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Overview: Procedure Versus Protection: An Impossible Separation
Overview: Procedure Versus Protection: An Impossible Separation Gerald D. Buckberg This overview focuses upon the fundamental cohesion between myocardial protection and mechanical repair for surgical success. Currently, our attention is directed toward the natural evolution of more complex surgical methods, while there is slower rise in interest in advanced methods of protection. The absence of manuscripts on myocardial protection in major meetings suggests that the concept of protection has been solved, even though there remain reports of use of intraaortic balloon and mechanical devices that appear when protection is inadequate. This Seminar volume will introduce a series of articles about risk patients for whom evolving methods of protection are used. We will point out frontiers of protection that should develop together with advances in technical surgical approaches so that these two essential components that insure the safe conduct of cardiac operations can grow together. Copyright © 2007 by W.B. Saunders Company Key words: Myocardial protection, evolving strategies, delivery methods.
T
he early and late success of a cardiac surgical procedure is related to how well the surgery corrected the mechanical problem, and how carefully myocardial prot ection avoided secondary effects of aortic clamping for technical rcpair. There is no separation betwee n the blending of these two central events. Th e mechanically perfect heart cannot undergo early or late survival if surgical damage from protection is severe. An example is the development of "stone" heart after 30 minutes of normothermic aortic clamping for aortic stenosis. Similarly, the normal myocardium on bypass, with preserved structural and biochemical integrity, cannot maintain cardiac output if there is a technical surgical misconduct such as closed coronary anastomosis and iatrogenic valvar insufficiency. The validity of thc concert be tween these vital e le ments is well-known intellectually, yet, there are important differences in the cardiac surgical approaches to these two fundamental determinants of outcome. On one level, the meticulous From the Universi~y if Califomia il1edical Center. Thoracic and Cardiothoracic Surger),. Los Angeles. CA. Address reprint requests to Gerald D. Buckberg. MD. Thoracic alld CardiolllOracic Surgery. Unil'ersi{v if Californ ia Medical Cenler. Bo.\" 951741. Los Angeles. CA 90095·/7+ 1. Copyight © 2001 ~)' WE. Saunders Compan.!' 10-13·0679/ 01/ 1301·0006$35.00/0 doi: 10.1 053/ slcs. 2001. 22733
Seminars in Thoracic and Cardiovascular
pursuit of mechanical perfection is unending, for example, through cardiac vision (ie, eye glasses, 2.5-3.5 loops, 4.5 loops, 6.0 loops, the microscope, and finally robotic magnification away from the direct surgical field). Surgical sutures starting at 5.0 progress to 10.0 to secure perfect anastomosis or repair. Major changes in mitral valve repair are developed to avoid replacement, and mechanical interventions are introduced to return the ventricle in a normal elliptic cardiac position. This goal is the technical credo of cardiac surgery and the pursuit of this excellence will never end. Examples of this drive come from ongoing search for perfection through learning the Ross procedure for aortic valve replacement. Repeated coursework in valvuloplasty clinics is undertaken to understand our enlarging concepts of valve repair to avoid mechanical replacement. The undercurrent theme is that time, during aortic clamping, must be spent carefully to inspect the functional anatomy, and meticulously execute a novel technical repair. Th ere is an enlarging spectrum of surgeons wanting to use these creative approaches, but the numbers of clinical centers dealing with thes e more difficult valvular problems is limited. The surgical restriction, despite an available cadre of patients, is underlying concern about invoking extended intraoperative damage during the prolonged aortic clamping times required for novel technical success.
SlIrge~v,
Vol 13, No 1
(janua~y) .
2001:
pp 29·32
29
30
Gerald D. Buckberg
On the second level, these more extensive procedures are often withheld from patients with underlying impairment of ventricular function because of (I) recognized increased vulnerability to damage in the heart with hypertrophy and/or coronary disease; (2) limited functional reserve if protection is marginal, and/or (3) use of a shorter procedure to place an artificial valve to avoid superimposition of prolonged intra-aortic clamping for innovative proced ures for technical correction of the lesion. Pursuit of technical performance of evolving surgical tasks is halted in many centers by the conceptual barrier of, "prolonged aortic clamping will cause progressive tissue damage," when the n ew task is undertak en, and the nuance that repair, "burns extra minutes," to achieve mechanical success. The dilemma underlying this disparity between desire and accomplishment of surgical procedures is uncertainty of the value of current techniques of myocardial protection during prolonged aortic clamping in patients with advanced cardiac disease and diminished preoperative function. Unfortunately, the unbridled progress to learn n ew areas of technical prowess is unaccompanied, in many cente rs, with a similar, more intensive unde rstanding for reasons for invoking more damage. Consequently, techniques of protection have made slower educational progress during these years of technical evolution of mechanical eve nts. Several examples of protection bring into focus this disparity betwee n mechanical and metabolic excellence that must be dissolved so that all surgeons can render comparable techniques successfully through their carefully honed mechanical skills. The first method of protection is hypothermia, provided by cold perfusate and surface cooling based on findings by Shumway in 1959 to limit damage from normothermi a. ' To some, this became the historic end stop of myocardial protective strategies. This may reflect the "iceberg age," and has arrest ed progress toward full understanding of the mechanics of ischemic damage, and how to r everse these changes become cushioned by the idea of, "good results, why change?" The reason to change methods of protection is clear unless current methods allow complete avoidance of massive inotropic support, assist devices, or transpl antation for technically
successful repair. Hopefully, a rigid concept that cold is everything will not veil further understanding of the natural evolution of cardiac protection. Our capacity to stop m etabolic demands quickly, and simultaneously limit progressive extension of damage over time, was e nhanced by cardioplegic techniques, now used almost universally. H ypothermia is a vital component, but an addition, rather than the only solution with a unifying force. Further progression occurred through general agreement that blood had benefits over crystalloid techniqu es, and red blood cells become a natural component of cardioplegic solutions. Those who externally create a crystalloid component and exclude blood must now address the well-proven benefits of restoring the blood vehicle that is the natural nourishment of the nonbypassed heart. In addition, general methods to distribute solution, both antegrade, retrograde, and simultaneous ly antegrade/retrograde have developed, and are used commonly throughout the world. More importantly, new m e thods to prevent ischemic damage (ie, buffering, hypocalcemia, oxygen radical scavengers, reducing complement) und er more favorable conditions have been added. However, few centers are involved with the surgical adoption of these new protective techniques. Many use methods developed 20 yeas ago, before the wave of metabolic and delivery changes were initiated. The recognition that temperature and cardiologic vehicle do not insure adequate distribution has allowed the evolution of retrograde delivery. These methods of retroperfusion are used in more than 60% of patients in the United States a nd somewhat less worldwide. However, this is not a universal vehicle for cardioplegic delivery despite evidence that different areas of diseased hearts are perfused by antegrade and retrograde techniques. This is especially important in reoperative coronary procedures. The ready clinical demonstration that different regions are perfused by re trograde perfusion (ie, coronary sinus effluent during antegrade perfusions starting blue and becoming red, with retrograde perfusion, aortic effluent starting blue and then becoming red indicates that different areas are perfused during the period of aortic clamping) shows that some regions were imperfectly perfused by using one technique only. This
Procedure Versus Protection
clinical evidence has gradually attained general acceptance of combining these antegrade and retrograde delivery methodologies. These changes are further limited by those who have yet "made this step of transatrial cannulation." To many, this is a reason to limit pursuing retrograde methodology because of a slight prolongation of surgery to open the right atrium and directly cannulate the coronary sinus. Little attention is given to prolonged inotropic and metabolic support that are needed when this potentially 5-minute supplement is excluded. Some accept the prolonged intensive care unit and increased hospital stay and mortality by not using this methodology. The value in morbidity of consecutive hospital cases and reduced cost was shown nicely in a study by Loop et all several years ago at the Cleveland Clinic. The aforementioned applications of cold blood cardioplegia and retrograde perfusion are simply the start of the advanced techniques of myocardial protection because the numbers of centers that progress beyond this fundamental level becomes larger. Evidence is clear that there is increased vulnerability to damage in the jeopardized heart and that this can be controlled by controlled reperfusion. Despite this knowledge, there is much slower adaptation of proven concepts of controlled reperfusion before undoing the aortic clamp. Warm reperfusion is used in less than 50% of centers, and in Europe there are fewer participants. Furthermore, it should be recognized that ischemic damage during aortic clamping is not needed when direct heart visualization is unimpaired (ie, doing proximal anastomosis, placing sutures from the valve ring to the valve, and closing the aorta or atrium). During these times, perfusion is available yet is not commonly used. Ischemia is thereby prolonged unnecessarily. If there were understanding of the availability of reperfusion, especially retrograde at this time, the injury would be limited. This was shown recently in more than 1,500 patients with advanced heart disease and more extensively in a subset of patients with valve complex mitral valve disease 2 or Ross procedures with damaged ventricles in which ischemic times were greater than 180 to 250 minutes without inotropic support.3 This cohesion of benefits of individual strategies is called the integrated approach.
31
Further steps such as white blood cell filtration, oxygen radical addition, magnesium supplementation, P0 2 80-100 mm Hg to limit reoxygenation damage, reduce calcium to prevent calcium-related injury, adding sodium hydrogen ion exchanges, and other developing regions are at the frontier of better techniques to protect the heart. These have been developed, yet there is slower aggression toward incorporating these procedures into the surgery. Some think change is "living with the University." That is simply the wrong idea. We must advance in our learning of myocardial protection modalities the same way we progress with mechanical matters to provide our patients with the benefits of those aspects that should be in the armamentarium of the cardiac surgeon. The concepts of myocardial protection developed in adults are directly applicable to the pediatric population in whom vulnerability to damage is highest because of preoperative ischemia and cyanosis. These approaches are defined in this segment of Seminars. The increasing tendency to avoid cardiopulmonary bypass to reduce the inflammatory reaction to extracorporeal circulation has led to coronary artery bypass graft (CABG) without bypass. It is clear that the precursor to regional stunning (that we know globally as the low output syndrome) is brief occlusion for 10 to 15 minutes with normal blood reperfusion. This established technique of damage is applied to patients with coronary artery disease, but there is less damage in them because of collateral flow from stenotic lesions. Methods to protect the regional segment in patients undergoing CABG without bypass are addressed in this issue. The underlying principle in this dual bilateral program is for each of us to recognize that each effort (mechanical and metabolic) is of equal importance. Failure in either modality is not a surgical problem, but rather a problem for the patients and the existing cost of caring for those who have developed delayed recovery despite technical success mechanically. Improved myocardial protection is not a phase of surgical development, but rather intrinsic to improved surgical care. The virtual absence of papers at surgical meetings about myocardial protection indicate this problem of myocardial protection has been thought to be solved. Despite this, there are reports of problems with intra-aortic balloons and
32
Gerald D. Buckberg
mechanical assist devices when protection has been inadequate. The search for technical improvement must be accompanied by an ongoing learning of cardio protective methods that avoid completely the need to use machines to correct cardiac performance after the heart has been mechanically restored to more normal architectural capacity. We must adopt a position of how to provide this enhanced knowledge of protection so it becomes an essential component of surgical correction of cardiac defects. Protection and technical adequacy cannot be separated.
References I. Shumway, NE, Lower RR: Hypothermia for extended periods of anoxic arrest. Surg Forum 563; 1959 2. Loop FD, Higgins TL, Panda R, et al: Myocardial protection during cardiac operations. J Thorac Cardiovasc Surg 104:608-618, 1992 3. Buckberg GD, Beyersdorf F, Allen B, et al: Collective review: Integrated myocardial management. Background and initial application. J Card Surg 10:68-89, 1995 4. Allen BS, Murcia-Evans D, Hartz RS: Integrated cardioplegia allows complex valve repairs in all patients. Ann Thorac Surg 62:23-29, 1996
T
he early and late success of a cardiac surgical procedure is related to how well the surgery corrected the mechanical problem, and how carefully myocardial prot ection avoided secondary effects of aortic clamping for technical rcpair. There is no separation betwee n the blending of these two central events. Th e mechanically perfect heart cannot undergo early or late survival if surgical damage from protection is severe. An example is the development of "stone" heart after 30 minutes of normothermic aortic clamping for aortic stenosis. Similarly, the normal myocardium on bypass, with preserved structural and biochemical integrity, cannot maintain cardiac output if there is a technical surgical misconduct such as closed coronary anastomosis and iatrogenic valvar insufficiency. The validity of thc concert be tween these vital e le ments is well-known intellectually, yet, there are important differences in the cardiac surgical approaches to these two fundamental determinants of outcome. On one level, the meticulous From the Universi~y if Califomia il1edical Center. Thoracic and Cardiothoracic Surger),. Los Angeles. CA. Address reprint requests to Gerald D. Buckberg. MD. Thoracic alld CardiolllOracic Surgery. Unil'ersi{v if Californ ia Medical Cenler. Bo.\" 951741. Los Angeles. CA 90095·/7+ 1. Copyight © 2001 ~)' WE. Saunders Compan.!' 10-13·0679/ 01/ 1301·0006$35.00/0 doi: 10.1 053/ slcs. 2001. 22733
Seminars in Thoracic and Cardiovascular
pursuit of mechanical perfection is unending, for example, through cardiac vision (ie, eye glasses, 2.5-3.5 loops, 4.5 loops, 6.0 loops, the microscope, and finally robotic magnification away from the direct surgical field). Surgical sutures starting at 5.0 progress to 10.0 to secure perfect anastomosis or repair. Major changes in mitral valve repair are developed to avoid replacement, and mechanical interventions are introduced to return the ventricle in a normal elliptic cardiac position. This goal is the technical credo of cardiac surgery and the pursuit of this excellence will never end. Examples of this drive come from ongoing search for perfection through learning the Ross procedure for aortic valve replacement. Repeated coursework in valvuloplasty clinics is undertaken to understand our enlarging concepts of valve repair to avoid mechanical replacement. The undercurrent theme is that time, during aortic clamping, must be spent carefully to inspect the functional anatomy, and meticulously execute a novel technical repair. Th ere is an enlarging spectrum of surgeons wanting to use these creative approaches, but the numbers of clinical centers dealing with thes e more difficult valvular problems is limited. The surgical restriction, despite an available cadre of patients, is underlying concern about invoking extended intraoperative damage during the prolonged aortic clamping times required for novel technical success.
SlIrge~v,
Vol 13, No 1
(janua~y) .
2001:
pp 29·32
29
30
Gerald D. Buckberg
On the second level, these more extensive procedures are often withheld from patients with underlying impairment of ventricular function because of (I) recognized increased vulnerability to damage in the heart with hypertrophy and/or coronary disease; (2) limited functional reserve if protection is marginal, and/or (3) use of a shorter procedure to place an artificial valve to avoid superimposition of prolonged intra-aortic clamping for innovative proced ures for technical correction of the lesion. Pursuit of technical performance of evolving surgical tasks is halted in many centers by the conceptual barrier of, "prolonged aortic clamping will cause progressive tissue damage," when the n ew task is undertak en, and the nuance that repair, "burns extra minutes," to achieve mechanical success. The dilemma underlying this disparity between desire and accomplishment of surgical procedures is uncertainty of the value of current techniques of myocardial protection during prolonged aortic clamping in patients with advanced cardiac disease and diminished preoperative function. Unfortunately, the unbridled progress to learn n ew areas of technical prowess is unaccompanied, in many cente rs, with a similar, more intensive unde rstanding for reasons for invoking more damage. Consequently, techniques of protection have made slower educational progress during these years of technical evolution of mechanical eve nts. Several examples of protection bring into focus this disparity betwee n mechanical and metabolic excellence that must be dissolved so that all surgeons can render comparable techniques successfully through their carefully honed mechanical skills. The first method of protection is hypothermia, provided by cold perfusate and surface cooling based on findings by Shumway in 1959 to limit damage from normothermi a. ' To some, this became the historic end stop of myocardial protective strategies. This may reflect the "iceberg age," and has arrest ed progress toward full understanding of the mechanics of ischemic damage, and how to r everse these changes become cushioned by the idea of, "good results, why change?" The reason to change methods of protection is clear unless current methods allow complete avoidance of massive inotropic support, assist devices, or transpl antation for technically
successful repair. Hopefully, a rigid concept that cold is everything will not veil further understanding of the natural evolution of cardiac protection. Our capacity to stop m etabolic demands quickly, and simultaneously limit progressive extension of damage over time, was e nhanced by cardioplegic techniques, now used almost universally. H ypothermia is a vital component, but an addition, rather than the only solution with a unifying force. Further progression occurred through general agreement that blood had benefits over crystalloid techniqu es, and red blood cells become a natural component of cardioplegic solutions. Those who externally create a crystalloid component and exclude blood must now address the well-proven benefits of restoring the blood vehicle that is the natural nourishment of the nonbypassed heart. In addition, general methods to distribute solution, both antegrade, retrograde, and simultaneous ly antegrade/retrograde have developed, and are used commonly throughout the world. More importantly, new m e thods to prevent ischemic damage (ie, buffering, hypocalcemia, oxygen radical scavengers, reducing complement) und er more favorable conditions have been added. However, few centers are involved with the surgical adoption of these new protective techniques. Many use methods developed 20 yeas ago, before the wave of metabolic and delivery changes were initiated. The recognition that temperature and cardiologic vehicle do not insure adequate distribution has allowed the evolution of retrograde delivery. These methods of retroperfusion are used in more than 60% of patients in the United States a nd somewhat less worldwide. However, this is not a universal vehicle for cardioplegic delivery despite evidence that different areas of diseased hearts are perfused by antegrade and retrograde techniques. This is especially important in reoperative coronary procedures. The ready clinical demonstration that different regions are perfused by re trograde perfusion (ie, coronary sinus effluent during antegrade perfusions starting blue and becoming red, with retrograde perfusion, aortic effluent starting blue and then becoming red indicates that different areas are perfused during the period of aortic clamping) shows that some regions were imperfectly perfused by using one technique only. This
Procedure Versus Protection
clinical evidence has gradually attained general acceptance of combining these antegrade and retrograde delivery methodologies. These changes are further limited by those who have yet "made this step of transatrial cannulation." To many, this is a reason to limit pursuing retrograde methodology because of a slight prolongation of surgery to open the right atrium and directly cannulate the coronary sinus. Little attention is given to prolonged inotropic and metabolic support that are needed when this potentially 5-minute supplement is excluded. Some accept the prolonged intensive care unit and increased hospital stay and mortality by not using this methodology. The value in morbidity of consecutive hospital cases and reduced cost was shown nicely in a study by Loop et all several years ago at the Cleveland Clinic. The aforementioned applications of cold blood cardioplegia and retrograde perfusion are simply the start of the advanced techniques of myocardial protection because the numbers of centers that progress beyond this fundamental level becomes larger. Evidence is clear that there is increased vulnerability to damage in the jeopardized heart and that this can be controlled by controlled reperfusion. Despite this knowledge, there is much slower adaptation of proven concepts of controlled reperfusion before undoing the aortic clamp. Warm reperfusion is used in less than 50% of centers, and in Europe there are fewer participants. Furthermore, it should be recognized that ischemic damage during aortic clamping is not needed when direct heart visualization is unimpaired (ie, doing proximal anastomosis, placing sutures from the valve ring to the valve, and closing the aorta or atrium). During these times, perfusion is available yet is not commonly used. Ischemia is thereby prolonged unnecessarily. If there were understanding of the availability of reperfusion, especially retrograde at this time, the injury would be limited. This was shown recently in more than 1,500 patients with advanced heart disease and more extensively in a subset of patients with valve complex mitral valve disease 2 or Ross procedures with damaged ventricles in which ischemic times were greater than 180 to 250 minutes without inotropic support.3 This cohesion of benefits of individual strategies is called the integrated approach.
31
Further steps such as white blood cell filtration, oxygen radical addition, magnesium supplementation, P0 2 80-100 mm Hg to limit reoxygenation damage, reduce calcium to prevent calcium-related injury, adding sodium hydrogen ion exchanges, and other developing regions are at the frontier of better techniques to protect the heart. These have been developed, yet there is slower aggression toward incorporating these procedures into the surgery. Some think change is "living with the University." That is simply the wrong idea. We must advance in our learning of myocardial protection modalities the same way we progress with mechanical matters to provide our patients with the benefits of those aspects that should be in the armamentarium of the cardiac surgeon. The concepts of myocardial protection developed in adults are directly applicable to the pediatric population in whom vulnerability to damage is highest because of preoperative ischemia and cyanosis. These approaches are defined in this segment of Seminars. The increasing tendency to avoid cardiopulmonary bypass to reduce the inflammatory reaction to extracorporeal circulation has led to coronary artery bypass graft (CABG) without bypass. It is clear that the precursor to regional stunning (that we know globally as the low output syndrome) is brief occlusion for 10 to 15 minutes with normal blood reperfusion. This established technique of damage is applied to patients with coronary artery disease, but there is less damage in them because of collateral flow from stenotic lesions. Methods to protect the regional segment in patients undergoing CABG without bypass are addressed in this issue. The underlying principle in this dual bilateral program is for each of us to recognize that each effort (mechanical and metabolic) is of equal importance. Failure in either modality is not a surgical problem, but rather a problem for the patients and the existing cost of caring for those who have developed delayed recovery despite technical success mechanically. Improved myocardial protection is not a phase of surgical development, but rather intrinsic to improved surgical care. The virtual absence of papers at surgical meetings about myocardial protection indicate this problem of myocardial protection has been thought to be solved. Despite this, there are reports of problems with intra-aortic balloons and
32
Gerald D. Buckberg
mechanical assist devices when protection has been inadequate. The search for technical improvement must be accompanied by an ongoing learning of cardio protective methods that avoid completely the need to use machines to correct cardiac performance after the heart has been mechanically restored to more normal architectural capacity. We must adopt a position of how to provide this enhanced knowledge of protection so it becomes an essential component of surgical correction of cardiac defects. Protection and technical adequacy cannot be separated.
References I. Shumway, NE, Lower RR: Hypothermia for extended periods of anoxic arrest. Surg Forum 563; 1959 2. Loop FD, Higgins TL, Panda R, et al: Myocardial protection during cardiac operations. J Thorac Cardiovasc Surg 104:608-618, 1992 3. Buckberg GD, Beyersdorf F, Allen B, et al: Collective review: Integrated myocardial management. Background and initial application. J Card Surg 10:68-89, 1995 4. Allen BS, Murcia-Evans D, Hartz RS: Integrated cardioplegia allows complex valve repairs in all patients. Ann Thorac Surg 62:23-29, 1996