In patients undergoing noncardiac surgery, preoperative intervention for a cardiac condition is rarely needed simply to reduce the risk of the surgery unless such intervention is indicated separate from the preoperative context.
This is the overriding message of the 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery issued by the American College of Cardiology (ACC) and American Heart Association (AHA),1 for which I was privileged to chair the writing committee. This article outlines current best practices in cardiac risk stratification for noncardiac surgery, highlighting key recommendations from the ACC/AHA 2007 perioperative guidelines.
PURPOSE OF THE PREOPERATIVE CARDIAC EVALUATION
Provide clinical judgment, not clearance for surgery
A proper cardiac evaluation prior to noncardiac surgery involves a comprehensive patient assessment that draws on clinical findings, the clinical experience of the consulting physician (typically a cardiologist or internist), and an assessment of the literature. The purpose is not to give medical clearance for surgery but rather to provide informed clinical judgment to the anesthesiologist and the surgical team in terms of the following1:
- The patient’s current medical status
- Recommendations regarding the management and risk of cardiac problems during the perioperative period
- The patient’s clinical risk profile, to assist with treatment decisions that may affect short- or long-term cardiac outcomes.
Order tests only when results may change management
The consulting physician’s clinical judgment is critical in determining the need to order any specific tests. In general, a test to further define cardiac risk is valid only when its results could change the planned management and lead to a specific intervention. Potential interventions that may result from knowledge gained through testing include:
- Delaying the operation because of unstable symptoms
- Coronary revascularization
- Attempting medical optimization before surgery
- Involving additional specialists or providers in the patient’s perioperative care
- Modification of intraoperative monitoring
- Modification of postoperative monitoring
- Modification of the surgical location, particularly when the procedure is scheduled for an ambulatory surgical center.
The cardiac evaluation should result in an estimation of cardiac risk. If the consulting physician’s estimation of risk is not clearly above or below the threshold for a potential intervention, then further testing may be indicated to further define the need for interventions (ie, reaching the threshold for action).
WHAT TO WORRY ABOUT FIRST: HIGH-RISK CONDITIONS THAT REQUIRE EVALUATION AND TREATMENT
In a recommendation categorized as a Class I, Level B endorsement,* the ACC/AHA 2007 perioperative guidelines specify four active cardiac conditions for which an evaluation and treatment are required before noncardiac surgery1:
- Unstable coronary syndromes, including unstable or severe angina or recent myocardial infarction (MI). These syndromes should be the first and most important consideration. Unstable angina is a hypercoagulable state, as is recent MI. The hypercoagulability of these conditions is compounded by the hypercoagulability induced by the perioperative setting itself. As a result, the rate of perioperative MI or death in the setting of unstable angina is as high as 28%.2 In the case of unstable coronary syndromes, delaying surgery is appropriate if the risks of the surgery are deemed greater than its potential benefits.
- Decompensated heart failure, defined as New York Heart Association functional class IV disease or worsening or new-onset heart failure.
- Significant arrhythmias, defined as high-grade or Mobitz II atrioventricular block, third-degree atrioventricular heart block, symptomatic ventricular arrhythmias, supraventricular arrhythmias with uncontrolled ventricular rate, symptomatic bradycardia, and newly recognized ventricular tachycardia.
- Severe valvular disease, defined as severe aortic stenosis and symptomatic mitral stenosis.
(*The ACC/AHA 2007 perioperative guidelines make recommendations by classifying the magnitude of benefit versus risk [I = the intervention should be undertaken; IIa = the intervention is reasonable to undertake; IIb = the intervention may be considered; III = the intervention should not be undertaken] and assigning a level of supporting evidence [A = highest level of evidence; B = limited evidence; C = very limited evidence].)
CARDIAC RISK STRATIFICATION: INITIAL PATIENT ASSESSMENT
Clinical risk factors and functional capacity
The Revised Cardiac Risk Index of Lee et al3 remains the general paradigm for stratifying cardiac risk before noncardiac surgery. This validated index consists of six independent predictors of cardiac complications:
- High-risk surgery (intraperitoneal, intrathoracic, or suprainguinal vascular procedures)
- Ischemic heart disease
- History of congestive heart failure
- History of cerebrovascular disease
- Insulin therapy for diabetes mellitus
- Preoperative creatinine level greater than 2.0 mg/dL.
The more predictors a patient has, the greater the risk of perioperative complications. Thus, the Revised Cardiac Risk Index is a good tool for establishing a baseline risk level for use in determining whether a preoperative or perioperative intervention is likely to make a difference in the patient’s surgical outcome. For the purpose of the algorithmic approach to testing, the surgical procedure is not considered a risk factor. Additionally, type 2 diabetes mellitus is also considered a risk factor.
Another important determinant of risk is the patient’s functional capacity. A study of 600 patients undergoing major noncardiac procedures found that poor self-reported exercise capacity, defined as an inability to walk four blocks or climb two flights of stairs, was associated with significantly more perioperative complications than was good exercise capacity.4 Simple instruments such as the Duke Activity Status Index5 can be used to estimate the patient’s functional capacity.
In addition to patient-specific factors, surgery-specific cardiac risk can be important, especially in patients with more than two clinical risk factors. The ACC/AHA 2007 perioperative guidelines identify three categories of surgery-specific risk1:
- Vascular surgery (the highest-risk category and also the most extensively studied), which has been associated with cardiac morbidity rates of greater than 5% in many reports. Examples include aortic and other major vascular surgery, as well as peripheral vascular surgery.
- Intermediate-risk surgery, for which reported cardiac morbidity rates range from 1% to 5%. Examples include intraperitoneal and intrathoracic procedures, carotid endarterectomy, head and neck surgery, orthopedic surgery, and prostate surgery.
- Low-risk surgery, for which reported cardiac morbidity rates are generally below 1%. Examples include endoscopic and superficial procedures, cataract surgery, breast surgery, and ambulatory surgery. Patients undergoing these procedures do not generally require further preoperative cardiac testing.1
Of course, some variability exists within each risk level as a result of institutional differences in surgical volume and expertise as well as in preoperative evaluation and other processes of care. Endovascular surgery is considered intermediate risk from a perioperative perspective but is in the same risk category as vascular surgery from a 1-year perspective.
Risk stratification promotes good perioperative outcomes
Appropriate risk stratification can make the day of surgery among the safest times for patients undergoing outpatient procedures. A retrospective analysis of Medicare claims from the late 1990s for more than 500,000 elderly patients undergoing low-risk procedures in various outpatient settings found that the mortality rate was only 1 in 50,000 on the day of surgery but increased substantially over the following 7 days and 30 days.6 This was likely a reflection of the diligence applied to managing patient-specific risk factors before proceeding to outpatient surgery.