Patency and the Pump ¡ª The Risks and Benefits of Off-Pump CABG
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《新英格兰医药杂志》
In 1883, the eminent Viennese surgeon Theodor Billroth declared, "Let no man who hopes to retain the respect of his medical brethren dare to operate on the human heart." Billroth articulated what was at that time common knowledge. The heart was the impenetrable temple of life, the violation of which would result in certain death for the patient. Despite an increasing appreciation and understanding of cardiac pathology, surgery on the heart was an absolute noli me tangere until the middle part of the 20th century.
The heart¨Clung machine, which maintains perfusion to the body while the heart is stopped during cardiac surgery, is arguably among the greatest medical advances of the last millennium. Congenital, valvular, and atherosclerotic heart disease can now be repaired in and on the arrested heart. Coronary-artery bypass grafting (CABG) involving the use of a pump oxygenator continues to be the gold standard of treatment for patients with severe three-vessel coronary artery disease and stenosis of the left main coronary artery. CABG is a highly effective therapy that reduces the risks of myocardial infarction and death while improving the quality of life for patients with coronary artery disease. During the past decade, even patients of advanced age and patients with increasingly complex coexisting conditions that were previously considered to be contraindications to heart surgery have begun to be offered the option of CABG. Despite its proven benefits, CABG can occasionally result in devastating or debilitating outcomes. The prevailing myth is that the heart¨Clung machine remains a double-edged sword: although it permits surgeons to penetrate the physiological barriers of the heart, it can also wound or kill patients with reckless abandon.
The advent of and advances in "off-pump" CABG offered hope that patients could receive the benefits of long-lasting surgical CABG without incurring the risks associated with the use of the pump. Yet any intervention, particularly one performed in patients with heart disease, has associated risks. CABG, with or without the pump, is no different. The mortality associated with conventional CABG (1 to 3 percent) is amazingly low, given the complexity of the operation. Patients with disease of the cerebrovascular, pulmonary, renal, or coagulation system or with atherosclerotic aortas appear to have the highest rates of complications and death.
With conventional ("on-pump") CABG, the aorta and heart are cannulated for connection to the extracorporeal pump, which maintains perfusion to the body. The ascending aorta is clamped, and the heart is stopped (arrested) by cardioplegia. This technique allows for the retraction of the heart and the use of microsurgical techniques for sewing arterial or venous conduits to affected coronary arteries measuring 1 to 2 mm in diameter. These anastomoses are constructed in a still, bloodless field, permitting the optimization of the precision and presumably the patency of the bypasses. With off-pump CABG, the heart continues to beat and provides perfusion to the body throughout the procedure. The use of retraction and stabilizing devices allows the coronary arteries to be exposed while adequate blood pressure and cardiac output are maintained (see Figure). The individual coronary arteries are occluded, and the anastomoses are created with the same suture technique used in conventional CABG. The access to and stabilization of the coronary-artery targets during off-pump CABG are the critical factors determining the degree of difficulty of the procedure and perhaps the technical outcome (i.e., patency) of the anastomoses.
Figure. Photograph Showing the Surgical Field Used for Off-Pump Coronary-Artery Bypass Grafting to the Anterior Descending Coronary Artery.
A suction device attached to the apex of the heart exposes the coronary arteries; a second device exerts stabilizing force on a segment of the artery that is receiving the bypass ¡ª in this case, with the use of the left internal thoracic artery.
In a prospective, randomized comparison of off-pump and on-pump multivessel CABG reported in this issue of the Journal (pages 21¨C28), Khan et al. found that off-pump CABG was as safe as conventional CABG but that the proportion of the bypass grafts that were patent at three months was significantly lower in the off-pump group than in the on-pump group. Is there a biologic advantage that is conferred by the pump, or is there a deleterious effect of the retraction and stabilization during off-pump CABG that could account for these findings? There are physiological derangements resulting from the use of the pump that temporarily diminish coagulation function, possibly decreasing the risk of anastomotic thrombosis and graft occlusion; most of the hematologic consequences of the pump can be reproduced pharmacologically. Improvements in the stabilizing devices and experience with off-pump CABG techniques can improve the surgeon's ability to optimize the exposure of the coronary arteries and the performance of the technically demanding anastomoses.
It is extremely difficult to compare and draw conclusions about highly technical procedures. Results are dependent not only on the soundness of the technique, but also on the ability of the surgeon performing the procedure. Off-pump CABG is a highly demanding procedure with a long learning curve that surgeons should attempt only after mastering conventional CABG. There have been several comparisons of off-pump and conventional CABG that showed no difference in the rate of graft patency between the two treatment groups. Currently, some cardiac surgeons perform nearly all of their CABG procedures with the use of the off-pump technique, with excellent results. Other cardiac surgeons use off-pump CABG selectively, and still others never use it at all. Most CABG procedures continue to be performed with the use of the heart¨Clung machine. Off-pump CABG may not be the best option for all patients or for all cardiac surgeons. Patients with small, intramyocardial, diffusely diseased, or calcified coronary arteries may be best treated with the use of conventional CABG. Cardiac surgeons should embrace off-pump surgery as an important option that must be mastered with the same technical precision as conventional CABG.
The management of ischemic heart disease has evolved dramatically over the past two decades. Risk-factor modification, statins, percutaneous interventions, and surgical strategies have all improved the length and quality of life among patients with coronary artery disease. The surgical treatment options must be tailored to each patient in order to optimize the benefits and minimize the risk of detrimental effects. In deciding whether or not to use the pump, surgeons should consider which intervention will maximize the long-term benefits of coronary-artery revascularization while minimizing the risks. Off-pump CABG is a valuable technique that may benefit patients with coronary artery disease who are at high risk for pump-related complications ¡ª particularly patients with diffusely diseased aortas, pulmonary disease, hepatic dysfunction, or bleeding diatheses. Methods of treatment should not compete for patients but should be selected according to individual patients' needs in order to optimize their care.
Source Information
From the Division of Cardiac Surgery, Massachusetts General Hospital, Boston.
This article has been cited by other articles:
Chukwuemeka, A., Weisel, A., Maganti, M., Nette, A. F., Wijeysundera, D. N., Beattie, W. S., Borger, M. A. (2005). Renal Dysfunction in High-Risk Patients After On-Pump and Off-Pump Coronary Artery Bypass Surgery: A Propensity Score Analysis. Ann. Thorac. Surg. 80: 2148-2153
Aoki, J., Ong, A. T.L., Hoye, A., van Herwerden, L. A., Sousa, J. E., Jatene, A., Bonnier, J. J.R.M., Schonberger, J. P.M.A., Buller, N., Bonser, R., Lindeboom, W., Unger, F., Serruys, P. W. (2005). Five year clinical effect of coronary stenting and coronary artery bypass grafting in renal insufficient patients with multivessel coronary artery disease: insights from ARTS trial. Eur Heart Journal 26: 1488-1493(Thomas E. MacGillivray, M)
The heart¨Clung machine, which maintains perfusion to the body while the heart is stopped during cardiac surgery, is arguably among the greatest medical advances of the last millennium. Congenital, valvular, and atherosclerotic heart disease can now be repaired in and on the arrested heart. Coronary-artery bypass grafting (CABG) involving the use of a pump oxygenator continues to be the gold standard of treatment for patients with severe three-vessel coronary artery disease and stenosis of the left main coronary artery. CABG is a highly effective therapy that reduces the risks of myocardial infarction and death while improving the quality of life for patients with coronary artery disease. During the past decade, even patients of advanced age and patients with increasingly complex coexisting conditions that were previously considered to be contraindications to heart surgery have begun to be offered the option of CABG. Despite its proven benefits, CABG can occasionally result in devastating or debilitating outcomes. The prevailing myth is that the heart¨Clung machine remains a double-edged sword: although it permits surgeons to penetrate the physiological barriers of the heart, it can also wound or kill patients with reckless abandon.
The advent of and advances in "off-pump" CABG offered hope that patients could receive the benefits of long-lasting surgical CABG without incurring the risks associated with the use of the pump. Yet any intervention, particularly one performed in patients with heart disease, has associated risks. CABG, with or without the pump, is no different. The mortality associated with conventional CABG (1 to 3 percent) is amazingly low, given the complexity of the operation. Patients with disease of the cerebrovascular, pulmonary, renal, or coagulation system or with atherosclerotic aortas appear to have the highest rates of complications and death.
With conventional ("on-pump") CABG, the aorta and heart are cannulated for connection to the extracorporeal pump, which maintains perfusion to the body. The ascending aorta is clamped, and the heart is stopped (arrested) by cardioplegia. This technique allows for the retraction of the heart and the use of microsurgical techniques for sewing arterial or venous conduits to affected coronary arteries measuring 1 to 2 mm in diameter. These anastomoses are constructed in a still, bloodless field, permitting the optimization of the precision and presumably the patency of the bypasses. With off-pump CABG, the heart continues to beat and provides perfusion to the body throughout the procedure. The use of retraction and stabilizing devices allows the coronary arteries to be exposed while adequate blood pressure and cardiac output are maintained (see Figure). The individual coronary arteries are occluded, and the anastomoses are created with the same suture technique used in conventional CABG. The access to and stabilization of the coronary-artery targets during off-pump CABG are the critical factors determining the degree of difficulty of the procedure and perhaps the technical outcome (i.e., patency) of the anastomoses.
Figure. Photograph Showing the Surgical Field Used for Off-Pump Coronary-Artery Bypass Grafting to the Anterior Descending Coronary Artery.
A suction device attached to the apex of the heart exposes the coronary arteries; a second device exerts stabilizing force on a segment of the artery that is receiving the bypass ¡ª in this case, with the use of the left internal thoracic artery.
In a prospective, randomized comparison of off-pump and on-pump multivessel CABG reported in this issue of the Journal (pages 21¨C28), Khan et al. found that off-pump CABG was as safe as conventional CABG but that the proportion of the bypass grafts that were patent at three months was significantly lower in the off-pump group than in the on-pump group. Is there a biologic advantage that is conferred by the pump, or is there a deleterious effect of the retraction and stabilization during off-pump CABG that could account for these findings? There are physiological derangements resulting from the use of the pump that temporarily diminish coagulation function, possibly decreasing the risk of anastomotic thrombosis and graft occlusion; most of the hematologic consequences of the pump can be reproduced pharmacologically. Improvements in the stabilizing devices and experience with off-pump CABG techniques can improve the surgeon's ability to optimize the exposure of the coronary arteries and the performance of the technically demanding anastomoses.
It is extremely difficult to compare and draw conclusions about highly technical procedures. Results are dependent not only on the soundness of the technique, but also on the ability of the surgeon performing the procedure. Off-pump CABG is a highly demanding procedure with a long learning curve that surgeons should attempt only after mastering conventional CABG. There have been several comparisons of off-pump and conventional CABG that showed no difference in the rate of graft patency between the two treatment groups. Currently, some cardiac surgeons perform nearly all of their CABG procedures with the use of the off-pump technique, with excellent results. Other cardiac surgeons use off-pump CABG selectively, and still others never use it at all. Most CABG procedures continue to be performed with the use of the heart¨Clung machine. Off-pump CABG may not be the best option for all patients or for all cardiac surgeons. Patients with small, intramyocardial, diffusely diseased, or calcified coronary arteries may be best treated with the use of conventional CABG. Cardiac surgeons should embrace off-pump surgery as an important option that must be mastered with the same technical precision as conventional CABG.
The management of ischemic heart disease has evolved dramatically over the past two decades. Risk-factor modification, statins, percutaneous interventions, and surgical strategies have all improved the length and quality of life among patients with coronary artery disease. The surgical treatment options must be tailored to each patient in order to optimize the benefits and minimize the risk of detrimental effects. In deciding whether or not to use the pump, surgeons should consider which intervention will maximize the long-term benefits of coronary-artery revascularization while minimizing the risks. Off-pump CABG is a valuable technique that may benefit patients with coronary artery disease who are at high risk for pump-related complications ¡ª particularly patients with diffusely diseased aortas, pulmonary disease, hepatic dysfunction, or bleeding diatheses. Methods of treatment should not compete for patients but should be selected according to individual patients' needs in order to optimize their care.
Source Information
From the Division of Cardiac Surgery, Massachusetts General Hospital, Boston.
This article has been cited by other articles:
Chukwuemeka, A., Weisel, A., Maganti, M., Nette, A. F., Wijeysundera, D. N., Beattie, W. S., Borger, M. A. (2005). Renal Dysfunction in High-Risk Patients After On-Pump and Off-Pump Coronary Artery Bypass Surgery: A Propensity Score Analysis. Ann. Thorac. Surg. 80: 2148-2153
Aoki, J., Ong, A. T.L., Hoye, A., van Herwerden, L. A., Sousa, J. E., Jatene, A., Bonnier, J. J.R.M., Schonberger, J. P.M.A., Buller, N., Bonser, R., Lindeboom, W., Unger, F., Serruys, P. W. (2005). Five year clinical effect of coronary stenting and coronary artery bypass grafting in renal insufficient patients with multivessel coronary artery disease: insights from ARTS trial. Eur Heart Journal 26: 1488-1493(Thomas E. MacGillivray, M)