The worldwide elderly population with its associated health concerns is expanding rapidly. Globally, the proportion of individuals older than 80 years currently averages 5%. In the developed world, almost 15% of individuals will be older than 80 years in 2020; the proportion is expected to increase to 25% by 2050. This aging population has associated comorbidities; consequently, clinicians are often asked to evaluate the preoperative risk status of this high-risk population.
The cardiovascular systems of patients who undergo general anesthesia and noncardiac surgical procedures are subject to multiple stresses and complications. A previously stable patient may decompensate postoperatively, leading to significant postoperative morbidity and mortality. A substantial number of all deaths among patients undergoing noncardiac surgery are caused by cardiovascular complications.
Each year, approximately 30 million individuals in the United States undergo noncardiac surgery. Approximately one third have cardiac disease or major cardiac risk factors. Current estimated rates of serious perioperative cardiac morbidity vary from 1-10%. The incidence of perioperative myocardial infarction (MI) is increased 10- to 50-fold in patients who have had previous coronary events.
Cardiac risk stratification allows clinicians to group patients into various risk categories; therefore, low-risk patients can be spared further testing, whereas intermediate- and high-risk patients should undergo preoperative investigations and treatment to reduce overall cardiac perioperative morbidity and mortality.
Perioperative Cardiac Physiology
Cardiac effects of general anesthesia
The cardiovascular effects of general anesthesia include changes in the arterial and central venous pressures, cardiac output, and varying heart rhythms, which occur by the following mechanisms: decreased systemic vascular resistance, decreased myocardial contractility, decreased stroke volume, and increased myocardial irritability.
Induction of general anesthesia lowers systemic arterial pressures by 20-30%, tracheal intubation increases the blood pressure by 20-30 mm Hg, and agents such as nitric oxide lower cardiac output by 15%.
The use of fentanyl, sufentanil, or alfentanil results in less myocardial depression compared to inhaled anesthetics. Yet, these intravenous agents still cause venodilation, thus reducing preload and, hence, depressing cardiac output. Patients with congestive heart failure (CHF) are particularly sensitive to these hemodynamic changes. By increasing the preoperative volume status and applying the Frank-Starling principle, this decrease in cardiac output can be offset. Additionally, inhalational and intravenous anesthetics along with muscle relaxants can be detrimental by sensitizing the myocardium to circulating catecholamines. As a result of the stress of the surgical procedure, circulating catecholamine levels are elevated, thereby increasing the risk of ventricular ectopy.
Cardiac effects of regional anesthesia
Both epidural and spinal anesthetics cause arteriodilation and venodilation by blocking sympathetic outflow, decreasing preload, and, ultimately, reducing cardiac output. To offset this deleterious effect, the clinician may volume load the patient preoperatively. However, this intervention increases the risk of postoperative CHF by 10-15%.
Although many clinicians believe that regional anesthesia is safer than general anesthesia, randomized studies comparing the 2 modalities have shown no difference in cardiopulmonary complications or mortality. Combined epidural and general anesthesia with analgesia for pain control may attenuate sympathetic hyperactivity, reduce the need for additional parenteral analgesia postoperatively, improve postoperative pulmonary function, and reduce the duration of stay in the intensive care unit following surgery.
Patient- and Procedure-Related Factors
Approximately 50% of patients in the United States who are aware they have hypertension are either not treated or inadequately treated with pharmacological therapy.
In the perioperative period, poorly controlled hypertension is associated with an increased incidence of ischemia, left ventricular dysfunction, arrhythmia, and stroke. Patients with hypertension are at a higher risk for labile blood pressure and for hypertensive emergencies during surgery and immediately following extubation. Patients should continue taking preoperative antihypertensive medications throughout the entire perioperative period. The goal should be a systolic blood pressure less than 140 mm Hg and a diastolic blood pressure lower than 90 mm Hg before proceeding with elective surgery in the ideal situation. In any patient with stage 3 hypertension (ie, >180/110 mm Hg), blood pressure should be well controlled prior to surgery. Intravenous esmolol, labetalol, nitroprusside, or nitroglycerin may be used for acute episodes of hypertension, whereas calcium channel blockers or angiotensin-converting enzyme (ACE) inhibitors may be used in less acute situations.
Congestive heart failure
The mortality rate following noncardiac surgery increases with advancing New York Heart stage. The perioperative mortality rate appears to be more dependent on the patient’s condition at the time of surgery rather than on the myocardial depressant effects of the anesthesia. CHF should be aggressively and adequately treated before the patient undergoes major elective surgery. Therapy is aimed at reducing ventricular filling pressures in addition to improving cardiac output. Medications proven to show a morbidity and mortality benefit include ACE inhibitors, beta-blockers, spironolactone, and angiotensin receptor blockers. Digoxin and diuretics have been shown to improve morbidity rates without reducing mortality rates. In a 1986 report, Detsky et al suggest that patients with decompensated CHF should be stabilized for at least 1 week before undergoing elective surgery.1
Ischemic heart disease
Ischemic heart disease (IHD) is a major determinant of perioperative morbidity and mortality. During the 1970s, several studies reported a 30% risk of reinfarction or cardiac death for patients undergoing surgery within 3 months of an MI, 15% when surgery was performed 3-6 months after an infarction, and 5% when the operation was performed 6 months later. However, this traditional definition has been replaced by the consensus of the American College of Cardiology (ACC) Cardiovascular Database Committee. In particular, an acute MI is now defined as occurring within 7 days, a recent MI is defined as occurring within 7 days to 1 month, and a history of prior MI refers to an event occurring more than 1 month previously.
True lifesaving procedures should be performed regardless of cardiac risk, but consideration should be given to performing elective surgery 4-6 weeks following an MI. In patients requiring semi-urgent surgery, the patient’s risk should be evaluated with prognostic studies (see Preoperative Risk Assessment). In a 1990 report, Shah et al revealed that 25% of patients with unstable angina had an MI after noncardiac procedures.2 Medical therapy and/or revascularization are necessary to ameliorate this risk factor.
No evidence-based trials compare perioperative cardiac outcome after noncardiac surgery for individuals treated with preoperative percutaneous coronary intervention (PCI) versus medical therapy. Indications for PCI in the perioperative setting should adhere to the ACC/American Heart Association (AHA) guidelines established for PCI in general. In the setting of PCI without stenting, wait 1 week prior to surgery. In the setting of PCI with a coronary stent, wait 4-6 weeks prior to noncardiac surgery.
Aortic stenosis (AS) is associated with a 13% risk of perioperative death. Risk varies based on the severity of AS. The death rate associated with critical AS is approximately 50%.
While taking a history, the clinician should inquire about symptoms of syncope, angina, and dyspnea. During the examination, assess for a crescendo-decrescendo murmur in the right intercostal space radiating to the carotids. Pulsus parvus et pulsus tardus, a soft second heart sound (S2), a late peaking murmur, brachioradial delay, and an apical-carotid delay should raise the suggestion of AS. Critical AS is often characterized by an absent S2 and pulsus parvus et tardus. Echocardiography revealing an aortic valve area less than 0.7 cm2 and/or a mean gradient of 50 mm Hg/peak gradient of 80 mm Hg is deemed critical stenosis. The clinician should delay surgery, except for emergencies, and should consider preoperative valve replacement in these selected patients.
The clinician must remember that patients with atrial fibrillation and prosthetic heart valves are on anticoagulation therapy. Coumadin therapy should be discontinued 4-5 days before elective surgery, given its half-life. Patients at high risk for thromboembolic events include those with prosthetic valves in the mitral position, atrial fibrillation associated with mitral valve disease, and a history of thromboembolism. Such patients should be admitted for intravenous heparin treatment. Outpatient therapy with preoperative low molecular weight heparin instead of conventional unfractionated intravenous heparin is often used, although no randomized controlled trials have validated this protocol. Patients with highly thrombotic valves (eg, Star-Edwards valve), 2 prosthetic valves, or recent arterial embolism should be considered for standard intravenous heparin therapy perioperatively.
The clinician must consider 2 factors when assessing the patient’s cardiovascular risk: (1) the type of surgery, and (2) the hemodynamic stress associated with the procedure. Generally, the more extensive the surgical procedure, the greater the physiological stress, the more significant the postoperative pain, and the greater the incidence of cardiac complications. Surgical operations may be classified as follows:
High risk (>5% rate of perioperative death or MI) – Emergent major operations (particularly in elderly patients), peripheral vascular or aortic surgery, and prolonged procedures with large amounts of blood loss involving the abdomen, thorax, head, and neck
Intermediate risk (1-5% rate of perioperative death or MI) – Carotid endarectomy and urologic, orthopedic, uncomplicated abdominal, head, neck, and thoracic operations
Low risk (<1%) – Cataract removal, endoscopy, superficial procedure, and breast surgery
Preoperative Risk Assessment
A preoperative cardiac risk assessment involves obtaining a thorough history and physical examination, along with a baseline electrocardiogram. Established cardiac diseases, including IHD, hypertension, arrhythmia, valvular heart disease, CHF, and the presence of a pacemaker or implantable defibrillator should be sought as part of the patient’s history.
A number of studies pertaining to cardiac risk stratification have been published over the past 3 decades, including the Goldman, Detsky, and Eagle indices. In 2002, the ACC/AHA updated guidelines for the perioperative cardiovascular evaluation for noncardiac surgery. (See also New ACC/AHA Guidelines on Perioperative CV Evaluation for Noncardiac Surgery.) A stepwise strategy that includes the assessment of clinical markers, prior cardiac evaluation and management, functional capacity in mets, and surgery specific risk is followed.
Major clinical predictors – Unstable coronary syndrome, decompensated CHF, significant arrhythmia, and severe valvular disease
Intermediate clinical predictors – Mild angina, prior MI, compensated or prior CHF, diabetes mellitus, and renal insufficiency
Minor clinical predictors – Advanced age, abnormal findings on echocardiography, rhythm other than sinus, history of stroke, low function capacity, and uncontrolled hypertension
Poor functional class (<4 mets) – Energy expended during activities, including dressing, eating, and walking around the house
Adequate functional class (>4 mets) – Energy expended during activities, including walking up a flight of stairs, scrubbing floors, and swimming
See Patient- and Procedure-Related Factors.
See the algorithm presented in Media file 1.
Noninvasive Cardiac Evaluation
Tests for risk stratification
Dobutamine stress echocardiography
Dobutamine is a beta-receptor agonist that increases both heart rate and contractility. In combination with echocardiography, regional wall abnormalities and, thus, ischemia may be assessed. The negative and positive likelihood ratios of dobutamine stress echocardiography for detecting coronary artery disease are 0 and 4.5, respectively. Of note, avoid dobutamine stress echocardiography testing in patients with a history of ventricular tachyarrhythmia (see Media file 2).
Dipyridamole thallium imaging
Intravenous dipyridamole (Persantine) increases coronary blood flow to the myocardium 2- to 3-fold. Viable myocardial cells take up thallium-201, a radionucleotide tracer, in proportion to blood flow. Hence, delayed thallium redistribution following dipyridamole helps identify areas of ischemia (see Media file 3). The test has a negative predictive value (NPV) of 95-100% for coronary artery disease in patients having vascular surgery; negative results have a likelihood ratio (LR) of 0.12, whereas positive results have an LR of 3.02.
Of note, be cautious when performing Persantine thallium scanning in patients with an underlying history of reactive airway disease, including asthma and severe chronic obstructive pulmonary disease (COPD).
Studies to date have not evaluated the role of coronary angiography as a risk predictor. Coronary angiography should not be performed routinely in all vascular patients, but it is generally recommended for those individuals with clinical or noninvasive evidence of coronary artery disease, as determined by dobutamine echocardiography results or Persantine methoxyisobutyl isonitrile testing. Furthermore, indications for coronary artery bypass grafting (CABG) before noncardiac surgery are identical to those established by the ACC/AHA guidelines for CABG, in particular left main disease and critical 3 vessel disease with a reduced ejection fraction (see Media file 4).
Tests not recommended for risk stratification
Noninvasive measurement of left ventricular systolic dysfunction was once considered predictive of increased perioperative cardiac complications because the noninvasive measurement was considered an indirect measurement of left heart failure. This finding no longer holds true because transthoracic echocardiography does not provide any further data over the clinical cardiac examination for predicting perioperative cardiac complications. Although a high ejection fraction is associated with a low perioperative cardiac risk, even a normal ejection fraction cannot exclude severe coronary artery disease. Transthoracic echocardiography does play an important role in evaluating the severity of stenotic and regurgitant valvular lesions.
Exercise treadmill testing
Exercise stress testing is useful in patients who are able to exercise, but a significant percentage of patients undergoing noncardiac surgery are unable to reach the maximal predicted heart rate, given the magnitude of their concomitant vascular disease. In those individuals able to walk the treadmill, the sensitivity and specificity for predicting coronary artery disease are 65% and 85%, respectively.
Studies have confirmed that exercise stress testing does not provide a high NPV. Physiologically, exercise increases the heart rate and systemic vascular resistance, thus increasing oxygen consumption by the myocardium. Therefore, a positive test result indicates a high risk of developing ischemia perioperatively. However, many ischemic events occurring intraoperatively are not associated with changes in the heart rate or blood pressure; therefore, the minimal threshold of myocardial oxygen utilization to evoke ischemia is not reached, and the significance of a negative stress test result is misleading.
Ambulatory electrocardiographic monitoring
Although preliminary data suggested that the absence of ST depression had an NPV of 99%, this finding no longer holds true.
According to the revised guidelines of the AHA published in 1997, cardiac conditions in which antimicrobial prophylaxis is indicated prior to invasive dental or surgical procedures include the following:
Prosthetic heart valve
Prior history of infective endocarditis
Cyanotic congenital heart defect
Surgically constructed systemic or pulmonary conduit
Mitral valve prolapse with regurgitation, valve thickening, or both
Endocarditis prophylaxis is not recommended for the following:
Atrial septal defect
Surgically repaired ventricular septal defect
Patent ductus arteriosus
Isolated mitral valve prolapse
Mild tricuspid regurgitation
Previous rheumatic fever or Kawasaki disease without valvular dysfunction
The following antimicrobial regimen is suggested for prophylaxis:
Dental, oral, or upper respiratory tract procedures – Amoxicillin 2 g PO 1 hour prior to the procedure; if allergic to penicillin, alternatives include clindamycin 600 mg PO, cephalexin 2 g PO, or azithromycin 500 mg PO 1 hour prior to the procedure
Genitourinary or gastrointestinal procedures – Ampicillin 2 g IV and gentamicin 1.5 mg/kg 30 min prior to procedure, followed by amoxicillin 1 g PO/IV/IM 8 hours later; if allergic to penicillin, alternatives include vancomycin 1 g IV and gentamicin 1.5 mg/kg 1-2 hours prior to the procedure