The prevalence of cardiovascular disease and the death rate associated with it rise sharply after age 45, an age when the incidence of noncardiac surgeries is also increasing, and approximately one-third of the 25 million surgical procedures done annually are performed in patients with cardiovascular diseases. Cardiac deaths and nonfatal myocardial infarction (MI) occur in about 0.2% of all cases of general anesthesia and surgery (about 500,000 events annually). Cardiac deaths account for approximately 40% of all perioperative mortality, the same proportion as sepsis, although in many cases the cause of death is multisystem organ failure. These figures underestimate the total effect of cardiovascular diseases because another 500,000 persons a year suffer nonfatal MI, unstable angina, or congestive heart failure (CHF) perioperatively, prolonging both their time in the intensive care unit and the total hospital stay.

Although there is great potential to reduce perioperative cardiovascular risk, it is also impractical, unnecessary, and potentially harmful to perform cardiovascular testing in all patients prior to noncardiac surgery. Therefore, it is important to determine perioperative risk, decide whether cardiac testing is appropriate, and provide prophylactic treatment to reduce risk.

An individual patient’s preoperative risk profile depends on three main factors: the patient’s age, current medical and functional status, and the type of surgery. Preoperative electrocardiography can detect arrhythmias and prior silent MI, but it rarely changes management. Preoperative echocardiography would probably provide more useful information, but the cost effectiveness of such testing has not been determined.

Table 10–1 lists cardiac risk based on type of noncardiac surgery. In the evaluation of perioperative patients, understanding the nature of the surgery is of prime importance. Is this an emergency surgery? If yes, the clinician should advise to proceed with the surgery and evaluate the patient’s cardiac risk postoperatively. On the other hand, if the patient is young, without systemic disease, and undergoing a minor surgery or procedure, the clinician should advise to proceed with surgery without further cardiac workup. However, most patients who require perioperative cardiac consultation are not so straightforward. In these patients, there are various algorithms that can help identify perioperative risk and the need for further cardiac testing.

Algorithms

Revised Cardiac Risk Index (RCRI)

This algorithm is simple to use, and it helps identify patients who require β-blockers perioperatively. However, the RCRI may have less accuracy in patients undergoing major vascular surgery. Use the RCRI as follows:

1. 
   

   Assign 1 point to each of the following risk factors if present:

   
   
   
   
   • High-risk surgery (intraperitoneal, intrathoracic, suprainguinal vascular)
     
   • Ischemic heart disease (history of MI or current angina, use of sublingual nitroglycerin, recent abnormal stress test, Q waves on electrocardiogram [ECG], or history of coronary revascularization with ongoing chest pain)
     
   • History of heart failure
     
   • History of cerebrovascular disease (stroke, transient ischemic attack)
     
   • Diabetes mellitus requiring insulin
     
   • Preoperative creatinine > 2.0 mg/dL
   
   
   
   
2. 
   

   Assign a risk class to determine the major cardiac complication rate to help counsel the patient and also the surgeon:

   
   
   
   
   • Class I: zero risk factors, 0.4%
     
   • Class II: one risk factor, 0.9%
     
   • Class III: two risk factors, 6.6%
     
   • Class IV: three or more risk factors, 11.0%
   
   
   
   
3. 
   

   Patients who are categorized as having risk class III or IV may require additional cardiac testing for risk stratification and more aggressive perioperative medical management to reduce the risk of complications.

American College of Cardiology/American Heart Association (ACC/AHA) Guidelines

These guidelines are somewhat cumbersome. In simplified terms, the ACC/AHA guidelines recommend noninvasive cardiac stress testing in patients with two or more of the following risk factors:

• Intermediate clinical predictors: mild angina, prior MI, compensated or prior heart failure, diabetes mellitus, or renal insufficiency
  
• Poor functional capacity (< 4 metabolic equivalents): cannot walk more than one or two blocks on level ground; cannot do light housework, such as washing dishes or dusting; cannot climb a flight of stairs or walk up a hill
  
• High-risk surgery: vascular surgery, prolonged procedure, or anticipated large fluid shifts or blood loss

Online Cardiac Risk Calculator

With the increased use of mobile computerized devices by physicians, access to interactive surgical databases is possible. This has been used successfully by cardiac surgeons to assess the risk of cardiac surgery by the use of the Society of Thoracic Surgery (STS) database and the Euroscore from the European Society of Cardiology database. These societies collect data from their members about each surgery performed and its outcome. Then they use multiple regression analysis of the clinical variables in the database to compare with a specific patient’s same variables entered into a Web-based calculator to determine the risk of a proposed surgery. The beauty of these databases is that they are constantly being updated, so as surgical techniques and medical therapy improve these advances are reflected in the risk calculation. A similar schema has been proposed and tested for noncardiac surgery by a group of investigators in Canada and has been shown to be superior to the RCRI. It is based on five variables: the type of surgery; the functional status of the patient; serum creatinine; American Society of Anesthesiology class; and age. We predict that such online Web-based approaches will be the dominant approach to preoperative risk stratification for noncardiac surgery in the future.

Intermediate-Risk Patients

Although perioperative management of low-risk and high-risk patients is relatively straightforward, the management of patients who fall into the intermediate-risk group is more challenging. Low-risk patients can proceed to surgery without further cardiac evaluation. For high-risk patients, management should include one or more of the following: postpone or cancel surgery until high-risk features improve or resolve, start treatment of the underlying high-risk features, or proceed to invasive testing. In high-risk patients with a high pretest probability of disease, noninvasive tests are not helpful, because a negative result will most likely be a false negative.

Intermediate-risk patients derive the most benefit from perioperative medical management or stress testing, or both.

For most patients in the intermediate-risk category, it is important to obtain imaging with the stress test because ECG alone is unlikely to move the posttest probability beyond the threshold for treatment or no treatment.

Exercise versus Pharmacologic Stress Testing

The choice between exercise and pharmacologic stress testing follows the same guidelines as those for routine, nonperioperative stress testing. Exercise testing can provide valuable information on functional capacity, but patients may not be able to reach 85% of maximal predicted heart rate due to deconditioning or β-blocker use. Since β-blockers are important in the perioperative period, withholding them is not ideal.

Dipyridamole or adenosine is preferred in cases where arrhythmia (eg, rapid atrial fibrillation) or frequent premature atrial or ventricular beats are present. These agents are relatively contraindicated in patients with significant bronchospasm, in whom dobutamine is the agent of choice.

Type of Imaging Technique

When choosing either echocardiography or nuclear imaging (the two most commonly available stress imaging modalities), it is most important to determine which modality has better reliability and expertise at the clinician’s hospital or clinic. In published studies, both imaging techniques have good negative predictive value (> 90%) but poor positive predictive value (< 25%). Echocardiography with contrast (to assist in endocardial border definition) may be more helpful in obese patients (who may have more attenuation defects on nuclear imaging). Nuclear imaging may be more useful in patients with left bundle branch block and when atrial fibrillation is present. Newer modalities include rubidium positron emission tomography (PET) scanning, which provides better resolution images. However, patients must be cooperative and must be able to hold still for longer periods of time. Cardiac computed tomography provides anatomic assessment of the coronary arteries but does not provide data on ischemic burden and has not been adequately evaluated in the perioperative setting.

Understanding Cardiac Complications

Despite the risks during general anesthesia, including myocardial depression, transient hypotension, and tachycardia, very few cardiac events occur during the surgery itself. The incidence of perioperative cardiac complications actually peaks between 2 and 5 days postoperatively. These data imply that factors activated during or following surgery, and not only the surgery itself, are crucial in determining adverse outcomes.

Pneumonitis and microatelectasis produce ventilation-perfusion mismatch, and sedation or analgesia may cause respiratory depression and interfere with coughing, all of which contribute to arterial hypoxemia. Thrombocytosis and a generalized hypercoagulable state, caused by increased fibrinogen and activators from the damaged tissue, favor thrombosis. At the same time, sympathetically mediated increases in heart rate, blood pressure, and contractility increase myocardial oxygen consumption, whereas thrombotic tendencies, anemia, and arterial desaturation impede oxygen delivery to the myocardium. In a patient with underlying coronary artery disease, this situation may lead to myocardial ischemia or infarction. The imbalance may be further exaggerated because antihypertensive or anginal medications are often withheld. By the third or fourth postoperative day, the patient is hypermetabolic, with negative nitrogen and potassium balances. A natriuresis follows, which can produce hypovolemia and further activate the sympathetic nervous system.

All of these factors provide the exact setting in which a perioperative MI may occur. Perioperative MI carries a high mortality and presents atypically (usually without chest pain). Clues such as hypotension, pulmonary edema, altered mental status, and arrhythmia may be the only signs alerting the clinician to the possibility of a perioperative MI. Therefore, those caring for perioperative patients must have a high level of suspicion in order to detect perioperative MI.