Department of Cardio Thoracic Surgery, Apollo Hospitals, Chennai

Background: The off-pump technique reduces the complications of coronary artery bypass grafting performed with extracorporeal circulatory assistance. This hypothesis was tested by analyzing the results of 53 patients operated with and 48 without cardiopulmonary bypass by a single surgeon (ARR) from February 2001 to September 2001.

Methods and Results: The angiograms of all the patients scheduled for isolated coronary artery bypass grafting were carefully analyzed and a plan for revascularization made. After sternotomy and inspection of the vessels, a decision was taken to perform the surgery on- or off-pump. All the demographic, operative and postoperative data were prospectively collected and analyzed statistically. Major end-points, such as mortality, perioperative infarction and organ dysfunction, were not different between the two techniques. The incidence of renal and pulmonary dysfunction was similar. There were no neurological problems in either group. In contrast to many reports, bleeding complications and the use of blood products were the same in both groups (1.6±2.3 in the on-pump group and 0.8±1.7 in off-pump group; p=0.06). The only important difference between the two groups was the incidence of low cardiac output and use of inotropes, being more common in the on-pump group. 

Conclusions: Off-pump coronary artery bypass grafting is as safe as that done on-pump. The claims of a lower incidence of organ dysfunction and blood product use in the off-pump group were not substantiated in this study. The incidence of low cardiac output and use of inotropes was significantly lower in the off-pump group. (Indian Heart J 2002; 54: 379–383)

Key Words: Coronary artery bypass grafting, Off-pump surgery, On-pump surgery

Beating heart coronary artery bypass grafting (CABG) is a technique developed to do away with cardiopulmonary bypass (CPB). Till recently, CPB was considered to be the most important factor for creating a perfect vascular anastomosis in a quiet, motionless and bloodless field. Because of the many deleterious effects of CPB, recognized to be particularly important in the emerging scenario of an increasing number of elderly and high-risk patients being taken up for CABG, off-pump coronary artery bypass surgery (OPCAB) is gaining importance. Many of the technical difficulties of the off-pump technique have been overcome by the development of devices such as stabilizers, snares, shunts, suction cones, etc. by a responsive industry. At present, almost all the regions of the heart have become accessible for anastomosis with varying degrees of comfort and safety. Many studies have confirmed the satisfactory short-term patency rates.

The aim of this study was to evaluate the results of CABG with and without CPB in 101 patients who underwent primary isolated CABG between February and September 2001, performed by a single surgeon. 

Methods 

After obtaining informed consent, 101 patients who underwent primary isolated elective CABG between February and September 2001 were included in this study. When the study started, the surgeon (ARR) whose work is the subject of this paper had already performed 100 multivessel OPCAB. Of the 101 patients included in the study, 53 were operated on CPB [on-pump coronary artery bypass surgery (ONCAB)] and 48 underwent OPCAB. The angiograms of all the patients were carefully studied and a plan of revascularization made jointly by the cardiologist and the surgeon. The final decision whether to go ahead with OPCAB or ONCAB was made on the table after inspecting the vessels. The main criterion for deciding the method of operation was the technical feasibility of the procedure. No reduction in the number of grafts for the sake of performing OPCAB was accepted. Even if one of the planned grafts was difficult to do OPCAB, the patient was operated ONCAB. The major reasons for opting for on-pump surgery were intramyocardial vessels, calcified vessels, difficult exposure for lateral wall arteries, diffuse disease and small vessels (<1 mm). No patient needed conversion to CPB after making the decision. The preoperative variables of the patients are shown in Table 1.  

All the patients continued their preoperative medications till the morning of the surgery. The antiplatelet agents were stopped 5 days prior to the scheduled date of surgery. Patients were premedicated with midazolam. The same method of induction of anesthesia was used in all the patients, with midazolam, fentanyl and pancuronium and propofol infusion for maintenance. Most patients had a Swan-Ganz catheter for monitoring the pulmonary artery (PA) pressure during the surgery. 

Arterial and venous conduits were harvested simultaneously.  

The ONCAB patients received heparin at a dose of 3 mg/kg and an activated clotting time (ACT) of >400 s was maintained. A Medtronics Oxygenator (Affinity N.T. Trillium coated) was used with a crystalloid prime of 1500 ml ringer lactate with 5000 units of heparin. The flow was maintained at 2.4 L/min/m 2 . The temperature was allowed to drift up to 32°C but active rewarming was commenced if the drift was below that. At the completion of distal anastomoses, active rewarming was started to achieve a nasopharyngeal temperature of 37°C. The distal anastomoses were done with intermittent cross-clamping not exceeding 10 min at a stretch. Because of left ventricular venting through the right superior pulmonary vein, it was possible to do many of the anastomoses without cross-clamping the aorta. Cardioplegia was not used in any of the cases. Intraoperative autologous donation was employed in all the patients whose calculated hematocrit on CPB was >25%. After weaning away from CPB, all the blood remaining in the circuit was returned to the patient. Protamine sulphate was administered in a ratio of 1:1 of the heparin dosage. No antifibrinolytics were used. 

The OPCAB patients had an infusion warmer for fluid administration and a warming blanket during the procedure. All the patients were operated upon through a midline sternotomy. The OPCAB patients were administered heparin at a dose of 1.5 mg/kg and ACT was maintained at >250 s. The Octopus 3 stabilizer was used in all cases. In all the patients, the LIMA–LAD anastomosis was constructed first. The rest of the distal anastomoses were done serially and all the proximal anastomoses were done with a single partial clamping of the aorta. A silastic sling was used for proximal control. No distal control was used. Silastic shunts were used if the artery was >2 mm in diameter, distal bleeding troublesome or there were ST changes in the ECG. Shunts were avoided as far as possible if the vessel was diffusely diseased. A CO ₂ mister blower was used for achieving a bloodless field. At the end of all the anastomoses, protamine sulfate was administered at half the heparin dose. No cell-savers were used. Two hours after shifting to the ICU, clopidogrel 150 mg and aspirin 150 mg were administered to those patients who had satisfactory drainage.  

The following definitions were used for various hemodynamic and biochemical parameters:

Hypoxia: PaO ₂ of <60 torr with FIO ₂ of 0.4

  Low cardiac output: Clinical criteria of cold peripheries, mean arterial pressure of less than 60 torr, urine output of <0.5 ml/kg/hour, acidosis and a mixed venous saturation of <60%.

  Renal dysfunction: Serum creatinine >1.5 mg%. 

Inotropic usage: Dopamine >5 mcg/kg/min or adrenaline >0.05 mcg/kg/min  

Perioperative myocardial infarction: Development of new Q waves in the ECG or new wall motion abnormalities on echocardiogram or CPK-MB fraction >10% of total CPK. Abnormal potassium: Serum postassium <3 or >5 mEq/L. 

Statistical analysis: Demographic, preoperative clinical features, operative and postoperative data were collected and expressed as percentages/mean and standard deviation wherever applicable. The differences between the two groups were tested with the use of Fisher’s exact test, the Chi-square test, Student’s t test and Mann–Whitney U test. Analysis was peroformed with the use of SYSTAT (version).

The two groups were age-matched. Since there were fewer females in both the groups, the difference was not significant. All the preoperative variables were similar in the two groups except there being more smokers in the OPCAB group.

The operative variables are given in Table 2. The use of arterial conduits, the average number of grafts per patient or the operating time were not influenced by the technique. Because the surgeon made the decision after close inspection of the vessels on the table, there was no conversion in the technique during the procedure.

The postoperative variables are given in Table 3. Some of the often-claimed advantages of OPCAB such as decreased ventilation time, ICU stay, blood drainage and blood product usage are not substantiated by this study. Similarly, the lower incidence of renal and pulmonary dysfunction in the OPCAB group was also not evident in this study. The significant finding of lower incidence of low cardiac output and inotrope usage in the OPCAB group, is probably related to the lesser global myocardial ischemia and therefore edema in the OPCAB group. The WBC count and ESR were compared in the two group as gross evidence of systemic inflammatory syndrome. The rise in the ESR and WBC count was not different between the two groups.

The initial fear regarding patency of the grafts done off-pump has been allayed by many reports.¹ This is largely due to the development of excellent stabilizers such as the Octopus III, Genzyme and CTS Guidant systems. Broadly, there are two types of stabilizers, viz. suction devices and compression devices. The Octopus III is the most widely used system and is based on suction stabilization. The Genzyme and CTS Guidant use compression of the target area for immobilization. The Starfish (Medtronics) and Apical Suction Cone (CTS) may further increase the ease and reach of this technique in the future.

However, the completeness of revascularization is better with on-pump techniques. The reason for incompleteness of revascularization may be small vessel diameter, deep intramyocardial location, diffuse disease or proximal location of the ideal site for anastomosis in the high lateral wall. Since complete revascularization is the most important factor for good long-term results of CABG, there must be sufficient reason to trade for lesser grafts as against CPB support in a given case before embarking overzealously with the OPCAB. The policy of "brain before the heart" may be applicable in a few patients only. With the newer generation of stabilizers, the rate of complete revascularization in the OPCAB group is likely to increase. Cartier et al.² reported 90% and Bedi et al.³ achieved 100% complete revascularization with OPCAB with a negligible rate of conversion. In our experience, with a balanced judgment of all the factors, it is possible to achieve complete revascularization with no conversion to CPB as an emergency.

Off-pump CABG is claimed to have significantly brought down the complications attributed to the use of extracorporeal circulation. The systemic inflammatory syndrome is not peculiar to CPB though the degree of inflammation may be more with the use of CPB.⁴ The organ dysfunction ascribed to the nonpulsatile flow and microembolic load of the CPB have also not been found to be uniformly true. Most papers have reported that complications are fewer with the elimination of CPB but their statistical significance is not marked.^5-7,8 Czerny et al.⁸ have prospectively compared the feasibility of complete revascularization on the beating and still heart and have concluded that the completeness of revascularization is  better with the on-pump technique. Their rate of conversion is high (22.5%). Also, they have not observed any difference in the incidence of bleeding or blood use between the two groups. Bull et al.⁹ compared the morbidity and cost of the two procedures and did not find any significant difference with regard to cost, length of stay or incidence of complications. However, Plomondon et al.¹⁰ found, in a multicentre trial, that an off-pump approach is associated with lower risk-adjusted mortality and morbidity. The neurological complications are not only due to the pump but also because of aortic manipulation.¹¹

The results of OPCAB will not be very different if aortic anastomosis for inflow is used, because it entails partial clamping of the aorta. Epiaortic scanning and clampless proximal aortic anastomosis may contribute greatly to the reduction of stroke when aortic manipulation is unavoidable. Off-pump CABG using a single internal mammary artery (IMA) inflow may circumvent the need for aortic anastomosis. A recent report has allayed our fears about the adequacy of flow of this procedure.¹²

Some of the unsolved problems with OPCAB are the effects of snares, shunts and mister blowers. Hypercoagulabilty in the immediate postoperative period after OPCAB has been documented and vein graft occlusions with patent arterial graft have been reported.¹³ We do not as a rule use any distal snares after a disaster in our early experience wherein there was a perioperative infarct as a clot developed at the site of the distal snare in the postoperative period. Shunts are used if the proximal coronary obstruction is less than critical in an artery >1.5 mm in diameter or if there is ECG or hemodynamic evidence of ischemia after proximal snaring. A shunt is rarely used if the distal back-bleed is substantial so that blood loss can be avoided.

The important finding in this study, which is at variance with many reports in the published literature, is the postoperative blood loss and the need for blood transfusion in the two groups. One of the reasons for this may be that a single surgeon did the entire operation in this study and his method of opening and closure was standardized for both the techniques. The same finding may not hold good when multiple surgeons are involved, with varying methods and standards. However, in the paper by Bull et al.⁹ there was no significant difference in the drainage and usage of blood between the two groups. Meticulous hemostasis and avoidance of blood loss during coronary arteriotomy using a proximal snare reduces blood loss. Periodic measurement of ACT and proper topping-up of heparin rather than administering it periodically will reduce unnecessary over-anticoagulation and bleeding. Though it may be desirable to use a cell-saver to retrieve and re-transfuse all the shed blood, we could not resort to it for financial reasons. If the drainage in patients who were on antiplatelet agents till the date of operation is considered separately, there may be a difference in the blood loss and transfusion requirement between the two groups. This is borne out of a preliminary observation in such patients who do not form a part of this study group. This difference may be attributed to the damage suffered by the already dysfunctional platelets by the CPB circuit.

From the available literature, it is clear that OPCAB is safe and dependable and is as good as ONCAB in low- and moderate-risk cases, albeit with the possibility of lesser number of grafts per patient.¹⁴ The true value of OPCAB may be in the high-risk group. The report of Arom et al.¹⁵ in which the two techniques were compared in a high-risk group, is noteworthy. The operative mortality was 1.1 % for ONCAB and 1.4% for OPCAB in their low-risk group. However, in their high-risk group it was 28.5% and 7.7%, respectively (p=0.008). If other workers corroborate this finding consistently, OPCAB will be a great advancement in the technique for the care of aged high-risk candidates for CABG who are seen more often nowadays. 

Another approach worth considering is to make CPB safer. Reduction of the quantity of prime, improvements in hemocompatibilty of contact surfaces, reduction of blood damage by the pump, etc. are some of the methods being studied.

There are several limitations in this study. It is not a randomized blinded trial, thus leading to a selection bias. It represents the work of a single surgeon, which by design limits its value for general acceptance. The patients in this group were at low risk and the benefit of OPCAB may not be evident in them. The complication rate was low, and to determine differences in outcome between the two groups a very large sample size is required; hence the absence of multivariate analysis of the findings in this study.

Conclusions: The present study demonstrates that OPCAB is as safe as ONCAB in the low- and moderate-risk patients. Our findings do not support the claim of lesser blood loss and blood transfusion in OPCAB. Inotrope usage in compromised hearts is significantly less with the OPCAB technique. Its beneficial role in the high-risk group needs detailed scrutiny although the available trend points to its utility.

The authors are thankful to Dr BN Murthy, Deputy Director, National Institute of Epidemiology (ICMR), Chennai for his assistance in the statistical analysis of the data.

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