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Eur J Cardiothorac Surg 2003;24:953-960
© 2003 Elsevier Science NL
Division of Cardiac Surgery, University "G. D'Annunzio", S. Camillo de Lellis Hospital, via C. Forlanini 50, 66100 Chieti, Italy
Received 24 June 2003; received in revised form 29 July 2003; accepted 21 August 2003.
* Corresponding author. Tel.: +39-0871-358653; fax: +39-0871-402239
e-mail: calafiore{at}unich.it
| Abstract |
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Key Words: Coronary surgery On-pump Off-pump Early clinical outcome Late clinical outcome
| 1. Introduction |
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| 2. Patients and methods |
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2.1. Patient selection
Allocation to off-pump surgery was on the basis of the vessel size (>1.2 mm) and the absence of diffuse coronary calcifications. In presence of mechanical and/or electric instability the patient was selected preferably for on-pump surgery. The final decision was dependent on the basis and the expertise of the surgeon responsible of the operation.
2.2. Surgical technique
2.2.1. On-pump
CPB was instituted by cannulation of ascending aorta and right atrium. A standard circuit with a hollow fiber membrane oxygenator and a roller pump was used. The body temperature was kept to 37 °C. Myocardial protection was achieved by means of intermittent antegrade warm blood cardioplegia [7].
2.2.2. Off-pump
The method of exposure of the target coronary vessel and of stabilization has already been reported [8]. In the most recent years, apical suction was used to expose in particular the lateral and the inferior wall (Xpose, Guidant Corp., Cupertino, CA, USA). When the coronary artery was exposed, stabilization was achieved with a pressure (Acces Ultima System, Guidant Corp.) or suction (Axius Vacuum 2 System, Guidant Corp.) stabilizer. The target vessel was occluded with 4/0 Prolene, passed through a small piece of silicone tubing and then gently snared.
2.3. Clinical data collection, monitoring and definition
A set of perioperative data are collected prospectively for all patients undergoing CABG at our institution. The following were recorded and defined.
Mortality included death from any cause. Cardiac mortality included any death due to cardiac causes and sudden deaths. CVA (cerebrovascular accident) was defined as global or focal neurological deficit, diagnosed by a neurologist and confirmed by a brain computed tomography scan. AMI (acute myocardial infarction) was defined as enzymatic elevation, EKG sign of necrosis, new kinetic segment(s) at echocardiogram, ventricular arrhythmias non-K+-related. EME (early major events) were defined as the sum of death any cause, CVA, AMI, low output syndrome (need of intra-aortic balloon pump (IABP) and/or inotropic drugs for more than 12 h), need of mechanical ventilation for more than 24 h, acute renal failure (postoperative blood creatinine
2.0 mg%, if the preoperative value was normal (
1.4), or 1 mg higher if pathologic), gastrointestinal complications. ENPEP (early negative primary endpoints) were defined as death from any cause, AMI and CVA. Target cardiac events were defined as cardiac deaths, AMI in a grafted area and redo/PTCA (percutaneous transluminal coronary angioplasty) in a grafted area. Any event was defined as death from any cause, AMI any territory, redo/PTCA any territory.
The same events were evaluated according to the level of creatine kinase myocardial band (CKMB) release after surgery (19 IU/l was the highest normal). All of the patients, independently from the technique used, were divided into two Groups (Group N=normal, CKMB peak release
19 IU/l, and Group H=high, CKMB peak release >19 IU/l). Death and its causes, AMI, AMI in a grafted area, need of redo/PTCA, in all the areas or in a grafted area, incidence of target cardiac events and any event were recorded.
2.4. Follow-up
All the patients were followed up in our outpatient clinic 3, 6 and 12 months after surgery and thereafter at yearly intervals. The more recent information was obtained by calling the patient or the referring cardiologist. Follow-up was 100% complete up to August 31, 2002.
2.5. Statistical analysis
Results are expressed as mean value±standard deviation. Statistical analysis comparing two groups was performed with unpaired two-tailed t-testing for the means or
2 test for categorical variables. Stepwise logistic regression (SLR) was used to realize a model to calculate the propensity score (the probability to be selected for on-pump given a set of preoperative risk factors already reported [8]). Variables included in the SRL analysis are shown in Appendix A. The goodness of model was evaluated using the Hosmer and Lemeshow goodness-of-fit statistic and residual analysis. Each off-pump patient was matched with the on-pump patient with the closest propensity score. Variables at the basis of the model are shown in Appendix B. Patients converted to on-pump were compared with patients who underwent the procedure as scheduled. SLR was used to select the independent variables that could predict the end points of this study and included all the univariate variable with a P-value
0.2. In the final regression model independent variables were expressed as odds ratio (OR) with the 95% confidence limit (CL); the related P-value was also reported (Table 5). Actuarial curves were obtained with the KaplanMeier method. The statistical significance was calculated with the log-rank test. Cox analysis was used to evaluate the independent risk factors for reduced late events. In the Cox analysis model independent variables were expressed as hazard ratio (HR) with the 95% confidence limit (CL); the related P-value was also reported (Table 7). The SPSS software (Chicago, IL, USA) was used. P-values
0.05 were considered significant.
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| 3. Results |
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35% (OR 3.0, CL 1.37.1, P=0.0129) were independent predictors of conversion.
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3.2. Late clinical outcome
Follow-up ranged from 0.7 to 7.8 years (mean 3.7±1.9). Eighty-four more patients died (4.4%), 41 (48.8%) for cardiac causes; 20 (1.1%) had a new AMI, 18 (90.0%) in a grafted area; 36 (1.9%) had a redo or PTCA, 23 (63.9%) in a grafted area; 58 (3.0%) had a target cardiac event and 115 (6.0%) any event. Table 6 shows 5-year actuarial results and Table 7 the independent risk factors identified by Cox analysis. On-pump was a risk factor only for higher freedom from AMI in a grafted area. Conversion to on-pump was no longer a risk factor.
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19 IU/l (584, 69.0%, off-pump and 262, 31.0%, on-pump). Group H (high) included 1076 patients (56.0%) whose peak CKMB release was >19 IU/l (377, 35.0%, off-pump and 699, 65.0%, on-pump). Five-year actuarial results show that Group H had significantly lower freedom from death any cause, cardiac deaths, AMI, AMI in a grafted area, target cardiac events and any event both by the univariate (Table 8) and multivariate (Table 7) analyses. SLR identified only male gender (OR 1.4, CL 1.11.9, P=0.0068) and on-pump (OR 4.6, CL 3.85.6, P<0.0001) as independent predictors of higher CKMB release.
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| 4. Discussion |
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There is very little in the literature with regard to mid- and long-term clinical outcome in patients who have undergone off-pump surgery. Gundry et al. [10] reported a 7-year follow up experience with patients undergoing off-pump surgery. They found that, although actual survival was the same (80% on-pump versus 79% off-pump), more than 20% of patients in the off-pump group needed a second procedure in the form of surgical intervention or revascularization, compared with only 7% in the on-pump group. They concluded that, although long-term results were similar in both groups with regard to survival, the price to pay for an off-pump revascularization was a much higher, threefold, rate of reintervention. The main criticism of this paper is that most of the surgery was conducted prior to the 1990s when techniques, in particular with regard to exposure and stabilization, were rather crude and certainly not even remotely comparable to the ones which have been developed over the last few years.
More recently in a randomized study, Angelini et al. [1] found no difference between patients operated on on-pump and off-pump at mid-term follow-up, and they suggested that the early benefits in morbidity obtained with off-pump are not at the expense of reduced long-term patency rate. Similar results at 1-year follow-up were presented by Nathoe et al. [2]. Similar to those studies, we also found that 5-year actual outcome was identical whether patients had undergone on-pump or off-pump revascularization.
A significant finding of our study was the high freedom from AMI in the grafted area in the off-pump patients (Tables 6 and 7). When we correlated the occurrence of AMI with CKMB, we found that 56% of our patients had higher than normal CKMB release. Furthermore, we found a significant correlation between higher CKMB release and adverse late events. The relationship between the postoperative high CKMB release and late cardiac events is well known after cardiological intervention like PTCA [11,12], and more recently has also been found in surgical patients [13]. It is very likely that the increase in CKMB which we saw in our series, although not sufficient to produce an AMI at the time of the surgery, may create a condition for vulnerability to subsequent ischemic insult. The incidence of patients operated on off-pump was higher in patients with normal CKMB release: 60.8% of off-pump patients (n=584) was included in group N and 39.2% in Group H (n=377). On the contrary, more patients operated on on-pump were in Group H (72.7%, n=699) and fewer in Group N (27.3%, n=262).
As reported by others [5,6,14,15], in our study patients operated on off-pump had a significantly lower peak CKMB release than patients operated on on-pump (Table 3). Our study is the first to show a clear link between ischemic insult at the time of the surgery and late cardiac events. CKMB release was also raised in some of our patients who underwent off-pump surgery. A possible explanation for this is the temporary occlusion by snaring the coronary artery to be grafted which may produce some ischemic injury to the area distal to the vessel. A possible way to prevent this temporary ischemia may be the use of intravascular shunt which has been proposed as a possible way to reduce hemodynamic impairment during off-pump surgery [16].
4.1. Conclusion
In conclusion, our study, based on a propensity score analysis, seems to demonstrate that off-pump surgery, in patients selected according to our inclusion criteria, is associated with reduced mortality and morbidity when compared to on-pump surgery. These benefits are not at the expense of long-term clinical outcome which seems to be similar in the two groups. Patients who require conversion from off-pump to on-pump have a much higher mortality and morbidity, although this does not seem to affect their long-term clinical outcome. Elevation of peak CKMB above normal values during the early postoperative period seems to be a risk factor in terms of late myocardial infarction in the grafted area. Off-pump surgery is one of the tools we have to reduce perioperative ischemic injury.
4.2. Limitation of the study
This is a retrospective, non-randomized study, that reflects the experience of a center dedicated to off-pump surgery since 1994. The use of propensity score analysis improved the biases related to patients criteria selection, but did not fully eliminate them. Any component related to the quality of the target vessels could not be considered in our analysis. Reasonably, the number of distal anastomoses being identical, we can infer that the quality of distal vessels is roughly similar. It is true that, in our and other authors experience, there is no relationship between early and late results and quality or size of the coronary vessels, but we are aware that this finding could have improved the strength of our conclusions.
| Appendix A. List of variables included in the stepwise logistic regression |
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| Appendix B. Variables included in the propensity score model |
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| References |
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