CARDIAC RISK ASSESSMENT & REDUCTION

Cardiac complications of noncardiac surgery are a major cause of perioperative morbidity and mortality. The most important perioperative cardiac complications are myocardial infarction (MI) and cardiac death. Other complications include congestive heart failure (CHF), arrhythmias, and unstable angina. The principal patient-specific risk factor is the presence of end-organ cardiovascular disease. This includes not only coronary artery disease and CHF, but also cerebrovascular disease and chronic kidney disease if due to atherosclerosis. Diabetes mellitus, especially if treated with insulin, is considered a cardiovascular disease equivalent and has also been shown to increase the risk of cardiac complications. Major abdominal, thoracic, and vascular surgical procedures (especially abdominal aortic aneurysm repair) carry a higher risk of postoperative cardiac complications, likely due to their associated major fluid shifts, hemorrhage, and hypoxemia. These risk factors were identified in a validated multifactorial risk prediction tool: the Revised Cardiac Risk Index (Table 3–2). The Revised Cardiac Risk Index has become a widely used tool for assessing and communicating cardiac risk and has been incorporated into perioperative management guidelines. Limited exercise capacity (eg, the inability to walk for two blocks at a normal pace or climb a flight of stairs without resting) and greater severity of cardiac symptoms also predict higher cardiac risk. Emergency operations are also associated with greater cardiac risk. However, emergency operations should not be delayed by extensive cardiac evaluation. Instead, patients facing emergency surgery should be medically optimized for surgery as quickly as possible and closely monitored for cardiac complications during the perioperative period. 

Role of Preoperative Noninvasive Ischemia Testing

Most patients can be accurately risk-stratified by history, physical examination, and electrocardiogram (ECG). Patients without clinical predictors for cardiac complications (Table 3–2), who are undergoing minor operations, or who have at least fair functional capacity are at low risk for cardiac complications. Noninvasive testing in these patients generally does not improve risk stratification or management. Patients with poor functional capacity, or a high Revised Cardiac Risk Index score are much more likely to suffer cardiac complications. Stress testing prior to vascular surgery in these patients can stratify them into low-risk and high-risk subgroups. The absence of ischemia on dipyridamole scintigraphy or dobutamine stress echocardiography is reassuring. Similarly, the presence of only mild, limited ischemia in vascular surgery patients with multiple Revised Cardiac Risk Index predictors, but who are optimally managed with perioperative  β-blockers, predicts a generally acceptable risk of perioperative cardiac death or MI. In contrast, extensive inducible ischemia in his population predicts a very high risk of cardiac complications,  which may not be modifiable by either medical management or coronary revascularization. The predictive value of an abnormal stress test result for nonvascular surgery patients is less well established. An approach to perioperative cardiac risk assessment and management in patients with known or suspected stable coronary artery disease is shown in Figure 3–1.

Perioperative Management of Patients with Coronary Artery Disease

Patients with acute coronary syndromes require immediate management of their cardiac disease prior to any preoperative evaluation (see Chapter 10). Patients with stable coronary artery disease undergoing major surgery have a 1–5% risk of MI and about a 1% mortality rate. In a large cohort study, postoperative MI as evidenced by ECG changes and an elevated biomarker level typically occurred within 3 days of surgery, and was associated with a 30-day mortality rate of 11.6%. Postoperative MI is usually silent or may present atypically. Symptoms and signs that should prompt consideration of postoperative MI include unexplained hypotension, hypoxemia, or delirium. However, current evidence is insufficient to formulate specific recommendations for screening asymptomatic patients for perioperative ischemia through the use of ECG or cardiac enzyme monitoring.

A. Medications

Preoperative antianginal medications, including β-blockers, calcium channel blockers, and nitrates, should be continued preoperatively and during the postoperative period. Evidence for a cardioprotective effect of perioperative β-adrenergic blockade has been mixed. A randomized trial in vascular surgery patients with ischemia on dobutamine stress echocardiography found that bisoprolol reduced the 30-day risk of cardiac mortality or nonfatal MI from 34% to 3% in these high-risk patients. In contrast, subsequent trials found less benefit and potential harm in lower risk patients. In the largest of these studies, a high, fixed dose of β-blocker (metoprolol succinate 100 mg given by mouth a few hours before and after surgery) reduced the absolute risk of cardiac complications by only 1.1% in patients with at least one Revised Cardiac Risk Index predictor who underwent major surgery. This was offset, however, by a 0.8% absolute increase in total mortality. Hypotension and bradycardia were more common when patients received β-blockers; in addition, the risks of stroke and death from sepsis were higher in these patients. In contrast, a subsequent study demonstrated a 6% absolute risk reduction in cardiac mortality and nonfatal MI in patients who received a more conservative, titrated dose of β-blocker (bisoprolol 2.5 mg, started a median of 1 month prior to surgery, and increased by 1.25-2.5 mg daily after surgery to a maximum dose of 10 mg daily). Because of the uncertain benefit-torisk ratio of perioperative β-blockade, it should be reserved for patients with a relatively high risk of cardiac complications. Suggested indications for prophylactic β-blockade are presented in Table 3–3. Comparative trials between different cardioselective β-blockers are lacking. Reasonable starting oral doses for normotensive patients are atenolol 25 mg daily, metoprolol 25 mg twice daily, or bisoprolol 2.5 mg daily. Ideally, β-blockers should be started  well in advance of surgery, to allow time to gradually titrate up the dose without causing excessive bradycardia or hypotension. The dose should be adjusted to maintain a heart rate between 50 and 70 beats per minute while keeping systolic blood pressure above 100 mm Hg. β-Blockers should be continued for at least 3–7 days after surgery.

Observational studies show an association between the use of HMG-CoA reductase inhibitors (statins) during the perioperative period and lower rates of mortality and postoperative MI. A randomized trial in statin-naïve patients undergoing vascular surgery found that extended-release fluvastatin 80 mg orally daily reduced the 30-day risk of cardiac death or nonfatal MI from 10.1% to 4.8%. Statins should be considered in all patients undergoing vascular surgery and other patients deemed to be at high risk for

Figure 3–1. Assessment and management of patients with known or suspected stable coronary artery disease (CAD) undergoing elective major noncardiac surgery. (OR, operating room.) cardiac complications, regardless of lipid levels. Patients already taking statins should continue these agents during the perioperative period.

B. Coronary Revascularization

Retrospective studies suggest that patients who had previously undergone coronary artery bypass grafting (CABG) surgery or percutaneous coronary interventions (PCI) have a relatively low risk of cardiac complications when undergoing subsequent noncardiac surgery. However, one trial randomized over 500 patients with angiographically proven coronary artery disease to either coronary revascularization (with either CABG or PCI) or medical management alone before vascular surgery. Postoperative nonfatal MI, 30-day mortality, and long-term mortality did not differ, suggesting that prophylactic revascularization before noncardiac surgery does not prevent cardiac complications. Thus, current data argue that preoperative CABG or PCI should only be performed on patients who have indications for the procedure independent of the planned noncardiac operation. In patients who have undergone recent intracoronary stenting, observational studies suggest that perioperative cardiac mortality rate may be very high if antiplatelet therapy is stopped prematurely due to concern for surgical site bleeding. The presumed mechanism of this increased mortality is acute stent thrombosis that results from premature discontinuation of antiplatelet therapy. Therefore, elective surgery should be deferred for at least 4–6 weeks after placement of a bare-metal stent and for a full year after placement of a drug-eluting stent if antiplatelet therapy must be stopped perioperatively.

CHF & Left Ventricular Dysfunction 

Decompensated CHF, manifested by an elevated jugular venous pressure, an audible third heart sound, or evidence of pulmonary edema on physical examination or chest radiography, significantly increases the risk of perioperative pulmonary edema (roughly 15%) and cardiac death (2–10%). Elective surgery should be postponed in patients with decompensated CHF until it can be evaluated  and brought under control.

Patients with compensated left ventricular dysfunction are at increased risk for cardiac complications. In a cohort of over 1000 vascular surgery patients who had preoperative echocardiography, asymptomatic left ventricular dysfunction (either systolic or diastolic) was associated with a twofold increase in cardiac complications. A history of symptomatic CHF was much more predictive, being associated with a sevenfold increase in risk. Current guidelines recommend preoperative echocardiography in patients without known CHF with unexplained dyspnea and in patients with known CHF with clinical deterioration.

Patients should continue taking all medications for chronic heart failure up to the day of surgery. Patients receiving digoxin and diuretics should have serum electrolyte and digoxin levels measured prior to surgery because abnormalities in these levels may increase the risk of perioperative arrhythmias. Clinicians must be cautious not to give too much diuretic, since the volume-depleted patient will be much more susceptible to intraoperative hypotension. The surgeon and anesthesiologist should be made aware of the presence and severity of left ventricular dysfunction so that appropriate decisions can be made regarding perioperative fluid management and intraoperative
monitoring.

Valvular Heart Disease

Candidates for valve replacement surgery or valvuloplasty independent of the planned noncardiac surgery should have the valve correction procedure performed first. The severity of valvular lesions should be evaluated by echocardiography or cardiac catheterization before noncardiac surgery to allow for appropriate fluid management and consideration of invasive intraoperative monitoring. Patients with severe symptomatic aortic stenosis are at markedly increased risk for cardiac complications and should not undergo elective surgery. In a series of patients with aortic stenosis who underwent noncardiac surgery, death or nonfatal MI occurred in 31% in patients with severe aortic stenosis (aortic valve area < 0.7 cm2), in 11% in those with moderate aortic stenosis (aortic valve area 0.7–1.0 cm2), and in 2% in those without aortic stenosis. Other studies have found that patients with asymptomatic aortic stenosis appeared to be at lower risk than patients with symptomatic aortic stenosis. Patients with atrial fibrillation due to mitral stenosis require heart rate control to maintain diastolic filling time. Patients with aortic or mitral regurgitation likely benefit from afterload  reduction and careful attention to volume status.

Arrhythmias

The finding of a rhythm disturbance on preoperative evaluation should prompt consideration of further cardiac evaluation, particularly when the finding of structural heart disease would alter perioperative management. Patients with a rhythm disturbance without evidence ofunderlying heart disease are at low risk for perioperative cardiac complications. Patients with symptomatic arrhythmias should not undergo elective surgery until their cardiac condition has been addressed.

Management of patients with arrhythmias in the preoperative period should be guided by factors independent of the planned surgery. In patients with atrial fibrillation or other supraventricular arrhythmias, adequate rate control should be established prior to surgery. Symptomatic ventricular tachycardia must be controlled prior to surgery. There is no evidence that the use of antiarrhythmic medications to suppress an asymptomatic arrhythmia alters perioperative risk.

Patients who have indications for a permanent pacemaker should have it placed prior to noncardiac surgery. When surgery is urgent, these patients may be managed perioperatively with temporary transvenous pacing. Patients with bundle branch block who do not meet recognized criteria for a permanent pacemaker do not require pacing during surgery. The anesthesiologist must be notified that a patient has an implanted pacemaker or defibrillator so that steps may be taken to prevent device malfunction caused by electromagnetic interference from the intraoperative use of electrocautery.

Hypertension

Mild to moderate hypertension (systolic blood pressure below 180 mm Hg and diastolic blood pressure below 110 mm Hg) is associated with intraoperative blood pressure lability and asymptomatic myocardial ischemia but does not appear to be an independent risk factor for more serious cardiac complications. No evidence supports delaying surgery in order to better control mild to moderate hypertension. Most medications for chronic hypertension should generally be continued up to and including the day of surgery. Consideration should be given to holding angiotensin-converting enzyme inhibitors and angiotensin receptor blockers on the day ofsurgery, as these agents may increase the risk of intraoperative hypotension. Diuretic agents, if not needed to control heart failure, are also frequently held on the day of surgery to prevent hypovolemia and electrolyte disorders.

Severe hypertension, defined as a systolic pressure > 180 mm Hg or diastolic pressure > 110 mm Hg, appears to be an independent predictor of perioperative cardiac complications, including MI and CHF. It seems wise todelay surgery in patients with severe hypertension until blood pressure can be controlled, although it is not known whether the risk of cardiac complications is reduced with this approach.