABG, at the discretion of their attending physicians. More than half of these patients were treated conservatively at their initial presentations, whereas one-fifth received coronary angioplasty, and slightly fewer than one-fifth were selected for repeat CABG at the index admission. Patients who underwent conservative therapy had higher rates of disease and death during the admission and in the following year. Patients who had an MI without evidence of ongoing ischemia were more often managed conservatively. In contrast, for patients presenting with unstable angina or with a large area of viable myocardium at risk for further damage, PTCA or repeat CABG were more often selected. While almost equal proportions of patients in the PTCA group and drug-treatment group gained significant symptomatic relief (defined as more than 2 classes of symptomatic improvement in CCS classification), CABG was superior to these 2 methods in terms of symptomatic improvement, need for repeat invasive therapeutic methods, and death within 1 year in carefully selected candidates. Most of the patients in the PTCA group who experienced recurrent symptoms within 1 year were likely suffering from restenosis of the same lesion or lesions.

The mechanism of graft closure and the histopathology of graft lesions have been described in previous reports.3­6 Internal mammary grafting provides long-term patency superior to that achieved with vein grafting,7­9 and maximal use of internal mammary grafts to bypass lesions in the left anterior descending artery decreases the need for subsequent repeat CABG.2,7 Our study shows that, compared with saphenous vein grafts, a smaller proportion of internal mammary grafts were found to have stenosis in excess of 70%. Several hypotheses have been proposed to explain the superior patency of internal mammary grafting from a pathophysiologic standpoint.10­12 Coronary stenting was not used during our study period; however, stent implantation has been proven by randomized trials to achieve better clinical and angiographic outcomes than standard coronary angioplasty of native vessels13,14 and saphenous vein conduits.15 On the other hand, data comparing direct atherectomy with balloon angioplasty16 showed no long-term benefits of atherectomy over angioplasty in vein grafts, although 1 study17 suggested that atherectomy is an effective adjunct after unsuccessful PTCA of vein grafts.

The decision to use PTCA or repeat CABG in patients with previous CABG who later present with recurrent coronary syndromes depends on many clinical considerations.2 The important factors include the age of the grafts,18 left ventricular function, size of myocardium at risk,19 the general physical condition of the patient, and the location and extent of the lesions. Contrary to conclusions of a recent randomized trial comparing the efficacy of PTCA with CABG in treating coronary artery disease,20 the experience from our institution showed that the decision to use CABG versus PTCA was usually dictated by clinical factors, since the clinical characteristics differed between the 2 groups.

Angioplasty is an effective and a convenient way of managing discrete lesions and relieving patients' symptoms. It causes less short-term morbidity and results in fewer hospital days of stay than repeat CABG. At our institution, the success rate of PTCA was greater than 90%, and there was no significant difference in success rate when a native artery or a vein graft was dilated. This result was comparable to those reported in the medical literature.21­23 However, restenosis of the lesions represents a frequent problem, and, because of this, more than 50% of the patients in this study group experienced recurrent angina and required repeat PTCA or CABG within months. Superior symptomatic results could have been obtained in these patients if CABG had been performed at their initial presentation. During this time of fiscal restraint, further economic analysis may be needed before providing a guideline for selecting treatment methods when clinical considerations do not lean toward PTCA or CABG in these patients.

One deficiency of this study was the significant number of patients lost to follow-up. None of these patients had died, according to the hospital registry. Missing data were mainly due to lack of response to the questionnaire.

[ Top of document ]

Conclusion

Patients with a previous CABG and recurrent anginal symptoms are a distinct group from those without previous bypass surgery. Management decisions are much more complex and should be individualized before a consensus guideline is developed. In our patients, those with an MI were more likely to be given drug therapy than those presenting with unstable angina, who were frequently treated more aggressively. Repeat CABG was a safe procedure in selected patients. Patients who were candidates for repeat CABG generally enjoyed greater symptomatic improvement within the first year. PCTA is a suggested alternative to CABG in these patients, since it is associated with a lower incidence of morbidity, controllable rather than serious complications, shorter hospital stay and shorter recovery period. However, restenosis remained a problem. More than half of the PTCA-treated patients (without intracoronary stenting) had recurrent symptoms and required further invasive therapy (PTCA or CABG) within the first year. This may contradict the belief held by many clinicians that the use of PTCA rather than CABG reduces costs in the long term. Further economic analysis comparing these 2 methods may be useful for future decision-making.

[ Top of document ]

References
  1. ACC/AHA Task Force Report. Guidelines and indications for coronary artery bypass graft surgery -- a report of the American College of Cardiology/American Heart Association Task Force on assessment of diagnostic and therapeutic cardiovascular procedures (subcommittee on coronary artery bypass graft surgery). J Am Coll Cardiol 1991;17(3):543-89.
  2. Nwasokwa O. Coronary artery bypass graft disease. Ann Intern Med 1995;123:528-45.
  3. Grondin CM, Campeau L, Thornton JC, Engle JC, Cross FS, Schreiber H. Coronary artery bypass grafting with saphenous vein. Circulation 1989;79(suppl I):I24-9.
  4. Fuchs JCA, Mitchener JS, Hagen P. Postoperative changes in autologous vein grafts. Ann Surg 1978;188:1-15.
  5. Adcock OT Jr, Adcock GL, Wheeler JR, Gregory RT, Snyder SO Jr, Cayle RG. Optimal techniques for harvesting and preparation of reversed autogenous vein grafts for use as arterial substitutes: a review. Surgery 1984;96:886-94.
  6. Cox JL, Chiasson DA, Gotlieb AI. Stranger in a strange land: the pathogenesis of saphenous vein graft stenosis with emphasis on structural and functional differences between veins and arteries. Prog Cardiovasc Dis 1991;34:45-68.
  7. Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery graft on 10-year survival and other cardiac events. N Engl J Med 1986;314:1-6.
  8. Cameron A, Kemp HG Jr, Green GE. Bypass surgery with the internal mammary artery graft: 15 year follow-up. Circulation 1986;74(suppl III):III30-6.
  9. Cameron A, Davis KB, Green GE, Myers WO, Pettinger M. Clinical implications of internal mammary artery bypass grafts: the Coronary Artery Surgery Study experience. Circulation 1988;77:815-9.
  10. Sims FH. Discontinuities in the internal elastic lamina: a comparison of coronary and internal mammary arteries. Artery 1985;13:127-43.
  11. Luscher TF, Diederich D, Siebenmann R, et al. Difference between endothelium-dependent relaxation in arterial and in venous coronary bypass grafts. N Engl J Med 1988;319:462-7.
  12. Nguyen HC, Grossi EA, LeBoutillier M, et al. Mammary artery versus saphenous vein grafts: assessment of basic fibroblast growth receptors. Ann Thorac Surg 1994;58:308-11.
  13. Fischman DL, Leon MB, Baim DS, et al. A randomized comparison of coronary-stent placement and balloon angioplasty in the treatment of coronary artery disease. N Engl J Med 1994;331:496-501.
  14. Serruys PW, De Jaegere P, Kiemeneij F, et al. A comparison of balloon-expandable-stent implantation with balloon angioplasty in patients with coronary artery disease. N Engl J Med 1994;331:489-95.
  15. Brener SJ, Ellis SG, Apperson-Hansen C, Leon MB, Topol EJ. Comparison of stenting and balloon angioplasty for narrowings in aortocoronary saphenous vein conduits in place for more than five years. Am J Cardiol 1997;79:13-8.
  16. Molmes DR Jr, Topol EJ, Califf RM, et al. A multicenter, randomized trial of coronary angioplasty versus directional atherectomy for patients with saphenous vein bypass graft lesions. CAVEAT-II Investigators. Circulation 1995;91:1966-74.
  17. Harris WO, Berger PB, Holmes DR Jr, Garratt KN, Bresnahan JF, Bell MR. "Rescue" directional coronary atherectomy after unsuccessful percutaneous transluminal coronary angioplasty. Mayo Clin Proc 1994;69:717-22.
  18. Lytle WB, Loop FD, Taylor PC, et al. The effect of coronary reoperation on the survival of patients with stenoses in saphenous vein bypass grafts to coronary arteries. J Thorac Cardiovasc Surg 1993;105:605-14.
  19. Nwasokwa ON, Koss JH, Friedman GH, Grunwald AM, Bodenheimer MM. Bypass surgery for chronic stable angina: predictors of survival benefit and strategy for patient selection. Ann Intern Med 1991;114:1035-49.
  20. CABRI Trial Participants. First-year results of CABRI (Coronary angioplasty versus bypass revascularisation investigation). Lancet 1995;346:1179-84.
  21. Nobuyoshi M, Kimura T, Nosaka H, et al. Restenosis after successful percutaneous transluminal coronary angioplasty: serial angiographic follow-up of 229 patients. J Am Coll Cardiol 1988;12:616-23.
  22. Douglas JS Jr, Robinson K, Schlumpf M. Percutaneous transluminal angioplasty in aortocoronary venous graft stenoses: immediate results and complications [abstract]. Circulation 1986;74(suppl II):II-363.
  23. Roubin GS, King SB III, Douglas JS Jr. Restenosis after percutaneous transluminal coronary angioplasty: the Emory University Hospital experience. Am J Cardiol 1987; 60:39B-43B.
| CIM: October 1997 / MCE : octobre 1997 |
CMA Webspinners / >