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Ann Thorac Surg 2006;81:2089-2095
© 2006 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, Oslo, Norway
b The Interventional Centre, Oslo, Norway
c Department of Radiology, Oslo, Norway
d Department of Pediatrics, Oslo, Norway
e Department of Anesthesiology, Oslo, Norway
f Department of Cardiology, Oslo, Norway
g Department of Physiotherapy, Oslo, Norway
h Department of Surgery, Rikshospitalet University Hospital, Oslo, Norway
Accepted for publication December 1, 2005.
* Address correspondence to Dr Lingaas, Department of Thoracic and Cardiovascular Surgery, Rikshospitalet University Hospital, Oslo, N-0027 Norway (Email: per.snorre.lingaas{at}rikshospitalet.no).
| Adult cardiac surgery:
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Abstract |
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METHODS: One hundred twenty patients were randomized to off-pump or on-pump coronary surgery. Angiography was performed intraoperatively, at 3 and 12 months. Global myocardial function was estimated by magnetic resonance imaging (MRI) preoperatively and 12 months postoperatively, as well as functional class and stress testing.
RESULTS: After 12 months internal mammary artery patency was 94% in the off-pump group and 96% in the on-pump group. Vein graft patency was 80% and 87%, respectively. No statistically significant difference between the two groups existed. There were no differences in exercise capacity improvement and attenuation of symptoms between the groups.
CONCLUSIONS: At 12-months follow-up, off-pump coronary bypass surgery provided the same angiographic graft patency as the on-pump technique. Improvement in functional class and exercise capacity was the same in both groups.
Off-pump coronary artery bypass grafting is now widely recognized as an alternative to conventional on-pump coronary artery bypass grafting. Numerous studies have intended to prove the advantage of the off-pump technique. It has been reported to reduce the systemic inflammatory response [1, 2], myocardial injury [3], renal damage [4], and to decrease injury to the brain [5, 6]. Studies have shown a shorter length of stay [7], reduced incidence of coagulopathy, and use of blood products [3, 8]. However, it is still controversial whether off-pump surgery can acquire patency rates and degree of revascularization as good as on-pump surgery [9, 10]. Few randomized studies exist, and a systematically performed angiography follow-up has been lacking. The present study was undertaken to compare the intermediate clinical and angiographic results of coronary surgery performed off-pump and on-pump.
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Material and Methods |
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Operative Techniques
Details regarding the operative technique have been previously described [12]. A standard midline sternotomy was used. In the on-pump group, cardiopulmonary bypass including arterial line filters was established with heparin-coated circuits. Cold antegrade crystalloid cardioplegia was used for cardiac arrest. In the off-pump group, Octopus I & II stabilizers (Medtronic, Minneapolis, MN) and eventually an apical suction device (Starfish [Medtronic]) were used.
Saphenous vein grafts were used in addition to the internal mammary artery. In the off-pump group, a bloodless field was achieved using coronary snares (Gore-Tex 4-0 [W.L. Gore & Assoc, Flagstaff, AZ]). Coronary shunts were not routinely used unless large or noncollateralized coronary arteries were grafted or hemodynamic instability or segment elevations changes were observed, or both hemodynamic instability and segment elevations changes. Heparin was given to achieve a minimum allowed activated coagulation time of 480 seconds in the on-pump group and 250 seconds in the off-pump group. Protamine sulfate was given at the end of the procedure in the on-pump group. In the off-pump group, protamine sulfate was given only to achieve an activated coagulation time of less than 150 to 200 seconds or if there was excessive bleeding. Patients using warfarin preoperatively continued with warfarin as only anticoagulation therapy postoperatively. All other patients received aspirin 160 mg postoperatively. Quality control of the grafts included intraoperative transit time flow measurements (MediStim AS, Oslo, Norway) and on-table graft angiography after wound closure. The grafts were revised if flow measurements or angiography revealed stenotic or occluded grafts or questionable quality of the anastomoses. Revisions of the grafts were performed with the most convenient method, conversion to on-pump if indicated. The aim of the operation was to achieve complete revascularization and open grafts. After a revision, on-table angiography was repeated.
Self-Reported Angina Score
Before the operation, and at 3 and 12 months postoperatively, all patients were interviewed by the same interviewer, and self reported angina was classified according to the Canadian Cardiology Society score [13]. The interviewer was blinded to the operative technique and the interview was undertaken at first contact with the patient after admission to avoid bias. The mean score of each group was compared before, and at 3 and 12 months after surgery.
Exercise Test
Two days before surgery all patients performed an exercise electrocardiogram (ECG) on a bicycle according to a standardized protocol. All patients started at 50 watts, and increased by 50 watts every 6 minutes until the tests were terminated. Primary criteria for ending the test were angina, ST segment depression equal to or more than –1 mm, ventricular tachycardia, or the patient's inability to continue due to fatigue (Borg scale). Secondary criteria were a systolic blood pressure fall of more than 20 mm Hg, reaching maximal heart rate, supraventricular arrhythmia, repeated single occurring ventricular tachycardia, or dizziness. The test was repeated 12 months after surgery. The maximum ST segment depression during the test and the total exercise capacity were recorded in all patients. The investigators performing and interpreting the exercise ECG were blinded to the operative technique.
MRI
Magnetic resonance imaging of the heart was performed preoperatively and at 3 and 12 months in a 1.5 T MRI scanner (Magnetom Vision Plus [Siemens, Erlangen, Germany]). Cine images were acquired in two long-axis views (one parallel and one perpendicular to the septum) and at two short-axis views. One short-axis view was obtained at the transition of the proximal and middle third of the left ventricle, and the other at the transition of the middle and distal third ventricle. End-diastolic volume, end-systolic volume, ejection fraction, and myocardial mass of the left ventricle were calculated at each examination and compared between the groups. The investigators were blinded to the operative technique.
Coronary Angiography
Coronary angiography of the bypass grafts was performed intraoperatively and at 3 and 12-month follow-ups by two experienced interventional radiologists blinded to the operative technique. The angiography at follow-up also included visualizations of the native coronary vessels. Patency was defined as any flow through the graft or the native vessel (FitzGibbon class A and B) [14]. Patients with significant and clinically important stenoses or occlusions at follow-up were admitted to percutaneous coronary intervention (PCI) if indicated.
Statistical Analysis
The statistical comparison was based on the intention-to-treat principle; therefore possible crossover between groups was not taken into account. Accordingly, 7 off-pump cases that were converted to the on-pump technique were kept in the off-pump group. The primary outcome is presented as relative risk with 95% confidence interval. Normally distributed continuous data are presented as means with standard deviation and compared with a 2-sample Student's t test. Mann-Whitney test was used to compare nonparametric data. For categorical data, the 
2 or the Fisher's exact test were used. P < 0.05 was considered statistically significant.
None of the participants or the hospital received any financial support from commercial organizations.
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Results |
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Coronary Angiography
At 12 months, 112 of 120 patients were readmitted for follow-up study, and angiography was performed in 109 patients. The angiographic results are given in Table 3. Intraoperative internal mammary artery patency was 100% in the off-pump group and 98% in the on-pump group. The corresponding numbers were 96% versus 98% after 3 months and 94% versus 96% after 12 months. Intraoperative vein graft patency was 97% in the off-pump group and 98% in the on-pump group. The corresponding numbers were 84% versus 91% after 3 months and 80% versus 87% at 12 months. There was no statistically significant difference between groups at any point in time.
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Comment |
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In both groups, the patients improved a median two classes in self-reported angina score of the Canadian Cardiology Society. At 12 months, three quarters of the patients were free from angina. The improvement in angina symptoms was highly significant and equal in both groups. Previous randomized studies have demonstrated equal freedom from angina pectoris between off-pump and on-pump patients at 12 months follow-up, indicating the same clinical results [9, 22]. The somewhat lower number of patients free from angina in our study can possibly be explained because the assessment of angina at follow-up was undertaken at first contact with the patient and includes patients with unspecified chest pain.
The clinical improvement was also supported by the exercise ECG performed preoperatively and postoperatively. Absence of ischemia was observed in three quarters at 12 months. The improvement of exercise ECG and functional class at 12 months indicates that the patients were adequately revascularized, irrespective of operative technique.
The equivalence of the two surgical techniques was also supported by cardiac MRI measurements, as global left ventricular function and myocardial mass were not affected by the type of surgery. These findings correspond with previous observations [15].
The intraoperative patency of internal mammary artery and vein grafts was high [12], although this good result included graft revision in 10 cases. Only 3 of the 10 revisions were due to occluded grafts, 1 LIMA in each group and 1 vein graft in the off-pump group. The others were kinking of grafts, 1 leak and different degrees of stenoses. It is interesting that 4 of the revisions were performed due to long vein grafts that kinked probably upon closure of the chest. The intraoperative angiographic criteria to indicate revision of a graft are not easily defined; especially spasms of the anastomotic site can be difficult to interpret [16]. This may explain our relatively high number of graft revisions after angiography. In addition, more graft manipulation of the target vessel may explain the higher revision rate in the off-pump group. In some cases in which the coronary artery was considered to be too small or insignificant to justify a prolonged procedure, occluded grafts were accepted without revision.
In a larger, but nonrandomized study we have previously documented that as much as 4% of the grafts may have failures that can be corrected after intraoperative angiography [17]. The value of intraoperative angiography to assess graft quality is underlined by the fact that 9 of 10 grafts revised were patent at 12-months follow-up. However, it is impossible to state the occlusion rate of stenotic grafts, or anastomoses if the revisions had not been performed [18]. The study would be biased if the 10 revised patients were to be excluded.
One crucial question during off-pump coronary surgery is: do the patients receive the same amount of grafts as during on-pump surgery? In the present study, the mean number of grafts was relatively low, but the number of grafts did not differ between the groups. This corresponds with other randomized trials comparing off-pump and on-pump surgery [19–21]. The number of grafts was affected by the fact that the first 40 patients did not have circumflex lesions, as we at that time had an operation table that could not be tilted sideways to facilitate circumflex grafting.
Graft patency did not differ between groups at 3 or 12-months follow-up and is comparable with the literature [20] but lower than reported by Puskas and colleagues [9]. We have previously addressed the anticoagulative regimen in off-pump surgery [12]. We aimed at an intraoperative activated coagulation time of more than 300 seconds, and careful reversal by protamine was performed to achieve an activated coagulation time of less than 150 to 200 seconds or in case of excessive bleeding. In this study, none of the off-pump patients needed reoperation for bleeding. Acetyl salicylic acid was given to all patients until the morning of operation day. In a randomized trial, less thrombogenic activation was seen in off-pump surgery than in on-pump surgery in the first postoperative day, but the off-pump group demonstrated a delayed procoagulative response in the later postoperative period [22]. In another randomized trial, a significantly lower graft patency was observed in the off-pump cases. In their study they used proportionally more radial arterial grafts and only half the heparin dose in off-pump surgery compared with on-pump surgery [10]. They used the same anti-platelet regimen as in our study [12]. This procoagulant activity in the days after off-pump surgery may lead to an increased risk for early thrombotic complications such as graft occlusion. There were no reoperations in the 12-month observation period; however 7 patients in the off-pump group (12%) and 3 patients in the on-pump group (5%) underwent PCI of either the graft or the native vessel. Some of these patients were without symptoms, and had PCl only due to angiographic findings at follow up to prevent occlusion. All PCI procedures except one were successful. Our frequency of reinterventions was higher than that found by Angelini and colleagues [22] in which the numbers were 2.0% and 1.5%, respectively. However, in Angelini and colleagues' [22] study there was no systematical angiographic follow-up of all patients, and revisions were performed only in response to angina and positive exercise ECG. The sensitivity of angina score and exercise ECG as tools to discover occluded or stenotic grafts are low [23, 24]. Several of our patients with stenotic grafts, but without angina underwent PCI to prevent a possible future occlusion. A routine angiography detects subclinical findings that obviously influence the number of reinterventions in comparison with studies without angiographic control [11]. In other studies, we have demonstrated that postoperative occluded vein grafts may not give any subjective symptoms or change in function class [25].
Our ethical dilemma was whether or not to correct clear or possible mistakes found during these controls, and by this alter the natural outcome of the study. By doing this, we believed we could give our patients a better treatment after all. This clearly alters the results of our findings.
We are aware of the risks of coronary angiography [6]. Only one complication occurred, when at 3 months one LIMA graft dissected at coronary angiography. Otherwise this was totally uneventful, as the grafted left anterior descending artery was only partially stenotic, the patient was and still is without symptoms and is followed regularly.
Coronary angiography is a great burden to the patients. But to rely on the patient's clinical situation in determining the quality of the grafts at follow-up in a scientific study is misleading. We were struck by the incongruence between the patient's clinical situation and patency of the grafts at angiography. Until noninvasive methods are validated, angiography with near complete follow-up is still justifiable in controlled studies.
Limitations of the Study
Only 120 patients included give a relatively low statistical power, but our emphasis has been on the quality of the data with a complex and resource demanding follow-up. Due to the varying degrees of initial training by the surgeons involved, we did have a learning curve, reflected in the relatively high number of conversions. This may not be completely representative for the current state of the art in off-pump surgery, although many centers have surgeons with varying experience. The design of the study with intraoperative and postoperative routine angiography led to additional interventions (revision of the grafts and percutaneous interventions) that altered the outcome. Many of these corrections may have been unnecessary. However, it is difficult to predict the effect on the outcome if these had not been done.
Conclusion
In conclusion, at 12-months follow-up, off-pump coronary artery bypass surgery in our study did not differ from on-pump surgery with regard to cardiac function expressed as functional class, exercise ECG, MRI of the heart and graft patency. Until noninvasive methods are validated, intraoperative angiographic control is important to compare graft quality with controlled studies, as well as with a new method, such as off-pump technique, when it is introduced.
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