What are the primary causes of cardiogenic shock?

Primary Causes of Cardiogenic Shock

Acute myocardial infarction is the most common cause of cardiogenic shock, accounting for 50-70% of cases, with other primary causes including mechanical complications of AMI, valvular heart disease, cardiomyopathy, myocarditis, and acute aortic dissection. 1

Definition and Pathophysiology

Cardiogenic shock is defined as a state of inadequate cardiac output to meet tissue demands due to primary cardiac dysfunction, characterized by:

• Systolic blood pressure <90 mmHg for >30 minutes or requiring vasopressors
• Evidence of end-organ hypoperfusion (altered mental status, cold extremities, urine output <30 mL/h, lactate >2 mmol/L)
• Hemodynamic parameters: cardiac index <2.2 L/min/m², pulmonary capillary wedge pressure >15 mmHg 2

Major Etiologies of Cardiogenic Shock

1. Acute Myocardial Infarction-Related Causes (Most Common)

• Left Ventricular Dysfunction: Results from acute loss of ≥40% of LV function or additive loss in previously damaged LV 1

  • Manifests as depressed ejection fraction, regional wall motion abnormalities, decreased stroke volume
  • Can involve extensive myocardial necrosis or stunned but viable myocardium

• Right Ventricular Infarction: Most commonly associated with inferior AMI 1

  • Presents with RV dyssynergy, dilatation, and decreased tricuspid annular excursion
  • Can be diagnosed by tricuspid regurgitation with low pulmonary pressure

• Mechanical Complications of AMI: 1

  • Free ventricular wall rupture (most serious complication)
  • Ventricular septal rupture
  • Acute severe mitral regurgitation due to papillary muscle rupture or dysfunction

2. Non-AMI Cardiac Causes

• Severe Valvular Heart Disease: 1, 3

  • Acute severe mitral or aortic regurgitation
  • Critical aortic stenosis
  • Prosthetic valve thrombosis or dysfunction

• Cardiomyopathies: 1, 3

  • Acute decompensation of chronic heart failure
  • Stress-induced (Takotsubo) cardiomyopathy
  • Fulminant myocarditis
  • Peripartum cardiomyopathy

• Pericardial Disease: 1, 3

  • Cardiac tamponade
  • Constrictive pericarditis

• Arrhythmias: 1

  • Sustained ventricular or supraventricular tachyarrhythmias
  • Severe bradyarrhythmias

• Other Causes: 1, 3, 4

  • Myocardial contusion (trauma)
  • Acute aortic dissection with coronary involvement
  • Post-cardiotomy shock after cardiac surgery

Pathophysiological Cascade

Cardiogenic shock involves a vicious cycle: 5

1. Initial cardiac insult → decreased cardiac output
2. Decreased coronary perfusion → worsening myocardial ischemia
3. Further myocardial dysfunction → progressive shock
4. Systemic inflammation and multi-organ dysfunction
5. Potential development of sepsis due to bacterial translocation from intestines in prolonged shock

Shock Classification

The Society for Cardiovascular Angiography and Interventions (SCAI) classification system provides a standardized approach to categorizing cardiogenic shock severity: 2

• Stage A: At risk (pre-shock)
• Stage B: Beginning shock (compensated)
• Stage C: Classic shock (hypoperfusion despite initial interventions)
• Stage D: Deteriorating shock (worsening despite interventions)
• Stage E: Extremis (cardiac arrest, refractory shock)

Diagnostic Approach

Early recognition is critical for improving outcomes: 2

• Clinical Assessment: Hypotension, tachycardia, altered mental status, cold extremities, decreased urine output
• Laboratory Evaluation: Elevated lactate, liver enzymes, renal dysfunction
• Echocardiography: Essential for immediate assessment of ventricular function, mechanical complications, and shock phenotype (LV, RV, or biventricular) 1
• Invasive Hemodynamic Monitoring: Consider for unclear etiology or to guide therapy 2

Common Pitfalls in Diagnosis

• Pre-shock Misdiagnosis: Patients with compensatory vasoconstriction may maintain near-normal blood pressure despite tissue malperfusion 2
• Delayed Recognition: Failure to identify early signs of shock leads to delayed intervention and worse outcomes 2
• Failure to Identify Specific Shock Phenotype: Different phenotypes (LV, RV, biventricular) require tailored therapies 2

Management Considerations

The key to optimal treatment is a structured approach: 5

1. Rapid diagnosis and prompt initiation of therapy
2. Early coronary revascularization when indicated (particularly in AMI-related shock)
3. Appropriate pharmacological support (inotropes, vasopressors)
4. Consideration of mechanical circulatory support in selected cases

Despite advances in management, cardiogenic shock remains a condition with high mortality (40-60%), highlighting the importance of early recognition and intervention 5, 6.