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J Thorac Cardiovasc Surg 2003;126:1320-1327
© 2003 The American Association for Thoracic Surgery
Surgery for acquired cardiovascular disease |
a Department of Cardiac Surgery, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia
b Department ofCardiology, Austin Hospital, Melbourne, Victoria, Australia
c Statistical Consulting Centre, University of Melbourne, Parkville, Victoria, Australia
d Department of Cardiology, Queen Elizabeth Hospital, Adelaide, South Australia, Australia
Received for publication January 8, 2003; revisions received February 26, 2003; accepted for publication May 13, 2003.
* Address for correspondence: Professor Brian F. Buxton, Director of Cardiac Surgery, Austin Hospital, Melbourne, Victoria, 3084 Australia
brian.buxton{at}austin.org.au
| Abstract |
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METHODS: We prospectively studied 57 patients with stable coronary artery disease and poor left ventricular ejection function (<35%), enrolled between 1989 and 1994. Stress thallium was analyzed in 37 patients to identify reversible ischemia. To avoid patients with a stunned myocardium, we excluded those with unstable angina or myocardial infarction within the previous 4 weeks. Mean age of the patients was 67 ± 8 years, and 93% of patients were men. Mean left ventricular ejection fraction was 0.28 ± 0.04, 50% were in Canadian Cardiovascular Society angina class III-IV, and 65% were in New York Heart Association functional class III-IV.
RESULTS: Operative mortality was 1.7% (1/57). The mean left ventricular ejection fraction (0.30) at 15 months postoperatively did not change from before operation (0.28, P = .09). There were 8 deaths at 1 year and 42 deaths over the course of the study, producing a survival of 82.5% at 1 year, 55.7% at 5 years, and 23.9% at 10 years (95% confidence interval: 14.6%-39.1%). Symptom-free survival was 77.2% at 1 year and 20.3% at 10 years. The leading cause of death was heart failure in 29% (12/42). Multivariate analysis showed that large reversible defects on stress thallium were associated with improved left ventricular ejection fraction at 1 year (P = .01) but only male sex was associated with improved long-term survival (P = .036).
CONCLUSIONS: Myocardial revascularization for ischemic cardiomyopathy is associated with good functional relief from the symptoms of angina initially and, to a lesser extent, heart failure. Revascularization may have the advantage of preserving the remaining left ventricular function. However, the long-term mortality remains high.
We have reported short-term outcomes for patients with severe LV dysfunction undergoing coronary artery bypass grafting (CABG).12 This study reports the results of prospective 10-year follow-up on survival and relief from angina and heart failure in these patients.
| Patients and methods |
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0.35 on radionuclide ventriculography [RNVG]) were prospectively entered into the study between June 1989 and June 1994. Patients with unstable angina, myocardial infarction, and other significant ischemic events within 4 weeks of surgery were specifically excluded. Those requiring repeat CABG or concomitant procedures (including valvular operation and aneurysmectomy) were also excluded. Patients with left main coronary artery stenosis of 50% or more were not included because of the risk involved from investigational stress testing. Of 1708 patients undergoing primary coronary surgery over the entry period, 234 patients fulfilled the above criteria and had impaired LV function on contrast left ventriculography. Of these, 57 patients had an LVEF 0.35 or less on RNVG and were enrolled in the study. The protocol was approved by the Austin Hospital Ethics Committee for Human Research. Written informed consent of all the enrolled patients was obtained including specific consent for thallium and RNVG studies.
Coronary revascularization
All patients underwent CABG under mild hypothermic (34°C) cardiopulmonary bypass using a membrane oxygenator. In all cases, distal anastomoses between the bypass grafts and native coronary arteries were performed under aortic crossclamping on a heart arrested by blood cardioplegic solution infused at room temperature. In the initial part of the study, cardioplegic solution was given antegradely. The proximal ends of vein grafts were then anastomosed to the aorta during partial exclusion. As retrograde coronary sinus cardioplegia became more popular, this technique was adopted in patients enrolled in the latter part of the study. All patients had proximal anastomoses completed during the single aortic crossclamp period. Patients were weaned from cardiopulmonary bypass and maintained on milrinone (loading dose: 0.5 µg/kg in 15 minutes; infusion: 0.125-0.5 µg · kg-1 · min-1) for the first 12 hours postoperatively to maintain a cardiac index of 2.5 L · m2 · min or more in the latter part of the operative experience.
Patients received 1 to 6 coronary bypass grafts (mode of 3). Fifty-four patients (95%) had at least 1 internal thoracic artery used as a conduit, 8 of whom received bilateral internal thoracic artery grafts. The aortic crossclamp and cardiopulmonary bypass times were 61 ± 19 and 97 ± 27 minutes, respectively.
Radionuclide ventriculography
Patients with an LVEF of 35% or less on RNVG, using isotope, were enrolled in the study. Approximately 12 months after the operation, 47 of the 49 surviving patients (96%) had RNVG for reassessment of LVEF performed in the same institution as the preoperative studies, using an identical protocol. All studies were reported by observers blinded to the clinical details and other investigational findings.
Thallium-201 scintigraphy
All 57 patients underwent stress thallium-201 single-photon emission computed tomography (SPECT) before CABG. To provide uniform reporting, 2 independent nuclear medicine physicians reassessed all available studies during the first postoperative years. Twenty studies were not available or technically satisfactory, leaving 37 studies available for reanalysis. According to our previously published method to determine the presence and extent of ischemic myocardium,12 18 had large defects, 13 had defects of small to moderate size, and 6 had fixed perfusion defects.
Follow-up
All surviving patients were reviewed at 1 and 12 months postoperatively by an independent physician with no knowledge of preoperative clinical status. The surviving patients were assessed by clinical review or by telephone interview if they were unable to travel. Telephone interviews were conducted by an experienced research assistant. The clinical status, recurrence of symptoms, repeat hospitalization, and cause of death were carefully documented. For missing patients, the Australian National Death Index was used to track unrecorded deaths.
Outcome assessment
The major end points of the study were all-cause mortality at 30 days, 12 months, and 10 years. These are expressed as "survival" and "event-free survival." Events were defined as: onset of Canadian Cardiovascular Society (CCS) and/or New York Heart Association (NYHA) class III-IV, hospitalization for cardiac reasons, and mitral valve surgery or transplantation. Functional class was also assessed at 30 days, 12 months, and 10 years, angina using CCS class and dyspnea using NYHA class. The effect of CABG on LV function was assessed comparing preoperative and 12-month RNVG measurements of LVEF.
Statistical analysis
Continuous data were expressed as mean ± 1 SD. Survival was evaluated univariately by Kaplan-Meier analysis and multivariately by the Cox proportional hazards model. Variables considered for analysis in predicting survival were age, sex, diabetes, myocardial infarction, hypertension, peripheral vascular disease, chronic obstructive pulmonary disease, CCS angina class, NYHA functional class, LVEF, and perfusion defects on thallium scintigraphy.
| Results |
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Surgical complications
All but 1 patient survived the operation and hospital admission, yielding an operative (inpatient 30-day) mortality of 1.7%. None of the patients had perioperative Q-wave myocardial infarction. Three patients (5%) required insertion of an intra-aortic balloon pump during the perioperative period due to low cardiac output.
LV function
Of the 49 patients who survived beyond 12 months after the operation, 47 underwent repeat RNVG at a mean of 15 ± 3 months postoperatively. Their mean LVEF postoperatively (0.30 ± 0.09) did not differ significantly from that before operation (0.28 ± 0.04; P = .09). In a subgroup of patients who had large areas of reversible ischemia on thallium, the LVEF improved by 0.1 ± 0.04 (range: 0.05-0.21), rising from 0.30 ± 0.03 preoperatively to 0.40 ± 0.05 postoperatively (P = .01).
Early postoperative outcome
Severe preoperative angina and heart failure symptoms (classes III and IV), age at operation, presence of pathologic Q-waves on surface electrocardiograms, and cardiothoracic ratio on chest roentgenograms were examined in all patients. Findings of preoperative stress thallium-201 SPECT were available in 37 patients.
By multivariate analyses, the adjusted odds ratio for large reversible perfusion defects on preoperative stress thallium-201 SPECT, for improved outcome for survival and event-free survival at 15 months, was found to be 15 (95% confidence interval, 1.6-140, P = .03), indicating it to be an independent predictor of an early outcome. None of the other clinical variables were shown to have any predictive value.
All-cause mortality
During the course of study over 10 years, there were 42 events (40 deaths and 2 transplants). The main causes of death were heart failure in 12 (29%) patients, acute myocardial infarction in 7 (17%), sudden death in 4 (10%), and stroke in 3 (7%) (Figure 1). The survival in our study was 82.5% at 1 year, 55.7% at 5 years, and 23.9% at 10 years (Figure 2).
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| Discussion |
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Medical treatment alone for patients with coronary artery disease and LV dysfunction has been associated with poor results. Louie and colleagues5 reported 3-year survival of 25% in 54 patients (mean EF 22%), and Luciani and colleagues6 reported 5-year survival of 28% in 72 patients (mean EF 21%). Currently end-stage ischemic heart disease is one of the primary indications for heart transplantation and accounts for 40% to 50% of procedures performed. Only 10% of eligible patients undergo transplantation and many die on the waiting list17 because of limited donor availability.18 The present study demonstrates that myocardial revascularization can be offered to patients with ischemic LV dysfunction at a low operative risk (1.7%) but is associated with poor long-term survival.
The low operative mortality (1.7%) is in line with the estimates from other authors.13,19-21 Early cardiac morbidity was low with no perioperative myocardial infarction and use of intra-aortic balloon pumping in only 5% of patients. Other recent developments such as off-pump surgery or pump-assisted CABG might improve perioperative outcomes in this high-risk group of patients.22
The most common cause of death was heart failure, similar to other recent studies,16,18,19,21 and over half the deaths were due to noncardiac causes. The 5-year survival of 55% is slightly lower than those in other studies.13,19,21 The differences may be due to estimated survivals used in the other studies. No previous studies have described complete 10-year survival results.15 A 20-year survival study from the Emory group showed that low ejection fractions independently predicted poor long-term survival after CABG despite good relief of angina.23
Male sex was the only variable associated with good long-term survival similar to another report.19 Age and NYHA class did not affect long-term survival, unlike other studies.16,18,19,21 NYHA class III-IV did show a trend toward poor long-term survival. CCS class III-IV was associated with a trend toward better survival throughout the course of study, although not statistically significant. This could be explained by higher CCS class, possibly being associated with larger areas of reversible ischemic myocardium.
Few studies have provided details of functional outcomes after operation. In patients with chronic heart failure, functional capacity has very little relationship to LVEF.4 Early reports of revascularization have suggested that improvement in LVEF might be an index of successful functional outcome.5,6,11,24-26 However, more recent reports clearly show that an increase in LVEF is not necessarily associated with clinical improvement as measured by NYHA, exercise capacity, or quality-of-life scores.12,27-30 Our study also showed no significant increase in LVEF at a mean of 15 months postoperatively, except in a subgroup of patients with large areas of viable myocardium on thallium. However, extensive preoperative reversible ischemia did not predict a greater improvement in functional class at 15 months, despite the prediction of improved survival and event-free survival.
Symptom-free survival (from heart failure symptoms) of 20% at 10 years is low. The de novo appearance, recurrence, or persistence of heart failure symptoms may indicate the relentless progress toward LV insufficiency. Most of our patients were free from angina during the course of study, similar to recently reported studies,20,22 and compared favorably to the studies by Trachiotis and colleagues13 (40% at 5.8 years) and Kaul and coworkers10 (35% at 3.6 years). One of the important outcomes was that nearly all the 10-year survivors were symptom-free.
Limitations
The current study does not have a parallel control group of patients treated medically to determine which fared better. The symptomatic follow-up was incomplete between 12 months and 10 years. Nearly all patients were operated on more than 10 years ago and hence the possible additional effects of newly evolving surgical procedures, such as LV reconstructive surgery and mitral valve repair, were unknown. During the progress of this study, there have been major advances in medical management of chronic heart failure, especially blockade of renin-angiotension and sympathetic nervous system.3,31,32 In the absence of regular RNVG to assess LVEF and regular coronary angiograms to access graft patency, it is difficult to determine whether the poor late outcome was a result of progressive LV dysfunction, bypass graft disease, or other factors.
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| Acknowledgments |
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| References |
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