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Ann Thorac Surg 2004;78:2057-2062
© 2004 The Society of Thoracic Surgeons

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Original article: cardiovascular

Hemodynamic Changes During Posterior Vessel Off-Pump Coronary Artery Bypass: Comparison Between Deep Pericardial Sutures and Vacuum-Assisted Apical Suction Device

^a Department of Thoracic and Cardiovascular Surgery, Seoul, South Korea
^b Department of Anesthesiology, Clinical Research Institute, Seoul National University Hospital, Seoul, South Korea

Accepted for publication May 19, 2004.

^* Address reprint requests to Dr Kim, Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, 28 Yeun-Kun Dong, Chong-Ro Ku, Seoul 110–744, South Korea
kimkb{at}snu.ac.kr

	Abstract

Top Abstract Introduction Patients and Methods Results Comment References

 
BACKGROUND: Displacement of the heart to expose posterior vessels during off-pump coronary artery bypass may cause hemodynamic derangement. The aims of this study were (1) to elucidate the hemodynamic changes during off-pump coronary artery bypass for the obtuse marginal branch (OM) of the left circumflex artery; and (2) to compare the hemodynamic changes caused by a deep pericardial suture technique with those caused by a vacuum-assisted apical suction device for displacement of the heart.

METHODS: Hemodynamic changes during posterior vessel off-pump coronary artery bypass were studied in a prospective randomized manner. A deep pericardial suture technique (group 1, n = 10) or a vacuum-assisted apical suction device (group 2, n = 10) was used to facilitate the exposure of the OM. Hemodynamic variables such as cardiac index, stroke volume index (SVI), mean arterial pressure, mean pulmonary artery pressure, central venous pressure, pulmonary capillary wedge pressure, heart rate, systemic vascular resistance, pulmonary vascular resistance, left ventricular stroke work index, and right ventricular stroke work index were monitored during off-pump coronary artery bypass. Hemodynamic data were obtained before revascularization of the left anterior descending coronary artery at a baseline (T0), 3 minutes after heart displacement for revascularization of OM (T1), 3 minutes after the beginning of OM grafting (T2), and 3 minutes after the completion of OM grafting and heart repositioning (T3).

RESULTS: There were no significant differences in the baseline hemodynamic variables (T0) between the two groups. In group 1, SVI, cardiac index, left ventricular stroke work index, and right ventricular stroke work index decreased significantly, and central venous pressure and pulmonary capillary wedge pressure increased significantly, during displacement of the heart (T1, p < 0.05). In group 2, SVI decreased significantly, and central venous pressure, pulmonary capillary wedge pressure, and mean pulmonary artery pressure increased significantly during displacement of the heart (T1, p < 0.05). The percent changes of cardiac index, SVI, and right ventricular stroke work index during OM grafting (T2) in comparison with baseline values (T0) were significantly larger in group 1 than in group 2 (cardiac index, 73% ± 12% versus 90% ± 11%; SVI, 69% ± 12% versus 86% ± 8%; right ventricular stroke work index, 30% ± 17% versus 71% ± 25%, in groups 1 versus 2, respectively; p < 0.05).

CONCLUSIONS: Displacement of the heart using either a deep pericardial suture technique or a vacuum-assisted apical suction device caused a significant decrease in SVI. The hemodynamic changes during OM grafting were smaller when using a vacuum-assisted apical suction device.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment References

 
The increased use of off-pump coronary artery bypass (OPCAB) has been aided by technical advances and increased surgical experience but has been limited by the lack of an effective technique for successful grafting of the posterior coronary vessels (branches of the left circumflex artery). To facilitate exposure of the posterior coronary vessels and to overcome hemodynamic derangement during displacement of the heart, specialized surgical techniques and anesthetic support, such as placement of deep pericardial sutures, patient positioning, pharmacologic manipulation, widely opening the right pleura, and, recently, application of a suction-based cardiac positioning device, have been suggested [1–5].

The aims of this study were (1) to elucidate the hemodynamic changes during OPCAB for the obtuse marginal (OM) branch of the circumflex artery; and (2) to compare the hemodynamic changes caused by a deep pericardial suture technique with those caused by a vacuum-assisted apical suction device for displacement of the heart.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment References

 
Twenty patients who underwent elective OPCAB for both the left anterior descending coronary artery (LAD) and OM branch of the left circumflex artery were studied in a prospective randomized manner. Patients who underwent preoperative intraaortic balloon pump placement were excluded from this study. During the study period, none of the patients needed intraoperative intraaortic balloon pump placement or conversion to cardiopulmonary bypass during OPCAB for OM grafting. Patients who consented to participation in the study and met the inclusion criteria were randomized to use of deep pericardial sutures or a vacuum-assisted apical suction device after revascularization of the LAD and immediately before exposure of the OM. We compared the hemodynamic changes of 10 patients in whom a deep pericardial suture technique was used to facilitate the exposure of the OM (group 1) with those of 10 patients in whom a vacuum-assisted apical suction device was used (group 2). Preoperative, intraoperative, and postoperative data were collected and recorded. There were no differences in sex, age, ratio of unstable to stable angina, left ventricular ejection fraction measured by transthoracic echocardiography, and preoperative risk factors, except diabetes, between the two groups (Table 1). All patients stopped taking aspirin the day before surgery and resumed taking aspirin (300 mg/day) at 1 day postoperatively.

Off-Pump Coronary Artery Bypass Technique
All operations were performed through a median sternotomy incision, and a cell-saving device was used routinely. Body temperature was maintained at normothermia using adequate room temperature, warm circulating water blankets, and warm infusion solutions. The patients were anticoagulated with an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time of greater than 300 seconds.

We routinely opened both pleural cavities before dissection of the bilateral internal thoracic arteries (ITAs) to facilitate exposure. After the pericardium was opened and the right pleuropericardial fat pads transected, the pericardial holding sutures were tied only in the left side. To facilitate exposure of the OM, two deep pericardial sutures were placed between the left pulmonary veins and left phrenic nerve, and a moistened gauze pad measuring 10 x 10 cm was placed behind the left ventricle in group 1. In group 2, a vacuum-assisted apical suction device (Xpose Access Device; Guidant, Cupertino, CA) was applied on the apex of heart to elevate and rotate the left ventricle into the midline. The level of vacuum pressure needed to maintain capture of the heart varied between 200 and 250 mm Hg. During displacement of the heart for OM grafting, the operating table was tilted 10 to 20 degrees toward the patient's right side and tilted again 10 to 20 degrees for the Trendelenburg maneuver in all patients. To reduce the amplitude of ventricular wall movement, a compression-type mechanical stabilizer (Ultima Stabilizer; Guidant) was used. After exposure of the coronary artery, vascular control was achieved with an intracoronary shunt (FloCoil Shunt; Guidant) for the LAD revascularization, or with a flow occluder (Florester, Bio-Vascular Inc, Saint Paul, MN) for OM revascularization.

In all patients, the LAD was revascularized first to provide a backup during exposure of the OM. Bilateral ITAs were used for revascularization of the left coronary territory. The right ITA was used to revascularize the LAD by crossing the midline. If the right ITA was too short to reach the left coronary territory or if the left coronary territory could not be completely revascularized with bilateral in situ ITA grafts, a Y graft was constructed before starting the distal anastomoses. In cases of Y graft construction, the right ITA was divided at its proximal section and was anastomosed to the side of the left ITA in a Y fashion.

Protamine was not given at the end of the procedure.

Anesthetic Management and Hemodynamic Monitoring
Anesthesia was induced with midazolam (0.1 mg/kg), etomidate (0.2 mg/kg), vecuronium (0.15 mg/kg), and sufentanil (2 µg/kg), and maintained with midazolam (0.05 mg · kg^–1 · h^–1), vecuronium (0.1 mg · kg^–1 · h^–1), and sufentanil (2.5 µg · kg^–1 · h^–1). Patients were given transfusions to maintain a preoperative level of hematocrit, and were infused with fluid to maintain the central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) to the upper normal limit before pericardial opening. The use of inotropic agents was avoided in most of the patients to maintain the heart rate less than 70 to 80 beats/min. Anesthesia management, including volume loading and placing the patient in the Trendelenburg position, controlled hemodynamic derangement during displacement or manipulation of the heart. Patients received routine monitoring consisting of a five-lead electrocardiograph with ST-segment analysis, radial artery cannulation for pressure and blood gas monitoring, Swan-Ganz pulmonary artery catheter, capillary pulse oximetry, capnography for end-tidal carbon dioxide determination, nasopharyngeal temperature monitoring, and urine output measurement. Hemodynamic variables such as mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), CVP, PCWP, and heart rate (HR) were monitored during OPCAB. Cardiac index (CI) was determined by the thermodilution technique and measured three times at each time point and averaged. Stroke volume index (SVI) was calculated as CI/HR, and systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), right ventricular stroke work index (RVSWI = 0.0136 x [PA – CVP] x SVI) and left ventricular stroke work index (LVSWI = 0.0136 x [MAP – PCWP] x SVI) were calculated using standard formulas. The zero levels for all measurements were corrected whenever the operating table was tilted or repositioned.

Hemodynamic data were obtained before revascularization of the LAD as a baseline (T0), 3 minutes after heart displacement for revascularization of the OM (T1), 3 minutes after beginning of the OM grafting (T2), and 3 minutes after the heart was repositioned (T3). Percent changes of the hemodynamic variables were calculated in reference to each baseline value and compared between the two groups.

Statistical Analysis
Statistical analysis was performed with the SPSS 10.0 software package for Windows (SPSS, Inc, Chicago, IL). Repeated measures analysis of variance (ANOVA) and Wilcoxon signed ranks test were used to assess the significance of differences at each time interval within the groups and between the two groups. All results were expressed as mean ± standard deviation, and a value of p < 0.05 was considered statistically significant.

	Results

Top Abstract Introduction Patients and Methods Results Comment References

 
Hemodynamic Data
There were no differences in any of the baseline hemodynamic variables (T0), including CVP and PCWP that represent preload status of the patient, between the two groups. In group 1, SVI, CI, LVSWI, and RVSWI decreased significantly, and CVP and PCWP increased significantly during displacement of the heart (T1). However, there were no significant changes in MAP, HR, MPAP, SVR, and PVR during displacement of the heart. The LVSWI and RVSWI decreased further during OM grafting (T2). In group 2, SVI decreased significantly, and CVP, PCWP, and MPAP increased significantly during displacement of the heart (T1). However, there were no significant changes in CI, MAP, HR, SVR, PVR, and LVSWI during displacement of the heart. The RVSWI decreased significantly during OM grafting (T2). All the hemodynamic variables returned to baseline in both groups after the heart was repositioned (Table 2).

Postoperative Course
All the patients were extubated the day after surgery, and coronary angiographies were performed in the first postoperative day to evaluate graft patency. No major postoperative complication except atrial fibrillation developed in both groups. There were no significant differences in postoperative atrial fibrillation (2 of 10 versus 2 of 10), peak postoperative creatine kinase-MB level (17 ± 11 versus 15 ± 11 U/L), postoperative ventilator support time (14.4 ± 8.2 versus 17.6 ± 9.2 hours), stay in the intensive care unit (23.6 ± 21.5 versus 20.4 ± 9.2 hours), hospital stay (6.9 ± 1.9 versus 8.1 ± 2.7 days), and early graft patency rate (34 of 34 versus 36 of 36) between the two groups.

	Comment

Top Abstract Introduction Patients and Methods Results Comment References

 
This study reveals two main findings. First, displacement of the heart using a deep pericardial suture technique significantly decreases CI, SVI, LVSWI, and RVSWI, and increases CVP and PCWP. Second, displacement of the heart using a vacuum-assisted apical suction device decreases CI, SVI, and RVSWI to a lesser degree, especially during OM grafting.

The ability to achieve optimal coronary exposure is a primary determinant of successful OPCAB. However, displacement of the heart during OPCAB may impair cardiac function by lowering systemic blood pressure, decreasing stroke volume and cardiac output, reducing the coronary blood flow, and further worsening regional myocardial ischemia; and it may sometimes cause incomplete revascularization [6–8]. Hemodynamic changes during displacement of the heart to expose posterior vessels have been elucidated by animal studies [6, 7]. Those studies demonstrated that vertical displacement of the pig heart induced a reduction in cardiac output and stroke volume that were primarily caused by impaired diastolic expansion of the right ventricle. Use of a mechanical stabilizer may further decrease cardiac output secondary to direct ventricular compression with reduced stroke volume [9, 10]. A more pronounced drop in coronary blood flow in the circumflex coronary artery compared with that in the LAD or right coronary artery was also demonstrated during displacement of the pig heart [11]. Mathison and colleagues [12] demonstrated in their clinical study that there was a significant increase in right ventricular and left ventricular end-diastolic pressures, especially during positioning for the circumflex artery. They suggested that the increase of right ventricular end-diastolic pressure, especially by direct ventricular compression, was the major cause of hemodynamic changes.

Specialized surgical techniques and anesthetic support, such as placement of deep pericardial sutures, patient positioning, pharmacologic manipulation, wide opening of the right pleura, and, recently, application of a suction-based cardiac positioning device, have been developed to permit completion of uncomplicated multiple-vessel OPCAB [1–5]. Preoperative intraaortic balloon pump therapy was also suggested to facilitate posterior vessel OPCAB, especially in high-risk patients [13, 14], on the assumption that it could result in a more favorable myocardial blood supply, increased stroke volume and cardiac output through augmentation of the diastolic pressure, and afterload reduction [15, 16].

Despite much surgical experience with the current OPCAB procedure, significant hemodynamic derangement that necessitates conversion of the procedure to cardiopulmonary bypass continues to occur on occasion [17, 18]. Because the hemodynamic alterations during OPCAB are higher with posterior coronary vessel access [12], the suction-based cardiac positioning device has been used with increasing frequency. Sepic and associates [19] demonstrated that application of the apical suction device during the exposure of posterior vessels in the beating pig heart minimized the hemodynamic changes. They suggested that the apical suction device minimized hemodynamic derangements by maintaining the long-axis dimensions of the ventricles. The drawbacks of the suction-based cardiac positioning device are myocardial hematoma formation over the area of device application, additional medical cost, and partial impairment of cardiac apical contractility.

In the present study, we routinely opened both pleural cavities, transected the right pleuropericardial fat pads, and tied the pericardial holding sutures only in the left side. During displacement of the heart for OM grafting, the operating table was tilted 10 to 20 degrees toward the patient's right side and tilted again 10 to 20 degrees for the Trendelenburg position. The LAD was revascularized first using the ITA to provide a backup during exposure of the OM. In group 1, deep pericardial sutures were placed between the left pulmonary veins and left phrenic nerve to facilitate exposure of the OM. Displacement of the heart decreased SVI, CI, LVSWI, and RVSWI, and increased CVP and PCWP significantly. The LVSWI and RVSWI decreased further during OM grafting. In group 2, a vacuum-assisted apical suction device was applied on the apex of heart to elevate and rotate the left ventricle into the midline. Displacement of the heart decreased SVI, and significantly increased CVP, PCWP, and MPAP. The RVSWI decreased significantly during OM grafting. When the changes of hemodynamic variables were compared between the two groups, the SVI, CI, and RVSWI were decreased more significantly during displacement of the heart and OM grafting in the group 1 patients. During OM grafting, the CI, SVI, LVSWI, and RVSWI were decreased to a lesser degree in the group 2 patients. In spite of those hemodynamic changes in both groups, there were no patients who required intraaortic balloon pump placement or conversion to cardiopulmonary bypass during displacement of the heart for OM grafting in this study. This suggests that the hemodynamic derangement during displacement of the heart could be minimized and overcome by current techniques, such as transection of the right pleuropericardial fat pads, patient positioning, placement of deep pericardial sutures or use of a suction-based cardiac positioning device, anesthetic support, and the strategy of revascularizing the LAD first.

There are limitations of our study that must be recognized. First, this study involved relatively small numbers, although it was performed in a prospective randomized manner. We recognized some variables with less than 60% power for analysis; however, those of SVI, LVSWI, and RVSWI showed greater than 70% power, which seemed to be acceptable for interpretation of the data. Although the changes in CI, SVI, and RVSWI were greater in group 1 patients than in group 2 patients, the hemodynamic status was stable during displacement of the heart in most patients, and none of the patients needed a conversion to cardiopulmonary bypass during OPCAB. More cases will need to be studied to determine the superiority of either method.

In conclusion, displacement of the heart using either a deep pericardial suture technique or a vacuum-assisted apical suction device caused a significant decrease of SVI. The hemodynamic changes during OM grafting were less when a vacuum-assisted apical suction device was used.

	References

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