Asian Cardiovasc Thorac Ann 2008;16:16-20
© 2008 Asia Publishing EXchange Ltd
Off-Pump Coronary Artery Bypass Grafting in Left Ventricular Dysfunction
Masoumali Masoumi, MD,
Mohammad R Saidi, MD,
Farhanaz Rostami, BSc,
Helen Sepahi, BSc,
Daem Roushani, MSc
Department of Cardiovascular Surgery, Imam Ali Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran
For reprint information contact: Masoumali Masoumi, MD Tel: 98 831 836 0752 Fax: 98 831 836 0043 Email: mmasoumi{at}kums.ac.ir, Imam Ali Heart Center, Shahid Beheshti Ave, Kermanshah, Iran.
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ABSTRACT
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Between August 2004 and May 2006, 124 patients undergoing coronary artery bypass grafting with ejection fractions 
35% were randomly assigned to off-pump or conventional procedures. Preoperative characteristics were the same in both groups, except for age and degree of mitral regurgitation. Off-pump coronary artery grafting was carried out using a tissue stabilizer and a single-suture technique; conventional coronary bypass employed cardiopulmonary bypass, moderate hypothermia, and antegrade-retrograde cold blood cardioplegic arrest. There were significantly fewer vessels grafted (3.09 ± 0.41) in the off-pump group than in those who had a conventional procedure (3.42 ± 0.86). The rates of mortality, morbidity, balloon pump support, inotropic usage, gastrointestinal bleeding, renal dysfunction, reintubation, as well as intensive care and hospital stay, were significantly lower in the off-pump group. The incidence of perioperative myocardial infarction did not differ significantly between groups. The results of this study indicate that beating-heart coronary bypass is safe and effective in patients with left ventricular dysfunction.
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INTRODUCTION
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The optimal conditions for coronary artery bypass grafting (CABG) are cardiopulmonary bypass (CPB) and cardiac arrest; however, CPB may increase postoperative complications, especially in high-risk patients.1 Thus off-pump CABG has been investigated and the benefits of decreased rates of operative mortality and perioperative myocardial infarction, preservation of renal function, shorter hospital stay and greater cost effectiveness have been reported.2–4 Although off-pump CABG is considered less invasive than conventional CABG, Okazaki and colleagues5 suggested that the risks of endothelial injury, blood cell deposition and delamination of endothelial cells were detrimental to the long-term results. Humidified gas insufflation attenuated these adverse effects. Heparin and dipyridamole-added humidification has a potential advantage in terms of reducing blood cell deposition on the endothelium, but there has been no objective assessment of its invasiveness. Therefore, routine use of this method in CABG, especially in patients with severe left ventricular (LV) dysfunction has not been established. The purpose of this study was to investigate the safety and efficacy of multivessel beating-heart revascularization in patients with severe LV dysfunction.
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MATERIALS AND METHODS
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From August 2004 to May 2006, 124 patients with an ejection fraction (EF) of 35% or less who were referred for isolated first-time CABG were randomly assigned to on-pump (n = 62) or off-pump (n = 62) surgery. The only exclusion criterion was single-graft CABG. Most baseline characteristics, except age, degree of mitral regurgitation, and the number of planned number of grafts, were similar in both groups (Table 1
). Perioperative data are collected prospectively from all patients undergoing CABG at our institution. Hospital mortality was defined as death within the same hospital admission, regardless of cause. Postoperative stroke was defined as a new focal neurological deficit or comatose state persisting for longer than 24 hours. We excluded intellectual impairment, confused states, and transient events to avoid any subjective bias. Myocardial infarction was defined as plasma creatine kinase-MB > 30 IU·L–1, electrocardiographic signs of necrosis, or new akinetic segment(s) on an echocardiogram. Acute renal failure was defined as postoperative creatinine > 2.0 mg·dL–1 with a normal preoperative value (< 1.4 mg·dL–1). Completeness of revascularization was defined as revascularization of all coronary arteries with stenosis 
50% and with a size 1 mm. Follow-up was completed by the referring cardiologist or hospital outpatient clinic. Any cardiac events after discharge from the hospital were reported, including myocardial infarction, congestive heart failure requiring hospitalization, plural effusion, native coronary artery or graft stenosis requiring any type of coronary intervention and sudden death.
All patients stopped aspirin (325 mg) therapy the day before surgery and resumed it 8–10 hours postoperatively. A standardized anesthetic protocol was used throughout the study. All patients underwent the operation through a median sternotomy. In conventional CABG, after systemic heparinization with 3 mg·kg–1, the activated clotting time was maintained at > 480 sec. Cardiopulmonary bypass was instituted with a single right atrial cannula and an ascending aortic perfusion cannula. Standard bypass management included roller pump heads, membrane oxygenators, an arterial line filter, nonpulsatile flow at 2.4 L·min–1·m–2, with mean arterial blood pressure > 50 mm Hg. Myocardial protection was achieved by antegrade induction of cold hyperkalemic crystalloid cardioplegic solution (St. Thomas’ Hospital solution) combined with blood from the arterial line, followed by retrograde infusion of blood cardioplegia. Distal coronary anastomoses were performed with a continuous running 7/0 monofilament suture. The left internal mammary artery was used to bypass left anterior descending artery stenosis, and saphenous vein grafts were used for other vessels. In off-pump CABG, a standby perfusionist with a primed bypass circuit was available in all cases. The pericardium was opened using an inverted T-shaped incision after harvesting the internal thoracic artery. Opening the right plural space created space for the rotated and vertically displaced heart, to minimize hemodynamic compromise. Lidocaine 1 mg·kg–1 was infused to prevent arrhythmias. After systemic heparinization (3 mg·kg–1), distal anastomoses of grafts were carried out using an Octopus II stabilizer (Medtronic Inc., Minneapolis, MN, USA) and a single-suture technique. One deep pericardial retraction suture was placed at the posterior fibrous pericardium, close and medial to the most proximal part of the inferior vena cava, and snared over an open sponge. The 2 arms of the sponge and the snared suture acted as a lever to manipulate and rotate the heart in vertical and lateral positions along the stabilizer. In the off-pump group, appropriately sized intracoronary shunts were used routinely for the left anterior descending artery and for all other nonoccluded arteries. Visualization was aided with a humidified carbon dioxide blower (Medtronic, Inc.). Hypothermia was prevented by application of warming blanket. Three patients in the off-pump group were switched intraoperatively to on-pump surgery because of intractable ventricular tachycardia. Their operations continued without cardiac arrest (beating on-pump) with no further problems. Protamine was used to reverse the effects of heparin. A standardized protocol for immediate postoperative care was followed in the adult intensive care unit.
Results are expressed as mean ± standard deviation for continuous variables. Statistical analyses were performed using Student’s t test or the Mann-Whitney U test, as appropriate. The chi-squared test was used for categorical variables. A p value < 0.05 was considered significant.
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RESULTS
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Although the proportion of patients with triple-vessel disease was similar in both groups, off-pump patients received significantly fewer grafts during the procedure (Table 2). The postoperative data are listed in Table 3. There were significantly fewer incidences of mortality and morbidity in the off-pump group compared to conventional CABG patients. Among the off-pump patients, only 9 had inotropic infusions of 5–10 µ·kg–1·min–1 for a mean of 16.3 ± 7 hours (range, 5–24 hours), while 29 of the on-pump patients need inotropic infusions of 3–50 µ·kg–1·min–1 for 26 ± 15 hours (range, 5–72 hours). Intraaortic balloon pump requirements, duration of ventilatory support, time in the intensive care unit and hospital stay were significantly less in the off-pump group. All of these factors are indices of low cardiac output postoperatively. Furthermore, in the off-pump patients, there were significantly reduced incidences of arrhythmias, renal failure and gastrointestinal hemorrhage. Follow-up ranged from 6–28 months, and no patient was lost to follow-up. One patient who had undergone off-pump CABG died 2 months after the operation from pneumonia.
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DISCUSSION
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This study showed that the mortality, morbidity and lengths of intensive care and hospital stay were reduced in high-risk patients with severe LV dysfunction by performing CABG without CPB. The rate of perioperative myocardial infarction, which may correlate with the quality of distal anastomoses, was also lower (although not significantly) in the off-pump patients. There was a significant difference in the number of grafts constructed in each group, which may have been due to grafting more vessels with diffuse disease in patients having conventional CABG. However, other reports have also shown that fewer vessels were grafted in patients undergoing off-pump CABG compared to conventional CABG.6 The use of an intraaortic balloon pump in conventional CABG in our series was the same as in a previous study (30%), where it was found to be very beneficial in reducing operative mortality.7 It was also shown that more liberal preoperative use of an intraaortic balloon pump reduced the 30-day mortality.8 In our center, we use an intraaortic balloon pump postoperatively before the onset of severe hemodynamic instability, especially in patients with severe LV dysfunction.
There has been increasing interest in off-pump CABG because it is thought to be less invasive than conventional CABG using CPB and cardioplegic arrest. Cardiopulmonary bypass causes a systemic inflammatory reaction that may result in morbidity after cardiac surgery. In a multicenter study on 2,108 patients from 24 US institutions, Roach and colleagues1 concluded that adverse cerebral outcomes after conventional CABG are relatively common and serious; they are associated with substantial increases in mortality, length of hospitalization and use of intermediate or long-term care facilities. They concluded that new diagnostic and therapeutic strategies must be developed to lessen such injury. Many previous studies have shown that off-pump CABG is safe and effective, with excellent results, minimal morbidity and low operative mortality relative to on-pump CABG.9,10 The development of specialized techniques, tissue stabilizers and apical suction devices allows the application of off-pump CABG to almost all patients, as surgeon experience matures. Furthermore, there are several reports that off-pump CABG is a safe alternative to on-pump grafting in high-risk patients such as redo CABG cases or those with advanced age, female sex, or impaired LV function.11–13 Some studies found that off-pump CABG for patients with LV impairment was associated with surgical outcomes similar to those with normal LV function, and others noted that certain high-risk groups may be better treated with off-pump CABG.14 In contrast, Di Mauro and colleagues6 reported unsatisfactory midterm results of off-pump CABG, probably due to incomplete revascularization. Khan and colleagues15 found in another randomized trail that the graft patency rate was lower at 3 months after off-pump CABG, which has implications for long-term outcome. Experimental studies showed that stabilization devices and non-humidified gas blowing damage the coronary endothelium.5 Other research found no significant difference in hospital mortality and morbidity with on-pump or off-pump techniques in low-risk patients.16
Numerous studies suggest that off-pump CABG is associated with decreased mortality and morbidity after CABG, and may prove superior to conventional CABG in appropriately selected patients. There are several other reports that in the absence of risk factors for CPB, off-pump CABG does not improve early and midterm clinical outcome, and on-pump patients experience better long-term survival and freedom from revascularization. Moreover, despite increasing experience in many centers, hemodynamic collapse can occur during off-pump bypass, requiring rapid institution of CPB.17 Conversion to an on-pump procedure carries high risks of hospital mortality and morbidity.18 There is increasing evidence that snares can cause arterial damage and spasm, although shunting avoids this problem while enhancing hemodynamic stability and facilitating accurate anastomoses.19 As Dewey and Edgerton17 noted, off-pump CABG has specific problems, such as complications of the ascending aorta and target vessels and hemodynamic collapse requiring institution of CPB. Thus it is prudent to define the indications for off-pump CABG. Benetti and colleagues20 concluded that the main indications for off-pump coronary surgery were the experience and comfort level of the surgeon.
The major limitation of this study was the lack of long-term follow-up. Nevertheless, we consider off-pump CABG to be an excellent choice for high-risk patients. Low-risk patients can tolerate CPB and cardiac arrest, a motionless, bloodless surgical field provides optimal conditions for the construction of coronary anastomoses and with antegrade-retrograde cold blood cardioplegia, this procedure is usually well tolerated in patients with good LV function. We also have not been convinced of the long-term superiority of off-pump CABG over conventional CABG in all groups of patients. Therefore, we limit off-pump CABG to selected patients such as those with poor LV function, advanced age, left main stenoses with LV dysfunction and severe 3-vessel disease with mild aortic regurgitation.
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REFERENCES
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- Roach GW, Kanchuger M, Mangano CM, Newman M, Nussmeier N, Wolman R, et al. Adverse cerebral outcomes after coronary bypass surgery. Multicenter Study of Perioperative Ischemia Research Group and the Ischemia Research and Education Foundation Investigators. N Engl J Med 1996;335:1857–63.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
