Asian Cardiovasc Thorac Ann 2000;8:207-211
© 2000 Asia Publishing EXchange Pte Ltd
Coronary Artery Bypass Grafting in Left Ventricular Dysfunction
Haq Md-Maksumul, MD,
Mullasari Ajit Sankaradas, DM,
Renuka Murali, MVS,
Eldho Paul, MSc,
Kotturathu Mammen Cherian, MS
Institute of Cardiovascular Diseases
Madras Medical Mission
Chennai, Tamil Nadu, India
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For reprint information contact: Mullasari Ajit Sankaradas, DM Tel: 91 44 656 5961 Fax: 91 44 656 5859 email: mmmbits{at}giasmd01.vsnl.net.in Institute of Cardiovascular Diseases, Madras Medical Mission, 4A Dr. J Jayalalitha Nagar, Mogappair East, Chennai, Tamil Nadu 600050, India.
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Abstract
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Postoperative mortality and morbidity were assessed in 75 patients with left ventricular dysfunction (ejection fraction < 35%) undergoing coronary artery bypass surgery between January 1995 and February 1999. The operative mortality was 10.7%. A rise in creatine kinase-MB isoenzyme, respiratory infection, ventricular arrhythmias, and hypotension were the most frequent complications. Of 25 variables evaluated by bivariate analysis, use of intraaortic balloon pump support, duration of intensive care stay, episodes of hypotension, low cardiac output, and deterioration of renal and liver function were associated with increased mortality. Morbidity, defined as postoperative hospital stay > 14 days, correlated with higher preoperative dyspnea class, longer cardiopulmonary bypass time, postoperative wound infection, pleural effusion, increased serum creatinine, perioperative intraaortic balloon pump support, and stroke. Postoperative low cardiac output with consequent renal failure, liver failure, and ultimately multiorgan failure, was the most important cause of mortality.
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Introduction
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Most large multicenter trials of coronary artery bypass grafting (CABG) have been confined to patients with relatively well-preserved ventricular function: ejection fraction (EF) > 35% in the Coronary Artery Surgery Study;1 EF > 50% in the European Coronary Surgery Study.2 Patients with coronary artery disease and poor left ventricular (LV) function are either treated medically or undergo CABG with or without transmyocardial laser revascularization. These patients may also be listed for cardiac transplantation. In fact, ischemic cardiomyopathy remains the most common cause of cardiac trans-plantation.3 Long-term outcome after CABG is better than that of medical therapy.4 Within the last two decades, improvements in anesthesia, myocardial protection, and postoperative pharmacological and mechanical support have resulted in reduced operative mortality. The aim of this study was to evaluate the results of CABG in patients with a low EF.
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Patients and Methods
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Data from 75 patients with a low EF (< 35%) who underwent CABG from January 1995 to February 1999 were retrospectively analyzed. Preoperative EF was calculated in 11 patients by multigated acquisition scan and by left ventriculography during left heart catheteri-zation in the other 64. Patients undergoing concomitant procedures such as aneurysmectomy or valve replacement were excluded from the study.
Patients were divided into 2 groups; survivors and nonsurvivors. The clinical, angiographic, operative, and postoperative variables were analyzed for differences between these groups, which might predict hospital mortality. Survivors were subgrouped according to postoperative hospital stay of up to 14 days and more than 14 days. Variables were compared in these 2 subgroups to assess predictors of prolonged hospitalization.
Statistical analysis was performed using SPSS software (SPSS, Inc., Chicago, IL, USA). Continuous variables are reported as mean ± standard deviation. Categorical variables are given as percentages. Comparisons between groups were made using the chi-squared test, Fisher's exact test, Student's unpaired t test, or the Mann-Whitney U test, as appropriate. All calculated p values were two-tailed. A p value < 0.05 was considered significant.
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Results
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The preoperative clinical characteristics are listed in Table 1
. Despite the low EF, only 12% of patients complained of class III to IV dyspnea, mainly because of their restricted activities. Angiographic findings are summarized in Table 2. Surgical details are described in Table 3. The majority of patients required inotropic support postoperatively (Table 4). Mortality and postoperative complications are tabulated in Table 5. Eight (10.7%) patients died in the postoperative period: 2 from low cardiac output; 3 from multiorgan failure following low cardiac output; and 1 from gastrointestinal bleeding. Although 13.7% of patients above the age of 50 years died compared to 4.2% aged 50 years or less, this was not statistically significant.
Twenty-five variables were analyzed as predictors of mortality (Table 6). Intraaortic balloon pump (IABP) support, episodes of postoperative hypotension, post-operative low cardiac output, respiratory tract infection, elevated serum creatinine, and abnormal liver function tests each had a significant association with mortality. The left anterior descending coronary artery was grafted in all but 2 cases: 50 patients had saphenous vein grafts, of whom 6 (12%) died, and 23 patients had left internal mammary artery grafts, of whom 1 (4.3%) died; this was not statistically significant.
Among the 19 variables analyzed for increased post-operative hospital stay, preoperative dyspnea class III to IV, prolonged cardiopulmonary bypass time, perioperative IABP support, postoperative wound infection, elevated serum creatinine, pleural effusion, and perioperative cerebrovascular accident appeared to be associated with increased hospital stay (Table 7). Among patients with prolonged postoperative hospital stay, 15.4% had an EF below 20% compared to 9.3% in the other subgroup, but this difference was not statistically significant.
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Discussion
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It is well known that patients with coronary artery disease and poor LV function have a poor prognosis with medical therapy. The 2-year and 5-year survival rates of patients with congestive heart failure caused by ischemic cardio-myopathy were reported as only 31% and 18%, respec-tively.5,6 Surgery prolongs survival in patients with depressed LV function, particularly with EF < 25%.7 In the past, perioperative mortality after CABG in patients with poor LV function was 10% to 37%, but more recent reports indicate a much lower mortality of 2.3% to 5%, attributed to advances in myocardial protection, surgical and postoperative care.6 Increased perioperative mortality after CABG in patients with depressed LV function has previously been associated with advanced age, female gender, severity of coronary artery disease, inadequate myocardial protection, and ventricular arrhythmogenicity.6
In this study, the mean age was lower than in series reported from outside India. However, Trehan and colleagues8 had a similar mean age of 56.2 ± 9.4 years in a study from northern India, reflecting the predilection of patients to have advanced coronary disease at a younger age in this part of the world. The incidence of female patients was low in all study groups and in this series, there was only one female. Most patients had a history of Q-wave myocardial infarction. Hence, the presence of viable myocardium should be assessed preoperatively to predict which patients might benefit most in the long-term from CABG. Triple-vessel disease was most common, as described by others.9 Poor LV function is considered as a relative contraindication to arterial grafts. Concern has centered on the lower early flow rate of internal mammary artery, especially with the use of inotropics during the early postoperative period, but some studies reported using internal mammary artery grafts in 95% of cases.10 There was no significant increase in postoperative mortality due to arterial grafts in our study. The proportion of patients requiring endarterectomy was high, indicating poor quality of target vessels for revascularization. These patients did as well as those who did not have endarterectomy. An IABP was used only when required. Several groups have demonstrated the safety and efficacy of perioperative IABP support in patients undergoing either elective or urgent CABG with severe LV dysfunction.5,6,11 The use of an IABP peri-operatively in selected patients might decrease the incidence of low cardiac output that was the major cause of death in our study.
All preoperative variables analyzed in this study were poor predictors of early postoperative mortality. Post-operative low cardiac output with consequent renal failure, liver failure, and ultimately multiorgan failure, was the most important cause of mortality. Most (64%) of our patients were operated under intermittent aortic cross-clamping with ventricular fibrillation and 26.7% of patients had increased (> 6%) postoperative creatine kinase-MB levels. Decreased myocardial protection during surgery may have been responsible for the low cardiac output in these patients. Although better techniques of myocardial preservation are used nowadays, no difference in mortality could be found between the patients operated under ventricular fibrillation with intermittent crossclamping and those who had other techniques. Postoperative respiratory tract infection was another important predictor of mortality. An issue to be addressed is selection of patients with coronary artery disease and severe LV dysfunction for the best immediate and long-term outcome, especially in the setting of younger patients. Improved myocardial preservation techniques during surgery and treatment of low cardiac output by more liberal use of IABP support may prevent hospital deaths.
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References
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Abstract
Introduction
