Cardiac Risk in Noncardiac Surgery

The preoperative evaluation and management of the patient potentially at risk for cardiac complications of noncardiac surgery require the collaborative efforts of the surgeon, anesthesiologist, and medical physician. Each brings a somewhat different perspective and expertise to the problem, and ideal decisions are possible only if all work together in a collaborative, mutually respectful manner. Cardiologists and internists should refrain from trite recommendations such as "avoid hypotension" and should not pretend to make recommendations regarding anesthetic routes and techniques except in very unusual circumstances. In the context of the appropriate role for the consulting internist and cardiologist, this review will emphasize important issues in the preoperative and postoperative periods and highlight a probabalistic approach to risk assessment and decision-making, in which additional information is helpful only if it provides incremental assistance. Understanding Probability A fundamental principle of risk assessment and medical decision-making is that a group of patients has an "average" probability of a diagnosis or outcome that can then be modified by considering additional individual risk factors or results of diagnostic tests. This principle, which is quantified by Bayes theorem, explains why the same test result has different implications in patients with different prior probabilities of disease [1]Table 1.Table 1: How the Positive and Negative Predictive Values of the Same Test Vary Depending on the Prior Probability of DiseaseSensitivity and specificity are intrinsic properties of a test--its ability to identify patients with or without the condition of interest, be it a diagnosis or a predicted outcome. Although sensitivity and specificity are independent of the prior or pretest probability of the diagnosis or outcome, they are dependent on the spectrum of patients being studied [1]. For example, the sensitivity and specificity of an exercise test will depend on whether it is used on a wide spectrum of consecutive patients with chest pain or whether it is evaluated in a bimodal population of normal medical students and patients with known coronary stenoses. By comparison, predictive value, which is the posttest probability of the diagnosis or outcome, depends critically on the estimated pretest probability as well as on the sensitivity and specificity of the test [1]. This principle has direct applications to the assessment of cardiac risk in noncardiac surgery. For example, in large series of consecutive unselected patients more than 40 yr old undergoing major noncardiac surgical procedures, the risk of perioperative myocardial infarction has been approximately 1.4% (1%-2%) and the risk of perioperative cardiac death has been approximately 1% (0.5%-2%) [2-5]. By comparison, in studies of consecutive patients with higher risk characteristics, such as patients undergoing vascular surgery or patients with known or highly suspected coronary heart disease, these risks have been twice as high: approximately 3.1% and 1.7%, respectively [5-11]. In more highly selected patients, such as patients who have been referred for dipyridamole thallium scintigraphy in the larger series, the risks are increased yet again by another twofold to approximately 6% and 3%, respectively [12-17]. It should not be surprising that the reported value of additional pieces of information or diagnostic tests could be substantially different when applied to patient populations in whom the underlying risks of complications vary by fourfold. The difficulty in interpreting the relevant literature is further exacerbated by the small size of many individual studies. Factors that have been shown clearly to be important in a series of 1000 or more patients may be present too infrequently to achieve statistical significance in studies with 100-200 patients. A third issue relates to the way in which additional information and diagnostic tests are assessed. Fortunately, almost all recent analyses have used multivariable approaches to assess the independent impact of various pieces of information. Unfortunately, many studies have not included a careful, comprehensive, prospective clinical evaluation prior to assessing the impact of a diagnostic test. The key issue is the extent to which such a test will provide incremental information after the most appropriate clinical assessment has already been performed. Clinical Factors That Affect Cardiac Risk Although different studies have used somewhat different methods, several specific factors clearly influence cardiac risk in noncardiac surgery. When the review focuses on the larger prospective series, those with 400 or more patients who were evaluated comprehensively prior to surgery, a remarkably consistent picture emerges [2-10]. These larger, prospective series should be distinguished from smaller series, which may be of insufficient size to detect important correlations between risk factors and outcomes and that may be overly influenced by the characteristics of a small number of patients. They also differ from studies that used chart review to identify risk factors and outcome. These latter studies relied on the preoperative historical and physical examination data recorded by physicians who cared for the patients, as opposed to the comprehensive evaluation that can be performed and recorded in a prospective study, and on routine postoperative clinical practice rather than a standardized surveillance protocol to detect postoperative outcomes. Among the studies that met these criteria, several included all consecutive, unselected patients more than 40 yr old undergoing major noncardiac surgery [2-5], and others included consecutive selected patients who had high risk characteristics such as known coronary artery disease, vascular disease, multiple coronary risk factors, or old age [5-10]. Ischemic Heart Disease Various measures of coronary artery disease have been associated with cardiac risk in all major studies. The most striking risk factor is a recent myocardial infarction [2,4,18,19]. Although data up until the mid-1970s suggested that the risk of perioperative myocardial infarction or cardiac death was approximately 30% in patients who had surgery within 3 mo of a myocardial infarction and approximately 15% in patients who had surgery between 3 and 6 mo after a myocardial infarction [2,18,19], subsequent data suggest far lower risks after elective noncardiac surgery [20-22]Table 2. In two of these studies [20,21], these lower risks were reported in patients who were selected based on an overall risk assessment and for whom aggressive intraoperative and postoperative monitoring protocols were used. In a series of patients undergoing urgent or emergent vascular surgery within 6 wk after a myocardial infarction between 1980 and 1989, the risks remained high [22].Table 2: Risk of Reinfarction or Cardiac Death from Surgery in Post-MI PatientsNo data specifically address whether patients who have had reperfusion by thrombolysis or percutaneous transluminal coronary angioplasty (PTCA) face different subsequent risks with noncardiac surgery. However, newer medical and intervention therapies have improved the overall prognosis of the patient after infarction and likely have reduced their risks for subsequent noncardiac surgery as well. Patients with a recent preoperative myocardial infarction can generally be divided into three groups: 1) those in whom the surgery is emergent and potentially life-saving and in whom it will nearly always be performed regardless of cardiac risk; 2) those in whom it is purely elective and should be delayed for approximately 3 mo, when the infarction is likely to have healed and the patient is back to baseline functional status, or for a full 6 mo for patients who have not fully recovered; and 3) those for whom the surgery is not absolutely emergent but in whom it cannot be delayed for many months without incurring substantial risk that the surgical condition will worsen. In these latter patients, which include those with severe vascular disease or with potentially resectable tumors, the recommended approach is to undergo the usual evaluation and rehabilitation after the infarction. Patients who develop signs or symptoms at low exercise levels will be candidates for coronary angiography and revascularization. Those who are able to rehabilitate without more than mild symptoms can be considered for necessary noncardiac surgery between 6 wk and 3 mo after the infarction, when they normally should be at their baseline functional status if their exercise performance and noninvasive cardiac evaluation permits. This approach, which must be tailored to the needs and risks of the individual patient, appears to balance the competing risks of the cardiac and noncardiac conditions. Few data are available to assess risk in patients with unstable or accelerated angina or with very advanced and disabling angina. In general, such patients routinely undergo coronary angiography and attempted revascularization for their coronary disease independent of their noncoronary conditions. The availability of PTCA [23,24] has provided an attractive option for these patients without requiring an inordinate delay of the noncardiac surgery or heroic attempts to perform two major operations under the same anesthesia. A more difficult issue is the evaluation of the patient with suspected or known coronary disease that is not obviously unstable or disabling. Patients with a prior myocardial infarction or stable, Class I-II angina Table 3 are at higher risk of cardiac complications with perhaps a 10-fold relative increase in risk as compared with patients who do not have coronary disease [4,6,8,11,25]. However, the 10-fold relative increase in risk corresponds to a rather low absolute risk: approximately a 4% risk of myocardial infarction and approximately a 1%-2% risk of cardiac death [6,8,11,25]. These risks tend not to exceed the very similar risks for both myocardial infarction and cardiac death that would be associated with an aggressive strategy of coronary angiography and revascularization followed by the noncardiac surgery [11], so a routinely aggressive approach to these patients does not appear to be warranted. Strategies for attempting to identify the subset of patients with suspected or known coronary disease who are at sufficiently increased risk to warrant more aggressive approaches are described later.Table 3: Assessment of Cardiac Functional Class Using Two Different SystemsLeft Ventricular Dysfunction and Congestive Heart Failure Although the precise factors vary from study to study, large series have consistently noted that patients with substantially depressed left ventricular function or evidence of advanced congestive heart failure have an increase in cardiac risk [2,4,11]. To the extent that the left ventricular dysfunction is a manifestation of prior large or multiple myocardial infarctions, the dysfunction also serves as a marker of the severity of coronary artery disease. Even in the absence of known coronary disease, patients with left ventricular dysfunction or heart failure based on hypertension, valvular heart disease, or cardiomyopathy are less able to handle the fluid shifts and volume changes that are often associated with major surgery. Patients more than 40 yr old who have persistent evidence of congestive heart failure at the time of major surgery are at highest risk for pulmonary edema (15% or so), whereas those with well controlled congestive heart failure have risks that are lower (approximately 5%) than those with persistent heart failure but clearly higher than those who have never had heart failure (approximately 2%) Heart Disease series had insufficient of patients with valvular heart disease to regarding Patients with severe appear to be at highest risk data suggest that a of these patients can surgery under perioperative management patients with who are candidates for surgery should generally have the surgery performed prior to noncardiac surgery. the noncardiac surgery is urgent or the patient may not be a for can provide several months of and and provide a of for surgery Patients who have but who are and have a exercise generally do well with noncardiac surgery Patients with are at increased risk for coronary artery disease and congestive heart and they tend to have more myocardial with surgery, whether or not they have clinical coronary disease However, does not appear to be a major independent risk factor for the of myocardial infarction or of cardiac death with noncardiac surgery Although aggressive approaches can and perhaps evidence of myocardial surgery data suggest that patients with or persistent mild to can undergo and surgery without the risks of major and ventricular are often of the severity of underlying coronary disease and left ventricular In an when noninvasive cardiac tests were generally or infrequently used to assess the severity of coronary disease or depressed left ventricular the of preoperative was an way to assess which patients had more severe from these underlying cardiac these appear to be of underlying heart disease, they tend to with both and heart failure complications In if patients have these but underlying heart disease, the rather to the absolute risk of a major cardiac by their risks for such an in the perioperative are also is evidence that the of in the perioperative will or that to be patients with for the of these should such have consistently shown that patients have higher risk of cardiac and in most studies age has been an independent predictive after for the severity of cardiac disease and Although age is not a of patients clearly have less and more cardiac disease, the severity of which may be by their exercise of Surgery that are associated with more difficult postoperative major and tend to higher risk than those that are not as likely to be associated with postoperative major fluid and major noncardiac Patients undergoing major vascular surgery are more likely to have coronary disease as well and have increased risk of the of this underlying The highest risk noncardiac is these patients have both a high risk of noncardiac postoperative complications and a high of underlying coronary disease The higher of postoperative complications in patients undergoing these of operations is not to the of appears to be if between the of an and the probability of postoperative complications after for the of surgery In studies of perioperative suggest that intraoperative myocardial is somewhat predictive of postoperative cardiac it is less predictive than preoperative or postoperative intraoperative monitoring with can provide information but are data to that it is for clinical or decision-making, or for important patient outcomes and Patients who undergo operations are at higher risk than similar patients undergoing elective surgery they are more likely to noncardiac complications all being are then more likely to on the and cardiac Patients with evidence for important such as or or also have higher risk of cardiac again their unstable condition on the which many important characteristics of the patient, are to on clinical factor when assessing perioperative different large studies have different Table of which has substantial in of the factors that are these the only to have been evaluated in large prospective series is the In consecutive, unselected patients, this has performed nearly in two large prospective in and as in of patients in the It also performed well in a consecutive series of patients with prior coronary or valvular surgery who then noncardiac surgery In selected patients, such as those who had medical or surgery, the performed than but not as well as in the series work by and and by should the factors that important in the Cardiac Risk 1: of the in various large studies. characteristics of the on the the on the of the ability of the to patients with and without major cardiac in the left tests. In all the performed than by statistical and in the two studies of consecutive, unselected patients, performance was very similar to the and a fundamental principle of clinical is that such as from a diagnostic test or must be with prior information to an it is not surprising that risk on more patient populations would not be to more selected patient in the context of the result of a risk can be considered in the same way that would the result of a diagnostic test. By a on a risk with the prior probability of major complications in a large population of similar patients, the risk a predictive value described in Table will be than the prior probability or the risk Table of the Cardiac Risk to the Probability of Cardiac in Different of of Patients with Ischemic Heart Disease Patients with known heart disease or who are at very high risk for it a of Even if they are to be at low risk on of several cardiac risk specific must be to the status of their coronary disease that surgery is low the most important of risk in the patient with coronary artery disease or multiple risk factors for it is the functional In the of patients with well coronary disease, patients with coronary artery disease who had Class or Class angina or who were after myocardial infarction had a after a subsequent noncardiac surgery if their coronary disease was However, only 6 of the were to cardiac a cardiac Although the of death and cardiac death were lower patients with similar of coronary disease who had coronary artery prior to noncardiac surgery, the absolute were small the from elective coronary artery is the strategy of coronary surgery prior to noncardiac surgery would be to an overall that would be to the strategy of noncardiac surgery under medical for routine preoperative coronary revascularization must be further by the that was in the risk of perioperative myocardial infarction between the two in this study approach for patients with known coronary artery disease would be preoperative In a large series of preoperative PTCA patients with advanced coronary disease were with PTCA of which were of were patient, and PTCA was in of the patients. In the in whom it was had a myocardial infarction. additional myocardial in patients who were able to undergo their with the PTCA and three postoperative myocardial infarctions, of which was the on substantial data regarding the relative risks and of PTCA as compared with coronary artery it should not be that PTCA will be sufficiently less than coronary artery to a routine preoperative strategy for patients with known angina. patients with and mild or Class angina have risks up to or more higher than patients without coronary disease, are not sufficiently high to warrant routine preoperative coronary and can such patients be the approach is to or the functional In two different studies of patients more than yr old undergoing major or noncardiac surgery, the ability to a heart of or more with exercise was a of perioperative complications than the or exercise or In a study of vascular surgery patients were substantially lower in patients who could of their predicted heart than in patients who could exercise to be more important than the of at In another study, the was 1% in vascular surgery patients with a exercise test as compared with a in patients with a test The of evidence that patients who are known to be Class or Class functional status or who can be shown to have such a functional status by exercise are at sufficiently low risk for major complications that is for routine coronary angiography and revascularization. In patients who cannot of such as or vascular disease, the assessment of functional and of cardiac risk for noncardiac surgery is more difficult The of symptoms cannot be used as a for functional patients may have symptoms that would be if their noncardiac to to be more It is in such patients that a of newer diagnostic tests have been and are used but with different physicians Assessment based on functional status may patients with However, is most often in patients who also have for are most likely to be in patients who already have symptoms or who are at very high risk for coronary disease and are to exercise of noncardiac conditions. Cardiac in Patients have reported that preoperative dipyridamole thallium scintigraphy can cardiac risk in patients undergoing vascular surgery In many of these the thallium result was the most important predictive that the dipyridamole thallium is most helpful in patients who are at very high very low risk based on a clinical of whether a clinical assessment is based on their factors of of ventricular requiring requiring or a on the or on the factors reported in Table patients with of their factors or who are Class on a and have prior of known coronary heart disease are at low risk for complications regardless of the thallium the patients with three or more of the factors reported by or who are known to be Class or Class by approaches Table are at high risk regardless of the thallium The thallium was helpful with the risk those with or two factors and a thallium had a 30% which was similar to the in patients with three or more factors, patients with or two factors and a thallium had a similar to patients with clinical factors In the large series of patients who were referred for dipyridamole thallium the risks of major cardiac complications to 6% or more and the risk of perioperative death [12-17]. In this selected group of patients, all studies have shown dipyridamole thallium scintigraphy to important incremental information. By comparison, unselected patients undergoing or vascular surgery have risks only approximately as high as in these selected patients. In both large and smaller series of dipyridamole thallium scintigraphy in this less selected patient the not predictive information. It appears that dipyridamole thallium scintigraphy can be a very test in patients who are referred for the test and who are known to have coronary disease or be at high risk for but the test is not as and perhaps not at all when applied to consecutive unselected vascular surgery patients. thallium scintigraphy can also be used in patients undergoing surgery if they are at high risk for the test to be potentially In such study on the dipyridamole thallium was for postoperative cardiac all such patients were also more than yr old or had known congestive heart two cardiac both in patients who were in Class or Class on the risk to dipyridamole thallium scintigraphy is In study were major postoperative cardiac patients with preoperative compared with patients without preoperative Although preoperative was the most important of postoperative the test was not helpful in a group of patients who were less than yr were Class on the risk and had of myocardial infarction, or In subsequent studies by the of postoperative was of almost to preoperative intraoperative a of postoperative was substantially less predictive than preoperative or postoperative In a prospective study of with coronary artery disease or at high risk for it preoperative was again a of major postoperative but in this latter series it was less important than postoperative for postoperative compared with for preoperative intraoperative was a of postoperative but was not nearly as important as preoperative or postoperative studies also have the of preoperative and postoperative for postoperative is important if it for or more These studies on make several important clinical both preoperative and postoperative are and they are in intraoperative predictive of postoperative is not nearly as predictive as preoperative and postoperative the same of that can be used to increase the of dipyridamole thallium scintigraphy can also be used to increase the of with postoperative monitoring has that is often a of or more between the of and the of a clinical These data suggest a of for possible if patients could be dipyridamole or has been reported by several to postoperative This and the number of patients who have this test is too low for at data suggest that may be associated with results than dipyridamole thallium scintigraphy or However, it is likely that dipyridamole thallium scintigraphy and will be most in patients functional status cannot be by the or by exercise monitoring the only of these three that is for postoperative of patients who were at higher risk for postoperative complications in study but many studies have incremental value for major postoperative after exercise In the study the was predictive of postoperative congestive heart failure but was not an independent of postoperative myocardial infarction, myocardial or cardiac preoperative whether with exercise or direct risks and may of the information they However, these tests should be recommended only when they are sufficiently likely to to an appropriate in to the with Ischemic Heart Disease By the information in cardiac risk and the of diagnostic patients with known angina can be Table In patients who are low risk by this approach, further does not appear to be and surgery should be with appropriate and postoperative to Patients with patients are not at low risk by this approach, option is to the medical and to the A approach is to coronary and then to appropriate A third approach is to to surgery, after of medical with more perioperative monitoring and The data available suggest that coronary revascularization should be recommended in in which it would be regardless of the noncardiac surgery, but that medical management is in patients. However, the must be for individual patient, with the that the of studies are associated with a of must on appropriate of in in which the risk of complications is sufficiently high that additional preoperative studies are likely to be the cardiac patient to be at risk for noncardiac complications the and for cardiac complications after In the assessment and management by all physicians is to the outcome of the cardiac patient undergoing noncardiac surgery. A and mutually respectful is in which the expertise of the but with or