What to do if a prior myocardial infarction (MI) is found on an electrocardiogram (ECG)?

Management of Prior Myocardial Infarction Detected on ECG

When a prior myocardial infarction (MI) is discovered on an electrocardiogram, the patient should be evaluated for cardiovascular risk factors, started on aspirin therapy, considered for beta-blocker and ACE inhibitor therapy, and referred for further cardiac assessment including stress testing and possible coronary angiography. 1

Recognizing Prior MI on ECG

• Pathological Q waves or QS complexes in the absence of QRS confounders are pathognomonic of a prior MI in patients with ischemic heart disease, regardless of symptoms 1 • The specificity of ECG diagnosis for MI is greatest when Q waves occur in several leads or lead groupings 1 • Minor Q waves (0.02-0.03 sec) that are ≥0.1 mV deep are suggestive of prior MI if accompanied by inverted T waves in the same lead group 1 • Be aware that some conditions can confound ECG diagnosis of MI, including pre-excitation, cardiomyopathies, LBBB, LVH, and myocarditis 1

Immediate Assessment

• Take a focused history to determine if the patient was aware of the prior MI or if it represents a "silent MI" 1 • Silent Q wave MIs account for 9-37% of all non-fatal MI events and are associated with significantly increased mortality risk 1 • Confirm the diagnosis with a repeat ECG with correct lead placement if there's any doubt about the finding 1 • Assess for current symptoms of ischemia, as patients with prior MI are at higher risk for recurrent events 1

Risk Stratification

• Evaluate the patient's cardiovascular risk profile, including hypertension, diabetes, smoking status, and lipid levels 1 • Consider standard exercise testing to:

1. Assess functional capacity
2. Evaluate efficacy of current medical regimen
3. Stratify risk for subsequent cardiac events 1 • Consider cardiac imaging (echocardiography) to assess for regional wall motion abnormalities and left ventricular function 1

Medical Management

• Start aspirin therapy (75-150 mg daily) indefinitely, as it reduces risk of subsequent MI, stroke, and vascular death by approximately 25% in patients with prior occlusive vascular events 1, 2 • Consider beta-blocker therapy for an indefinite period after MI 1 • Initiate ACE inhibitor therapy, particularly for patients with large or anterior MI, heart failure without hypotension, or previous MI 1 • Manage modifiable risk factors:

• Target LDL cholesterol <100 mg/dL through diet and lipid-lowering medications if necessary 1
• Implement smoking cessation strategies 1
• Control hypertension and diabetes if present 1

Further Cardiac Assessment

• Refer for standard exercise testing (submaximal at 4-7 days or symptom-limited at 10-14 days if MI was recent) 1 • Consider coronary angiography, especially if:

• Patient has recurrent chest pain thought to be caused by myocardial ischemia
• Exercise testing shows significant ischemia
• Patient has high-risk features 1 • Consider revascularization therapy (PCI or CABG) based on coronary anatomy and clinical presentation 1

Long-term Follow-up

• Encourage participation in a formal cardiac rehabilitation program 1 • Recommend at least 20 minutes of moderate exercise (e.g., brisk walking) at least three times weekly 1 • Schedule regular follow-up visits to monitor medication adherence, risk factor control, and symptoms 1 • Perform periodic ECGs to monitor for new changes 1

Special Considerations

• For patients with LBBB or ventricular pacing, diagnosing prior MI is more difficult; concordant ST-segment elevation or a previous ECG may be helpful 1, 3 • In patients with right bundle branch block (RBBB), ST-T abnormalities in leads V1-V3 are common, making assessment of ischemia difficult; however, new ST elevation or Q waves should prompt consideration of MI 1 • Be aware that improper lead placement may result in what appear to be new Q waves; confirm with repeat ECG if uncertain 1