Cardiac Evaluation for Noncardiac Surgery



Cardiac Evaluation for Noncardiac Surgery


Hugo Quinny Cheng



INTRODUCTION


Epidemiology

The annual worldwide surgical volume may exceed 300 million cases.1 Because intraoperative techniques and postoperative care and monitoring have improved, the surgical population has expanded to include patients who once would have been considered too sick to undergo surgery because of their cardiovascular disease (CVD). However, although these patients are now receiving surgery, they remain at increased risk for perioperative cardiac complications. In the Perioperative Ischemia Evaluation (POISE) and POISE 2 trials examining over 18,000 patients with established CVD or other high-risk features undergoing major surgery, the incidence of cardiac-related death or nonfatal myocardial infarction (MI) was approximately 7%.2,3


Risk Factors

The risk of perioperative cardiac complications depends on both patient-related risk factors and the risk of the operation. The presence of end-organ CVD or its equivalents is the main patient-related risk factor. This includes coronary artery disease (CAD), heart failure (HF), severe valvular heart disease, and serious arrhythmias. In addition, disease in other organ systems resulting from atherosclerotic vascular disease or chronic hypertension, such as chronic kidney disease or stroke, is also associated with higher risk of perioperative cardiac complications.4 Diabetes has also been shown to be an independent predictor, especially if it requires insulin to treat, is long standing, or has been poorly controlled. In contrast, many traditional atherosclerotic risk factors such as hyperlipidemia, tobacco smoking, family history of premature heart disease, and mild-moderate hypertension add little to risk prediction in the absence of identifiable end-organ disease. Advanced age likely increases risk independently of comorbidity. Severe systemic disease, even if unrelated to the cardiovascular system, also increases cardiac risk.

High-risk noncardiac operations are typically prolonged cases involving extensive blood loss, large-volume fluid shifts, or abrupt changes in afterload. Major vascular surgery involving the aorta (eg, abdominal aortic aneurysm repair) is often considered the epitome of a high-risk operation. A major operation performed on an emergency basis can have a much higher risk of cardiac complications than does the same surgery done electively. In contrast, minimally invasive operations, endoscopic cases, or procedures performed on the skin or eye have a very low risk of cardiac complications. Patients undergoing low-risk procedures generally do not require an in-depth preoperative cardiac evaluation.


Outcome Definitions

Death from cardiac causes (cardiac arrest) and nonfatal MI are the most important complications, and are often combined as a composite endpoint termed major adverse cardiac events or MACE.5 The definition sometimes also includes other events such as stroke, need for urgent coronary artery revascularization, or overall mortality. In some cases, the definition of perioperative cardiac complication is expanded to include pulmonary edema, angina, and non-life-threatening arrhythmia. Although the risks of these less serious complications cannot be ignored, their impact on the decision on whether to perform surgery is substantially lower. Thus, when contemplating or communicating risk estimates, it is important to understand what outcomes are included.


APPROACH TO CARDIAC EVALUATION FOR NONCARDIAC SURGERY

When evaluating a patient’s cardiovascular status before non-cardiac surgery, the clinician must identify patients at increased risk for cardiac complications to implement appropriate diagnostic and prophylactic strategies. However, it is equally important to avoid unnecessary tests or interventions that delay surgery, increase costs, and potentially harm the patient. On a fundamental level, the preoperative cardiac evaluation addresses these goals by asking three questions:



  • What is the patient’s risk for perioperative cardiac complications based on clinical assessment?


  • Is diagnostic testing needed to supplement clinical assessment to better define and manage risk?


  • On the basis of clinical assessment and diagnostic testing (if done), what management strategies should be implemented to reduce risk?


PATHOGENESIS

One proposed mechanism for postoperative ischemia and MI centers on the increase in sympathetic nervous system activity that is triggered by perioperative stressors such as blood loss, tissue injury, and pain.6 Catecholamines and stress hormone
levels rise acutely with surgery, leading to elevated myocardial oxygen demand as heart rate and contractility increase. Patients unable to accommodate the greater need for myocardial oxygen because of coronary artery obstruction can suffer myocardial ischemia and injury. Blood loss anemia and perioperative hypotension can further potentiate ischemia. Most postoperative MIs are demand-mediated (type 2) MIs. It is also possible that elevated sympathetic tone causing hypertension and tachycardia, perioperative hypercoagulability, and other factors may cause vascular injury or destabilization of coronary artery plaques, leading to acute coronary artery thrombosis and type 1 MI (Algorithm 25.1).







CLINICAL RISK ASSESSMENT

Preoperative cardiac evaluation begins with a detailed history. For patients without an established cardiac diagnosis, it is important to elicit a history of suggestive symptoms such as exertional chest pain, dyspnea, edema, or syncope. For patients with known CVD, the clinician should ask about complications, current symptom severity, prior diagnostic test results, and the timing and nature of prior invasive procedures such as percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) surgery. In addition, the patient’s functional status and exercise capacity should be assessed. Independent patients who are able to perform at least moderate physical activity without symptoms have a lower risk of cardiac complications, whereas patients who require assistance with activities of daily living or have limited exercise capacity are at increased risk. It is also easy to overlook CVD in patients with poor function because they may never perform activities strenuous enough to provoke symptoms. A threshold of four metabolic equivalents (METs) is often used to define adequate exercise capacity, which corresponds to the ability to walk several blocks at a normal pace or climb one or two flights of stairs.7

Physical examination should focus on looking for signs that confirm a clinical suspicion of undiagnosed or decompensated CVD, such as elevated jugular venous pressure, a third heart sound, and pulmonary crackles pointing to acute HF or a murmur suggestive of severe aortic stenosis. An electrocardiogram (ECG) is not routinely needed for all preoperative cardiac evaluations. However, an ECG should be done in patients with known or suspected CVD and considered for other patients undergoing major surgery. Patients undergoing low-risk surgery do not benefit from receiving an ECG or other cardiac testing unless indicated for reasons other than the operation.8

Patients with severe chronic CVD may be reasonable candidates for noncardiac surgery if benefits are felt to outweigh risks, but some conditions warrant delaying or canceling elective noncardiac surgery because of excessive risk. Patients with severe or decompensated heart disease that require urgent or emergent evaluation or treatment regardless of upcoming surgery should have their cardiac problem thoroughly addressed before elective noncardiac surgery. Examples include acute coronary syndrome, new or decompensated HF, symptomatic valvular heart disease, symptomatic ventricular arrhythmia, and supraventricular arrhythmia with uncontrolled ventricular rate. Conversely, emergency noncardiac surgery should not be delayed to perform a detailed cardiac evaluation. The clinician assessing a patient undergoing emergency noncardiac surgery should quickly identify conditions that affect the risk of MACE; discuss risk, monitoring, and postoperative care with the rest of the perioperative care team; and pursue a more thorough cardiac evaluation after surgery.


Prediction Tools

Owing to the complex interaction between patient-related risk factors and risk that is intrinsic to the operation, clinical risk assessment has long relied on formal multivariate prediction tools. The most widely used tool is the Revised Cardiac Risk Index (RCRI).9 The RCRI uses six predictive variables: history of ischemic heart disease; HF; stroke or transient ischemic attack; serum creatinine greater than 2.0 mg/dL (177 µmol/L); diabetes treated with insulin; and high-risk surgery defined as major vascular surgery or an open abdominal or thoracic operation (see Table 25.1). The risk for MACE (defined as MI, primary cardiac arrest, pulmonary edema, and complete heart block) increases with the number of predictors present. More recently, a cardiac risk calculator was derived from the American College of Surgeons’ National Surgical Quality Improvement Program (NSQIP) database.10 The NSQIP calculator (available online or through a mobile device application at qxmd.com/calculate/calculator_245/gupta-perioperative-cardiac-risk) uses five variables: type or location of surgery; age; serum creatinine; ability to perform activities of daily living; and the American Society of Anesthesiology (ASA) physical status classification. The ASA classification is an overall subjective assessment of the severity of systemic disease in a surgical patient (see Table 25.2). The outcome predicted by the NSQIP tool is
the 30-day incidence of myocardial infarction or cardiac arrest, leading to it being called the MICA calculator.








When assessing the risks predicted by these two tools, only the risk of MI, cardiac death, and nonfatal cardiac arrest outcomes from the RCRI should be used for comparison.11 The NSQIP calculator has greater external validity, because it was derived and validated in a large database that included patients and hospitals across the United States, whereas the RCRI originated from a single tertiary care hospital. Routine postoperative surveillance ECG and cardiac enzyme levels were obtained in many of the patients who were evaluated to derive the RCRI, whereas screening for MI was not part of the NSQIP study.

Although other prediction models and tools exist and may perform better in specific populations, the RCRI and NSQIP MICA calculator are broadly applicable, easy to use, and incorporated into clinical practice guidelines from North America and Europe. The 2014 American College of Cardiology (ACC) and American Heart Association (AHA) guideline on cardiac evaluation for noncardiac surgery endorses both the RCRI and NSQIP MICA tool for clinical risk assessment.12 Patients with two or more RCRI predictors or an estimated complication risk greater than or equal to 1%, as calculated by the NSQIP tool, are defined as being at elevated risk.









PREOPERATIVE DIAGNOSTIC TESTING

Most surgical patients can be adequately evaluated using clinical assessment alone. The ACC/AHA guideline recommends no further testing for patients with less than two RCRI predictors or an NSQIP-derived risk of less than 1%. In addition, some patients with increased clinical risk have good exercise capacity and may be able to forego formal diagnostic testing. Finally, in many cases, the results of diagnostic testing will not influence treatment or the decision to proceed to surgery. This situation frequently occurs in acutely ill, hospitalized patients where the patient and surgeon are willing to accept a relatively high risk of cardiac complications to treat life- or limb-threatening disease. Algorithm 25.2 provides a stepwise approach to preoperative cardiac evaluation in patients with stable CVD undergoing major, nonemergency surgery, based on the ACC/AHA guideline.


Noninvasive Stress Testing

Preoperative noninvasive stress testing is sometimes performed to improve risk stratification in patients with known or suspected ischemic heart disease. Most studies on the predictive utility of stress testing have been conducted in patients undergoing major vascular surgery and utilized radionuclide
myocardial perfusion imaging or echocardiography. It remains unclear how well the conclusions from these studies apply to patients undergoing nonvascular operations, especially where the baseline risk for MACE is much lower than that with vascular surgery. In patients undergoing vascular surgery (and presumably other surgical populations), stress testing has strong negative predictive value. Patients without demonstrated ischemic potential typically have a very low risk of cardiac death or MI and can proceed to surgery without further cardiac testing. The positive predictive value of a stress test is limited. Evidence of ischemic potential on a stress test predicts increased risk in major vascular surgery; however, the large majority of patients with a positive stress test will not suffer a serious perioperative cardiac complication.13,14 The complication rate correlates with the amount of myocardium at risk. In a meta-analysis, stress tests showing only fixed abnormalities or very limited ischemic potential (<20% of myocardium at risk) had no predictive value.15 Tests results showing 20% to 29% reversibility were associated with a borderline significant increase in pretest probability of adverse events (positive likelihood ratio of 1.6). In patients with 30% to 49% of myocardium at risk, the posttest probability of complications increased by roughly threefold (positive likelihood ratio of 2.9), and those showing greater than or equal to 50% reversibility had an 11-fold increase in risk.






Because a positive test result generally does not increase the probability of complications by a large margin, stress testing should only be reserved for patients determined to have a high pretest probability of MACE based on clinical assessment or who have indications for the test independent of the surgery. Guidelines from the ACC/AHA and European Society of Cardiology and European Society of Anesthesiology (ESC/ESA) identify patients who have both multiple RCRI predictors and poor functional capacity (<4 METs) who are undergoing major surgery as the most appropriate population for noninvasive stress testing.16 A pharmacologic stress test (pharmacologic myocardial perfusion imaging or dobutamine stress echocardiography) is generally preferred because these modalities have been better studied, and many stress testing candidates will have limited exercise capacity.


Echocardiography

The indications for preoperative resting transthoracic echocardiography (TTE) are similar to those for nonsurgical patients. Patients with a new or suspected HF diagnosis without a prior TTE should undergo the study before surgery, if possible. Similarly, patients with worsening HF symptoms should have a reassessment of left ventricular function with TTE. Patients with a murmur or other findings that raise concern for serious valvular heart disease (particularly aortic stenosis) should be evaluated with TTE. Patients with established moderate to severe valvular disease should undergo surveillance echocardiography if not performed in the prior year or if cardiovascular symptoms have worsened. Similarly, TTE should be considered when there is concern for other undiagnosed structural heart disease that can assessed by echocardiography (eg, hypertrophic obstructive cardiomyopathy, severe pulmonary hypertension).

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May 8, 2022 | Posted by in CARDIOLOGY | Comments Off on Cardiac Evaluation for Noncardiac Surgery
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