What are the anatomical regions, affected vessels, EKG (electrocardiogram) changes, and potential complications for different types of myocardial infarctions (heart attacks)?

Different Types of Myocardial Infarctions: Anatomical Regions, Affected Vessels, ECG Changes, and Complications

Understanding the different types of myocardial infarctions (MI) is crucial for proper diagnosis and management, as each type affects different anatomical regions, involves specific coronary vessels, produces characteristic ECG changes in particular leads, and carries unique potential complications.

ST-Elevation Myocardial Infarction (STEMI)

Anterior MI

• Anatomical region: Anterior and anterolateral wall of the left ventricle 1
• Vessel involved: Left anterior descending (LAD) coronary artery 1, 2
• ECG changes: ST-segment elevation in leads V1-V4; may extend to V5-V6, I, and aVL 3
• Potential complications:
  • Left ventricular dysfunction and heart failure 1
  • Cardiogenic shock 1
  • Ventricular septal rupture 1
  • Ventricular arrhythmias 1
  • Left bundle branch block 1

Inferior MI

• Anatomical region: Inferior wall of the left ventricle 1, 3
• Vessel involved: Right coronary artery (RCA) in 80-90% of cases; circumflex artery in 10-20% 2, 4
• ECG changes: ST-segment elevation in leads II, III, and aVF; reciprocal ST depression in leads I and aVL 3
• Potential complications:
  • Bradyarrhythmias and heart blocks (especially AV blocks) 1
  • Right ventricular infarction (in 30-50% of inferior MIs) 3
  • Hypotension 1
  • Papillary muscle dysfunction leading to mitral regurgitation 1

Lateral MI

• Anatomical region: Lateral wall of the left ventricle 1, 3
• Vessel involved: Left circumflex artery (LCx) or diagonal branches of LAD 2, 4
• ECG changes: ST-segment elevation in leads I, aVL, V5, and V6 3
• Potential complications:
  • Lateral wall dysfunction 1
  • Mitral regurgitation due to papillary muscle involvement 1
  • Left ventricular aneurysm (less common than with anterior MI) 2

Posterior MI

• Anatomical region: Posterior wall of the left ventricle 1, 3
• Vessel involved: Right coronary artery or left circumflex artery 3, 4
• ECG changes: ST depression in leads V1-V3 with tall, upright T waves; ST elevation in posterior leads V7-V9 (≥0.05 mV, or ≥0.1 mV in men <40 years) 1, 3
• Potential complications:
  • Often occurs with inferior or lateral MI 1
  • Mitral regurgitation 1
  • Conduction abnormalities if RCA is involved 1

Right Ventricular MI

• Anatomical region: Right ventricle 3
• Vessel involved: Proximal right coronary artery (before RV branches) 3
• ECG changes: ST elevation in right precordial leads V3R and V4R (≥0.05 mV, or ≥0.1 mV in men <30 years) 1, 3
• Potential complications:
  • Right ventricular failure with elevated JVP but clear lung fields 1
  • Hypotension 1
  • High-grade AV block 1
  • Cardiogenic shock with different hemodynamic profile than LV shock 1

Non-ST-Elevation Myocardial Infarction (NSTEMI)

• Anatomical region: Variable, often subendocardial rather than transmural 1
• Vessel involved: Can involve any coronary artery; often associated with partial occlusion or microvasculature disease 1
• ECG changes: ST depression and/or T-wave inversion in multiple leads; no ST elevation 1
• Potential complications:
  • Lower initial mortality than STEMI but similar long-term mortality 1
  • Recurrent ischemia 1
  • Heart failure 1
  • Higher risk of recurrent events 1

Special Considerations

MI in Left Bundle Branch Block

• ECG diagnosis: Modified Sgarbossa criteria are recommended 3, 2
  • Concordant ST elevation ≥1 mm in leads with positive QRS complex 2
  • Concordant ST depression ≥1 mm in V1-V3 2
  • Excessively discordant ST elevation ≥5 mm in leads with negative QRS complex 2
• Challenges: LBBB masks the typical ST-segment changes of acute MI 1, 2

MI in Women

• Presentation differences: Women more often present with atypical symptoms (indigestion, dyspnea, back pain, fatigue) 1
• Vessel involvement: Higher proportion of non-obstructive coronary disease, coronary microvascular dysfunction, and spontaneous coronary artery dissection 1
• Complications: Higher mortality rates, especially in younger women (<50 years) 1

Evolution of ECG Changes in MI

1. Hyperacute phase (minutes to hours):

   • Tall, hyperacute T waves 1, 3
   • ST-segment elevation begins 3

2. Acute phase (hours to days):

   • Prominent ST-segment elevation 1
   • Reciprocal ST depression in opposite leads 1
   • Q waves may begin to develop 1

3. Subacute phase (days to weeks):

   • ST segments begin to normalize 3
   • T waves invert 3
   • Q waves become more defined 1

4. Chronic phase (weeks to permanent):

   • Persistent Q waves 1
   • T-wave inversion may persist for weeks to months 3
   • ST segments usually return to baseline 3

Clinical Pearls

• The ECG should be obtained as soon as possible in suspected MI, but even at an early stage, it is seldom normal 1
• Serial ECGs at 15-30 minute intervals are recommended in symptomatic patients with initially non-diagnostic ECGs 1, 3
• Comparison with previous ECGs, when available, is essential for accurate interpretation 1, 3
• Additional leads (posterior V7-V9, right precordial V3R-V4R) should be recorded when standard leads are non-diagnostic but clinical suspicion remains high 1, 3
• The presence of reciprocal changes increases the specificity for diagnosing acute MI 1