747
From: Essential Cardiology: Principles and Practice, 2nd Ed.
Edited by: C. Rosendorff © Humana Press Inc., Totowa, NJ
41 Assessment of Patients
With Heart Disease for Fitness for Noncardiac Surgery
Joseph Savino, MDand Lee A. Fleisher, MD
INTRODUCTION
The tendency in medicine over the past decade is to decrease preoperative testing, as the evi- dence for improved outcomes for these often expensive procedures is lacking. Population-based management decisions are often steered by clinical trials, cost-effectiveness analysis, and resource allocation. However, few doctors take care of populations. Most of us care for individuals. Evi- dence-based paradigms based on “population medicine” define the most effective management scheme for the vast majority of patients, but not for every patient. Individual patient decisions by attending physicians are not consistently based on evidence but are often made in the context of
“what would I do if it was my mother?” with the premise that more information is better. Should every patient undergoing repair of an abdominal aortic aneurysm undergo dipyridamole or dobut- amine stress testing? The evidence supports not. Nonetheless, the practice in many centers is to obtain a dipyridamole or adenosine thallium stress test even if the patient is asymptomatic. Despite the reassurances provided by large clinical trials, practitioners do not consistently adhere to their recommendations and often rely on tradition, anecdote, and impression in their decision-making.
If physicians are to remain the dispensers of medical care and resources, then we need to be cognizant of the effects of our decisions on all patients, not just the one sitting in the examination room. Exor- bitant sums spent on unnecessary testing exhausts valuable resources that could be diverted to the more needy. Unfortunately, the risk of uncertainty and medicolegal liability results in more testing than is often indicated.
The evaluation of the patient scheduled for anesthesia for noncardiac surgery remains a diagnos- tic dilemma because of competing issues of economics, expediency, and the desire to have a com- plete knowledge base regarding the extent of cardiovascular disease. Multiple medical specialties are involved in the evaluation of the high-risk patient, each of which may have complementary or redundant contributions. In many institutions, anesthesiologists have established preoperative evaluation clinics and the surgeon will defer to the anesthesiologist’s judgment regarding the need for extensive cardiovascular consultation (1). However, these same “preoperative clinics” are at a significant cost to the hospital or the physician practices as their activity is not independently reimbursable by payers, and their cost-effectiveness has never been determined. Not uncommonly, the surgeon may initiate a cardiology consultation. The most effective paradigm to accomplish the preoperative assessment of cardiovascular fitness may be institution dependent, based on allocation of resources and expertise of staff. A preoperative evaluation clinic and a preoperative medical clearance by the primary physician for all patients seems redundant and unnecessary. Whatever the model, the goal of all individuals involved in the care of the surgical patient with heart disease
is to ensure that critical information is attained and communicated to the appropriate personnel so that optimal care can be provided.
CONCEPTS FOR PREOPERATIVE CARDIAC EVALUATION
The underlying premise for the need for preoperative evaluation is that the information will be used to modify perioperative care and improve outcome. The preoperative evaluation will also be used to provide the patient and physicians with information to assess risk and to determine if the ben- efits of the planned procedure outweigh these risks. The benefits of some elective surgeries may be small or may not accrue for several years. Alternatives to complex surgery, such as external beam or seed radiation implants for the treatment of prostate cancer, may be preferable for the patient at high risk of perioperative cardiac morbidity. Endovascular stents for the treatment of aortic aneurysm have revolutionized the discipline of vascular surgery (2). Initially considered an alternative for the aortic aneurysm patient who was considered at high risk for surgery and aortic clamping, stenting has rapidly become the treatment of choice for many patients, even in the absence of comorbidity.
The most important role is the evaluation of patients with unstable symptoms, as these patients have been shown to be at prohibitive risk (3). Management of unstable cardiovascular symptoms is achieved prior to elective surgery because the risk of tachycardia, hypercoagulability, and plaque rupture may be greater during the perioperative period. Coronary revascularization should be con- sidered for patients with unstable angina, although the culprit lesion for a postoperative myocar- dial infarction is not reliably the coronary artery with the angiographically most significant stenosis (4). Alternative treatment strategies need to be considered if the procedure is emergent. The use of invasive monitoring during anesthesia and surgery is not without cost and risks. The use of a pulmonary artery catheter is unlikely to change outcome (5). The preoperative evaluation should be used to identify those individuals for whom postoperative intensive care is warranted.
ROLE OF THE CONSULTANT
As outlined in the recent American Heart Association/American College of Cardiology Guide- lines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery, the role of the consult- ant is to define the extent and stability of a patient’s cardiac disease and determine if the patient is in optimum medical condition (6).Unfortunately, there is no assurance that optimization of pre- operative disease leads to improved outcome, although it appears that postoperative myocardial infarction and death are more likely to occur in patients with preexisting left main or three-vessel coronary artery disease (4). If these patients can be identified in advance of their surgery, treatment or alternatives to surgery can be sought. There is a small but growing body of data that suggests that risk modification may actually improve outcome in the operative setting. The treatment of active coronary artery disease is efficacious before surgery. The perceived benefit of treatment of heart failure before surgery is based on the increased morbidity associated with NYHA class III and IV heart failure. Systolic or diastolic dysfunction leading to heart failure may produce the greatest car- diovascular risk, especially if the etiology is ischemic heart disease (7). The incidence of diastolic dysfunction and abnormal ventricular filling is often ignored during preoperative assessment, despite its marked prevalence in the aged (8). Although studies in surgical patients are lacking, diastolic dysfunction has been associated with significant increases in “all-cause” mortality during long term follow-up after adjustment for age, gender, and ventricular ejection fraction (9). An asympto- matic systolic murmur warrants an echocardiogram to assess aortic and mitral valve function. Occult aortic stenosis can lead to a catastrophic response to the vasodilatory effects of anesthetic induc- tion or neuroaxial blockade and sympathectomy. Mitral regurgitation is typically better tolerated, as the vasodilation during anesthesia typically decreases regurgitant fraction and improves for- ward flow. Rheumatic mitral stenosis is much less common, but may become symptomatic during the perioperative period, especially during pregnancy. Severe pulmonary hypertension with mitral disease may lead to right heart failure and circulatory instability. Patients with prosthetic valves
need meticulous attention to bacterial prophylaxis, depending on the nature of the operation. A growing population in the United States is adults with corrected congenital heart disease who often present with complex reconstruction of the great vessels of the mediastinum, residual shunts, pul- monary hypertension, and increased risk of endocarditis. Pathophysiology can vary significantly among cohorts of patients who carry the same diagnosis. Their response to intraoperative derange- ments may differ substantially, not allowing them to be considered under the same rubric (10).
Preoperative assessment often includes echocardiography, electrocardiogram, and chest radiograph.
Age-related cardiovascular disorders, as well as postoperative cardiac residua, need to be considered in their preparation for noncardiac surgery. Aggressive control of blood glucose levels during and after surgery leads to a decrease in wound infection, renal insufficiency, other major comorbidities, and mortality in surgical patients in the intensive care unit (11). It is appropriate to suggest that aggressive perioperative glucose control in diabetics begins with the preoperative period and the preoperative assessment. The benefits of preoperative “optimization” of hypertension, hypercho- lesterolemia, and smoking cessation are less clear. From the anesthesiologist’s perspective, the necessary critical factors that modify intraoperative technique and monitoring are preexisting dis- ease and the complexity of the operative procedure. The guidelines state that the specific choice of anesthetic technique and agents are best determined by the anesthesia providers (6). Inhalation anes- thetics pose a potential advantage (preconditioning) and disadvantage (steal effect) in patients with coronary artery disease (12–14). The choice of anesthetic technique and agents does not influence cardiovascular outcome. There appears to be no evidence to support the use of regional (epidural and spinal) anesthesia over general anesthesia. Hence, the preoperative evaluation should target not the type of anesthetic, but rather the patient’s condition in the context of the planned operation.
PATHOPHYSIOLOGY OF PERIOPERATIVE CARDIAC EVENTS
The pathophysiology underlying perioperative cardiac events is multifactorial, which influences the potential value of preoperative cardiac testing. There has been a great deal of attention focused on the association of perioperative myocardial ischemia and cardiac morbidity. In several large- scale studies, the presence of postoperative ischemia had the strongest association with myocar- dial infarction and cardiac death (15,16). Further analysis has suggested that prolonged ischemia is a critical factor for predicting events (17). If mismatches of supply and demand in patients with critical coronary stenoses are the underlying substrate for these events, then either coronary revas- cularization or tight hemodynamic management should reduce morbidity (Fig. 1). The use of -adre- nergic blockade has been associated with a reduction in perioperative myocardial ischemia and a significantly improved long-term survival (18,19).Statins and their lipid-modifying and antiinfl- ammatory properties were associated with a reduction in operative mortality in patients undergoing major noncardiac vascular surgery (20). Maintenance of normothermia significantly decreased the rate of cardiac complications in a randomized clinical trial of intraoperative forced-air warming (21).
Anemia (hematocrit <28%) was associated with an increased incidence of cardiac morbidity in a small cohort study (22). All of these factors could contribute to ischemia, which, if prolonged, may lead to infarction. Yet symptomatic cardiac events and cardiac death may result from acute coronary thrombosis of a noncritical stenosis. Plaque rupture and acute coronary thrombosis and occlusion occur in preexisting critical and noncritical coronary lesions. Downstream myocardium in the latter case may be at greater risk than myocardium supplied by a significantly obstructed coronary artery, because there is unlikely to be an established collateral circulation (4). Preoperative evalua- tion of significant preoperative coronary disease fails in this instance in identifying a high-risk event.
Value may be gained by affecting the coagulation profile of surgery (23). It is unclear which surgical procedures and which anesthetics are associated with an increased propensity for arterial thrombosis.
CARDIAC RISK INDICES
Does treating the risk factor change the risk? Many studies have adopted the approach of defin- ing a cohort of patients, identifying risk factors, and using multivariate modeling to determine those
factors associated with increased risk. A major limitation was the assumption that the intraoperative period is a “black box,” and that care is not modified by knowledge of the risk factor. Once a risk factor is identified, anesthesiologists will often attempt risk modification in an attempt to reduce risk, such as the use of -blockers in the setting of known coronary artery disease. Risk modifica- tion is not without controversy. In only a few instances has risk modification been associated with improved outcome. Caution is heeded when risk modification poses a significant risk of its own.
In the aggressive management of blood glucose levels after surgery in the intensive care unit, for example, despite hourly checks, the incidence of hypoglycemia increased 10-fold (11).
There are numerous specific disease states that increase perioperative risk. Cardiovascular dis- ease is the most extensively studied, with the goal of identifying patients at greatest risk for fatal and nonfatal myocardial infarctions. In 1977, Goldman and colleagues at Massachusetts General Hospital (24) used multivariate logistic regression to demonstrate that nine clinical factors were associated with increased morbidity and mortality in a population of 1001 patients over the age of 45 yr (Table 1). Each of these risk factors was associated with a given weight in the logistic regres- sion equation, which was converted into a point system to calculate the Goldman Cardiac Risk Index.
A higher point total resulted in a higher risk index and greater likelihood of a cardiac event. The validity of this classic study has not survived the test of time, as perioperative care has improved outcome and decreased complications. Hence, the current relevance of the Goldman Index is that risk stratification is a dynamic process. We have made substantial strides toward improvements in cardiovascular outcomes since 1977 and anticipate further advances in the years to come.
Other investigators have attempted to develop risk indices. Detsky studied a cohort of individu- als who were referred to an internal medicine service for preoperative evaluation (Table 2) (25).
Many of the factors identified by Goldman were confirmed or slightly modified in the Detsky index, although angina was added to the risk factors. Detsky realized that the nature of the planned opera- tion affected the risk of a complication. Detsky advocated the calculation of a pretest probability of complication based upon the type of surgery, after which the Modified Risk Index is applied using a nomogram. The Detsky index, defined in 1987, has been advocated as the starting point for risk stratification for the American College of Physicians Guidelines on preoperative evalua- tion published a decade later (26). Hence, the overall probability of complications can be estimated as a function of both the surgical procedure and patient disease.
Fig. 1. Pathophysiology of acute coronary syndromes during the perioperative period. In the setting of a coro- nary stenosis, the normal ability of vasculature to adjust flow and meet an increase in myocardial oxygen demand is limited. Even if demand is steady, acute decreases in oxygen supply can occur. Both conditions may lead to myocardial ischemia. Prolonged ischemia, in turn, may lead to infarction, although an alternative hypothe- sis implicates plaque rupture and thrombus formation at a noncritical stenosis. HR, heart rate; CBF, coronary blood flow; HCT, hematocrit.
Table 1
Computation of the Cardiac Risk Index
Multivariate discriminant
Criteria function coefficient “Points”
I. History:
a. Age >70 yr 0.191 5
b. MI in previous 6 mo 0.384 10
II. Physical examination:
a. S3 gallop or JVD 0.451 11
b. Important VAS 0.119 3
III. Electrocardiogram:
a. Rhythm other than sinus or PACs on last preoperative ECG 0.283 7 b. >5 PVCs/min documented at any time before operation 0.278 7 IV. General status:
PO2 < 60 or PC02 > 50 mmHg, K < 3.0 or HCO3 < 20 mEq/L, 0.132 3 BUN > 50 or Cr > 3.0 mg/dL, abnormal SGOT, signs of
chronic liver disease, or patient bedridden from noncardiac causes 3 V. Operation:
a. Intraperitoneal, intrathoracic, or aortic operation 0.123 3
b. Emergency operation 0.167 4
Total possible 53 points
MI, myocardial infarction; JVD, jugular vein distention; VAS, valvular aortic stenosis; PACs, premature atrial con- tractions; ECG, electrocardiogram; PVCs, premature ventricular contractions; PO2, partial pressure of oxygen; PCO2, partial pressure of carbon dioxide; K, potassium; HCO3, bicarbonate; BUN, blood urea nitrogen; Cr, creatinine; SGOT, serum glutamic oxalacetic transaminases. (From ref. 24 with permission.)
Table 2
Modified Cardiac Risk Index by Detsky et al.
Variables Points
Angina
Class IV 20
Class III 10
Unstable angina <3 mo 10
Suspected critical aortic stenosis 20
Myocardial infarction
<6 mo 10
>6 mo 5
Alveolar pulmonary edema
<1 wk 10
Ever 5
Emergency surgery 10
Sinus plus atrial premature beats or rhythm other than sinus
on preop ECG 5
>5 PVCs at any time before surgery 5
Poor general medical status 5
Age >70 yr 5
Reproduced with permission from ref. 25.
In an attempt to update the original Cardiac Risk Index, investigators at Brigham and Women’s Hospital studied 4315 patients aged 50 yr undergoing elective major noncardiac procedures in a tertiary-care teaching hospital (27). Six independent predictors of complications were identified and included in a Revised Cardiac Risk Index: high-risk type of surgery, history of ischemic heart
disease, history of congestive heart failure, history of cerebrovascular disease, preoperative treat- ment with insulin, and preoperative serum creatinine >2.0 mg/dL. Rates of major cardiac complica- tion increased with an increasing number of risk factors.
CLINICAL RISK FACTORS (TABLE 3)
In virtually all studies, the presence of active congestive heart failure (CHF) is associated with the highest perioperative risk. The American College of Cardiology/American Heart Association Guidelines differentiate active CHF, which is considered a major risk factor, from compensated CHF, which is considered an intermediate risk factor.
Time from a prior MI has traditionally been an important predictor of perioperative risk. The more recent the myocardial infarction, particularly within 3 to 6 mo, the greater the perioperative risk (28–30). However, like the Goldman Index, medicine has changed and outcomes are improved.
The classic Rao paper published in 1983 cited a reinfarction rate of nearly 30% if noncoronary surgery occurred within 3 mo of a prior infarction. These catastrophic events had a very high mortal- ity rate. With the advent of dedicated postoperative intensive care units, more vigilant monitoring, and early intervention, the postoperative reinfarction rate has decreased to almost an order of mag- nitude less (31). The ACC/AHA Guidelines advocate the use of 30 d as the acute period, with high risk continuing up to 6 to 8 wk (6). After that time, a prior MI places the patient in the intermediate clinical risk category and further evaluation depends on clinical symptoms.
Table 3
Clinical Predictors of Increased Perioperative Cardiovascular Risk (Myocardial Infarction, Congestive Heart Failure, Death) Major
Unstable coronary syndromes
Recent myocardial infarctiona with evidence of important ischemic risk by clinical symptoms or noninvasive study
Unstable or severb angina (Canadian Class III or IV)c Decompensated congestive heart failure
Significant arrhythmias
High-grade atrioventricular block
Symptomatic ventricular arrhythmias in the presence of underlying heart disease Supraventricular arrhythmias with uncontrolled ventricular rate
Severe valvular disease Intermediate
Mild angina pectoris (Canadian Class I or II)
Prior myocardial infarction by history or pathological Q waves Compensated or prior congestive heart failure
Diabetes mellitus
Chronic renal insufficiency 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 (e.g., inability to climb one flight of stairs with a bag of groceries) History of stroke
Uncontrolled systemic hypertension ECG indicates electrocardiogram.
aThe American College of Cardiology National Database Library defines recent MI as greater than 7 d but less than or equal to 1 mo (30 d).
bMay include “stable” angina in patients who are unusually sedentary.
cCampeau L. Grading of angina pectoris. Circulation 1976;54:522–523.
ECG, electrocardiogram. (Reproduced with permission from ref. 6.)
The presence of angina has not consistently been established as a risk factor. However, the pres- ence of unstable angina was associated with a 28% incidence of perioperative MI (3). Such patients would benefit from the delay of surgery and stability of the coronary symptoms. For patients with chronic stable angina, exercise tolerance appears to be a good method of assessing risk. The ACC/
AHA Guidelines advocate the use of the Canadian Cardiovascular Society Classification as a means of stratifying risk, with those in class III or IV at high risk, and class I and II considered intermediate risk.
Risk Factors for Coronary Artery Disease
Hypertension has not been found to be an independent risk factor for perioperative myocardial infarction, heart failure, or arrhythmia in the vast majority of studies, but was shown to be predic- tive of perioperative myocardial ischemia. The history of hypertension should be a cue to the prac- titioner to target the cardiovascular system in preoperative questioning and evaluation. The patient with a sustained diastolic blood pressure greater than 110 mmHg often triggers a delay in surgery, although the data do not support such an assertion (32,33). In fact, none of the patients with “uncon- trolled systemic hypertension” sustained a major cardiac event, and the authors (33) simply state that surgery is safe with hypertension up to a diastolic of 110 mmHg. Patients with a diastolic blood pressure greater than 110 mmHg may be at risk for hemodynamic lability, but there appears to be no increased risk of postoperative complications (32). They are more likely to develop hypotension and hypertension during anesthesia and surgery, but no evidence suggests they are at increased risk of MI. Isolated systolic hypertension was shown in one study of coronary artery bypass graft- ing (CABG) to be associated with a 30% increase in cardiovascular complications (34). Chronic hypertension may increase cardiac risk simply because coronary artery disease is more prevalent in this patient cohort. Left ventricular hypertrophy, particularly with a strain pattern, has been asso- ciated with an increased risk of perioperative myocardial ischemia (35).
Diabetes has been associated with a high incidence of perioperative cardiac morbidity in several studies, particularly those involving vascular surgery patients (36). Diabetics have a high incidence of both silent ischemia and silent myocardial infarction (37). Based on the preponderance of evi- dence regarding the high incidence of cardiac morbidity in diabetic patients, particularly those with concomitant peripheral vascular disease, the ACC/AHA Guidelines consider diabetes a moderate risk. As mentioned above, aggressive glucose control during surgery and postoperatively appears to affect outcome in patients who remain in the intensive care unit for several days.
IMPORTANCE OF SURGICAL PROCEDURE
It is well recognized that the surgical procedure itself significantly influences perioperative risk. In virtually every study performed, emergency surgery is associated with additional risk. The mechanism of this phenomenon has eluded explanation. Plausible mechanisms include that the underlying emergent or volatile condition is more vulnerable to the perturbations and stresses of surgery. Perhaps the care team is less prepared for emergency surgery compared with the elective case with an unhurried review and plan. The risk related to the surgical procedure is often a func- tion of both the underlying disease processes and the stress related to the specific procedure. Vascu- lar surgical procedures are represents among the highest risk group of the noncardiac procedures.
Although aortic reconstructive surgery has traditionally been considered the highest-risk vascular procedure, infrainguinal vascular procedures have a similar rate of cardiac morbidity, likely due to an increased severity of coronary disease in the infrainguinal patients (38).
In contrast to the high-risk vascular operations, the perioperative complication rate is very low for superficial procedures. Backer et al. evaluated the rate of perioperative myocardial reinfarction in patients undergoing ophthalmologic surgery and demonstrated that the rate of perioperative car- diac morbidity was extremely low, even in patients with a recent myocardial infarction (39). Virtu- ally all studies have confirmed that ophthalmologic surgery is very safe under anesthesia, further supporting the premise that risk is not independent of the operation. Warner et al. studied patients undergoing ambulatory surgery, and reported no anesthetic deaths in more than 45,000 cases (40).
The association of invasive surgery and increased complications is a major impetus for increasing minimally invasive operations.
Eagle and colleagues evaluated the contribution of coronary artery disease and its treatment on perioperative cardiac morbidity and mortality by surgical procedure (41). They evaluated patients enrolled in the Coronary Artery Surgery Study who had documented coronary artery disease and received either medical therapy or coronary revascularization and then underwent noncardiac sur- gery during the subsequent 10-yr period. The rates of perioperative myocardial infarction and death were determined, and the surgical procedures were divided into three broad categories. Major vas- cular surgery was again demonstrated to be associated with the highest risk, with a combined mor- bidity and mortality greater than 10%. Procedures associated with a combined complication rate greater than or equal to 4% included intraabdominal, thoracic, and head and neck surgeries. In all of these cases, patients who had prior CABG had a significantly lower combined morbidity and mortality than the medically treated group. Low risk procedures included breast, skin, urologic, and orthopedic surgery. These broad groups of surgical procedures were the basis for defining surgical risk in the AHA/ACC Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Sur- gery (Table 4) (6).
IMPORTANCE OF EXERCISE TOLERANCE
There is disagreement on the value of using exercise tolerance as a means of determining peri- operative risk. Specifically, the AHA/ACC Guidelines advocate its use, while the American College of Physicians Guidelines suggest there is insufficient evidence for its use. A lack of evidence does not translate into evidence of a lack of effect, and most clinicians have advocated its use. Several studies demonstrate that the ability to raise heart rate on a stress test is the strongest predictor of perioperative outcome (42). Excellent exercise tolerance, even in patients with stable angina, sug- gests that the myocardium can undergo the stress of surgery without becoming dysfunctional. Exer- cise tolerance can be assessed with formal treadmill testing or with a questionnaire that assesses activities of daily living (Table 5) (6). The inability to walk four blocks and climb two flights of stairs increased the incidence of cardiovascular complications during surgery twofold compared to patients with improved functional status (43). Hence, exercise capacity can determine the need for further diagnostic testing.
Table 4
Cardiac Riska Stratification for Noncardiac Surgical Procedures High (Reported cardiac risk often >5%
Emergent major operations, particularly in the elderly Aortic and other major vascular
Peripheral vascular
Anticipated prolonged surgical procedures associated with large fluid shifts and/or blood loss
Intermediate (Reported cardiac risk generally <5%) Carotid endarterectomy
Head and neck
Intraperitoneal and intrathoracic Orthopedic
Prostate
Lowb (Reported cardiac risk generally <1%) Endoscopic procedures
Superficial procedure Cataract
Breast
aCombined incidence of cardiac death and nonfatal myocardial infarction.
bDo not generally require further preoperative cardiac testing. (Reproduced with permission from ref. 6.)
Approach to the Patient
The American College of Cardiology/American Heart Association Task Force has published Guidelines on Perioperative Evaluation of the Cardiac Patient Undergoing Noncardiac Surgery based on the available evidence and expert opinion. The approach advocated integrates clinical history (Table 3), surgery specific risk, and exercise tolerance (Fig. 2) (6). First, the clinician must evaluate the urgency of the surgery and the appropriateness of a formal preoperative assessment.
Next, determine whether the patient has undergone a previous revascularization procedure or coronary evaluation. Patients with unstable coronary syndromes should be identified, and appro- priate treatment instituted. Finally, the decision to undergo further testing depends on the inter- action of the clinical risk factors, surgery-specific risk, and functional capacity. For patients at intermediate clinical risk, both the exercise tolerance and the extent of the surgery are taken into account with regard to the need for further testing.
The authors of the guidelines suggest that all patients undergoing aortic or infrainguinal bypass surgery should be considered at high surgical risk, and therefore further evaluation should be con- sidered. In an editorial in Annals of Internal Medicine, two of the authors of the guidelines (Fleisher and Eagle) suggest that routine preoperative testing of all major vascular patients would lead to a high incidence of false positive test, and advocate a more Bayesian approach (44).
The American College of Physicians Guidelines apply an evidence-based approach (26). The initial decision point is the assessment of risk using the Detsky modification of the Cardiac Risk Index. If the patient is class II or III, he or she considered high-risk. If they are class I, the presence of other clinical factors, according to work by Eagle and colleagues (36) or Vanzetto and colleagues (45), are used to further stratify risk. Those with multiple markers for cardiovascular disease accord- ing to these risk indices and those undergoing major vascular surgery are considered appropriate for further diagnostic testing by either dipyridamole imaging or dobutamine stress echocardiography.
Coronary Revascularization
Patients who survive CABG are at decreased risk for subsequent noncardiac surgery (46).While there are few data to support the notion of coronary revascularization solely for the purpose of im- proving perioperative outcome, it is true that for specific patient subsets long-term survival may be enhanced by revascularization. Rihal et al. utilized the Coronary Artery Surgery Study database and found that CABG significantly improved survival in those patients with both peripheral vascular disease and triple-vessel coronary disease, especially the group with decreased ventricular function (47). In contrast, McFalls and colleagues demonstrated no difference in 30-d and 2.7-yr outcomes in patients with mild to moderate coronary artery disease undergoing vascular surgery who were randomized to medical therapy versus coronary revascularization (48).
Table 5
Estimated Energy Requirement for Various Activitiesa
1 MET Can you take care of yourself? 4 METs Climb a flight of stairs or walk up a hill?
Eat, dress, or use the toilet? Walk on level ground at 4 mph or 6.4 km/h?
Walk indoors around the house? Run a short distance?
Walk a block or two on level ground Do heavy work around the house like at 2–3 mph or 3.2–4.8 km/h? scrubbing floors or lifting or moving heavy Do light work around the house like furniture?
dusting or washing dishes? Participate in moderate recreational activities like golf, bowling, dancing, doubles tennis, or throwing a baseball or football?
>10 METs Participate in strenuous sports like swimming, singles tennis, football, basketball, or skiing?
aAdapted from the Duke Activity Status Index and AHA Exercise Standards.
MET, metabolic equivalent. (Reproduced with permission from ref. 6.)
Fig. 2. The American Heart Association/American College of Cardiology Task Force on Perioperative Eval- uation of Cardiac Patients Undergoing Noncardiac Surgery has proposed an algorithm for decisions regarding the need for further evaluation. This represents one of multiple algorithms proposed in the literature. It is based on expert opinion, and incorporates six steps. First, the clinician must evaluate the urgency of the surgery and the appropriateness of a formal preoperative assessment. Next, he or she must determine whether the patient has had a previous revascularization procedure or coronary evaluation. Patients with unstable coronary syn- dromes should be identified, and appropriate treatment should be instituted. The decision to have further testing depends on the interaction of the clinical risk factors, surgery-specific risk, and functional capacity. (Adapted with permission from the ACC/AHA Guidelines for Perioperative Cardiovascular Evaluation for Noncardiac Surgery [ref. 6].)
The value of percutaneous transluminal coronary angioplasty (PTCA), drug-eluting stents, ather- ectomy, and aggressive risk modification are well established in the nonsurgical population. In several series, a low incidence of cardiovascular complications was observed in patients under- going “prophylactic” PTCA before vascular surgery, but it is difficult to determine the expected complication rate in a comparison group with single- or double-vessel disease (49,50). For peri- operative MIs that result from plaque rupture and coronary thrombosis in noncritical lesions, as seen in the ambulatory setting, single-vessel PTCA of more critical stenoses will theoretically have minimal benefit. Ellis et al. studied 21 patients who had coronary angiography before major vas- cular surgery and sustained a perioperative cardiac event (4). None of the myocardial infarctions occurred in areas distal to a critical stenosis, while approximately one third occurred distal to non- critical stenoses (4). An administrative dataset from Washington State was analyzed to assess the value of preoperative PTCA using a case-controlled approach (51). Patients who had undergone a PTCA more than 6 wk prior to noncardiac surgery had an improved outcome compared to matched controls with coronary artery disease, while no difference in outcome was observed if the period between PTCA and noncardiac surgery was less than 6 wk. Although analysis of administrative datasets has some inherent limitations related to an inability to determine the potential selection bias for those being treated, these data suggest that “prophylactic” PTCA simply to get the patient through surgery may be of minimal or no benefit. Coronary stent placement may be a unique issue.
In a case series of 39 patients who had undergone coronary stent placement within 1 mo of noncar- diac surgery there was a significant incidence of perioperative death and major bleed for patients who had surgery within 14 d of stent placement (53). Wilson and colleagues identified 207 patients who underwent surgery in the 2 mo following successful coronary stent placement (54). Eight patients died or suffered a myocardial infarction or stent thrombosis among the 168 patients undergoing surgery 6 wk after stent placement. No events occurred in the 39 patients undergoing surgery 7 to 9 wk after stent placement. These data suggest that, whenever possible, noncardiac surgery should be delayed 6 wk after stent placement, by which time stents are generally endothelialized, and a course of antiplatelet therapy to prevent stent thrombosis has been completed.
Boersma and colleagues reevaluated the value of dobutamine stress echocardiography with respect to the extent of wall motion abnormalities and use of -blockers during surgery for the entire cohort of patients screened for the Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography (DECREASE) trial (55). They assigned one point for each of the following characteristics: age 70 years, current angina, myocardial infarction, congestive heart failure, prior cerebrovascular accident, diabetes mellitus, and renal failure. As the total of number of clinical risk factors increases, perioperative cardiac event rates also increase. When the risk of death or myocardial infarction was stratified by perioperative -blocker usage, there was no significant improvement in those without any of the prior risk factors. In those with a risk factor score between 0 and 3, which represented over half of all patients, the rate of cardiac events was reduced from 3% to 0.9%. Most importantly, in those without at least three risk factors, comprising 70% of the population, -blocker therapy was very effective in reducing cardiac events in those with new wall motion abnormalities in 1 to 4 segments (33% vs 2.8%), having smaller effect in those with- out new wall motion abnormalities (5.8% vs 2%), but had no effect in those patients with new wall motion abnormalities in 5 segments. The group with extensive wall motion abnormalities may be the group to consider for coronary revascularization.
Risks vs Benefits of Coronary Revascularization
An alternative approach to determining the optimal strategy for medical care in the absence of clinical trials is construction of a decision analysis. Three decision analyses have been published on the issue of cardiovascular testing before major vascular surgery (52,56,57). All assumed that patients with significant coronary artery disease would undergo coronary artery bypass grafting prior to noncardiac surgery. Using decision analysis modeling, preoperative testing for the pur- pose of coronary revascularization is not the optimal strategy if perioperative morbidity and mor-
tality is low (52,56,57). The primary cost (both in dollars and morbidity) of preoperative testing and revascularization is the revascularization procedure itself. Therefore, the indications for revas- cularization, and thus the frequency of its use, have a significant impact on the model. However, potential long-term benefits of coronary revascularization in this population were included in only one analysis. If long-term survival is enhanced by revascularization, then it may lead to improved overall outcome and be a cost-effective intervention (57). Hence, a patient’s age should be included in the equation. An 80-yr-old diabetic patient with significant comorbid diseases may gain few additional life-years and may actually have a decrease in the quality of the final years by under- going CABG. In contrast, a 55-yr-old man with an abdominal aortic aneurysm and left main disease would have a substantial increase in both the length and quality of his life from preoperative car- diovascular testing and coronary revascularization. Therefore, identification of appropriate patients with significant disease or left main stenosis amenable to surgery with an acceptable risk should undergo revascularization before high-risk noncardiac surgery.
CHOICE OF DIAGNOSTIC TEST
Exercise electrocardiography is a useful test to diagnose CAD, but is rarely indicated preopera- tively since it requires the patient to have a good exercise capacity (therefore not requiring testing).
There have been a number of studies that suggest that preoperative ambulatory electrocardiography for silent myocardial ischemia is a sensitive and specific test for perioperative cardiac events;
however, there are two major problems. The majority of patients at highest risk have electrocardio- grams that prohibit the accurate diagnosis of silent ischemia, and attempts to relate the amount of preoperative ischemia and degree of risk have not been conclusive. In a study comparing preoper- ative ambulatory electrocardiography to dipyridamole thallium imaging, those patients with a greater number of minutes of preoperative ischemia did not have an increased perioperative and long-term risk compared with those with a shorter duration of preoperative ischemia (56).
For patients who are unable to exercise, particularly those undergoing major vascular surgery with claudication, pharmacologic stress testing has been advocated. A redistribution defect on dipy- ridamole thallium imaging in vascular patients predicts postoperative cardiac event, with the larger the defect the more serious the risk. The negative predictive value of dipyridamole thallium imaging has consistently been high (above 90%), although the positive predictive value has decreased over time, related to the overall decrease in perioperative cardiac morbidity. The test is best utilized, and has its best predictive value, in those at moderate clinical risk: patients with multiple risk factors undergoing major vascular surgery (45). Patients at greatest risk have larger areas of reversible defect or increased lung uptake on thallium imaging, and were associated with both an increased incidence of perioperative cardiac morbidity and decreased survival at 2 yr after surgery (57).
Dobutamine stress echocardiography has very good positive and negative predicative values and may most closely mimic the hyperdynamic state seen during the perioperative period. Those patients at greatest risk develop new regional wall motion abnormalities at lower heart rates (58).
Similar to the findings of Eagle et al. for dipyridamole thallium imaging, dobutamine stress echo- cardiography has its best predictive value in those at moderate clinical risk. In two meta-analyses, dobutamine stress echocardiography had the best predictive value, but there was much overlap with dipyridamole imaging (59,61). Other modalities to noninvasively assess coronary burden, such as MRI and CT imaging to quantify coronary calcium, have not been validated as markers for perioperative risk stratification.
SUMMARY
Increasing emphasis is placed on the patient’s symptoms and exercise tolerance. If a patient has reduced exercise tolerance, angina pectoris, heart failure, or anginal equivalents, then further cardio- vascular evaluation is warranted whether or not the patient is preparing for surgery. If the patient with risk factors for coronary artery disease has excellent exercise tolerance and is asymptomatic,
then a further diagnostic workup is not indicated. The perioperative physicians may elect to add
-blockers in an attempt to decrease the incidence of tachycardia and associated perioperative ische- mia. Atenolol and bisoprolol have been shown to decrease cardiovascular morbidity when started preoperatively in patients undergoing noncardiac surgery (6,61), although achievement of thera- peutic levels (as assessed by heart rate control) may be critical to achieving the effect. If there is no indication for stress testing or cardiac catheterization in the absence of surgery, then why should a planned operation trigger the testing? Exercise stress testing is a helpful adjunct in the triage of the high risk patient. High risk is defined by symptoms and activity–exercise tolerance in the con- text of the planned operation. Preoperative evaluation should focus on obtaining information regard- ing the extent and stability of the cardiovascular system in order to modify perioperative management.
The decision to perform further evaluation and diagnostic testing depends on the interactions of patients and surgery-specific factors, as well as exercise capacity.
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RECOMMENDED READING
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