A 68-year-old woman with multiple cardiac risk factors experienced sudden onset of crushing substernal chest pain. Despite aggressive thrombolytic therapy, the patient had electrocardiogram (ECG) evidence of a transmural anterolateral myocardial infarction (MI). She developed acute cholecystitis 3 weeks later and was scheduled for cholecystectomy.
How do you evaluate cardiac risk in a patient scheduled for noncardiac surgery?
Preoperative cardiac evaluation and assessment include a review of the history, physical examination, and laboratory results. Knowledge of the planned surgical procedure is also important. The history should assess the following:
Severity and reversibility of coronary artery disease (CAD) (e.g., risk factors, anginal patterns, history of MI)
Left ventricular (LV) and right ventricular function (e.g., exercise capacity, pulmonary edema, pulmonary hypertension)
Presence of symptomatic arrhythmias (e.g., palpitations, syncopal or presyncopal episodes)
Coexisting valvular disease
Presence of a pacemaker or implantable cardioverter defibrillator
Comorbidities that commonly occur in patients with CAD include peripheral vascular disease, cerebrovascular disease, diabetes mellitus, renal insufficiency, and chronic pulmonary disease. A calculation of the patient’s metabolic equivalents (METs) of tasks helps to determine cardiac risk ( Figure 2-1 ).
On physical examination, particular attention should be paid to the vital signs, specifically heart rate, blood pressure, and pulse pressure. These parameters provide information about the balance of myocardial oxygen consumption and delivery. Additionally, the presence of left-sided or right-sided failure (jugular venous distention, peripheral edema, pulmonary edema, or S 3 ) and the presence of murmurs should be assessed.
Routine laboratory tests, electrolytes, blood urea nitrogen, creatinine, and complete blood counts may have some predictive value of cardiac risk. These tests may reveal the presence of anemia, hypokalemia from diuretic therapy, and increasing creatinine levels heralding renal insufficiency. Also, specific cardiac drug levels such as digoxin should be considered. Point-of-care testing for the efficacy of medications such as clopidogrel and aspirin may be useful as well. Chest radiograph aids in assessing heart size and shape. An ECG should be obtained; however, a normal ECG may be present in 50% of patients with CAD. The most common ECG findings in patients with CAD are ST-T wave abnormalities (65%–90%), LV hypertrophy (10%–20%), and pathologic Q waves (0.5%–8%). ECGs are indicated for patients with at least one clinical risk factor who are undergoing vascular surgical procedures or for patients with known congestive heart failure (CHF), peripheral arterial disease, or cerebrovascular disease who are undergoing intermediate-risk surgical procedures. ECGs are not indicated for asymptomatic patients undergoing low-risk surgical procedures.
Further evaluation depends on the results of the aforementioned preliminary investigations and the planned surgical procedure.
Assigning clinical risk
The standard of care, as of this writing, is defined by the American College of Cardiology/American Heart Association (ACC/AHA) 2007 Guidelines for Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery. The general paradigm is that patients are risk-stratified based on clinical risk factors ( Box 2-1 ), surgical procedures ( Table 2-1 ), and noninvasive testing. In elective procedures, this algorithmic approach should be used by internists, surgeons, and anesthesiologists as a cardiovascular evaluation strategy.
Major clinical risk factors
Unstable coronary syndromes
Unstable or severe angina
Recent myocardial infarction
Decompensated heart failure
Severe valvular disease
Intermediate clinical risk factors
History of ischemic heart disease
History of compensated or prior heart failure
History of cerebrovascular disease
Minor clinical risk factors
Advanced age (>70 years old)
Left ventricular hypertrophy
Left bundle-branch block
Rhythm other than sinus rhythm
Uncontrolled systemic hypertension
|Cardiac Risk Stratification||Procedure Example|
|High||Aortic and other major vascular surgery|
|Peripheral vascular surgery|
|Intermediate||Intraperitoneal and intrathoracic surgery|
|Head and neck surgery|
In the past, numerous classification systems (e.g., Goldman, Detsky, and Eagle) were designed to predict the risk of cardiac morbidity. These classification systems did not include patients with high-risk conditions that are considered to be major predictors of perioperative cardiac events (PCE). The ACC/AHA 2007 Guidelines reflect Lee’s Revised Cardiac Risk Index, which is the most commonly used system today. Another commonly employed system is the National Surgical Quality Improvement Program risk model. Both of these models assess patients with high-risk characteristics and are more applicable today.
Unstable angina is a major clinical predictor of PCE in the ACC/AHA Guidelines, whereas chronic stable angina is an intermediate clinical predictor of PCE. ) suggested that patients should be classified in a more functional way. They contended that not all patients with stable angina have the same disease process (i.e., coronary anatomy, frequency of ischemia, and LV function). The number of ischemic episodes is especially difficult to quantitate without some sort of continuous monitoring (i.e., ambulatory ECG). This information is probably important because >75% of ischemic episodes are silent, and >50% of patients with CAD (not just diabetics) have silent ischemia. It is unclear what the role of silent ischemia is in myocardial injury, although it seems to portend a worse prognosis if present in patients with unstable angina or patients after MI.
The relationship between history of MI and PCE varies significantly based on the age of the infarction. Recent infarctions are defined by cardiologists as infarctions within the last 7–30 days and are acknowledged as a major clinical predictor of PCE. Prior MI by history or pathologic Q waves on ECG is an intermediate clinical predictor. Interpretation of history of MI and PCE is complicated in anesthesia practice because anesthesiologists traditionally refer to recent infarctions as occurring within the preceding 6 weeks to 6 months. Classic “reinfarction” studies from data collected 20–40 years ago found that patients with an infarct within 3 months had a 5.7%–30% incidence of reinfarction. Between 3 and 6 months, the risks range from 2.3%–15%, and an infarct >6 months before surgery is associated with a 1.9%–6% incidence. The mortality rate of repeat MI was about 50%, and this figure varies very little among the various studies. The lower numbers in each group are from the study of ), in which aggressive hemodynamic monitoring was used and patients recovered in the intensive care unit postoperatively. The problem with applying these data to modern care is that they precede the widespread use of XXgw:math1XXbZZgw:math1ZZ blockers, coronary interventions, and enzyme-based diagnosis of infarctions. Nevertheless, there is no doubt that more recent MIs represent a significant risk factor for PCE. The severity of the infarction must also be considered.
Medical literature distinguishes mortality rates in Q wave versus non–Q wave MIs, infarctions involving the right versus the left coronary artery distribution, uncomplicated versus complicated infarctions (i.e., recurrent pain, CHF, or arrhythmias), and negative versus positive post-MI exercise stress test results. It seems reasonable to assume that mortality rates from all recent MIs should not be classified together based solely on the time since the infarction.
CHF in the general population has a poor prognosis. The 5-year survival rate is approximately 50%, although this may be improving with modern afterload-reduction and antiarrhythmic therapies. The 1-year mortality rate is approximately 30% in patients with LV ejection fractions <30%. The ACC/AHA guidelines include uncompensated CHF as a major clinical predictor and compensated or prior CHF as an intermediate clinical predictor.
Arrhythmias are a common problem, especially in elderly patients. Arrhythmias are usually benign except in patients with underlying heart disease, in whom they serve as markers for increased morbidity and mortality. Many patients with LV dysfunction and arrhythmias die as a result of LV failure and not an arrhythmia. Acknowledged major clinical predictors include high-degree atrioventricular block, symptomatic ventricular arrhythmias in the presence of underlying heart disease, and supraventricular arrhythmias with uncontrolled ventricular rate. Minor predictors include abnormal ECG (i.e., LV hypertrophy, left bundle-branch block, and ST-T wave abnormalities). Rhythm other than sinus (e.g., atrial fibrillation) is also a minor clinical predictor.
Patients with valvular heart disease are difficult to evaluate because the lesions cause changes that are independently associated with increased risk (i.e., CHF, rhythm changes). However, severe valvular disease is considered a major clinical predictor. If aortic stenosis is symptomatic, the surgery generally should be postponed or canceled for possible aortic valve replacement or other intervention before elective surgery. Patients with severe aortic stenosis undergoing noncardiac surgery have a mortality rate of approximately 10%.
Assigning surgical risk
In addition to patient characteristics, risk is determined by the surgical procedure (see Table 2-1 ). Higher risk surgeries include procedures with greater potential for hemodynamic cardiac stress. Such stressors could be alterations in heart rate, blood pressure, intravascular volume, clotting, oxygenation, neurohumoral activation, blood loss, and pain.
It is generally agreed that patients with a “combined” risk of PCE (i.e., based on patient and surgical factors) of >10% warrant further evaluation. Noncardiac surgical procedures associated with the highest PCE rate are mostly vascular surgical procedures. Peripheral vascular and aortic surgeries have high PCE rates, whereas carotid artery surgery has PCE rates of about 5%. Although the data are still emerging, it appears that endovascular repairs have low associated risk. The high PCE rate of vascular surgical procedures is usually attributed to the high incidence of CAD in patients undergoing vascular surgery (estimated to be 90%) and to the stress imposed on the myocardium by hemodynamic changes.
The metabolic changes induced by surgery, such as increased levels of stress hormones and increases in platelet adhesiveness, are also implicated as factors that increase PCE. Nonvascular surgical procedures associated with higher morbidity and mortality include intrathoracic and intraabdominal surgeries. Presumably, the increased risk is because of the greater hemodynamic changes associated with large fluid shifts, compression of the great veins, and aberrations in cardiopulmonary function during thoracic surgery. Emergency surgery is also associated with increased risk. Procedures associated with a lower risk of PCE include extremity surgery, transurethral prostate resections, and cataract surgery. The risk of surgery must always be included in the estimation of patient risk, and this is constantly changing owing to the emergence of less invasive techniques that cause less physiologic disturbance.
The assignment of “cardiac risk” to a particular patient for a particular surgical procedure is difficult, but there are guidelines and an algorithm that should be followed ( Figure 2-2 ). The need for further evaluation depends on whether the information gained would change the planned surgical or anesthetic management. These changes in management might include altering the surgical procedure to one associated with lower risk, medical or surgical treatment of CAD, perioperative anticoagulation, or perhaps more aggressive intraoperative and postoperative monitoring. Although many of these strategies sound logical, there is relatively weak evidence of outcome improvements with interventions.