Assessing and Minimizing Cardiac Risk of Noncardiac Surgery

Wei C. Lau

Hitinder Gurm

Kim A. Eagle

More than 40 million people will undergo noncardiac surgical procedures in the United States annually. The aging patient population and advances in surgical and anesthetic techniques have resulted in the performance of an increasing number of complex surgical procedures in greater numbers of patients with a higher likelihood of significant cardiovascular disease (1). It is estimated that the incidence of cardiac complications after noncardiac surgical procedures is between 0.5% and 1% (2). Consequently, approximately 200,000 to 400,000 people will have perioperative cardiac complications. Moreover, one of four or more of these patients will die (3). Patients who survive a postoperative myocardial infarction are twice as likely to die in the following 2 years as compared with patients with uneventful surgical procedures (4). Because of the magnitude of this problem, emerging evidence-based practices dictate that the practicing physician should thoughtfully perform an individualized evaluation of the surgical patient to provide an accurate preoperative risk assessment, risk stratification, and modification of risk parameters that can then guide the framework for optimal perioperative risk-reduction strategies. This chapter outlines a systematic algorithm approach for cardiovascular risk assessment to guide strategically the perioperative preventive therapies that may favor optimal outcome.

RISK OF PERIOPERATIVE CARDIAC EVENTS DURING NONCARDIAC SURGERY

Underlying significant coronary artery disease (CAD) is an important component in the pathophysiologic processes of perioperative myocardial infarction (MI) (5). Patients with no history of MI have a low risk of perioperative MI (0.1% to 0.6%); those with a history of MI are at significantly higher risk (2.8% to 7%) (6,7,8,9); and the highest risk is in patients who sustained MI within 3 months before noncardiac surgery (7). The majority of perioperative MIs are known to occur in the first 3 days after surgery, with peak incidence on day 2 (8,9). The lack of classic symptoms of chest pain and, instead, an atypical presentation with new-onset congestive heart failure, hypotension, arrhythmias, nausea, or altered mental status makes the clinical diagnosis challenging. Perioperative MI is associated with greater than 50% mortality rates (8,10). Therefore it is important to identify patients who are at risk for untoward outcomes after surgery by using a systematic stepwise preoperative assessment strategy. A contemporary composite algorithm is thus provided in this chapter the better to incorporate the consensus-derived algorithms (11,12), such as those suggested by the American College of Cardiology/American Heart Association (ACC/AHA) Task Force on Practice Guidelines (11), and empiric risk indices (13,14), such as the Revised Cardiac Risk Index (RCRI) (14).

ASSESSING PERIOPERATIVE CARDIAC RISK FOR PATIENTS UNDERGOING NONCARDIAC SURGERY

A stepwise approach for assessing risk for patients undergoing noncardiac surgery (3,11,14,15,16) should address the following questions (Fig. 38.1):

Is noncardiac surgery urgently required?
Has the patient undergone recent coronary revascularization?
Has the patient been evaluated for CAD in the past 2 years?
Is patient at risk for adverse cardiac events?
What is the risk of cardiac complication in relation to severity of the surgical procedure?
What is the RCRI?
Is a noninvasive cardiac test necessary?
Is there a benefit for perioperative coronary revascularization?
What additional preoperative, intraoperative, and postoperative risk modification besides coronary revascularization should be initiated?
What long-term risk-stratification and management strategies should be implemented?

Is Noncardiac Surgery Urgently Required?

Determining the urgency of the surgery should be included in the initial thorough history and physical examination in the evaluation of the surgical patients. The urgency of surgery is dictated by patient- or surgery-specific factors, and in some instances, time may not be available for further cardiac assessment, as true emergency procedures are associated with an unavoidably higher morbidity and mortality. Recommendations should be provided for perioperative medical management and surveillance in such instances. Selected patients, at high risk for long-term coronary events, should undergo risk stratification after their recovery from surgery (11,17).

Has the Patient Undergone Recent Revascularization?

A complete revascularization, in the form of coronary artery bypass grafting (CABG) in the previous 5 years or percutaneous transluminal coronary angioplasty in the previous 6 months to 5 years in a functionally active patient who is otherwise free of clinical symptoms of ischemia, is associated with a low likelihood of perioperative cardiac events (18). Usually, such patients may proceed to surgery without further cardiac testing.

Has the Patient Been Evaluated for Coronary Artery Disease in the Past Two Years?

In the patients who have been evaluated in the past 2 years with either invasive or noninvasive techniques with favorable findings, no further cardiac workup is generally necessary if they have been free of cardiac symptoms after the test. Patients with changing symptoms or signs of ischemia should be considered for further evaluation (11).

Is the Patient at Risk for Adverse Cardiac Events?

A baseline thorough history and physical examination with 12-lead resting electrocardiogram (ECG) provide important data with which to estimate cardiac risk. Evidence-based clinical predictors of adverse cardiac outcomes are listed in Table 38.1 (11,13,18,19,20,21). These studies have combined various clinical features associated with poor prognosis into composite clinical risk scores to help quantitate the risk of postoperative events. Since then, more simplistic algorithms have been used (5,16,17). If a patient has a major clinical predictor (Table 38.1) and is scheduled for elective surgery, it is best to stratify the patient further by using RCRI, and if indicated, to postpone surgery until the cardiac problem is adequately worked up and optimally treated, if necessary (Fig. 38.1). Patients with moderate or excellent functional capacity and one or more intermediate predictors of clinical risk can normally undergo low- and intermediate-risk surgery (Table 38.2) with low perioperative cardiac risk. Conversely, patients with poor functional capacity or a combination of high-risk surgery, moderate functional capacity, and intermediate clinical predictors of cardiac risk (especially two or more) should be evaluated by further RCRI stratification. In general, patients with minor or no clinical predictors of risk and with moderate or excellent functional capacity [greater than four to six metabolic equivalents (METs)] can safely undergo most types of noncardiac surgery with low risk of cardiac complications (11,16,17).

FIGURE 38.1. A stepwise approach for assessing risk for patients undergoing noncardiac surgery.

TABLE 38.1. Clinical predictors of increased perioperative cardiovascular risk (myocardial infarction, congestive heart failure, death)

Major

Unstable or severe angina (Canadian Cardiovascular Society class III or IV)

Recent myocardial infarction (>7 days but ≤30 days) with evidence of important ischemic risk by clinical symptoms or noninvasive testing

Decompensated CHF

Symptomatic arrhythmias, including high-grade atrioventricular block, symptomatic ventricular arrhythmia in the presence of underlying heart disease, and supraventricular arrhythmias with uncontrolled ventricular rate

Intermediate

Mild angina (Canadian Cardiovascular Society classes I and II)

Prior myocardial infarction documented by history or ECG

Compensated or prior CHF

Diabetes mellitus

Renal insufficiency (creatinine, ≥2.0 mg/dL)

Minor

Advanced age

Abnormal ECG (left ventricular hypertrophy, left bundle-branch block, ST-T abnormalities)

Rhythm other than sinus (e.g., atrial fibrillation)

Low functional capacity

History of stroke

Uncontrolled systemic hypertension

CHF, congestive heart failure; ECG, electrocardiogram.

From: von Knorring J. Postoperative myocardial infarction: a prospective study in a risk group of surgical patients. Surgery 1981;90:55-60; Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100:1043-1049; and Fleisher LA, Beckman JA, Brown KA, et al. ACC/AHA 2006 guideline update on perioperative cardiovascular evaluation for noncardiac surgery: focused update on perioperative beta-blocker therapy: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Update the 2002 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery): developed in collaboration with the American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Rhythm Society, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, and Society for Vascular Medicine and Biology. Circulation 2006;113:2662-2674, with permission.

TABLE 38.2. Surgery-specific cardiac risk (combined risk of cardiac death and nonfatal myocardial infarction)

High (reported cardiac risk, often >5%)

Emergency major operation, particularly in the elderly

Aortic and other major vascular

Peripheral vascular

Anticipated prolonged surgical procedures associated with large fluid shifts or blood loss or both

Intermediate (reported cardiac risk, generally <5%)

Intrathoracic

Intraperitoneal

Carotid endarterectomy

Head and neck

Orthopedic

Prostate

Low (reported cardiac risk, generally <1%)

Endoscopic procedures

Superficial procedures

Cataract

Breast

From: von Knorring J. Postoperative myocardial infarction: a prospective study in a risk group of surgical patients. Surgery 1981;90:55-60; and Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100:1043-1049, with permission.

Functional capacity

Functional capacity (expressed as MET levels) may be classified as excellent (more than 7 METs), moderate (4 to 7 METs), poor (less than 4 METs), or unknown. Table 38.3 represents a sample of activities that characterize each functional class (16,22,23). Functional status is predictive of future cardiac events (24,25) and should be assessed by history in all preoperative patients. However, be mindful that the positive predictive value of poor exercise capacity in the perioperative setting is only 10% (26), with a negative predictive value of 95%. If patients reduce exertion because of cardiac symptoms but are able to achieve 4 METs, the clinician will underestimate risk. Conversely, presence of noncardiac functional limitations (e.g., osteoarthritic knee or hip pain) may lead to a false overestimate of cardiac risk. Thus assessment of exercise tolerance in preoperative risk stratification and precise prediction of inhospital perioperative risk is most applicable in patients who self-report worsening exercise-induced cardiopulmonary symptoms, patients who may benefit from noninvasive or invasive cardiac testing regardless of scheduled surgical procedure, and patients with known coronary artery disease or with multiple risk factors and the ability to exercise. Patients with poor functional capacity facing intermediate- or high-risk surgery should be further stratified by using the RCRI. Patients with moderate or excellent functional capacity and few or no clinical predictors of risk, or patients with a combination of intermediate predictors of cardiac risk, low- or intermediate-risk surgery, and preserved functional capacity, can generally proceed to elective surgery without undergoing further risk stratification or cardiac workup.

TABLE 38.3. Functional-capacity assessment from clinical history

Excellent (activities requiring >7 METs)

Carry 24 lb. up eight steps

Carry objects that weight 80 lb.

Outdoor work (shovel snow, spade soil)

Recreation (ski, basketball, squash, handball, jog/walk 5 mph)

Moderate (activities requiring >4 but <7 METs)

Have sexual intercourse without stopping

Walk at 4 mph on level ground

Outdoor work (garden, rake, weed)

Recreation (roller-skate, dance, foxtrot)

Poor (activities requiring <4 METs)

Shower/dress without stopping, strip and make bed, dust, wash dishes

Walk at 2.5 mph on level ground

Outdoor work (clean windows)

Recreation (play golf, bowl)

MET, metabolic equivalent.

From: von Knorring J. Postoperative myocardial infarction: a prospective study in a risk group of surgical patients. Surgery 1981;90:55-60; Mehta and Eagle; Tarhan S, Moffitt EA, Taylor WF, et al. Myocardial infarction after general anesthesia. Anesth Analg 1977;56:455-461; Mangano DT. Perioperative cardiac morbidity. Anesthesiology 1990;72:153-184; Mahar LJ, Steen PA, Tinker JH, et al. Perioperative myocardial infarction in patients with coronary artery disease with and without aorta: coronary artery bypass grafts. J Thorac Cardiovasc Surg 1978;76:533-537; and Hertzer NR, Beven EG, Young JR, et al. Coronary artery disease in peripheral vascular patients: a classification of 1000 coronary angiograms and results of surgical management. Ann Surg 1984;199:223-233, with permission.

What Is the Risk of Cardiac Complications for a Patient in Relation to the Severity of the Surgical Procedure and the Institutional Experience?

The specific type of surgery also affects the pretest probability of cardiac complications, as depicted in Table 38.2 (11). Emergency surgery is associated with a fourfold to fivefold increase in risk in comparison with elective surgery (13). In addition, patients undergoing aortic, peripheral arterial, and other major vascular surgery or operations associated with large fluid shifts or blood loss have a relatively high probability (nearly twofold to threefold increase) of cardiac complications. Risk classification of various surgical procedures should be considered along with the predictors of clinical risk and functional capacity in properly risk-stratifying patients before noncardiac surgery (11,13,27,28).

What Is the Revised Cardiac Risk Index?

Previous studies have prospectively compared several cardiac risk indices with one another, and the revised cardiac risk index (RCRI) (14) is favored by many, given its excellent accuracy and simplicity (Table 38.4) (14). The RCRI relies on the presence or absence of six identifiable predictive factors, which include high-risk surgery, ischemic heart disease, congestive heart failure, cerebrovascular disease, diabetes mellitus, and renal failure. Each of the RCRI predictors is assigned 1 point, when present. The risk of cardiac events (including myocardial infarction, pulmonary edema, ventricular fibrillation or primary cardiac arrest, and complete heart block) can then be predicted. Based on the presence of 0, 1, 2, 3, or more of these clinical predictors, the rate of major cardiac complications is estimated to be 0.4% to 0.5%, 0.9% to 1.3%, 4% to 6.6%, and 9% to 11%, respectively. Cardiac risk particularly increases with two or more predictors, and is greatest with three predictors or more. The clinical utility of the RCRI is to identify patients at higher risk for cardiac complications, and to determine whether they may benefit from further risk stratification with noninvasive cardiac testing or initiation of preoperative preventive medical management (Figure 38.1).

TABLE 38.4. Revised cardiac risk index clinical markers

1.	High-risk surgical procedures
2.	Ischemic heart disease
	a. History of myocardial infarction
	b. Current angina considered to be ischemic
	c. Requiring sublingual nitroglycerin
	d. Positive exercise test
	e. Pathologic Q-waves on ECG
	f. History of PTCA or CABG or both with current angina considered to be ischemic
3.	Congestive heart failure
	a. Left ventricular failure by physical examination
	b. History of paroxysmal nocturnal dyspnea
	c. History of pulmonary edema
	d. S₃ gallop on cardiac auscultation
	e. Bilateral rales on pulmonary auscultation
	f. Pulmonary edema on chest radiograph
4.	Cerebrovascular disease
	a. History of transient ischemic attack
	b. History of cerebrovascular accident
5.	Diabetes mellitus
	a. Treatment with insulin
6.	Chronic renal insufficiency
	a. Serum creatinine >2 mg/dL
From: Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100:1043-1049.

Is Noninvasive Cardiac Testing Necessary?

Evidence discourages widespread application of preoperative noninvasive cardiac testing for all patients. Rather, a selective approach based on clinical risk categorization appears to be both effective and cost-effective. The selection of noninvasive cardiac stress tests for the occasional patient should anticipate that the patient will meet guidelines for coronary revascularization after coronary angiography or an adjustment in medical therapy, and no testing is recommended when it might delay surgical intervention for urgent or emergency conditions.

Current thought recognizes the potential benefit of occasional coronary revascularization through identification of asymptomatic but high-risk patients (patients with left main, left main equivalent disease, or triple coronary vessel disease with poor left ventricular function). However, that evidence does not support aggressive attempts to identify intermediate-risk patients with asymptomatic but advanced coronary artery disease for which coronary revascularization appears to offer little advantage over excellent medical therapy (29,30).

The ACC/AHA Guidelines on Perioperative Cardiovascular Evaluation summarize recommendations for supplemental preoperative evaluation in patients whose clinical history, physical examination, or exercise tolerance suggests that they are intermediate to high risk regardless of planned major noncardiac surgery (11). Based on the RCRI score, evidence-based medical therapy is appropriate to reduce perioperative cardiovascular risk in selected intermediate (RCRI score 1 to 2) to high-risk (RCRI score 3 or more) patients (14). A stepwise approach is illustrated in Fig. 38.1. Patients with an RCRI score of 3 or more should be considered for either preoperative noninvasive cardiac testing or initiation of perioperative medical therapy if either limited or no ischemia occurs during stress testing or if risks of coronary revascularization are thought to exceed any potential benefit. An RCRI score greater than 3 in patients with severe myocardial ischemia suggestive of left main or three-vessel disease should lead to consideration of coronary revascularization before noncardiac surgery for appropriate patients.

Noninvasive cardiac testing is most appropriate if it is anticipated that a patient will meet guidelines for coronary angiography and coronary revascularization in the event of a very positive test. Thoughtful selection of tests recognizes that pharmacologic stress tests are more useful in patients with functional limitations as compared with exercise testing. Dobutamine echocardiography and nuclear perfusion testing for purposes of identifying patients at risk for perioperative myocardial infarction or death have excellent negative predictive values (near 100%) but poor positive predictive values (less than 20%). Thus a negative study is reassuring, but a positive study is still a relatively weak predictor of a “hard” perioperative cardiac event. Which higher-risk patients’ are most likely to benefit from preoperative noninvasive cardiac testing and treatment strategies to improve outcomes is not well defined.

Evidence-based Indications for Noninvasive Cardiac Testing in Perioperative Assessment

Exercise testing:

Historically the role of exercise stress testing in preoperative assessment has been described in numerous studies (31,32,33,34,35). McPhail et al. (34) reported using preoperative exercise testing in 100 patients undergoing vascular surgery and that the highest cardiac complication rate (33%) was evident in patients with exercise-induced ischemia and low workload achieved. Cutler et al. (33) documented that the ability to attain 75% to 85% of maximal age-predicted heart rate was predictive of a low rate of perioperative cardiac events. Poor functional capacity associated with ischemia indicated high risk for perioperative cardiac events (36). According to the guidelines of the ACC/AHA (11), preoperative cardiac exercise testing is recommended for patients with intermediate pretest probability of CAD; prognostic assessment of patients undergoing initial evaluation for suspected or proven CAD; evaluation of subjects with significant changes in clinical status; demonstration of proof of myocardial ischemia before coronary revascularization; evaluation of adequacy of medical treatment; and prognostic assessment after an acute coronary syndrome. In patients with baseline ECG abnormalities and inability to exercise secondary to comorbid conditions, pharmacologic stress echocardiography or nuclear imaging is preferred.

Pharmacologic stress test and myocardial perfusion imaging

The utility of preoperative dipyridamole-thallium imaging for risk stratification was first reported by Boucher et al. (37) in 1985 and has since been validated in numerous investigations (27,38,39,40,41,42,43). The positive predictive value has been consistently low, between 6% and 67% (44,45). This is attributed in part to the fact that stress-testing results are now used for risk modification in the form of preoperative coronary revascularization, adjustment of medical management, aggressive monitoring, or selection of a different surgical or anesthetic approach. Conversely, pharmacologic stress testing appears to have excellent negative predictive value (between 90% and 100%), making it more useful for reducing risk estimates when negative than for identifying very high risk when positive. The presence of thallium redistribution, especially in increasing numbers of myocardial segments, identifies patients at high risk of perioperative cardiac complications (38,42), whereas the presence of fixed defects identifies patients at intermediate risk, particularly for late cardiac events (41).

Dobutamine stress echocardiography

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