Because of the high mortality and morbidity associated with perioperative myocardial infarction, considerable effort is made to predict perioperative cardiac risk. A prospective evaluation of preoperative cardiac risk factors using a multivariate analysis identified independent cardiac risk factors for patients undergoing noncardiac surgery (177). Using these factors, a cardiac risk index was created that placed a patient in one of four risk classes. This cardiac risk index was further modified and validated prospectively, resulting in a tool for clinical risk assessment in nonemergent major noncardiac surgery, the Revised Cardiac Risk Index (178). Risk factors include high-risk surgical procedures, history of ischemic heart disease, history of congestive heart failure, history of transient ischemic attack or stroke, preoperative insulin therapy, and preoperative serum creatinine levels greater than 2.0 mg/dL. Depending on the number of risk factors, the risk of major cardiac events (myocardial infarction, cardiac arrest, pulmonary edema, and complete heart block) range from 0.5% to 9.1% (Table 22.14).
Risk assessment is stratified into three major categories: (i) clinical predictors, (ii) functional capacity, and (iii) surgery-specific risk (179). Clinical predictors of increased perioperative
Table 22.14 Major Cardiac Event Rates by the Revised Cardiac Risk Index
CI, confidence interval. Adapted from Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100: 1043–1049.
cardiac risk were formerly divided into major, intermediate, and minor factors. The intermediate category was replaced by clinical risk factors from the revised cardiac risk index (Table 22.15). The patient’s functional status is assessed by a thorough history (Table 22.16), and self-reported exercise tolerance can be used to predict perioperative risk, based on a system of metabolic equivalents (METS) (180). Surgery-specific risk is subdivided into high-risk procedures (emergent major operations, aortic and vascular procedures, and prolonged surgical procedures associated with large ﬂuid shifts or blood loss), intermediate-risk procedures (intraperitoneal and intrathoracic), and low-risk procedures (endoscopic, breast surgery, and ambulatory procedures). Patients with poor functional capacity and any clinical risk factor undergoing more than low-risk nonemergent surgery should undergo preoperative testing, based on American Heart Association (AHA) guidelines (179).
In an effort to quantify preoperative cardiac risk, several tests are used to assess cardiovascular function. Electrocardiogram should be considered for anyone other than asymptomatic persons undergoing low risk procedures. Echocardiography may be used to evaluate left ventricular function (179). Patients who have dyspnea of unknown origin, current or past heart failure,
Table 22.15 Clinical Predictors of Increased Perioperative Cardiovascular Risk
Unstable coronary syndromes: acute (≤7 days) or recent (7 < days ≤ 1 month) MI, unstable or severe angina Decompensated congestive heart failure Significant arrhythmias (high-grade AV block, symptomatic ventricular arrhythmias, supraventricular arrhythmias with uncontrolled ventricular rate) Severe valvular disease
History of cerebrovascular disease Prior ischemic cardiac disease Compensated or prior congestive heart failure Diabetes mellitus Renal insufficiency
Advanced age Abnormal ECG (LVH, LBBB, ST-T abnormalities) Rhythm other than sinus Uncontrolled systemic hypertension