Preoperative evaluation: Take it step by step
Preoperative evaluation: Take it step by step
Identifying patients at higher risk for mortality and morbidity during the perioperative period can lead to strategies to minimize those risks.
A thorough preoperative cardiac evaluation uses a stepwise approach and various tools to identify patients at risk of a cardiac event. Interventions designed to prevent perioperative mortality and morbidity as well as intensive intraoperative monitoring can be recommended for high-risk patients. Since cardiac events pose the most serious risk to patients, most preoperative evaluation strategies attempt to quantify risk for perioperative MI and sudden death.
The American College of Cardiology and the American Heart Association developed a clinical practice guideline that was published in 1996 and updated in 20021 and 2007.2 This guideline uses an explicit evaluation of current evidence and includes cohort, case-control, and observational studies as well as expert opinion (level B evidence).
A stepwise approach
A stepwise approach is employed to determine which patients need preoperative cardiac evaluation prior to surgery. There are no specific recommendations for the type of noninvasive cardiac evaluation. Selection of cardiac testing is determined by resources, patient history, and the clinician.2
For example, the patient who regularly walks and does not have significant orthopedic problems is best assessed with the typical graded exercise stress test. On the other hand, the older, overweight, diabetic patient with peripheral neuropathy would require pharmacologic stress testing with perfusion imaging since it would be unlikely this patient would be able to exercise to the required heart rate.
Figure 1 shows the stepwise assessment for cardiac risk.
Step 1—Determine the timing of and need for noncardiac surgery. If the situation is emergent, proceed to the operating room and manage risk postoperatively. If surgery is elective or nonemergent, perform a preoperative evaluation.
Step 2—Determine the presence of active cardiac conditions. These include unstable coronary syndromes, such as unstable or severe angina and recent MI. Perioperative risk is also increased by decompensated heart failure (HF), e.g., HF that is worsening, of recent onset, or consistent with New York Heart Association class IV. Significant arrhythmias also put surgical patients at risk. Assess for such conditions as high-grade atrioventricular block, symptomatic ventricular arrhythmias, uncontrolled supraventricular arrhythmias (heart rate >100 beats per minute), symptomatic bradycardia, and new-onset ventricular tachycardia. Severe valvular disease, such as severe aortic stenosis or symptomatic mitral stenosis, should also raise a red flag. If none of the previously noted conditions exists, proceed with the surgery. Presence of one of these conditions indicates the need for delay until the condition can be further clarified and treated. Many patients in this group undergo coronary angiography to assess further treatment options.
Step 3—Is the surgery low risk? If the patient is undergoing surgery with a <1% risk of cardiac death (cataract, skin, breast, endoscopy), proceed with surgery.
Step 4—Determine functional capacity. If the patient can tolerate a metabolic equivalent (MET) level >4 without symptoms, he can proceed to the operating room without further testing. Examples of activities with a MET value of 4 include climbing a flight of stairs or walking uphill, running a short distance, bowling, and playing golf or doubles tennis. METs for other activities can be found in Table 2 of the 2002 guideline update1 (available at: http://circ.ahajournals.org/cgi, accessed June 3, 2008).
Step 5—Cannot tolerate >4 METs, or capacity is unknown. Consider cardiac testing based on cardiac risk factors and the type of surgery planned. For patients who have no clinical risk factors, proceed with surgery. Patients who have one or two risk factors may proceed to surgery with or without beta blockade as appropriate.
Use beta blockade only in patients with one or two risk factors where there is a very high clinical concern for coronary artery disease (CAD). For example, patients with diabetes and ischemic heart disease who have hypertension and hyperlipidemia would most likely benefit from beta blockers.
For patients who have three or more clinical risk factors, the type of surgery planned is important. Patients undergoing vascular surgery should go through coronary testing only if the results will change patient management. Those whose surgery involves intermediate risk can undergo noninvasive testing if it will change management or proceed to surgery with beta blockade.
Bottom line: If the results of noninvasive cardiac testing could change patient management, then do it.
Noninvasive coronary testing
If noninvasive coronary testing is called for, which assessment method is best? There are a number of options. Exercise stress testing (EST) without perfusion imaging is the most common and least expensive. The goal is to achieve 75%-85% of the predicted maximum heart rate or a high workload in terms of METs. This test can be limited by pre-existing ST-T abnormalities or comorbid conditions, such as arthritis. Sensitivity of EST without imaging is approximately 68% with specificity of 77%.3
EST with perfusion imaging using thallium or sestamibi identifies myocardium at risk for coronary ischemia. This test is costlier, but it provides more information in terms of specific myocardium at risk and left ventricular dysfunction.
Pharmacologic stress testing with perfusion imaging is helpful for patients who are unable to exercise enough to get their heart rate to target range. Sensitivity and specificity for identifying CAD are similar to exercise thallium testing. Patients who have reversible ischemia should be managed according to current guidelines for CAD, using beta blockers and nitrates as appropriate. Those patients with left main coronary artery or severe multivessel disease may need referral to a cardiologist for assistance with clinical management.
Pharmacologic stress testing with echocardiography using dobutamine infusion is another option. This test is expensive and can trigger bronchospasm. Left ventricular function can also be assessed with this test.
Modifying care to improve outcome
It is important to reduce the probability of cardiac complications after surgery by modifying preoperative or intraoperative care. Clinicians should consider coronary artery bypass surgery or percutaneous coronary intervention (PCI) for patients with ischemia inadequately controlled by medical management or those with left main coronary artery or three-vessel disease.
Coronary intervention is not indicated to simply “get a patient through” noncardiac surgery. Patients identified as needing bypass surgery should have the procedure whether or not they are considering other surgery. Symptoms of congestive HF must be controlled; these patients should be considered for regional anesthesia. Hemodynamic monitoring can help patients with limited ventricular reserve and those undergoing vascular surgery whose exercise capacity is unknown or <4 METs.
Understanding the pathophysiology of the postoperative period and attempting to modify it can help reduce surgery risks. The role of the postoperative neurohumoral response in myocardial ischemia is becoming more important. Use of perioperative beta blockers reduces the rate of postoperative MI in high-risk patients who are undergoing vascular surgery (level B evidence).
One protocol uses metoprolol 50 mg twice daily prior to surgery to get the patient's heart rate below 70 beats per minute. Ideally, start the metoprolol one to two weeks prior to surgery to allow titration of the dose to the optimal heart rate. This medication is continued throughout the patient's hospital stay but held if the pulse is <50 beats per minute or systolic BP is <100 mm Hg.4
Perioperative statin and alpha2-agonist therapy also appear to reduce cardiac mortality and morbidity during this period.1 Patients on these medications should continue to take them perioperatively.
Perioperative preparation for patients who have had PCI presents the clinician with unique challenges, especially in managing the dual antiplatelet agents that are used postoperatively. For patients who have recently undergone coronary balloon angioplasty without a stent, scheduling the new surgery for between two and eight weeks post-PCI appears to give the best results.
Weigh the continuation of aspirin therapy against the bleeding complications of the surgery.1 Patients with bare-metal stents should have their surgery delayed for four to six weeks after stent placement to minimize the risk of myocardial ischemia from stent thrombosis. It is prudent to withhold thienopyridine medications (ticlopidine [Ticlid] or clopidogrel [Plavix]) for one week before surgery.
Late thrombosis of a drug-eluting stent is a major concern. In these patients, continuation of dual antiplatelet therapy is recommended for at least 12 months after stent placement, and elective procedures that involve significant risk for bleeding complications should be delayed for that time period. If a patient undergoes a procedure mandating the discontinuation of the thienopyridine medication, continue aspirin if possible and restart the thienopyridine as soon after the procedure as it can be safely done.1
Long-term risk stratification is crucial following surgery. Postoperative myocardial ischemia is an important predictor of subsequent myocardial events, and clinicians must aggressively evaluate and treat this condition with beta blockers and aspirin.
Dr. Holman is a captain in the United States Navy, stationed at Camp Pendleton, Calif. The opinions in this article are those of the author and should not be construed as official or as reflecting the views of the Department of the Navy or the Department of Defense.
1. Eagle KA, Berger PB, Calkins H, et al. ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgery—executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery). Circulation. 2002;105:1257-1267. Available at: http:// circ.ahajournals.org/cgi/reprint/105/. Accessed June 3, 2008.
2. Fleisher LA, Beckman JA, Brown KA, et al. ACC/AHA 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: executive summary. A report of the American College of Cardiology/American Heart Association task force on practice guidelines. Circulation. 2007;116:1971-1996. Available at: http://circ.ahajournals.org/cgi/reprint. Accessed June 3, 2008.
3. Zuniga RE, Rappaport W, Valente J, et al. Preoperative screening for perioperative cardiac risk. Am Fam Physician. 1991;44:1285-1291.
4. Grecu L, Mehaffey C, Isselbacher E. Preoperative noninvasive cardiac testing: which test and why? Int Anesthesiol Clin. 2002;40:121-132.