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Routine Off-Pump Coronary Artery Bypass: Reasons for On-Pump Conversion

Hirose, Hitoshi MD, FACS; Amano, Atsushi MD

Innovations: Technology & Techniques in Cardiothoracic & Vascular Surgery: Fall 2005 - Volume 1 - Issue 1 - pp 28-31
Review Articles: Original Articles

Objective: To assess the feasibility of routine off-pump coronary artery bypass (OPCAB) and investigate risk factors for on-pump conversion.

Methods: Between July 1, 2002, and June 30, 2004, OPCAB was attempted for all patients who required isolated coronary artery bypass in our institution. The perioperative results of patients were prospectively entered into a structured database, and the results were analyzed to identify the risks of requirement for cardiopulmonary bypass.

Results: Off-pump coronary artery bypass was successfully performed in all but 9 patients, giving an OPCAB success rate of 97.3% (329/338). The reason for cardiopulmonary bypass was hemodynamic instability occurring during reoperative surgery in 7, and cardiogenic shock in 2. The OPCAB success rate was significantly higher in primary coronary artery bypass grafting (99.3%, 314/316) than in reoperative coronary artery bypass grafting (68.1%, 15/22; P < 0.0001), and higher in patients without cardiogenic shock (97.9%, 329/336) than in those with cardiogenic shock (0%, 0/2; P = 0.0005). Mean number of distal anastomoses performed under OPCAB was 3.5 ± 1.4. There were 2 hospital deaths (0.6%). During a mean follow-up period of 1.0 ± 0.4 years, 7 patients developed angina, which was treated with catheter intervention; there were no other cardiac events.

Conclusion: Routine OPCAB is feasible with acceptable short-term results. Patients undergoing reoperation or in persistent cardiogenic shock are more likely to require conversion to on-pump coronary artery bypass grafting.

From the Department of Cardiovascular Surgery, Juntendo University Hospital, Tokyo, Japan.

Dr. Hirose is currently affiliated with the Department of Cardiothoracic Surgery, Drexel University College of Medicine, Philadelphia, PA.

Address correspondence and reprint requests to Hitoshi Hirose, MD, FACS, Dept. Cardiothoracic Surgery, Drexel University, College of Medicine, Broad & Vine Street, Philadelphia, PA; e-mail:

The advantages of off-pump coronary artery bypass (OPCAB) grafting compared with on-pump coronary artery bypass (ONCAB) include less systemic inflammatory response, better neurologic outcome, lower blood transfusion requirement, and shorter length of postoperative recovery period.1–5 The disadvantages of OPCAB are always related to technical limitation and include incomplete revascularization, especially for the posterior or lateral wall of the heart, and quality of anastomosis. However, the development of new devices and techniques for OPCAB allow us to perform multivessel OPCAB safely.6,7 Since we moved into our current institution in July 2002, OPCAB has been performed routinely, regardless of the anatomy of the coronary lesions, urgency of surgery, or status of reoperations. This study investigated the feasibility of the routine OPCAB and analyzed the risk factors of on-pump conversion

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Perioperative and remote data of patients who underwent cardiac surgery at Juntendo University Hospital were prospectively entered into a structured database since staff surgeons moved to Juntendo University in July 2002. All patients, except those requiring valvular or left ventricular surgery, were scheduled for OPCAB rather than ONCAB. Informed consent was obtained from patients before surgery, and all patients were advised of the possibility of intraoperative conversion to ONCAB. No patient was excluded from this study based on pattern of coronary artery disease, urgency of surgery, or status of reoperation. Between July 1, 2002, and June 30, 2004, a total of 338 consecutive isolated coronary artery bypass grafting (CABG) procedures were performed in our institution, and the demographic data are shown in Table 1. There were no patients in cardiogenic shock requiring salvage operation in our series. The mean EuroSCORE8 was 4.1 ± 3.1 (range 0–17), and the predicted mortality rate was 4.6 ± 7.8% (range 0.8–70.7).

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All patients underwent midline sternotomy, with the exception of patients undergoing mini left thoracotomy for single vessel revascularization (n = 34) of the left anterior descending artery (LAD) using the left internal mammary artery. Cardiopulmonary bypass and perfusionists were on standby without priming the pump. After harvest of appropriate conduits, the target vessels were examined. Distal anastomoses were performed using a suction-type coronary stabilizer (Octopus III or IV, Medtronic, Minneapolis, MN). Posterior wall exposure was facilitated with the placement of retropericardial sutures and with the patient in a Trendelenburg position. The usual order of bypass was posterior wall, lateral wall, and anterior wall. For unstable angina with a culprit lesion in the LAD or with a left main lesion, the LAD was anastomosed first with one of the internal mammary arteries (IMAs). Electrocardiographic changes during local occlusion or high-flow coronary arteries were an indication for intracoronary shunt. The bypass conduits and targets were based on the patient’s coronary anatomy; however, in general, LAD was bypassed with one of the IMAs, the right coronary artery was bypassed with the gastroepiploic artery, and the circumflex artery was bypassed with the radial artery or saphenous vein, as described previously.9

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Data Collection

Perioperative data was prospectively collected. Outpatient follow-up was completed by the end of October 2004 by reviewing the medical record or contacting the primary cardiologist of the patient. Remote myocardial infarction, angina, arrhythmia requiring hospitalization, congestive heart failure requiring hospitalization, coronary reintervention, and sudden death were defined as cardiac events. Catheterization at 1 year was recommended for patients being followed up at our institution1 regardless of symptoms. All symptomatic patients were evaluated by catheterization. A total of 59 patients (7 symptomatic patients and 42 asymptomatic patients) underwent postoperative angiography at 1 year (0.8 ± 0.4)1 and results were analyzed.

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Statistical Analysis

Results are expressed as the mean and standard deviation or number and percentage, as appropriate. Statistical analysis was performed using the t test for continuous variables or chi-square tests (Fisher’s exact tests if n < 5) for categorical variables if needed. All statistical analyses were carried out by JMP version 5 (SAS, Cary, NC).

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Off-Pump Coronary Artery Bypass

Among 338 consecutive patients, 9 patients required conversion to ONCAB, giving OPCAB success rate of 97.3% (329/338). Of these cases requiring cardiopulmonary bypass support, 7 involved reoperation (2 patients sustained graft injury during chest re-entry, and the others had dense adhesion that prevented dissection of the heart without decompression using cardiopulmonary bypass) and 2 had unstable angina and developed cardiogenic shock after induction of anesthesia. Three reoperation patients were cannulated from the groin1 but the other patients were cannulated from the ascending aorta and right atrium in a standard fashion. All 9 patients who required cardiopulmonary bypass completed CABG without clamping the aorta and recovered without any postoperative complications. The OPCAB success rate was significantly higher in primary CABG (99.3%, 314/316) than in reoperative CABG (68.1%, 15/22; P < 0.0001), and in patients without cardiogenic shock (97.9%, 329/336) than in those with cardiogenic shock requiring cardiopulmonary resuscitation (0%, 0/2; P = 0.0005).

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Surgical Results

Surgical results of 338 patients initially scheduled for OPCAB are shown in Table 2. There were 2 hospital deaths (0.6%); 1 death was due to arrhythmia related to perioperative myocardial infarction and the another was due to multiorgan failure. The major complications are listed in Table 3. The incidence of each major complication was less than 1.5%. Intubation time, intensive care unit stay, and postoperative stay were 6.5 ± 9.1 hour, 2.1 ± 1.8 days, and 12.2 ± 8.5 days, respectively. The mean in-hospital rehabilitation was 5.5 ± 6.3 days.

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Remote Results

Postoperative follow-up was completed for all patients with a mean follow-up period of 1.0 ± 0.4 years. There were 2 noncardiac remote deaths. Seven patients developed angina recurrence. Among them, five patients were related to graft failure and two were related to de novo native coronary artery disease. All patients with angina recurrence were successfully treated by catheter interventions. No cases of myocardial infarction, congestive heart failure, or arrhythmia were observed. Overall cardiac event-free rate was 97.9% (329/336). Postoperative angiography at 1 year in 7 symptomatic patients and 42 asymptomatic patients showed a perfect anastomosis (without any stenosis) patency rate of 93.4%: left IMA 94.8% (55/58), right IMA 93.0% (14/15), radial artery 92.4% (61/66), gastroepiploic artery 93.3% (28/30), and saphenous vein 100% (10/10). The anastomosis to the LAD graft was perfect in 96.7% (57/59) and patent in 100% (59/59) of patients.

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In our series, transient hemodynamic instabilities were occasionally observed; however, most patients tolerated OPCAB, including that performed by revascularizing the LAD with the IMA, placing a shunt tube, giving more fluid, administering vasoconstrictors, or repositioning the heart. In our series, only 2 patients undergoing primary CABG experienced ischemic changes in the distribution of a culprit vessel and developed cardiogenic shock after induction of the anesthesia. We believe patients experiencing cardiogenic shock requiring cardiopulmonary resuscitation should be placed on cardiopulmonary bypass for salvage. Otherwise all primary CABG can be accomplished by OPCAB, including emergency cases or patients with left main stenoses.10refA

Injury to a patent graft was the major cause of hemodynamic intolerance in reoperative cases. It is known to occur in 2% to 5% of reoperative cases and to cause abrupt hemodynamic collapse.11 Under these circumstances, cardiopulmonary bypass should be initiated without any delay. Other situations requiring cardiopulmonary bypass for reoperative surgery include dense adhesion and risk of injury to the heart or previous graft. Decompression of the heart by cardiopulmonary bypass makes dissection easier and safer. Once the heart is dissected completely, the remaining part of CABG can be performed without clamping the aorta under on-pump conditions.refB In our series, reoperation was a major risk factor for on-pump conversion; thus, cardiopulmonary bypass should always be standing by during reoperative OPCAB. Our conversion rate to ONCAB was 0.6% in primary surgery and 31.9% in reoperative cases. These numbers are within an acceptable range: 2% in the SMART study involving patients undergoing primary operation only5 and 9.8% by the European randomized OPCAB study including reoperation.12

Perioperative mean EuroSCORE in our study was 4.1 ± 3.11 and its predicted mortality rate was 4.6%. Our mortality rate after OPCAB (0.6%) was far below the predicted rate and other postoperative complications were minimal. Within our limited follow-up, angina recurrences were not common. A previous randomized study showed a lower distal anastomosis patency rate in the OPCAB group than the ONCAB group, suggesting a possible poor anastomosis quality under OPCAB compared with that under ONCAB.13 However, our angiographic results at 1 year were satisfactory (overall perfect anastomosis patency rate of 93.4%).

This study of OPCAB has several limitations. First, this was a retrospective, nonrandomized, single-center study, although the data were collected in a prospective manner. In fact, our policy of systematic OPCAB prohibited randomization of the patients to ONCAB. Second, the number of patients requiring on-pump conversion in this study was small, which may have limited the analysis of risk factors for on-pump conversion. Third, we did not compare the results of OPCAB with the historical cohort of on-pump CABG, because on-pump CABG was only performed for patients requiring valve or ventricular surgery in our institution since our staff surgeons moved to the current hospital in July 2002. Fourth, the postoperative stay in Japan may be longer than that in reports from western countries because of differences in cultural background. Patients, except for a few patients who were referred from a chronic rehabilitation facility, were kept in the hospital until completion of in-hospital rehabilitation. Fifth, the number of the participants for postoperative angiography at 1 year was small because most patients remained asymptomatic.

In conclusion, systematic OPCAB is feasible and its clinical outcome was satisfactory. Conversion to ONCAB can be expected in reoperation. Patients in cardiogenic shock requiring cardiopulmonary resuscitation should be immediately placed on cardiopulmonary bypass for life-saving purposes.

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Off-pump coronary artery bypass; On-pump conversion; Coronary artery bypass; Mortality and morbidity; Off-pump

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