What is cardiogenic shock?

Cardiogenic Shock: Definition and Management

Cardiogenic shock is a hemodynamically complex syndrome characterized by inadequate cardiac output leading to tissue hypoperfusion and multiorgan dysfunction, typically defined by sustained hypotension (systolic BP <90 mmHg for >30 minutes) despite adequate preload, requiring vasopressors, and accompanied by evidence of end-organ hypoperfusion. 1, 2

Diagnostic Criteria

Cardiogenic shock is diagnosed based on both clinical and hemodynamic parameters:

Clinical Criteria:

• Systolic blood pressure <90 mmHg for >30 minutes or requiring vasopressors/inotropes to maintain SBP >90 mmHg 1
• Evidence of end-organ hypoperfusion:
  • Altered mental status
  • Cold, clammy extremities
  • Decreased urine output (<30 mL/hr)
  • Livedo reticularis
  • Lactate >2 mmol/L 2

Hemodynamic Criteria:

• Cardiac index <2.2 L/min/m² 1, 2
• Cardiac power output <0.6 W 1
• Pulmonary capillary wedge pressure >15 mmHg 2

Pathophysiology

Cardiogenic shock results from a primary cardiac dysfunction that creates a cascade of maladaptive responses:

1. Initial cardiac insult → decreased cardiac output
2. Compensatory mechanisms → neurohormonal activation, increased systemic vascular resistance
3. Vicious cycles develop:
   • Myocardial ischemia → further contractile dysfunction
   • Systemic inflammation → vasodilation and myocardial depression
   • Tissue hypoperfusion → metabolic acidosis → further cardiac dysfunction 1

The syndrome is perpetuated by overlapping cycles of inflammation, ischemia, vasoconstriction, and volume overload that worsen the initial cardiac dysfunction 1.

Classification and Staging

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

Stage	Description	Key Features
A	At Risk	Not in shock but at risk (e.g., large MI)
B	Beginning	Hypotension but normal perfusion
C	Classic	Hypotension with hypoperfusion
D	Deteriorating	Worsening despite initial interventions
E	Extremis	Cardiac arrest, refractory shock requiring CPR or escalating support

2

Etiology

The most common causes of cardiogenic shock include:

• Acute myocardial infarction (50-70% of cases) 1, 2
• Mechanical complications of AMI:
  • Free wall rupture
  • Ventricular septal defect
  • Papillary muscle rupture 1
• Acute decompensated heart failure 1
• Valvular heart disease (acute severe mitral or aortic regurgitation) 2
• Myocarditis 2
• Right ventricular failure 1
• Acute aortic dissection 2

Diagnostic Approach

Immediate Assessment:

1. Echocardiography: Essential for immediate assessment of:

   • Ventricular function (global and regional)
   • Mechanical complications
   • Shock phenotype (LV, RV, or biventricular) 1, 2

2. Invasive hemodynamic monitoring: Provides definitive parameters for diagnosis and guides therapy:

   • Pulmonary artery catheter measurements
   • Cardiac output/index
   • Filling pressures
   • Systemic vascular resistance 1, 2

3. Laboratory evaluation:

   • Cardiac biomarkers (troponin, BNP)
   • Lactate (marker of tissue hypoperfusion)
   • Liver and kidney function tests
   • Complete blood count
   • Coagulation profile 2

Management Approach

Management of cardiogenic shock requires a standardized, team-based approach focusing on:

1. Early recognition and rapid diagnosis 1, 2
2. Hemodynamic stabilization:
   • Vasopressors/inotropes to maintain adequate perfusion
   • Careful fluid management 1
3. Identification and treatment of underlying cause:
   • Early revascularization for AMI-CS
   • Correction of mechanical complications 1
4. Tailored therapy based on shock phenotype (LV, RV, or biventricular) 1, 2
5. Mechanical circulatory support when appropriate 1

Pharmacological Management:

• Vasopressors: Norepinephrine is preferred for hypotension with adequate cardiac output 1
• Inotropes: Dobutamine for low cardiac output; milrinone for high-afterload LV failure 1
• Vasodilators: For patients with adequate blood pressure and high systemic vascular resistance 1

Mechanical Circulatory Support:

Consider early implementation in refractory cases based on shock phenotype:

• LV-dominant shock: Intra-aortic balloon pump, Impella, VA-ECMO
• RV-dominant shock: Right-sided Impella, ECMO
• Biventricular shock: VA-ECMO, biventricular support 1, 2

Special Considerations

RV Failure:

• Often associated with inferior AMI
• Echocardiographic findings include RV dyssynergy, dilatation, and decreased TAPSE
• Management includes volume optimization, inotropes, and minimizing intrathoracic positive pressure 1

Multidisciplinary Approach:

• Implementation of shock teams and protocols improves outcomes
• Early consultation with advanced heart failure specialists for consideration of durable mechanical support or transplantation in selected cases 1

Prognosis

Despite advances in management, cardiogenic shock continues to have high mortality rates:

• In-hospital mortality: 40-50%
• One-year mortality: 50-60% 1

Early recognition, rapid implementation of appropriate therapies, and a standardized team-based approach offer the best chance for improved outcomes in this critical condition.