What is cardiogenic shock?

Cardiogenic Shock Definition and Classification

Cardiogenic shock is defined as a clinical state of hypoperfusion characterized by systolic blood pressure <90 mmHg and central filling pressure >20 mmHg, or a cardiac index <1.8 L/min/m², resulting from primary cardiac dysfunction. 1

Clinical Diagnostic Criteria

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

Clinical Criteria

• Systolic blood pressure <90 mmHg for at least 30 minutes or requiring inotropes/vasopressors to maintain systolic blood pressure >90 mmHg 1
• Evidence of end-organ hypoperfusion manifesting as:
  • Decreased urine output (<0.5 mL/kg/h) 1
  • Altered mental status 1
  • Cool extremities due to peripheral vasoconstriction 1
  • Elevated lactate levels (>2 mmol/L) 1
  • Acute liver or kidney injury 1

Hemodynamic Criteria

• Cardiac index <1.8 L/min/m² without vasopressors/inotropes 1
• Cardiac power output <0.6 W 1
• Central filling pressure/pulmonary capillary wedge pressure >20 mmHg 1

Classification Systems

Killip Classification

The Killip classification was originally developed for acute myocardial infarction patients 1:

• Stage I: No heart failure, no clinical signs of cardiac decompensation
• Stage II: Heart failure with rales, S3 gallop, pulmonary venous hypertension
• Stage III: Severe heart failure with frank pulmonary edema
• Stage IV: Cardiogenic shock with hypotension (SBP <90 mmHg) and evidence of peripheral vasoconstriction (oliguria, cyanosis, diaphoresis) 1

SCAI Classification

The Society for Cardiovascular Angiography and Interventions (SCAI) classification provides a more nuanced staging system 1:

• Stage A: At risk for cardiogenic shock but not currently experiencing signs/symptoms
• Stage B: Beginning shock with relative hypotension or tachycardia without hypoperfusion
• Stage C: Classic shock requiring intervention (inotropes, pressors, mechanical support) beyond volume resuscitation
• Stage D: Deteriorating/doom shock not responding to initial interventions
• Stage E: Extremis with cardiac arrest requiring ongoing CPR and/or ECMO 1

Etiology and Pathophysiology

Cardiogenic shock results from primary cardiac dysfunction leading to inadequate cardiac output and tissue hypoperfusion 1:

• Most common cause is acute myocardial infarction (AMI), occurring in 7-10% of AMI cases 1
• Other causes include:
  • Valvular heart disease 1
  • Cardiomyopathy 1
  • Pericardial disease 1
  • Arrhythmias 1

Clinical Presentation

The presentation of cardiogenic shock involves a constellation of findings:

• Hypotension (SBP <90 mmHg) 1
• Tachycardia (compensatory mechanism) 1
• Signs of pulmonary congestion (rales, orthopnea) 1
• Signs of systemic venous congestion (elevated jugular venous pressure, hepatomegaly) 1
• Decreased urine output 1
• Altered mental status 1
• Peripheral vasoconstriction with cool extremities 1
• Metabolic acidosis with elevated lactate 1

Common Pitfalls in Diagnosis

• Failure to exclude other causes of shock (hypovolemic, septic, etc.) before diagnosing cardiogenic shock 1
• Not recognizing early stages of shock (pre-shock) when intervention could prevent progression 1
• Overlooking right ventricular failure as a cause of cardiogenic shock 1
• Not accounting for the impact of cardiac arrest on prognosis (cardiac arrest significantly worsens outcomes at every stage of shock) 1
• Delaying invasive hemodynamic assessment when clinical diagnosis is uncertain 1

Prognostic Considerations

Despite advances in treatment, cardiogenic shock remains associated with high mortality:

• 30-day mortality rates of 40-45% in contemporary studies 1
• Mortality increases stepwise with progression through SCAI shock stages A to E 1
• Presence of cardiac arrest significantly increases mortality at every stage of shock 1

Recognizing cardiogenic shock early and implementing appropriate management strategies is critical for improving outcomes in this high-mortality condition.