What are the signs of acute myocardial ischemic changes on a 12-lead electrocardiogram (EKG)?

Signs of Acute Myocardial Ischemic Changes on EKG

The most significant signs of acute myocardial ischemic changes on a 12-lead EKG include ST-segment elevation ≥0.1 mV in two contiguous leads (except V2-V3 which require higher thresholds), ST-segment depression ≥0.05 mV in two contiguous leads, new pathological Q waves, and T-wave inversions ≥0.1 mV in leads with prominent R waves. 1

Primary EKG Findings in Acute Myocardial Ischemia

ST-Segment Abnormalities

• ST-segment elevation:

  • ≥0.1 mV in all leads except V2-V3 1
  • In V2-V3: ≥0.2 mV in men ≥40 years, ≥0.25 mV in men <40 years, ≥0.15 mV in women 1
  • Must be present in two or more contiguous leads
  • Often associated with reciprocal ST depression in opposite leads

• ST-segment depression:

  • New horizontal or downsloping ST depression ≥0.05 mV in two contiguous leads 1
  • ST depression in V1-V3 may indicate posterior wall MI (inferobasal) 2, 1
  • ST depression >0.1 mV in eight or more surface leads with ST elevation in aVR/V1 suggests left main coronary obstruction 2, 1

T-Wave Abnormalities

• T-wave inversion ≥0.1 mV in two contiguous leads with prominent R wave or R/S ratio >1 1
• Hyperacute T waves (tall, peaked T waves) in early ischemia 1
• Pseudo-normalization of previously inverted T waves during chest pain 1

Q-Wave Abnormalities

• Q wave ≥0.03 sec and ≥0.1 mV deep in leads I, II, aVL, aVF, or V1-V6 1
• QS complex in two contiguous leads 1
• Pathological Q waves generally indicate irreversible myocardial damage 1

Location-Specific EKG Patterns

Anterior Wall Ischemia

• ST elevation in leads V1-V4 (LAD occlusion) 1
• Reciprocal ST depression may be seen in inferior leads (II, III, aVF) 1

Inferior Wall Ischemia

• ST elevation in leads II, III, aVF (RCA occlusion) 1
• Reciprocal ST depression in leads I and aVL 1

Lateral Wall Ischemia

• ST elevation in leads I, aVL, V5-V6 (circumflex artery occlusion) 1

Posterior Wall Ischemia

• ST depression in leads V1-V3 with upright terminal T waves 2, 1
• Requires posterior leads (V7-V9) for direct visualization 1
• Cut-point of 0.05 mV ST elevation in V7-V9 (0.1 mV in men <40 years) 2, 1

Right Ventricular Ischemia

• Often accompanies inferior MI 1
• Requires right-sided leads (V3R, V4R) 1
• ST elevation ≥0.05 mV in V3R/V4R (≥0.1 mV in men <30 years) 1

Special Considerations

Bundle Branch Blocks

• LBBB makes diagnosis more difficult 2, 1
• Look for concordant ST-segment elevation with LBBB 1
• In RBBB, ST elevation or Q waves should still raise suspicion for ischemia 1

Ventricular Paced Rhythm

• May prevent interpretation of ST-segment changes 2
• Consider reprogramming pacemaker if patient is not pacemaker-dependent 2

Diagnostic Approach

Serial EKGs

• Obtain ECG promptly (within 10 minutes) of presentation 2, 1
• Perform serial ECGs at 15-30 minute intervals in symptomatic patients with initially non-diagnostic ECGs 1
• Compare with prior ECGs when available 1

Atypical Presentations Requiring Prompt Management

• LBBB (especially new or presumed new) 2
• Ventricular paced rhythm 2
• Persistent ischemic symptoms without diagnostic ST-segment elevation 2
• Isolated posterior MI 2
• ST-segment elevation in lead aVR 2

Common Pitfalls

• Relying on a single ECG when the condition is evolving 1
• Overlooking posterior MI by not using posterior leads (V7-V9) 1
• Missing right ventricular involvement by not recording right precordial leads (V3R, V4R) 1
• Failing to compare with previous ECGs when available 1
• A normal ECG does not exclude ACS (1-6% of patients with normal ECG later proven to have MI) 1

By systematically evaluating these EKG findings, clinicians can quickly identify acute myocardial ischemia and initiate appropriate treatment to reduce morbidity and mortality associated with acute coronary syndromes.