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Ann Thorac Surg 2001;72:S2205-S2207
© 2001 The Society of Thoracic Surgeons
a VA Boston Healthcare System, West Roxbury, Massachusetts, USA
* Address reprint requests to Dr Khuri, VA Boston Healthcare System, 1400 VFW Parkway, West Roxbury, MA 02132, USA
e-mail: shukri.khuri{at}med.va.gov
Presented at Monitoring and Improving Patient Safety During and Following Cardiac Surgery, San Diego, CA, May 5, 2001.
In health care today, there is increasing concern about patient safety, particularly in light of the report published in 1999 by the National Academy of Science’s Institute of Medicine [1]. The report estimated that iatrogenic injury in the United States accounted for more than 98,000 deaths per year—more than suicides, highway accidents, breast cancer, or AIDS. Safety has been defined in the dictionary as "the state of being safe; freedom from danger or injury." Cardiac surgery is a major potential source of injury because of its complexity and the wide variation in severity of illness of the patients who undergo it.
Evidence of patient injury in cardiac surgery
Many cardiac surgeons have lulled themselves into believing that they perform safe surgery because the 30-day postoperative mortality rate in a large subset of their patients is very low. A live patient brought to cardiac surgery should come out of it at least in the same condition that he or she was brought into it. The mere fact that an operative mortality or morbidity is encountered in such a patient is an indication that some form of injury had been sustained in the course of the operation. In fact there are many indications that cardiac surgery is a major potential cause of patient injury, as discussed below.
First, despite relatively low 30-day mortality rates following cardiac surgery in general, the mortality and morbidity rates remain unacceptably high in relatively large subsets of patients undergoing cardiac surgery. The Platelet Glycoprotein IIb–IIIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy (PURSUIT) trial, which comprised 10,948 patients, recently reported the outcomes of 1,558 study patients who underwent in-hospital coronary artery bypass grafting (CABG) because of non–ST-segment elevation acute coronary syndrome. The 30-day postoperative mortality in the 692 patients who comprised the placebo group was 5.8%. The rate of 30-day postoperative myocardial infarction in this group was 28.1%, and the rate of postoperative MI or death was 30.8% [2]. The placebo group in the PURSUIT trial is fairly representative of the patients in this country who normally undergo CABG because of unstable angina that is not accompanied with ST-segment changes. These patients are common; yet, the PURSUIT trial shows that, currently, nearly one third of such patients are likely to die or to sustain a myocardial infarction after coronary artery bypass surgery. The Northern New England Cardiovascular Study Group [3] recently reported a 12.2% in-hospital mortality following CABG in patients on chronic dialysis, versus a 3.0% mortality in patients not on dialysis, and investigators at the Mayo Clinic [4] recently reported a postoperative mortality rate of 21% in a population of patients with severe aortic stenosis and left ventricular dysfunction. These relatively high postoperative morbidity and mortality rates indicate that total patient safety in these patient groups remains elusive even today.
Second, there are still many patients who are denied cardiac surgery because of what is perceived as an unacceptably high risk of operative mortality. This indicates that surgeons are worried that these patients might incur serious injury during or after the operation. Quality improvement programs in cardiac surgery, such as the Veterans Affairs Continuous Improvement in Cardiac Surgery Program [5], have shown a wide variation in the severity of the preoperative risk of patients undergoing cardiac surgery at various institutions. Although this indicates that some institutions are willing to take on "riskier" patients, it also indicates that surgeons have varied perceptions about their ability to ensure the safety of their patients throughout the total episode of cardiac surgical care.
Third, a low 30-day postoperative mortality rate is not as good an indicator of the safety of cardiac surgery as some surgeons would want us to believe. Cardiac surgery continues to be accompanied with increased 30-day morbidity, poor long-term outcomes, and added costs, even when the 30-day mortality is low [6]. It is not unusual for a cardiologist to encounter late postoperative heart failure in a patient whose hospital course after cardiac surgery was totally uneventful. Recent basic science investigations that have implicated acidosis as a primary trigger of apoptosis [7], as well as the demonstration that cardiac apoptosis can lead to heart failure [8], suggest that apoptotic changes might be triggered in the course of a cardiac operation, thus effecting an injurious cascade of adverse clinical events that become manifest late in the postoperative course.
Fourth, 30-day postoperative mortality rates are not invariably low at all institutions. When properly adjusted for preoperative risk, the 30-day mortality rate is a reliable comparative measure of the quality of surgical care among various institutions [9]. Two of the best risk-adjustment/quality improvement programs in cardiac surgery, The Northern New England Cardiovascular Study Group and the Veterans Affairs Continuous Improvement in Cardiac Surgery Program (CICSP), have demonstrated a wide variation in risk-adjusted 30-day mortality and morbidity rates among various institutions. For example, risk-adjusted 30-day mortality of CABG in the VA CICSP over a 6-month period may vary over a spectrum in which the highest outlier institution has an operative mortality that is five times that of the lowest outlier institution. This clearly indicates that there is a wide variation in patient safety among various institutions, and it calls for setting up structures and processes that are aimed at improving patient safety and outcomes.
All the above considerations indicate that patient safety is being jeopardized in cardiac surgery. An understanding of the potential sources of patient injury in cardiac surgery is paramount to improving safety and, hence, the long-term outcomes of cardiac surgical patients.
Potential sources of patient injury in cardiac surgery
There are six potential sources of patient injury that are somewhat unique to cardiac surgery.
The first source of patient injury is a technically inadequate operation. Although not unique to cardiac surgery, technical adequacy is imperative to achieving good outcomes after cardiac operations. Failure of an aortocoronary bypass graft because of a poorly constructed distal anastomosis, and prosthetic valvular regurgitation secondary to inadequate placement of an aortic valve prosthesis, are common manifestations of the compromise in patient safety that a cardiac surgery to which a patient can be exposed. Errors in intraoperative judgment, in addition to errors in intraoperative technique, can also lead to a technically inadequate operation, such as the decision not to bypass a specific coronary artery obstruction in the course of a valve replacement, or the decision to repair a mitral valve instead of replacing it. Provider competency is therefore a primary determinant of patient safety, and often is not sufficiently appreciated.
The second source of patient injury is the interruption of blood supply to the heart. In almost every cardiac operation, the heart is temporarily deprived of its blood supply, either regionally or globally. Considering that progressive pathologic ischemic changes start to occur in the myocardium within minutes after the interruption of its blood flow [10], a time-dependent hazard for myocardial injury is present in every patient undergoing cardiac surgery. The compendium of methods that we have come to call "myocardial protection techniques" are aimed primarily at prevention of this type of injury, although it is well recognized that, today, these techniques are limited in their ability to achieve complete protection of the heart in all patients undergoing cardiac surgery [11]. The time-dependence of this type of injury limits the protective efficacy of current myocardial protection techniques, particularly in complex operations requiring prolonged periods of aortic clamping. Both the duration of the period of aortic clamping and the duration of cardiopulmonary bypass have been consistently shown to be the main determinants of postoperative outcomes in all studies that have attempted to identify the determinants of outcomes of cardiac surgery.
The third source of patient injury is reperfusion of an ischemic myocardium Restoration of blood flow to myocardial tissues that had been subjected to relatively prolonged periods of ischemia is known to cause "reperfusion injury" [12]. The magnitude of reperfusion injury is directly related to the magnitude of the ischemic injury that precedes it. In its severe form, it manifests in a "no-reflow" phenomenon. In cardiac surgery, prevention of myocardial injury after the release of the aortic clamp, including the prevention of no-reflow, are directly dependent on the adequacy of myocardial protection during the period of aortic clamping. The combination of ischemic and reperfusion injury is probably the most frequent and serious type of injury that leads to poor outcomes in cardiac surgery today.
The fourth source of patient injury is inadequate revascularization. Failure to achieve complete revascularization of the ischemic myocardium is a common cause of myocardial infarction and death after cardiac surgery in patients with coronary artery disease. Aside from the technical inadequacy of the bypass grafting procedure, the two main causes of inadequate revascularization are: (1) failure to recognize the presence of significant coronary artery disease, and (2) advanced coronary artery disease that does not lend itself to adequate revascularization. Ensurance of adequate, complete revascularization is imperative to the prevention of patient injury and poor outcomes
The fifth source of injury and compromised long-term survival in patients undergoing surgery for coronary artery disease is short-term and long-term aortocoronary bypass conduit failure. Although short-term graft patency may be dependent primarily on intraoperative technical factors, the determinants of long-term graft patency are still poorly understood. It is clear, however, that current vein harvesting techniques might be injurious to the endothelium and, hence, might impact on the long-term patency of these grafts [13]. Research efforts are currently being expended to improve preservation of the endothelium of the harvested conduits. Until such improvements materialize, however, one needs to appreciate the potential short-term or long-term injury that the patient might incur as a result of inadequate conduit preservation.
Finally, the sixth source of patient injury is the adverse systemic effects of cardiopulmonary bypass. Subjecting a patient to extracorporeal circulation is known to generate a cascade of potentially injurious systemic events [14]. In an effort to reduce the potential adverse effects of cardiopulmonary bypass, research is being carried to better understand the pathophysiology of blood contact with the extracorporeal circuit, and clinical innovations such as off-pump coronary artery bypass (OPCAB) surgery are being advanced to avoid cardiopulmonary bypass altogether. Although techniques for cardiopulmonary bypass have improved appreciably over the past decade, it is not yet certain whether avoiding it altogether will completely eliminate the adverse systemic effects observed during cardiac surgery.
Assessment and monitoring of patient injury in cardiac surgery
As evident above, there are numerous indications that cardiac surgery can result in patient injury, and there are many potential hazards in cardiac surgery that can cause such injury. Improving the safety of cardiac surgery requires that patient injury be recognized—preferably in time to effect a change that would prevent the onset of irreversible damage. A symposium on the topic "Monitoring and Improving Patient Safety During and Following Cardiac Surgery" was held in San Diego, CA, on May 5, 2001; the proceedings of this symposium are contained in this Supplement to The Annals of Thoracic Surgery. Methods of identifying and assessing patient injury during cardiac surgery were described and reviewed in seven papers. These methods included assessment of postoperative outcomes [15]; intraoperative transesophageal echocardiography [16]; intraoperative periodic measurement of coronary sinus metabolites [17]; continuous measurement of myocardial tissue pH [18]; measurement of myocardial temperature [19]; and functional assessment of conduits used as aortocoronary bypass grafts [13, 20]. The eighth paper elucidates adverse effects of the extracorporeal circuit and addresses the question of whether these effects could be avoided by operating on the beating heart without cardiopulmonary bypass [21]. Each paper was discussed by an expert in the respective field, and the symposium concluded with a panel discussion in which these experts exchanged ideas regarding their approaches to monitoring and improving patient safety in the course of cardiac surgery. The papers presented at the symposium, the discussions that followed each of them, and the panel discussion that concluded the symposium provided a comprehensive review of the state of the art and a critique of the methods available today for the assessment of patient injury and its potential in cardiac surgery. The limitations of most of these methods in depicting evidence of patient injury in time to effect meaningful preventive measures was underscored. The need to develop practical and reliable clinical tools for intraoperative assessment of potential and actual myocardial injury in real time was also underscored. The panel discussion focused on a particularly promising tool in this regard: the on-line measurement of myocardial tissue pH and its potential to guide interventions that would prevent the onset of, or would reverse, myocardial tissue acidosis in real time. This technology has been developed and assessed clinically at one institution; its promise needs to be confirmed in more generalized clinical trials. Newer and more promising means of intraoperative assessment of anastomotic adequacy also need to be confirmed in generalized clinical trials. Irrespective of the methodology used, prevention and, hopefully, elimination of patient injury in the course of open heart surgery rests, in good measure, on the development of sensitive intraoperative monitoring tools that would allow the surgeon to recognize, in real time, the onset of myocardial injury, and to initiate, in the course of the operation, interventions that would prevent it.
Acknowledgments
The editorial assistance of Mrs Nancy Healey with this and other sections of this publication is gratefully acknowledged.
Footnotes
Doctor Khuri discloses that he has a financial relationship with Terumo Cardiovascular Systems, Inc.
References
This article has been cited by other articles:
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  E. Gongora and T. M. Sundt III Myocardial Revascularization with Cardiopulmonary Bypass Card. Surg. Adult, January 1, 2008; 3(2008): 599 - 632. [Full Text]
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 S. Matsushita, Y. Sakakibara, T. Imazuru, M. Noma, Y. Hiramatsu, O. Shigeta, T. Jikuya, and T. Mitsui High-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery Ann. Thorac. Surg., April 1, 2004; 77(4): 1293 - 1297. [Abstract] [Full Text] [PDF]
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H. S. Thatte, J.-H. Rhee, S. E. Zagarins, P. R. Treanor, V. Birjiniuk, M. D. Crittenden, and S. F. Khuri Acidosis-induced apoptosis in human and porcine heart Ann. Thorac. Surg., April 1, 2004; 77(4): 1376 - 1383. [Abstract] [Full Text] [PDF]
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