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ORIGINAL ARTICLE |
Department of Cardiac Surgery
1 Department of Cardiology, Makassed Hospital, Jerusalem, Israel
Ahmad K Darwazah, FRCS, Tel: +972 2 6270222, Fax: +972 2 628839, Email: darwaz30{at}hotmail.com, Department of Cardiac Surgery, Makassed Hospital, Jerusalem, PO Box 19482, Israel.
ABSTRACT
Emergency coronary artery bypass is associated with increased operative mortality. The objective of this study was to evaluate the efficiency and safety of off-pump emergency coronary artery bypass, and to compare the outcome with that of the conventional on-pump procedure. Data of 79 patients who underwent emergency isolated coronary artery bypass were reviewed retrospectively; 45 had off-pump coronary bypass and 34 had conventional surgery. In the off-pump group, mean ejection fraction was significantly lower (28% ± 9% vs. 39% ± 10%), and there were fewer grafts per patient (1.8 ± 0.7 vs. 3.2 ± 0.8). Early mortality was higher in the conventional surgery group (14.7% vs. 8.9%), but late mortality was similar in both groups. Patients who had on-pump surgery had lower rates of recurrent angina (16% vs. 34%) and symptoms of heart failure (20% vs. 51%). Re-hospitalization was more common in off-pump patients, but cardiac re-interventions were similar. There was no significant difference in 5-year survival rates. The results of off-pump coronary bypass were better than the preoperative predicted EuroSCORE, thus it was concluded that patients treated on an emergency basis should have an off-pump revascularization procedure.
Key Words: Cornoary Artery Bypass • Off-Pump • Emergencies
INTRODUCTION
Off-Pump coronary artery bypass (OPCAB) is a well-established technique for myocardial revascularization. It has been shown to reduce both the mortality and morbidity associated with extracorporal circulation.1 Initially, it was used in highly selected cases, such as young patients with single- or double-vessel coronary artery disease. Indications have gradually expanded, especially with the development of cardiac stabilizers, and it is now routinely used for multivessel coronary disease. Recently the importance of using an off-pump technique in high-risk patients with multiple comorbidities, and its superiority over conventional coronary artery bypass grafting (CABG) has been established.2,3 The mortality of patients undergoing emergency coronary revascularization, whether after acute myocardial infarction (MI) or due to angioplasty complications, remains high.4,5 Minimizing the inflammatory reaction and ischemic injury caused by cardio-pulmonary bypass (CPB) may be of great benefit to these patients. The objective of this study was to evaluate the efficiency and safety of OPCAB in emergency coronary revascularization, and to compare the outcome with that of CABG.
PATIENTS AND METHODS
This retrospective study was performed in patients with isolated coronary artery disease who underwent emergency myocardial revascularization between April 1999 and April 2005. Those who had combined procedures or beating-heart on-pump operations and those who were converted from off-pump to on-pump CABG were excluded. The patients were divided into 2 groups according to surgical technique: 45 had OPCAB and 34 had CABG. The emergency status of these patients was based on the Society of Thoracic Surgeons guidelines that include ongoing ischemia despite maximum medical therapy, acute evolving MI, and cardiogenic shock with or without support.7 The criteria used to select either technique were based on the hemodynamic status of the patient, anatomy of their coronary vessels, and associated risk factors. Patients with diffuse multivessel disease, poor quality vessels, or evidence of coronary calcification were considered for CABG. Patients with associated comorbidities, a low ejection fraction (EF), and suitable coronary anatomy (accessible vessels, no evidence of calcification, and good vessel size) were considered candidates for OPCAB. Unstable patients were initially supported with inotropic drugs, intraaortic balloon pumping, or mechanical ventilation. Further evaluation was made intraoperatively, taking into consideration the size of the heart and the effect of manipulation on hemodynamics. Those with a reasonable heart size who tolerated manipulation underwent OPCAB, otherwise conventional CABG under CPB was used. The operative risks were evaluated in all patients by preoperative EuroSCORE.
All patients underwent surgery within 24 h after admission. Hemodynamic stability was maintained using inotropic drugs or intraaortic balloon pumping. A standard median sternotomy was performed in all cases for exposure of the heart. After harvesting the saphenous vein and left internal mammary artery (LIMA), full heparinization was carried out, keeping the activated clotting time > 400 sec in both groups. Standard cannulation of the aorta and right atrium was employed in the CABG group, and myocardial protection was achieved with intermittent antegrade blood cardioplegia and systemic hypothermia at 32°C. In the OPCAB group, anterior vessels were exposed simply by elevation of the heart. Deep pericardial retraction sutures were used to expose the circumflex and right coronary artery. A Starfish device (Medtronic, Inc., Minneapolis, MN, USA) was used to access the circumflex artery from early 2005. Stabilization of target vessels was accomplished with either a U-shaped pressure foot stabilizer (Guidant, Indianapolis, IN, USA) or a suction stabilizer (Medtronic Octopus II or III). Intracoronary shunts (Medtronic) were used in the construction of bypass grafts in all cases.
Preoperative and postoperative variables are presented as mean ± standard deviation. They were analyzed using Student’s t test. Data are expressed as percentages, and comparisons were made using Fisher’s exact test. Postoperative survival was calculated by the Kaplan-Meier method. Statistical significance was assumed when p < 0.05 (2-tailed). Analyses were performed using SPSS version 13 software (SPSS, Inc., Chicago, IL, USA).
RESULTS
Preoperative demographics and risk factors in both groups are listed in Table 1
. Patients who underwent OPCAB had a higher incidence of associated comorbidities, angina, and symptoms of congestive heart failure. This correlated with a significantly lower EF (49% of OPCAB patients had EF <25%), and significantly higher EuroSCORE. The number of diseased coronary vessels and incidence of left main stem stenosis were higher in the CABG group. The majority of patients who underwent OPCAB had single- or double-vessel disease. In the OPCAB group, the delay between admission and surgery varied from immediate transfer to 24 h (mean, 9.1 ± 7.6 h). In the CABG group, the time between admission and surgery varied from 2 to 24 h (mean, 10.6 ± 6.8 h). There were more grafts per patient in the CABG group; this was mainly due to more grafting of obtuse marginal and posterior descending arteries (Table 2). This was reflected in the higher percentage of CABG patients achieving complete revascularization. Operative mortality was similar in both groups (Table 3). Patients who died after OPCAB had a mean EF of 19% ± 6% vs. 33% ± 13% in the CABG group (p < 0.001). All deaths were due to low cardiac output, except in 2 patients who had uncontrolled arrhythmias. Only one patient undergoing CABG died in the operating room due to difficulty in weaning from CPB despite maximum support. Among the patients who died, 5 had suffered MI <24 h preoperatively, 1 had an old MI, and the other 3 showed no evidence of previous MI. Five of the patients who died had complicated percutaneous coronary angioplasty preoperatively. Postoperative inotropic support was used in 53% of all patients. There was no significant difference in postoperative morbidity between groups. Late follow-up (15–82.3 months) was achieved in 95.7% of patients (Table 4). During that time, 7 (10.4%) patients died: 6 deaths were cardiac-related and 1 (OPCAB group) was noncardiac. Patients operated on under CPB had lower rates of recurrent angina (16% vs. 34%; p = 0.08) and symptoms of heart failure (20% vs. 51%; p = 0.04). Although the incidences of angina and heart failure were higher in OPCAB patients, the symptoms were less severe than those preoperatively. Five-year survival, excluding operative mortality, was 90% in OPCAB patients and 83% in the CABG group; Cox regression analysis showed no significant difference between groups (p = 0.94; Figure 1).
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Use of the off-pump technique in emergency myocardial revascularization is still debated. When it was first used, emergency cases were considered an absolute contra-indication, and these patients were treated using CPB in the belief that they would benefit more from the protective effect of cardioplegic arrest.6,8 However, operative mortality remained high, which was considered to be due to multiple factors including the intense inflammatory response associated with extracorporal circulation. Inflammatory mediators can cause temporary dysfunction of nearly every organ.9 The effect is usually minor and reversible, but in high-risk patients, it can be irreversible and fatal.10 In spite of the major advance in myocardial protection offered by cardioplegia, some degree of myocardial stunning still occurs; this was clearly shown by higher levels of serum troponins and creatine kinase-MB compared to patients undergoing off-pump CABG.11 Also, the use of aortic crossclamping during bypass may precipitate hemodynamic failure in patients who already have an impaired left ventricle.12
Clinical experience of emergency OPCAB is limited.4,5,13–16 Most studies showed that off-pump surgery can be applied effectively with low risk despite the compromised hemodynamic state of these patients. Operative mortality varies from 0% to 5%.14,15 Operative mortality in our OPCAB patients was 8.9%, but most of them had MI <24 h prior to surgery, low EF, or complications of angioplasty. Those who underwent conventional CABG had significantly more grafts per patient, but LIMA use was similar in both groups. Our findings regarding the number of grafts was similar to previous studies.5,14 Concerning the use of LIMA, various results have been reported. Kerendi and colleagues14 noted no significant difference between groups; LIMA was used in 82% of OPCAB patients and 75.5% of CABG patients. Locker and colleagues4 used LIMA significantly more often in conventional CABG (92% vs. 82%). The decreased use of LIMA in our OPCAB patients was directly related to their more severely compromised hemodynamic state; in our series, the incidence of cardiogenic shock, angioplasty complications, and recent MI was higher than in previous reports. Furthermore, the mean EF was lower in our patients. These factors contributed to the high early mortality in our patients. Operative mortality of patients undergoing emergency CABG using the conventional technique varies from 6.3% to 24%.4,14,15 Those undergoing conventional CABG have higher mortality rates than OPCAB patients.4,15 Our operative mortality of 14.7% was equivalent to the preoperative EuroSCORE in these patients, and the difference in operative mortality between our 2 groups was not significant. However, it is important to emphasize that patients who underwent OPCAB had a significantly higher EuroSCORE than the CABG group: this highlights the importance of using an off-pump technique in these high-risk patients.
The timing of surgical intervention is an extremely difficult issue to tackle. Our policy was to perform early surgical intervention to reduce the duration of myocardial ischemia. Hemodynamic stabilization was an important factor determining the time of surgery. The time spent in hospital before surgical intervention was similar in both groups, and subsequently, we had similar incidences of postoperative MI and death. It is important to mention that all 8 patients who were transferred immediately from the catheterization laboratory survived the operation. The relationship between preoperative hemodynamic state, completeness of myocardial revascularization, and late control of symptoms was clearly seen in previous studies.4,15 We found that control of symptoms (angina or heart failure) was better after CABG, but these patients had higher preoperative EF, less cardiogenic shock, and fewer angioplasty complications. Also, the number of grafts per patient was significantly higher in the CABG group.
Late mortality was the same in both groups, although patients in the OPCAB group died earlier (within 1–2 years) than CABG patients who died after 3 years. As control of symptoms was better in CABG patients, hospitalization and re-interventions were less frequent. Previous studies have shown higher rates of late mortality (19%–23%) in patients who had OPCAB.4,15 Similarly, symptoms were less controlled in these patients. The higher mortality rates in previous studies may be due to the fact that all patients had MI within 1 week before surgery. In the first report by Locker and colleagues,15 their patients had MI within 48 h, thus higher early and late mortality in comparison to their more recent study where mortality rate was lower as patients had MI within 7 days.4 Besides the timing of intervention, the technique used (CABG or OPCAB) is also important. Studies in patients with recent MI confirmed the superiority of OPCAB over conventional CABG in this group.4,15,17 Evaluating early and late mortality in our patients who had MI <24 h before surgery, we noticed that the majority underwent conventional CABG. This emphasizes the importance of using OPCAB in patients with early acute MI.
Our study had some limitations: it was an observational retrospective trial; it contained a relatively small number of patients with inequality of preoperative left ventricular function, which may have been a potential source of bias in the choice of surgical approach; however, the surgeon’s preference and the general agreement that OPCAB represents a safe approach for patients with a severely compromised left ventricle may ameliorate this bias. Of course, the nature of the study precluded the investigators being blinded to the procedure. Nevertheless, we believe that the use of either off-pump or conventional CABG in emergency situations is associated with high operative and late mortality. Both techniques showed similar results, although the results of OPCAB surgery were much better than the pre-operative predicted EuroSCORE. This highlights the importance of using the off-pump technique for emergency revascularization.
REFERENCES
35%: effect of pump technique on early morbidity and mortality. J Card Surg 2006;21:22–7.[Medline]Asian Cardiovasc Thorac Ann 2009;
17:133-138
© 2009 by SAGE Publications
DOI: 10.1177/0218492309103288
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