Asian Cardiovasc Thorac Ann 2003;11:23-27
© 2003 Asia Publishing EXchange Ltd
Coronary Artery Bypass Grafting for Patients With Poor Left Ventricular Function
Hitoshi Hirose, MD,
Atsushi Amano, MD1,
Syuichirou Takanashi, MD2,
Akihito Takahashi, MD2
Department of Cardiovascular Surgery, Kobari General Hospital, Chiba, Japan
1 Department of Cardiovascular Surgery, Showa University Northern Yokohama Hospital, Kanagawa, Japan
2 Department of Cardiovascular Surgery, Shin-Tokyo Hospital, Chiba, Japan
For reprint information contact: Hitoshi Hirose, MD Tel: 1 216 707 9445 Fax: 1 216 707 9446 email: genex{at}nifty.com Thoracic and Cardiovascular Surgery, Cleveland Clinic Foundation, F25, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
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ABSTRACT
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Patients undergoing isolated first-time elective coronary bypass surgery were classified according to their preoperative ejection fraction: group 1 comprised 131 patients with poor left ventricular function (ejection fraction < 40%); group 2 was 1,496 control patients. The mean number of distal anastomoses was not significantly different in the 2 groups, however, clamp time, pump time, and operative time were longer in group 1. Patient recovery was significantly slower in group 1. Morbidity (14.5% in group 1 versus 7.4% in group 2, p < 0.005) and mortality (2.3% versus 0.1%, p < 0.0001) were higher in group 1. During late follow-up, the 5-year survival rate (70.1% versus 90.5%) and 5-year event-free rate (65.6% versus 81.9%) were significantly inferior in group 1 compared to group 2. The results of bypass surgery in cases of decreased left ventricular function were poor, and such patients need to be carefully followed up.
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INTRODUCTION
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Patients with decreased left ventricular (LV) function are considered to be high-risk candidates for coronary artery bypass grafting (CABG).1 Medical treatment for the control of angina and ongoing congestive heart failure is disappointing.2 Ischemic cardiomyopathy with severely decreased LV function is one of the indications for cardiac transplantation; however, heart transplantation has rarely been performed in Japan. Isolated CABG is an acceptable alternative treatment modality to control angina and preserve LV function, although the short- and long-term benefits have not been clearly defined.3 This study was undertaken to evaluate the surgical results of isolated CABG in patients with decreased LV function.
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PATIENTS AND METHODS
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Between May 1991 and December 2000, 1,627 consecutive patients underwent isolated first-time elective CABG in the Shin-Tokyo Hospital Group (Shin-Tokyo Hospital, Kobari General Hospital, and Yokohama City Northern Hospital). All patients underwent preoperative echocardiography; an ejection fraction (EF) of less than 40% was defined as poor LV function. There were 131 patients identified as having poor LV function (group 1). The other 1,496 patients served as controls (group 2). Patients who had concomitant valvular or LV surgery (aneurysmectomy, Dor’s procedure, or Batista’s operation) were excluded from this study. Patients who underwent minimally invasive direct coronary artery bypass were also excluded. The demographics of both groups are described in Table 1
. The mean preoperative EF was 33% ± 5.9% in group 1 and 63.2% ± 10.6% in group 2. Most patients in group 1 were in New York Heart Association functional class III (90, 68.7%) or IV (18, 13.7%).
Surgery was performed under cardioplegic arrest with normothermia (36°C) supported by cardiopulmonary bypass. To assure the delivery of the cardioplegic solution in patients with poor LV function, cardioplegia was administered both antegradely and retrogradely. Hypothermic arrest was not used because of hospital policy. After September 1996, off-pump CABG was adopted and selected cases were referred for off-pump CABG with a beating heart.4 Efforts were made to achieve complete revascularization with arterial grafts as much as possible. By retrospective chart review, the following parameters were recorded: age, sex, cardiac profile, preoperative risk factors, graft material, surgical data, postoperative complications, and mortality. Outpatient follow-up was completed by the referring cardiologist or hospital outpatient clinic. Any cardiac events after discharge from hospital were reported, including myocardial infarction, angina, arrhythmia requiring hospitalization, congestive heart failure requiring hospitalization, native coronary artery or graft stenosis requiring any type of coronary intervention, and sudden death. These follow-up data were complied by December 31, 2001. The endpoints were death or the occurrence of one of these cardiac events.
Results were expressed as mean ± standard deviation. Statistical analyses were performed using Student’s t test or the Mann-Whitney U test, as appropriate, for continuous variables, or the chi-squared test (Fisher’s exact test if n < 5) for categorical variables. The survival and event-free rates were calculated by the Kaplan-Meier method. A p value < 0.05 was considered significant. Relative risk (RR) and the 95% confidence interval (CI) were calculated by logistic models. Factors with a p value < 0.05 on univariate analysis were further analyzed using the multivariate model. All statistical analyses were performed using Stat-View version 5.0 (SAS Institute, Cary, NC, USA).
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RESULTS
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Operative data are shown in Table 2. In group-1 patients with poor LV function, mean clamp time, pump time, and operative time were significantly longer, and blood transfusion was required more frequently than in the controls. Postoperative recovery in group 1 was associated with prolonged intubation, intensive care stay, and postoperative hospital stay (Table 3). Major complications were observed significantly more often in group 1 than group 2. There were 3 hospital deaths in group 1, giving a mortality rate of 2.3%, significantly higher than in the control group (0.1%). Preoperative risk factors in Table 1
and the graft materials in Table 2 were entered into the logistic analysis to identify predictors of hospital death. Logistic regression analysis demonstrated that poor LV function was the single independent predictor of hospital death in this study (RR 35.04, 95% CI 3.62–3339.36, p < 0.0001). No other risk factor achieved statistical significance.
The EF improved after surgery in 85/131 patients (64.9%) in group 1, compared to 373/1,496 patients (24.9%) in the control group (p < 0.0001). In group 1, mean EF increased from 33% ± 5.9% preoperatively to 40.3% ± 11.3% postoperatively (p < 0.0001). When group 1 was divided into 2 subgroups: severe LV dysfunction (EF < 30%, n = 29) and moderate LV dysfunction (EF 31%–39%, n = 102), hospital mortality and morbidity rates were 3.4% and 17.2% in patients with severe LV dysfunction, respectively, and 2.0% and 17.2% in those with moderate LV dysfunction (p > 0.05).
Among the survivors, follow-up was complete in 93.1% of group 1, with a mean follow-up period of 3.4 years, and in 97.7% of group 2, with a mean follow-up of 4.2 ± 2.2 years (Table 4). During follow-up, there were 33 deaths (25.8%) in group 1, including 15 cardiac deaths (11.7%), while there were 126 deaths (8.4%) including 39 cardiac deaths (2.6%) in the control group. Actuarial 3-, 5-, and 7-year survival rates after surgery in group 1 were significantly inferior to the control group (p < 0.0001; Figure 1). Univariate followed by multivariate logistic survival analysis demonstrated significant predictors of late death: poor LV function (RR 3.14, 95% CI 2.07–4.76), preoperative congestive heart failure (RR 2.22, 95% CI 1.53–3.24), insulin use (RR 1.88, 95% CI 1.19–2.97), age over 75 years (RR 1.71, 95% CI 1.11–2.61), and hemodialysis (RR 3.83, 95% CI 1.83–8.00).
Late cardiac events occurred more frequently in group 1 than group 2 (p < 0.0001; Figure 2). Analysis of the late cardiac events revealed that congestive heart failure was more frequent in group 1 than group 2 (Table 4). Univariate followed by multivariate logistic survival analysis found significant predictors of late cardiac events to be poor LV function (RR 1.17, 95% CI 1.17–2.47) and congestive heart failure (RR 2.44, 95% CI 1.82–3.26). In the two subgroups of group 1, late survival was significantly inferior (5-year survival 48.8%) in those with severe LV dysfunction (EF < 30%) compared to those with moderate LV dysfunction (EF 31%–39%) who had a 5-year survival rate of 75.9% (p < 0.005). However, the late cardiac event-free rate was not significantly different between the two subgroups (5-year event-free rates: 54% versus 69.4%, p = 0.12).
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DISCUSSION
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In general, the definition of poor LV function is unclear. The registry of the Society of Thoracic Surgery classified preoperative EF into 5 categories: 55% and above, 45%–54%, 35%–44%, 25%–34%, and 24% and less; mortality rates increased as EF decreased.5 Most publications discuss patients with EF less than 30%, and their clinical outcomes have proven to be poor.6–9 As the number of patients with EF < 30% in our study group was only 29, we chose EF < 40% as the criterion of poor LV function. However, we found no significant differences in terms of hospital mortality or morbidity between patients with EF 30%–39% and those with EF < 30%, but our study excluded patients who underwent LV surgery, which may have influenced our results. During the study period, an additional 21 patients with EF 30%–39% and 10 patients with EF < 30% underwent CABG with LV surgery. The mortality rate in those who underwent LV surgery was 3.2%, which is not significantly different from isolated CABG; however, the morbidity rate was 25.8% which is significantly inferior to isolated CABG. The hospital mortality in group 1 (2.3%) was significantly higher than in the control group, but it was below the range of previous reports of isolated CABG in patients with poor LV function (3%–5.2%).7,8 Our study demonstrated that EF < 40% was the sole predictor of hospital mortality in isolated elective first-time CABG. Heart transplantation would be the alternative choice of treatment for patients with LV dysfunction. Although heart transplantation provides good long-term survival (82% at 5 years), hospital mortality is high (11.6%).8 Furthermore, only a few heart transplants have been performed in Japan, and no long-term outcome data are available.
Although the number of distal anastomoses was not significantly different between the two groups, the procedure was longer in group 1 where coronary lesions tended to be more diffuse, and the diameters of the coronary arteries were smaller, which prolonged anastomosis time and clamp time. The pump time was directly influenced by LV function. The use of arterial grafts was similar in both groups; even with poor LV function, arterial bypass is feasible. Graft designs were not changed and complete revascularization was adequately achieved regardless of LV function. Preoperative viability studies for revascularization were not performed routinely as we believe that all patients with coronary arteries suitable for grafting will benefit from revascularization, regardless of LV function or regional wall motion. Intraoperative assessment of regional wall thickness, contractility, and ventricular aneurysm formation was carried out by esophageal echocardiography. Intraoperative esophageal echocardiography was undertaken routinely in patients with EF < 40% to evaluate LV function. If the area in question was scarred, thinned, and nonfunctioning, we proceeded with LV volume reduction surgery, as proposed by Mickleborough and colleagues.9
The slower postoperative recovery in group 1 may be related to postoperative complications. Severe arrhythmias such as ventricular tachycardia, cardiac arrest, or complete AV block was more frequent in this group; however, the occurrence of postoperative atrial fibrillation was not significantly different (30 patients, 22.9% in group 1 versus 339 patients, 22.7% in group 2). The increased incidence of respiratory failure and cerebral vascular accident may have influenced the duration of intubation and intensive care unit stay. Perioperative myocardial infarction was observed in 5 patients in group 1, due to native coronary spasm in 4 and early occlusion of the gastroepiploic artery graft in 1. Left ventricular EF in group 1 was significantly improved after CABG surgery, as previously noted by Trachiotis and colleagues.7
Congestive heart failure was a major problem during follow-up in group 1, accounting for 10 of the 15 late cardiac deaths. The incidence of congestive heart failure was more than 5 times higher group 1 than in the control group. While CABG adequately controlled late angina, it did not suppress congestive heart failure. Similar findings were noted by Mickleborough and colleagues9 who reported that 15 of 20 patients with preoperative EF < 20%, who were readmitted for cardiac reasons during 4 years of follow-up, were in congestive heart failure. Reported 5-year survival rates after CABG in patients with poor LV function are 64.4% for EF < 25%, 71% for EF 25%–35%, and 86.5% for EF < 30%.7,10 These results are comparable to our 5-year survival rate of 70.1% and the finding that EF < 40% was a predictor of both late deaths and cardiac events. Thus, postoperative follow-up should focus on the occurrence of congestive heart failure.
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Footnotes
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Presented at the 9th International Congress of Cardiomyopathy and Heart Failure, Kyoto, Japan, May 30–June 1, 2002.
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ABSTRACT
INTRODUCTION
