What is cardiogenic shock, its etiology, pathophysiology, signs, symptoms, diagnosis, treatment, and potential complications?

Cardiogenic Shock: Definition, Etiology, Pathophysiology, Diagnosis, and Management

Cardiogenic shock is a life-threatening condition characterized by inadequate cardiac output resulting in systemic hypoperfusion and end-organ damage, with mortality rates exceeding 40% despite advances in treatment. 1, 2

Definition

• Cardiogenic shock is clinically defined as persistent hypotension (systolic BP <90 mmHg for >30 minutes) despite adequate filling status with signs of hypoperfusion 2
• Hemodynamically defined as systolic BP <90 mmHg with central filling pressure >20 mmHg, or cardiac index <1.8 L/min/m² 1
• Also considered present when inotropes/vasopressors or mechanical circulatory support are required to maintain systolic BP >90 mmHg 1, 3

Etiology

• Acute myocardial infarction (AMI) is the most common cause, complicating 5-12% of AMIs 1
• AMI-related cardiogenic shock typically occurs with >40% loss of left ventricular myocardium 1
• Mechanical complications of AMI: free wall rupture, ventricular septal defect, papillary muscle rupture 1
• Acute decompensated heart failure with pre-existing ventricular dysfunction 1
• Post-cardiotomy shock (complicates 0.1-0.5% of cardiac surgeries) 1
• Other causes: severe valvular disease, myocarditis, cardiomyopathy, and acute aortic dissection 1

Pathophysiology

• Central pathophysiologic derangement is diminished cardiac output leading to systemic hypoperfusion 1
• Creates maladaptive cycles of:
  • Myocardial ischemia → decreased contractility → further reduced cardiac output 1
  • Inflammatory mediator release → impaired tissue metabolism and nitric oxide production → systemic vasodilation → worsening hypotension 1
  • Pulmonary inflammation → pulmonary vasoconstriction → increased biventricular afterload 1
  • Renal hypoperfusion → neurohormonal activation → fluid retention → increased preload → increased myocardial oxygen demand 1
• Ultimately leads to multiorgan system failure and death if not reversed 1

Signs and Symptoms

• Hypotension (systolic BP <90 mmHg) 1, 2
• Signs of hypoperfusion: cold extremities, decreased urine output, altered mental status 1
• Tachycardia (compensatory mechanism) 1
• Pulmonary congestion (in left ventricular failure) with dyspnea and rales 1
• Elevated jugular venous pressure 1
• Peripheral edema 1
• Killip classification: Class 4 represents cardiogenic shock 1

Diagnosis and Evaluation

• Clinical assessment: hypotension, signs of hypoperfusion, elevated jugular venous pressure 2
• Laboratory evaluation:
  • Cardiac biomarkers (troponin, CK-MB) 2
  • Lactate levels (>2 mmol/L indicates tissue hypoperfusion) 2, 3
  • Organ function tests (renal, hepatic) 2
  • Arterial blood gases 2
• Immediate echocardiography is essential to:
  • Assess ventricular function and ejection fraction 1, 2
  • Identify mechanical complications 1
  • Evaluate valvular function 1, 2
• Invasive hemodynamic assessment:
  • Arterial line for accurate blood pressure monitoring 2
  • Pulmonary artery catheter to measure:
    • Cardiac index (<1.8 L/min/m² in cardiogenic shock) 1, 3
    • Pulmonary capillary wedge pressure (>20 mmHg) 1, 2
    • Cardiac power output (<0.6 W indicates severe shock) 3
• Coronary angiography to identify culprit lesions in AMI-related shock 1, 2

Interventions and Treatments

Immediate Management Algorithm

1. Revascularization (for AMI-related shock):

   • Immediate percutaneous coronary intervention (PCI) is the standard of care 1, 2
   • Emergency CABG if coronary anatomy is not suitable for PCI 2
   • Consider immediate fibrinolysis if PCI would be delayed >120 minutes 2

2. Hemodynamic Support:

   • Vasopressors and Inotropes:
     • Norepinephrine is the preferred first-line vasopressor 2, 3
     • Dobutamine (2-20 μg/kg/min) is the first-line inotropic agent 1, 2
     • For renal hypoperfusion, dopamine (2.5-5.0 μg/kg/min) may be considered 1

3. Respiratory Support:

   • Oxygen supplementation to maintain adequate oxygenation 1, 2
   • Non-invasive positive pressure ventilation for pulmonary edema with respiratory distress 2
   • Endotracheal intubation and mechanical ventilation if unable to maintain adequate oxygenation 1, 2

4. Mechanical Circulatory Support (MCS):

   • Consider in patients with refractory shock 2
   • Options include:
     • Intra-aortic balloon pump (IABP) - consider for mechanical complications 2
     • Percutaneous ventricular assist devices 1
     • Extracorporeal membrane oxygenation (ECMO) 1

Special Considerations

• Complete revascularization during index procedure for AMI-related shock 2
• Mechanical complications require urgent surgical consultation 1, 2
• Right ventricular failure management: minimize positive pressure ventilation, correct acidosis, improve oxygenation 3
• Multidisciplinary shock team approach improves outcomes 2, 3

Potential Complications

• Multiorgan system failure (associated with nearly 50% in-hospital mortality) 1
• Acute kidney injury 1
• Acute liver injury 1
• Respiratory failure 1
• Coagulopathy 1
• Metabolic acidosis 1
• Arrhythmias 1
• Sepsis (secondary complication) 1

Red Flags and CVICU Tips

• Early recognition is critical - mortality increases with delayed diagnosis and treatment 2
• Exclude other causes of shock before confirming cardiogenic shock (hypovolemia, sepsis, etc.) 1
• Monitor for RV failure which may require different management strategies 1, 3
• Avoid volume overload in patients with RV infarction as it might worsen hemodynamics 2
• Do not delay revascularization in AMI-related shock 1, 2
• Implement a standardized protocol for shock management 1, 2
• Consider transfer to specialized shock centers with 24/7 cardiac catheterization and MCS capabilities 2, 3
• Reassess frequently - cardiogenic shock is dynamic and requires ongoing evaluation and treatment adjustments 2
• Target hemodynamic parameters: wedge pressure <20 mmHg and cardiac index >2 L/min/m² 2