Cardiac Risk Stratification for Noncardiac Surgery

Cardiac Risk Stratification for Noncardiac Surgery



Mazen K. Khalil, Wael A. Jaber


One of the most common questions posed to physicians is about assessment of the cardiac risks of noncardiac surgery. Once the physician estimates the risk of a patient, he or she will be able to apply measures to decrease the risk for the patient and improve the outcome. Often in these cases, an opportunity is created for the first time to address cardiac risk factors in the patient undergoing surgery. This opportunity often is limited by time constraints and short contact with the patient, especially if the surgery is semiurgent or prescheduled at short notice. The major goal is to assess the risk of myocardial infarction, heart failure, or both, the most common causes of morbidity and mortality with noncardiac surgery. The mortality rate among patients with perioperative myocardial infarction ranges from 30% to 50%.


Conversely, there are very few cases in which the surgical outcomes and treatments are affected by extensive preoperative cardiac testing. Although preoperative testing is indicated in some cases, it does not always lead to a scientifically tangible improvement in outcome. Indiscriminate and extensive preoperative cardiac testing is an ineffective way of using health care funds and can lead to more unwarranted and risky procedures. In addition to the loss of resources, unnecessary testing might cause harm to the patient by delaying surgery. For a test to be considered useful it should be accurate, influence outcome, and have a favorable risk-to-benefit ratio. Therefore, it is essential for the physician to identify patients who will benefit most from an in-depth preoperative evaluation. It is important for the physician to explore noncardiac issues (e.g., lung disease, coagulopathy, anemia, renal disease, cerebrovascular events, diabetes) that can negatively affect the outcome of the surgery. A preoperative evaluation should be considered as an opportunity for a thorough medical evaluation in patients who might not have been in contact with the medical system.


There are various factors to be considered when assessing anesthesia and surgical cardiac risks. These are generally divided into patient-related and surgery-specific risks, as well as test-specific considerations (Box 1).



Box 1 Factors to be Considered When Assessing Cardiac Risk



Patient-Related Factors



Age

Chronic diseases (e.g., coronary artery disease, diabetes dellitus, hypertension)

Functional status

Medical therapy

Implantable devices

Previous surgeries


Surgery-Related Factors



Type of surgery (e.g., vascular, endoscopic, abdominal)

Urgency of the operation (e.g., emergent, urgent, elective)

Duration of the operation, possibility of blood loss and fluid shifts


Test-Related Factors



Sensitivity and specificity of a test

Effect on management


CARDIAC RISK INDICES



Goldman Risk Index


About 3 decades ago, Goldman and coworkers developed a user-friendly point system that identified perioperative fatal and nonfatal cardiac events. This system created four classes of risk, depending on the total points accumulated (Table 1).


Table 1 Goldman Multifactorial Cardiac Risk Index

































Risk Factor Points
Preoperative third heart sound or jugular venous distention indicating active heart failure 11
Myocardial infarction in the past 6 months 10
≥5 premature ventricular complexes/min before surgery 7
Rhythm other than sinus 7
Age >70 years 5
Emergency surgery 4
Significant aortic stenosis 3
Intraperitoneal, intrathoracic, or aortic surgery 3
Markers of poor general medical condition (e.g., renal dysfunction, liver disease, lung disease, electrolyte imbalance) 3

Patients in the lowest risk quartile (0 to 5 points) had less than a 1% risk of postoperative major cardiac complications. In the two quartiles with 6 to 25 points, the major cardiac event risk was 9%, and 22% of the patients in the highest risk group (≥26 points) had a major perioperative cardiac event.



Eagle’s Cardiac Risk index


One of the limitations of the Goldman criteria was the inability to predict the operative risk for patients undergoing vascular surgery because of the low number of patients with vascular operations included in the study population. This limitation was addressed by Eagle and colleagues in a study of patients undergoing vascular surgery. Multivariate analysis has shown that the following factors predict an adverse event following vascular surgery:


• Q waves on the electrocardiogram (ECG)

• History of angina pectoris

• History of ventricular ectopy requiring treatment (most specific for predicting events)

• Diabetes mellitus requiring therapy other than diet

• Age older than 70 years

• Thallium redistribution (most sensitive for predicting events)

• Ischemic electrocardiographic changes during or after dipyridamole infusion

Combining both the clinical data and thallium imaging was more sensitive and specific than either alone in predicting postoperative complications. In this model, the following can be noted:


• No clinical predictors of risk factors: 3.1% risk of perioperative ischemic cardiac complications

• Thallium redistribution in addition to one or two clinical predictors: 29.6% risk of perioperative complications

• Three clinical predictors: 50% risk of perioperative cardiac complications


Detsky’s Cardiac Risk Index


A modified cardiac index that included a change in the scores allocated to risk factors such as type of operation, age, frequency of premature ventricular contractions (PVCs), and aortic stenosis was published by Detsky and associates in 1986. However, heart failure was defined in this study as pulmonary edema determined by chest radiograph or by history of severe respiratory distress and resolution of the symptoms by use of diuretics. In addition, angina was subdivided into four classes according to the Canadian Cardiovascular Society classification. The score obtained from the patient’s risk factors, along with the risk associated with the type of surgery, were used to calculate the probability of a cardiac event.



Revised (Lee’s) Cardiac Risk Index


The modified cardiac index was revised by Lee and coworkers, who devised a six-point index score for assessing the risk of complications with noncardiac surgery. The Revised Cardiac Risk Index (RCRI) includes the following variables and risks:


• High-risk surgery (intrathoracic, intra-abdominal. or suprainguinal vascular)

• Ischemic heart disease (defined as a history of myocardial infarction [MI], pathologic Q waves on the ECG, use of nitrates, abnormal stress test, and chest pain secondary to ischemic causes)

• Congestive heart failure

• History of cerebrovascular disease

• Insulin therapy

• Preoperative serum creatinine level higher than 2 mg/dL

Each of the six risk factors was assigned one point. Patients with none, one, or two risk factor (s) were assigned to RCRI classes I, II, and III, and patients with more than two risk factors were considered Class IV. The risk associated with each class was 0.4%, 1%, 7%, and 11% for patients in Classes I, II, III, and IV, respectively. We recommend the use of this index because it is simple, has been extensively validated, and provides a good estimate of the preoperative risk.



American College of Cardiology Cardiac Risk Classification


The American College of Cardiology (ACC) has divided predictors of perioperative risks into three categories: major, intermediate, and minor (Box 2). Patients presenting with major predictors of risk need extensive investigation and postponement or cancellation of elective surgery, or urgent noncardiac surgery might ensue. Minor predictors of risk are not known to influence the perioperative course of patients. Patients with intermediate risk need careful assessment to decide on the need for noninvasive cardiac testing.



Box 2 Clinical Predictors of Increased Perioperative Cardiovascular Risk*


Adapted from Campeau L: Grading of angina pectoris. Circulation 1976;54:522-523.



Major Predictors



Unstable coronary syndromes
• Acute or recent MI† with evidence of important ischemic risk by clinical symptoms or noninvasive study

• Unstable or severe‡ angina (Canadian Class III or IV)

Decompensated 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 Predictors



Mild angina pectoris (Canadian Class I or II)

Previous MI by history or pathologic Q waves

Compensated or prior heart failure

Diabetes mellitus (especially insulin-dependent type)

Renal insufficiency


Minor Predictors



Advanced age

Abnormal ECG (e.g., 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, electrocardiogram; MI, myocardial infarction.



* Myocardial infarction, heart failure, death.


† The American College of Cardiology National Database Library has defined recent MI as >7 days but ≤1 month (30 days); acute MI is within 7 days.


‡ May include “stable” angina in patients who are unusually sedentary.



FACTORS AFFECTING CARDIAC RISK



Patient-Related Factors



Patients with Known Coronary Artery Disease


Patients with known coronary artery disease (CAD) should be classified into a specific risk class according to one of the risk indices cited previously, preferably Lee’s revised cardiac risk index. For patients classified into the low-risk group, we recommend a preoperative ECG and chest radiograph. Postoperative care should include monitoring for ischemia (serial ECGs, cardiac enzyme levels), especially if the patient has had intraoperative hemodynamic instability. We also recommend an ECG before discharge.


If the patient belongs to the intermediate risk group, he or she should be managed aggressively with beta blockers, lipid-lowering agents, and tight blood pressure control. Much debate is ongoing concerning the use of noninvasive stress testing in this patient subgroup. In any case, there is not much evidence supporting the use of revascularization before noncardiac surgery.


Retrospective data analyses of patients who have undergone coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI) months to years before noncardiac surgery have shown a lower incidence of perioperative complications compared with patients who had medical therapy alone. However, the average mortality rate of CABG in the United States in 2002 was 2.6%, which exceeds the risk of surgery in these patients. Furthermore, one study has shown that percutaneous angioplasty performed on stable CAD patients undergoing vascular surgery, with at least one coronary artery having more than 70% stenosis, resulted in no survival benefit over 2.7 years of follow-up.


Another study has revealed that in-stent restenosis might complicate noncardiac surgery if PCI is done within 6 weeks of surgery. In addition, some reports have suggested that the benefit of PCI might not be evident until 90 days after the procedure. To preserve the stent placed during PCI, the patient has to take aspirin and clopidogrel (Plavix) for at least 1 month, which might delay noncardiac surgery further.


More-recent data suggest that with drug-eluting stents, risks of stent thrombosis are high, even 1 year after stent placement, if antiplatelet drugs are stopped. In addition, the percentage of patients who needed revascularization by CABG or PCI was relatively small in most studies. Performing extensive testing to identify these patients is not a cost-effective strategy. Therefore, we recommend managing intermediate-risk patients with extensive medical therapy (see later discussion of medical therapy).


In high-risk patients (RCRI >2 or signs and symptoms of CAD), diagnostic catheterization should be carried out, followed by revascularization if indicated, irrespective of the noncardiac surgical plans.



Patients with Diabetes


Silent myocardial ischemia occurs commonly in diabetic patients because of diabetic neuropathy, even in patients with well-controlled glycemia. In addition, diabetic patients are more predisposed to infection, poor wound healing, and episodes of hypoglycemia and hyperglycemia, which might negatively affect the outcome of noncardiac surgery. Thus, the diabetic patient needs more aggressive evaluation than the euglycemic patient. A study of diabetic patients undergoing noncardiac surgery has concluded that diabetic patients are at high risk for perioperative mortality, mostly because of cardiovascular causes. Assessment should include history, physical examination, and noninvasive testing, depending on the patient’s risk factor profile (ECG, noninvasive imaging stress test, and creatinine level). It is recommended that an adequate glucose level be maintained perioperatively by insulin infusion to decrease the risk of wound infection.



Patients of Advanced Age


The association of age with cardiac and noncardiac complications with noncardiac surgery was significant in an analysis done by Polanczyk and colleagues. Advanced age adversely affects the rate of complications, mortality, and the length of stay. Perioperative mortality risk was low (0.3% in patients 50-59 years of age vs. 2.6% in patients >80 years; P = .002). However, it is unclear from this study whether older patients were excluded from surgery and that therefore the population studied was a low-risk cohort. It is also unclear from the literature whether the criteria of Goldman and Eagle and associates are sufficient to risk-stratify these patients or whether additional testing and triage will lead to improved outcomes.


The revised cardiac risk index predicts major adverse cardiac events (MACE) more reliably in patients younger than 55 years as compared to patients older than 75 years. Welten and colleagues, in a study on vascular surgery patients older than18 years (60% of the patients were >66 years and 20% were >75 years) showed that addition of age and the type of surgical procedure to the RCRI improves its predictive value; older patients were at higher risk for MACE, with the highest risk being in the 66 to 75 years age group.1


Likewise, Feringa and colleagues found that advanced age is an independent predictor of hospital and long-term mortality in patients older than 65 years undergoing major vascular surgery.2 In addition, the use of aspirin, beta blockers, and statins was associated with 47%, 68%, and 65% relative risk reduction of in-hospital mortality, respectively.2 The aforementioned drugs and ACE inhibitors were associated with reduced incidence of long-term mortality in the same study as well.2 Despite the benefit seen in this study, we recommend extreme caution when using beta blockers, diuretics, and other antihypertensive drugs given the reduced clearance of drugs and their metabolites in this age group.



Patients with Hypertension


The main issue with hypertensive patients is whether they have uncomplicated hypertension or hypertension with end-organ damage (e.g., renal dysfunction, cerebrovascular disease, left ventricular hypertrophy, systolic dysfunction, diastolic dysfunction, or coronary artery disease). Patients with hypertension with no evidence of end-organ damage are at no increased risk for major perioperative cardiovascular complications; they can be cleared for surgery without further investigations with tight blood pressure control.


Preoperative cardiac testing (e.g., stress echocardiography, scintigraphy) should be considered if hypertensive patients are undergoing high-risk procedures. If the blood pressure is above 180/110 mm Hg, it is recommended to delay surgery until the blood pressure is normalized. Blood pressure control can take days to weeks, which is acceptable in the setting of elective surgery. However, if the surgery is urgent, blood pressure can be controlled by infusion of IV antihypertensive medications, such as nitroprusside or labetalol. Blood pressure should be lowered slowly because of the risk of cerebral ischemia.


Hypertensive patients with end-organ damage should be considered for preoperative testing (electrocardiography, noninvasive imaging stress test), especially if they are scheduled for moderate- to high-risk surgery. In patients with hypertension and left ventricular hypertrophy, ischemia might ensue because of rapid reduction of coronary perfusion in the thickened ventricle rather than from CAD. Kidney dysfunction is a known sequela of hypertension. An elevated creatinine level is an independent predictor of worse outcome in patients undergoing noncardiac surgery. The serum creatinine level should be determined preoperatively in these patients; testing is indicated if it would change the patient’s treatment. Hypertensive medications should be continued, even on the day of surgery. Withdrawal of beta blockers and clonidine may be associated with adverse operative and postoperative complications.



Patients with Valvular Disease


All patients with prosthetic valves should receive antibiotic prophylaxis before noncardiac surgery. Patients with mitral valve prolapse can undergo surgery without antibiotics. The decision to repair or replace a diseased valve should be made in the context of indications for valve surgery, independently of whether the patient is to undergo noncardiac surgery.



Aortic Stenosis


Patients with severe aortic stenosis (AS) are at risk for fatal and nonfatal complications during noncardiac surgery, as has been shown in many observational studies. Proceeding with noncardiac surgery with uncorrected severe AS might have a mortality rate of 10%. Therefore, patients with symptomatic severe AS should undergo aortic valve replacement before noncardiac surgery. Valvuloplasty is a palliative option in patients who are not candidates for cardiac surgery. This approach is often risky, however, and provides only minimal and temporary benefit. Patients manifesting signs of both CAD and AS should undergo appropriate testing (e.g., cardiac catheterization, echocardiography) followed by coronary revascularization and valve replacement before noncardiac surgery. Patients with isolated asymptomatic severe AS and no evidence of CAD can proceed with minor noncardiac surgery; however, care should be taken to avoid hemodynamic instability and blood pressure fluctuations.1



Mitral Stenosis


Patients with severe mitral stenosis should undergo percutaneous or surgical correction of the stenosis before undergoing noncardiac surgery. For patients with mild to moderate mitral stenosis, care should be taken to avoid tachycardia postoperatively induced by blood loss or surges in catecholamine level. Tachycardia causes decreased filling time of the left ventricle, which can lead to a decreased cardiac output, pulmonary congestion, and congestive heart failure (CHF). If the patient with mitral stenosis is asymptomatic has no evidence of pulmonary hypertension or atrial fibrillation, the risk of noncardiac surgery is not substantially higher than for normal patients.



Aortic and Mitral Regurgitation


The presurgical management of patients with regurgitant aortic and mitral valves depends on the severity and chronicity of the regurgitation. Patients with preserved left ventricular ejection fraction (LVEF) and volumes by echocardiography, as well as good functional capacity, can undergo noncardiac surgery without excess risk. For patients with severe regurgitant valvular lesions, few guidelines are available to describe the indications and appropriateness of valve repair or replacement before noncardiac surgery.1 In patients with aortic regurgitation, hemodynamic intraoperative assessment with a pulmonary artery catheter is recommended to monitor afterload and to prevent hypotension, which can adversely affect these patients.1 Patients with severe mitral regurgitation may be treated with ACE inhibitors and diuretics. Any reduction in the ejection fraction should be considered abnormal and signals increased risk for CHF.1



Prosthetic Valves


Patients with prosthetic valves pose a special problem with anticoagulation. Stopping anticoagulation preoperatively can increase the risk of thromboembolic events. Patients with mitral valve mechanical prostheses are at a higher risk than patients with aortic valve mechanical prostheses because of slower flow. However, the risk is increased in both groups.1 Warfarin should be stopped 72 hours before the procedure; if the patient is on aspirin, it should be stopped 1 week before the procedure. In high-risk patients, anticoagulation is interrupted before the procedure for 4 hours if unfractionated heparin is used and for 12 hours if low-molecular-weight heparin is used. High-risk patients include those with mechanical mitral valve replacement, Björk-Shiley valves (old-generation valves), history of thromboembolic event in the past year, or at least three of the following four risk factors: atrial fibrillation, embolus at any time, hypercoagulable state, and mechanical prosthesis with LVEF of less than 30%, Resumption of anticoagulation in the postoperative period is recommended with heparin; heparin should be continued until warfarin anticoagulation reaches therapeutic target.1 If the patient is to undergo a minimally invasive procedure, anticoagulation can be withheld to maintain the international normalized ratio (INR) at the low therapeutic range and then resumed after the procedure.1

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Jul 18, 2017 | Posted by in GENERAL SURGERY | Comments Off on Cardiac Risk Stratification for Noncardiac Surgery

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