What is a type 2 myocardial infarction (MI)?

Type 2 Myocardial Infarction: Definition, Diagnosis, and Management

Type 2 myocardial infarction (MI) is defined as myocardial necrosis resulting from an imbalance between myocardial oxygen supply and demand in the absence of coronary plaque instability or thrombosis. 1 This distinguishes it from the more common Type 1 MI, which is caused by atherosclerotic plaque rupture or erosion with resulting intraluminal thrombus.

Pathophysiology and Causes

Type 2 MI occurs when conditions other than coronary plaque rupture create an oxygen supply-demand mismatch leading to myocardial injury. Common causes include:

• Decreased oxygen supply:

  • Severe hypotension or shock
  • Severe anemia
  • Hypoxemia
  • Coronary artery spasm
  • Coronary embolism
  • Spontaneous coronary artery dissection (SCAD)
  • Coronary microvascular dysfunction

• Increased oxygen demand:

  • Severe hypertension (especially with left ventricular hypertrophy)
  • Tachyarrhythmias
  • Severe aortic stenosis

• Combined mechanisms:

  • Severe heart failure
  • Sepsis
  • Critical illness

Diagnostic Criteria

According to the Universal Definition of Myocardial Infarction 1, diagnosis of Type 2 MI requires:

1. Detection of a rise and/or fall of cardiac troponin with at least one value above the 99th percentile upper reference limit
2. Evidence of myocardial ischemia as indicated by at least one of:
   • Symptoms of ischemia
   • New ischemic ECG changes
   • Development of pathological Q waves
   • Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
3. Identification of a condition other than coronary plaque instability contributing to oxygen supply-demand imbalance

Clinical Presentation

Type 2 MI patients often present differently than those with Type 1 MI:

• Less likely to have typical chest pain
• More frequently present with atrial fibrillation (15.6% vs. 4.9% in Type 1 MI) 2
• Higher rates of anemia (33.5% vs. 23.3% in Type 1 MI) 2
• Often have concurrent acute non-cardiac conditions (e.g., sepsis, respiratory failure)
• May have ECG changes that are less specific or pronounced

Management Approach

Management of Type 2 MI differs significantly from Type 1 MI and should focus on:

1. Identifying and treating the underlying cause of oxygen supply-demand imbalance:

   • Correct hypotension or hypertension
   • Treat anemia with blood transfusion if severe
   • Address hypoxemia
   • Control tachyarrhythmias
   • Treat sepsis if present

2. Assess for underlying coronary artery disease:

   • Non-invasive stress testing may be appropriate after stabilization
   • Coronary angiography may be considered in selected cases, though invasive strategies have not shown definitive benefit 3

3. Secondary prevention:

   • Unlike Type 1 MI, routine dual antiplatelet therapy is not recommended unless there is evidence of underlying coronary artery disease
   • Standard cardiovascular risk factor modification should be implemented

Prognosis

Despite differences in pathophysiology and treatment approach, Type 2 MI carries a significant risk:

• In-hospital mortality is similar to Type 1 MI (5.8% vs. 5.6%) 2
• Long-term outcomes may be poor, with mortality often driven by non-cardiac comorbidities

Common Pitfalls in Management

1. Misdiagnosis: Distinguishing Type 2 MI from Type 1 MI or non-ischemic myocardial injury can be challenging. Careful clinical assessment and consideration of the context of troponin elevation is essential.

2. Inappropriate treatment: Applying Type 1 MI treatments (aggressive antiplatelet therapy, early invasive strategy) to all Type 2 MI patients may increase bleeding risk without clear benefit.

3. Overlooking cardiac rehabilitation: Very few Type 2 MI patients are referred to cardiac rehabilitation, though evidence suggests they may benefit 4.

4. Failure to address the underlying cause: The primary goal should be treating the condition causing the oxygen supply-demand mismatch 5.

Type 2 MI represents a heterogeneous condition requiring individualized assessment and treatment focused on the underlying cause rather than the standardized approach used for Type 1 MI. Careful distinction between MI types is essential for appropriate management and optimal outcomes.