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Ann Thorac Surg 2003;75:S740-S744
© 2003 The Society of Thoracic Surgeons
a Harrisburg Hospital of the Pinnacle Health System, Harrisburg, Pennsylvania, USA
b Capital Area Cardiovascular Surgical Institute, Camp Hill, Pennsylvania, USA
* Address reprint requests to Dr Hart, Capital Area Cardiovascular Surgical Institute, 423 N 21st St, Camp Hill, PA 17011, USA
e-mail: jchart51{at}earthlink.net
Presented at the 3rd International Symposium on Myocardial Protection From Surgical Ischemic-Reperfusion Injury, Asheville, NC, June 2–6, 2002.
Abstract
Patients presenting for coronary artery bypass (CAB) surgery are now older and have more comorbid conditions. Off-pump (OPCAB) methods may reduce morbidity and mortality in these higher risk patients. Multivessel surgery has been limited by the difficulty in maintaining hemodynamic stability during lateral wall vessel grafting. Techniques for providing safe access to lateral wall vessels were applied in a largely unselected group of 665 OPCAB patients with emphasis on the avoidance of right ventricular compression. Safe access to essentially all target coronary arteries was achieved with very little need for pharmacological or mechanical support. No patient required new intraaortic balloon pumping and no patient required urgent conversion to cardiopulmonary bypass. Access to essentially all target coronary arteries can be achieved and myocardial performance can be maintained when strict attention is paid to operative strategies designed to minimize right-side heart compression.
| Doctor Hart discloses that he has a potential conflict of interest with Medtronic, Inc, and Speakers Bureau.
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Off-pump coronary artery bypass (OPCAB) surgery is being used with increasing frequency in many cardiac centers worldwide [1]. Early proponents of beating heart coronary artery bypass grafting limited their target arteries primarily to anterior wall vessels or to the proximal or middle right coronary artery (RCA) [2]. Lateral wall vessels were much more difficult to approach because of difficult access, limited exposure, and the prohibitive hemodynamic deterioration seen with cardiac displacement. These technical difficulties precluded OPCAB from being practical in most patients with multivessel coronary artery disease. Many surgeons felt that OPCAB could potentially provide substantial improvement in patient outcomes and several centers began to focus on the development of surgical techniques to allow safe access to the lateral wall vessels. This report will describe the author’s experience with OPCAB, focusing on techniques for preservation of hemodynamic variables during cardiac displacement.
Patients and methods
From June 10, 1997, through October 4, 2002, a total of 665 patients underwent OPCAB, representing 90.1% of the author’s CABG volume during that time. After January 1, 1998, 94.1% of CABG surgery was carried out without cardiopulmonary bypass (CPB). Reasons for the use of CPB varied during the time of the study period and included preoperative or intraoperative electrical or hemodynamic instability, inability to safely expose lateral wall vessels, unwillingness to approach intramyocardial, small or diffusely diseased vessels, and reoperative procedures with patent and diseased saphenous vein grafts. Demographic data, operative details, and early postoperative outcomes were prospectively entered into a locally maintained database and were retrospectively reviewed (Table 1).
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Every effort is made to avoid the need for pharmacologic support of the circulation. With proper cardiac positioning and individualized sequencing of grafting, the need for inotropic or vasopressor support has been minimized. Small boluses of neosynephrine are used to support blood pressure when necessary. Continuous infusion of vasoactive agents has seldom been used.
Operative techniques
After June 1997 a commercially available, suction-based coronary artery stabilizer (Medtronic Octopus 1, 2, 2+, 3, or 4; Medtronic, Inc, Minneapolis, MN) has been used for target artery immobilization in all OPCAB cases. Various surgical maneuvers are used to maintain hemodynamic stability, allowing for unhurried, precise anastomoses in virtually all target arteries. Anterior vessels and RCA targets are easily approached using previously described techniques [3]. Lateral wall anastomoses require strict attention to surgical details to allow for hemodynamic stability [4–6].
Many patients have been pretreated with ß-adrenergic blocking agents preoperatively and are bradycardic. During early attempts at beating heart CABG, slow heart rates were felt to be advantageous. However, with the excellent mechanical stabilization achieved with current suction stabilizers, bradycardia is not required. Decreases in cardiac output and systemic blood pressure during cardiac dislocation are partially caused by diminished stroke volume so temporary atrial pacing is used to help maintain cardiac output in bradycardic patients [7].
The following techniques all are used with the intent to minimize right-side heart compression during cardiac displacement for lateral vessel grafting. Unlike early attempts at cardiac tilting with the apex elevated outside of the chest, every effort is made to allow the heart to drop posteriorly in the chest and then to have the heart rotate into the right chest cavity attempting to avoid cardiac compression against the pericardium or the right hemisternum.
To allow for this posterior rolling of the heart the retrosternal musculofascial insertions to the posterior part of the inferior sternum are divided, allowing the mediastinum to drop posteriorly. A sternal spreading retractor that allows a lifting action on the right hemisternum is used, making more space for the heart to drop under the edge of the sternum.
The right pleural space is opened widely in virtually all patients needing lateral wall grafting. The right pleuropericardial fat pad is then removed using cautery, again to make more space for the apex to enter the right chest cavity.
Early attempts at cardiac displacement into the right chest cavity were impeded by the right pericardium. Currently the right pericardium is incised from its attachment to the diaphragm in a posterior direction. This incision is carried posteriorly nearly to the inferior vena cava while avoiding the identified phrenic nerve. With the right pericardial flap free to fold into the right chest, the heart has an unrestricted path to rotate behind the sternum into the pleural space without significant compression. Moderate right lateral decubitus positioning at 30 to 45 degrees allows for gravity-assisted rotation of the heart rightward and seems to preserve hemodynamics [8]. Trendelenberg positioning for augmentation of preload, popularized early in the development of OPCAB, is used sparingly as significant increases in central venous pressure may actually impair perfusion of secondary vascular beds by reducing perfusion pressure [9]. Deeply placed left pericardial stay sutures or fabric slings anchored in the oblique sinus are also used to assist gravity in cardiac displacement. Figure 1 shows a heart fully rotated into the right chest with the apex resting on the dome of the right hemidiaphragm with excellent exposure and access to the marginal branches of the circumflex coronary artery. This position reliably maintains hemodynamics. Over the last 12 months a suction-based cardiac positioning device has been used with increasing frequency (Starfish; Medtronic, Inc, Minneapolis, MN). These devices are purported to help in maintaining hemodynamics by maintaining the long axis dimension of the ventricles [10].
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Test occlusion of each target artery is undertaken for 5 minutes, watching for signs of electrocardiographic or hemodynamic deterioration. Significant changes are very unusual but, when encountered, will occur within 2 or 3 minutes. Restoration of flow and return to base line hemodynamics permits alterations in plans such as adding an intracoronary shunt, changing the order of grafting, or optimization of cardiac positioning. Intracoronary shunting is used sparingly (fewer than 5% of anastomoses), most often during grafting of large RCA vessels with only moderate proximal stenosis or when the target artery test occlusion is not tolerated.
Preoperative intraaortic balloon pumps have been placed for stabilization of symptoms in some patients but have been placed preoperatively for mechanical support to allow OPCAB in only 2 patients. Intraoperative right ventricular assistance with a small pump (AMED, West Sacramento, CA) was used on a trial basis in 3 patients.
Results
These 665 patients received a mean of 2.51 ± 0.90 grafts per patient (single 17.4%, double 28.3%, triple 41.2%, quadruple or more 13.1%). Multivessel disease patients received an average of 2.83 grafts. In the current calendar year patients received an average of 3.1 grafts. Internal thoracic artery grafts were used in 97.7% of patients. In the most recent year 68% of grafts have been arterial. A total of 473 grafts were constructed to intermediate ramus or circumflex marginal branches. Complication rates were low and are shown in Table 2. No patient suffered perioperative ascending aortic dissection. Operative mortality was likewise low at 1.20%.
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Six patients (0.9%) required hemodialysis or hemofiltration that were not on dialysis preoperatively. All 6 had abnormal renal function preoperatively and none required dialysis permanently. In 2 patients intestinal ischemia developed and required operative resection and both survived.
In the first 12 months of the study period several patients were converted to CPB and global cardioplegic arrest. Reasons for conversion were inability to accomplish lateral wall grafting, intolerance to target artery occlusion, or inability to expose intramyocardial coronary arteries. In the last 42 months 2 patients were converted to CPB-supported beating heart CABG. One of these patients was having reoperative surgery and target artery exposure could not be accomplished without CPB support. In the other patient lateral wall exposure could not be accomplished without unacceptable hemodynamic deterioration. All of these conversions were nonurgent and all converted patients survived without major complications.
Strict attention to anesthetic management, grafting sequence strategy, cardiac positioning and other operative details can assure hemodynamic stability during OPCAB surgery. Aggressive pharmacological support or intraoperative mechanical assistance is rarely necessary. The large majority of CABG patients can be safely approached and essentially all target vessels can be accessed. Urgent conversion to CPB can be avoided. Myocardial function can be preserved with little need for inotropic support leaving the operating room and the need for new IABP should be rare.
Comment
For OPCAB to be viable, graft patency rates and levels of revascularization must equal those achieved with arrested heart techniques. Maintenance of optimal hemodynamics, even in patients with impaired left ventricular function, can almost always be achieved and allows for precise unhurried anastomoses under ideal conditions, maximizing the chance for successful revascularization. Inattention to detail is likely to result in hemodynamic instability, hurried and imprecise anastomoses, altered secondary organ perfusion and inferior outcomes [11].
Grundeman and associates [7] studied the hemodynamic consequences of verticalization of the heart using suction stabilization in a porcine model. They demonstrated a 30% drop in cardiac output and mean arterial blood pressure, primarily related to a reduction in stroke volume. In an elegant echocardiographic analysis of their hemodynamic findings they identified impaired right ventricular filling as the primary cause of the observed abnormalities [12]. Augmentation of preload using 25 to 30 degrees of Trendelenberg position returned blood pressure and cardiac output to near base line levels at the expense of increased central filling pressures. Early practitioners of multivessel OPCAB relied primarily on this technique to help preserve hemodynamics during cardiac displacement. Access was still difficult and hemodynamic stability was unpredictable. Pharmacologic support with inotropic or pressor agents or both was frequently necessary, often at the expense of reduced cardiac output.
Burfeind and associates [13] assessed left ventricular function during compression stabilization of the left anterior descending coronary artery (LAD) in pigs and demonstrated significant reduction in cardiac output (4.2 L/min to 3.6 L/min). The authors believed that this fall in cardiac output was likely secondary to the left ventricular deformation caused by compression stabilization.
Mathison and associates [14] offered the first clinical evaluation of hemodynamic changes during OPCAB. Sternotomy incisions were used for multivessel OPCAB in 44 consecutive patients. After base line hemodynamic measurements, hearts were positioned for anterior, lateral obtuse marginal branch (OM), or posterior descending anastomoses. Hemodynamic status was optimized and measurements were repeated. There were demonstrable hemodynamic alterations in all three regions, with lateral wall access producing the most significant changes. There was evidence for biventricular failure, more pronounced on the right side. Unlike the porcine model, augmentation of preload with Trendelenberg’s positioning did not reliably normalize cardiac output.
Nierich and associates [15] reported on a similar group of 150 patients undergoing beating heart CABG (54 through anterolateral thoracotomy and 96 through midline sternotomy). Stabilization was accomplished with a suction stabilizer, avoiding left ventricular compression. When compared with LAD and RCA vessels OM anastomoses produced more hemodynamic alterations and required more frequent use of Trendelenberg’s position or inotropic support or both. Overall there was no clinically significant deterioration of global circulation when managed as described.
Watters and associates [16] reported on their technique of OPCAB using a sling technique for cardiac displacement and a reusable mechanical compression stabilizer. Twenty-nine patients having multivessel OPCAB were studied. No patient had a history of myocardial infarction within 1 month of the procedure and all patients had left ventricular ejection fractions (LVEF) of at least 40%. During occlusion and coronary grafting, intraluminal shunts were routinely employed. The hemodynamic results of this study echoed those described above. There were target vessel-dependent changes in filling pressures, stroke volume, and cardiac index that were most pronounced during exposure of circumflex marginal branches. These changes rapidly reversed with return of the heart to anatomical position and were clinically well tolerated.
Grundeman and associates [17] demonstrated that coronary artery blood flow is linearly dependent upon mean aortic pressure (MAP) during cardiac displacement. If MAP is not maintained by proper positioning techniques the reduction in coronary artery blood flow can produce regional or global myocardial dysfunction. The resultant drop in cardiac output and MAP will perpetuate a dangerous spiral of worsening hemodynamics and can lead to life-threatening acute circulatory failure. The resultant need for emergent conversion to CPB support is likely to result in adverse outcome and must be avoided [11].
Several forms of mechanical support have been described to facilitate beating heart surgery. Guyton [18] reported on the selective use of perfusion assisted OPCAB (PADCAB). This technique withdraws blood from the ascending aorta through a small pump-assisted circuit and provides perfusion to distal coronary beds though the arteriotomy or through completed grafts. The proposed advantage to this system is the ability to control flow rates through the distal perfusion arms independent of mean aortic pressure. Precise doses of chemical additives can be delivered to the myocardium through the perfusate giving the opportunity to alter local myocardial biochemistry. In a small clinical trial Vassiliades and associates [19] reported that active perfusion of grafts seemed to offer some myocardial protection compared with passive or no perfusion. Craver and Murrah [20] have reported on the elective use of intraaortic balloon pumping for higher risk OPCAB patients to minimize the effects of regional ischemia and cardiac displacement. Several authors have described the use of temporary right ventricular assist pumps (RVAD) during OPCAB procedures [21].
Routine shunting of target arteries is advocated by some. Preservation of some nutrient flow into distal beds may enhance myocardial performance during construction of distal anastomoses and reperfusion injury if present may be attenuated [22]. Concern exists that routine intracoronary shunting may result in endothelial injury or dysfunction [23]. Bedi and associates [24] have described the use of retrograde coronary sinus perfusion during target artery occlusion to minimize the risk of regional or global ischemia.
Surgeons, referring physicians, and patients have become more interested in the avoidance of CPB for CABG. Safe and reliable access to lateral and posterior wall vessels must be available to surgeons if OPCAB is to have an important role in surgical myocardial revascularization. Strict attention to the details of planning and execution of beating heart procedures has become increasingly important. By avoiding right-side heart compression with the techniques described above, hemodynamics can be preserved thereby maintaining cerebral, renal, gut, and myocardial perfusion. Only when these objectives are met can OPCAB patients enjoy maximum safety during their procedures with potentially improved outcomes.
References
This article has been cited by other articles:
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  P. Pepino, P. Oliviero, F. Petteruti, L. di Tommaso, M. Monaco, and P. Stassano Left Heart Pump-Assisted Beating Heart Coronary Surgery in High-Risk Patients Asian Cardiovasc Thorac Ann, April 1, 2008; 16(2): 159 - 161. [Abstract] [Full Text] [PDF]
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