▪ PATIENT HISTORY
A carefully addressed patient history may quickly identify high-risk factors, as well as the necessity and appropriateness of preoperative testing. Patients who provide a history that includes a previous MI, current or recent chest pain, complaints of worsening shortness of breath, worsening edema, and pacemaker and/or defibrillator placement should all be considered for further cardiac workup. Each of the above mentioned features or symptoms is associated with a higher cardiovascular risk. Patients who have pain while walking or pain of the extremities at rest may have peripheral vascular disease, which may suggest occult coronary artery disease in the absence of cardiac symptoms.
Several comorbidities have been suggested as factors that increase the risk of cardiovascular complications in the perioperative setting. A history of diabetes mellitus, renal impairment, pulmonary disease, and hematologic perturbations such as anemia are the most commonly described. Diabetes mellitus not only has an increased association with coronary artery disease, but the pathophysiologic effects on the visceral nervous system may lead to “silent” ischemia that does not manifest as chest pain. Furthermore, congestive heart failure is more common among elderly patients with diabetes mellitus than without, even when angiotensin-converting enzyme inhibitors are used appropriately. Renal impairment is also associated with increased cardiovascular risk. Azotemia alone has an association with cardiovascular disease and an increase in cardiovascular events.
4 Lee et al. demonstrated that a creatinine level >2.0 mg per dL was an independent predictor of cardiovascular complications.
5Both obstructive and restrictive pulmonary disease can lead to perioperative respiratory complications. In addition, hypoxia, hypercapnia, and acidosis can lead to worsening cardiovascular performance, and ultimately contribute to cardiovascular complications. Most significantly, the presence of pulmonary disease may limit the use of β-blockers, one of the most commonly used medical therapies for decreasing cardiovascular events. Anemia can further worsen myocardial supply, leading to potential worsening of ischemia, as well as heart failure. A hematocrit <28% is associated with an increased risk of myocardial ischemia and cardiovascular complications in prostate and vascular surgical patients.
4The Revised Cardiac Risk Index identifies six factors of a patient’s history that can be used to determine the risk of major cardiac complications in the perioperative setting.
5 The factors are of approximately equal prognostic value and include the following:
High-risk surgery
Ischemic heart disease
History of congestive heart failure
History of cerebrovascular disease
Insulin therapy for diabetes
Preoperative serum creatinine >2.0 mg per dL (see
Table 14.1).
In a prospective evaluation of 1,422 patients, the presence of ≥2 of these factors identified patients with moderate (7%) and severe (11%) cardiovascular complication rates (see
Table 14.2). However, according to the ACC/AHA guidelines, only four clinical features serve as major predictors (see
Table 14.3) of cardiac complications:
Unstable coronary syndromes include acute or recent MI, as well as unstable and severe stable angina. Significant arrhythmias include second-degree or higher atrioventricular block, uncontrolled supraventricular tachycardia, or symptomatic ventricular arrhythmia. Major predictors are those risk factors that have consistently been associated with a high perioperative risk, as well as an increased perioperative risk for MI, heart failure, and death.
Equally important in the patient history is the assessment of functional capacity and/or exercise tolerance. Despite the presence of cardiovascular risk factors, patients who are asymptomatic and involved in routine, vigorous activity may not warrant further cardiac
workup. In an effort to simplify the determination of a patient’s functional capacity, the ACC/AHA guidelines (see
Table 14.4) incorporate a method of stratifying functional capacity based on a calculated metabolic equivalent (MET). Patients exhibiting <4 METs, coupled with either the presence of intermediate-risk factors (
Table 14.3) or undergoing high-risk surgical procedures, should be referred for noninvasive testing.
▪ PHYSICAL EXAMINATION
In addition to a detailed medical history, a complete physical examination should be performed, with particular attention to a comprehensive cardiovascular examination. Vital signs should be evaluated. Previously unrecognized, untreated, or poorly treated hypertension may be of concern. Patients exhibiting stage 3 hypertension (systolic blood pressure > 180 mm Hg and diastolic blood pressure >110 mmHg) should be evaluated and treated before surgery. The data on which this recommendation is based is limited; furthermore, the impact that severe, poorly controlled hypertension (stage 3) has on perioperative mortality is unclear.
6 Hypertension alone is considered a minor risk factor; however, it must be considered in conjunction with additional clinical risk factors, the patient’s exercise capacity, and the surgical risk as assigned by the ACC/AHA guidelines.
A new or worsening heart murmur may also be of concern, particularly if it is a harsh, crescendodecrescendo murmur heard at the left upper sternal border. This murmur is characteristic of aortic stenosis and may prompt further workup. As indicated in the AHA guidelines, severe or critical aortic stenosis has a high risk of cardiovascular complications, including acute MI and asystole.
7 Similarly, both stenotic and regurgitant murmurs of the mitral valve are also associated with
heart failure. Signs of dependent edema, especially in the lower extremities, with or without accompanying dyspnea, may be signs of heart failure as well, regardless of valvular disease. Pulmonary rales, elevated jugular venous pressure, hepatojugular reflux, and a third heart sound may also be hallmarks of heart failure.
4
▪ ELECTROCARDIOGRAM
A routine electrocardiogram is often one of the first diagnostic studies to be performed—and arguably one of the simplest—in assessing cardiovascular risk. Any abnormal finding (e.g., arrhythmia, Q-waves, ST-segment changes, etc.) in high-risk patients confers a notable increase in perioperative risk, as much as 300%.
8 However, a normal electrocardiogram in a low-risk patient has very low sensitivity and often does not discriminate any further stratification of risk. Owing to the swift and noninvasive nature of an electrocardiogram, it is frequently performed as an early test in assessing perioperative cardiac risk, but are often most valuable when used in conjunction with additional studies and in patients with clinically determined intermediate or high risk.
▪ EXERCISE TREADMILL TESTING
The “stress response” is the natural reaction of the body to surgery. A well designed anesthetic, including the use of narcotics, volatile or intravenous agents, antibiotics, and regional anesthesia and so on, can reduce the level of psychologic stress experienced by the patient. In spite of the anesthesiologist’s best efforts, the conditions brought about by surgery elicit a stress response to some degree; for the cardiovascular system, this response often includes tachycardia, hypertension, and increased tissue oxygen demand. One of the noninvasive studies, termed a
stress test, is an exercise treadmill test. This is a diagnostic study that induces “stressful” conditions on the heart, pulmonary system, and peripheral vasculature to ascertain the patient’s tolerance of increased heart rate and subsequent cardiac oxygen demand. The exercise test typically involves the use of either a treadmill or a stationary bicycle, an electrocardiogram, and blood pressure monitoring. In general, exercise testing is a safe procedure; however, MI and even death have been reported during routine exercise testing, and can be expected to occur at a rate of up to 1 per 2,500 tests.
9 As a result, the AHA has developed recommendations for both absolute and relative contraindications for proceeding with exercise treadmill testing (see
Table 14.5). In addition, patients unable to walk or run on a treadmill (i.e., patients with severe arthritis, paralysis, or other neurologic conditions, amputees, etc.) require an alternative means of inducing an increased heart rate, which will be discussed in the subsequent text.
Patients with suspected or known coronary artery disease and new or changing symptoms that suggest ischemia should generally undergo exercise testing to assess the risk of future cardiac events. In fact, the exercise treadmill test is designed to produce ischemia in those with significant risk factors for coronary artery disease. Several studies have demonstrated that a positive ischemic response and a low exercise capacity can predict the outcome following noncardiac surgery.
2 An early study by Mangano et al. demonstrated an incidence of postoperative MI in 37% of patients who underwent vascular surgery and had a positive ischemic response by exercise treadmill testing, as opposed to a 1.5% incidence of perioperative MI in those who did not. Other studies, however, have not demonstrated such definitive results. It has been found that a 12-lead resting electrocardiogram and exercise capacity were independent predictors of perioperative cardiac complications, and not necessarily the variables related directly to ischemia.
▪ MYOCARDIAL PERFUSION STUDIES
In patients for whom further preoperative testing is desired (i.e., high-risk patients) yet who are unable to perform an exercise treadmill test, a myocardial perfusion scan (scintigraphy) may be considered. Patients with
exercise limitations are often at highest risk, including those with peripheral vascular, neurologic, or orthopedic disease. A dipyridamole/thallium or adenosine/thallium perfusion scan induces coronary vasodilation and assists in elucidating regions of redistribution defects. Dipyridamole blocks adenosine reuptake, thereby increasing adenosine concentration in the coronary vessels. Adenosine acts as a direct coronary vasodilator. By infusing these vasodilators, flow is preferentially distributed to areas distal to normal coronary arteries, and minimizes flow to areas distal to coronary stenoses. A radioisotope, thallium (99m-Technetium sestamibi is also used), is injected. Regions of normal myocardium appear on initial imaging, whereas areas of myocardial necrosis or areas distal to significant coronary lesions remain dark. Several hours later, a second infusion of radioisotope is injected. Areas that remain as defects represent regions of old scar, whereas those that reappear as normal suggest areas at risk for myocardial ischemia. Redistribution defects can be quantified; large areas of defect are associated with increased cardiac risk.
Numerous studies have examined the utility of perfusion scans for risk stratification, and much controversy has arisen over the findings. In the mid-1980s, positive perfusion scans were found to correlate with adverse perioperative events. On the other hand, very few adverse events occurred in patients who had no redistribution defects (e.g., a negative scan). As such, dipyridamole thallium scans found widespread use in the ensuing years. In the early 1990s, however, the former findings were challenged by a prospective, triple-blinded study which, contrary to previously reported findings, revealed no association between redistribution defects and adverse outcomes.
2,
10 Later studies corroborated the fact that thallium redistribution was not significantly associated with adverse perioperative cardiac events,
10,
11 and as a result, the routine use of perfusion scans decreased. More recent studies have demonstrated a greater predictive value of perfusion scans if used in conjunction with more complicated clinical markers and technical examinations. However, the most significant study may have been that by Baron et al., in which it was reported that myocardial perfusion imaging did not provide independent prognostic value beyond that of clinical risk stratification.
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