What are the American Heart Association (AHA) guidelines for predicting myocardial infarction (MI) in patients undergoing non-cardiac surgery?

Prediction of MI in Patients Undergoing Non-Cardiac Surgery: AHA Guidelines

Risk Stratification Framework

The AHA/ACC guidelines recommend a stepwise approach using the Revised Cardiac Risk Index (RCRI) as the foundation for predicting perioperative myocardial infarction, incorporating clinical risk factors, functional capacity assessment, and surgical risk stratification. 1

Active Cardiac Conditions Requiring Immediate Evaluation

The following conditions mandate intensive management and may result in delay or cancellation of surgery unless emergent 1:

• Unstable coronary syndromes including unstable or severe angina (CCS class III or IV) 1
• Recent MI (defined as more than 7 days but ≤1 month before surgery with evidence of important ischemic risk) 1
• Acute MI (≤7 days before examination) 1
• Decompensated heart failure (NYHA class IV, worsening or new-onset HF) 1
• Significant arrhythmias including high-grade AV block, third-degree heart block, symptomatic ventricular arrhythmias, or uncontrolled atrial fibrillation (HR >100 bpm at rest) 1
• Severe valvular disease (severe aortic stenosis with mean gradient >40 mmHg or symptomatic mitral stenosis) 1

Clinical Risk Factors from the RCRI

The guidelines identify five key clinical risk factors that predict perioperative MI 1, 2:

• History of ischemic heart disease (prior MI or abnormal Q waves on ECG) 1
• History of compensated or prior heart failure 1
• History of cerebrovascular disease 1
• Diabetes mellitus (particularly insulin-dependent) 1
• Renal insufficiency (serum creatinine >2 mg/dL) 1

The presence of 3 or more clinical risk factors substantially increases perioperative cardiac risk, with event rates ranging from 0.6% with zero factors to 11% or higher with multiple factors. 1

Functional Capacity Assessment

Functional capacity measured in metabolic equivalents (METs) is a critical predictor of perioperative MI risk. 1, 2

• Patients with excellent functional capacity (≥10 METs) can proceed to surgery without further cardiac testing, even with elevated risk factors 2
• Patients with functional capacity ≥4 METs without symptoms should proceed to planned surgery 1
• Patients with poor functional capacity (<4 METs) or unknown capacity require further risk stratification based on number of clinical risk factors and surgical risk 1

Surgical Risk Stratification

The guidelines categorize surgical procedures by cardiac risk 1, 2:

High-risk surgery (cardiac risk >5%):

• Emergent major operations
• Aortic and major vascular surgery
• Peripheral vascular surgery
• Prolonged procedures with large fluid shifts 1, 2

Intermediate-risk surgery (cardiac risk 1-5%):

• Intraperitoneal and intrathoracic surgery
• Carotid endarterectomy
• Head and neck surgery
• Orthopedic surgery
• Prostate surgery 1

Low-risk surgery (cardiac risk <1%):

• Endoscopic procedures
• Superficial procedures
• Cataract surgery
• Breast surgery 1

Algorithm for Preoperative Testing

Patients undergoing low-risk surgery should proceed to planned surgery without further cardiac testing, regardless of clinical risk factors. 1

For patients with poor (<4 METs) or unknown functional capacity and 3 or more clinical risk factors scheduled for vascular surgery, consider noninvasive testing if it will change management. 1

For patients with poor (<4 METs) or unknown functional capacity and 3 or more clinical risk factors scheduled for intermediate-risk surgery, proceed with planned surgery with heart rate control rather than routine testing. 1

Timing of Surgery After MI

It is reasonable to wait 4 to 6 weeks after MI to perform elective surgery. 1 This recommendation reflects that current MI management provides for risk stratification during convalescence, and if a recent stress test does not indicate residual myocardium at risk, the likelihood of reinfarction after noncardiac surgery is low 1.

Perioperative Surveillance for MI

Intraoperative and Postoperative Monitoring

ST-segment monitoring is recommended for patients with known coronary artery disease or those undergoing vascular surgery, as ST-segment changes are strong predictors of perioperative MI. 1, 3 Prolonged ST-segment depression (>30 minutes per episode or >2 hours cumulative duration) is particularly associated with increased risk 1.

Troponin Surveillance

The 2024 AHA/ACC guidelines provide updated recommendations on troponin surveillance 1:

In patients undergoing elevated-risk surgery with cardiovascular risk factors, routine postoperative troponin screening is reasonable for detecting myocardial injury after noncardiac surgery (MINS). 1

In patients undergoing low-risk surgery, routine postoperative screening with troponin is not indicated without signs or symptoms suggestive of myocardial ischemia or MI. 1

Postoperative troponin measurement is recommended in patients with ECG changes or chest pain typical of acute coronary syndrome. 1

Optimal Surveillance Strategy

For patients with known or suspected CAD undergoing high-risk procedures, ECGs obtained at baseline, immediately after surgery, and on the first 2 days after surgery appear to be cost-effective. 1 This strategy has the highest sensitivity for detecting perioperative MI 1.

Myocardial Injury After Noncardiac Surgery (MINS)

MINS is defined as any elevation in cardiac troponin (>99th percentile of upper reference limit) of presumed ischemic origin occurring within 30 days after surgery. 1 MINS encompasses both type 1 and type 2 MI, including asymptomatic myocardial injury, because surgical patients may be unable to report symptoms due to anesthesia or analgesia 1.

The 30-day mortality associated with MINS is approximately 10%, with risks proportional to peak troponin concentration (17% in highest quartile versus 1% in lowest quartile). 1 Even among the 80-90% of patients with MINS without ischemic signs or symptoms, 30-day mortality is substantial 1.

Predictors of MINS include cardiovascular risk factors and disease, kidney disease, and urgent or emergent surgery. 1

Important Caveats and Pitfalls

Minor Predictors

Minor predictors including advanced age (>70 years), abnormal ECG (LVH, LBBB, ST-T abnormalities), non-sinus rhythm, and uncontrolled hypertension are recognized markers for cardiovascular disease but have not been proven to independently increase perioperative risk. 1 The presence of multiple minor predictors might lead to higher suspicion of CAD but is not incorporated into treatment recommendations 1.

Limitations of the RCRI

While the RCRI is widely used, research demonstrates important limitations 4, 5, 6:

• The RCRI substantially underestimates cardiac events in vascular surgery patients, particularly after lower extremity bypass, EVAR, and open AAA repair. 5
• The RCRI discriminates moderately well for mixed noncardiac surgery (AUC 0.75) but performs less accurately for vascular surgery (AUC 0.64) and poorly for predicting death (median AUC 0.62). 6
• Vascular surgery-specific models like the VSG-CRI more accurately predict cardiac complications in this population. 5

Biomarker Enhancement

The addition of NT-proBNP or troponin to the RCRI improves prediction of MACE, with median delta c-statistics of 0.08 and 0.14, respectively. 7 When used in isolation, BNP and NT-proBNP may have higher discriminative performance than the RCRI alone for predicting MACE 7.

Emergency Surgery

Patients requiring emergency noncardiac surgery should proceed to the operating room with perioperative surveillance and postoperative risk stratification, rather than delaying for extensive preoperative cardiac evaluation. 1