Cardiogenic Shock 

Definition

Cardiogenic shock (CS) is a state of critical end-organ hypoperfusion due to primary cardiac pump failure, despite adequate intravascular volume, leading to:

• Persistent hypotension
• Low cardiac output
• Elevated filling pressures
• Multiorgan dysfunction

Operational definition (practical ICU):

• SBP <90 mmHg or MAP <65 mmHg for >30 min
• OR need for vasopressors/inotropes to maintain BP
• Plus signs of hypoperfusion (oliguria, altered mentation, cold clammy skin, ↑ lactate)

Epidemiology

• Accounts for 5–10% of acute MI
• AMI is the most common cause (>70%)
• Mortality remains 40–50% despite advances
• Leading cause of death in STEMI

Etiology (Causes)

1. Ischemic

• Acute myocardial infarction (LAD > RCA > LCX)
• Mechanical complications of MI:
• Papillary muscle rupture → acute MR
• Ventricular septal rupture
• Free wall rupture (tamponade)

2. Non-Ischemic

• Acute decompensated heart failure
• Severe cardiomyopathy (DCM, HCM)
• Myocarditis
• Takotsubo cardiomyopathy

3. Arrhythmia-Related

• Sustained VT/VF
• Complete heart block
• Rapid AF with poor LV function

4. Valvular

• Acute severe MR
• Acute severe AR
• Critical AS

5. Right Ventricular Failure

• RV infarction
• Massive PE (overlaps with obstructive shock)
• Pulmonary hypertension crisis

Pathophysiology

Core Hemodynamic Problem

↓ Myocardial contractility → ↓ Stroke volume → ↓ Cardiac output → ↓ MAP → tissue hypoxia

Maladaptive Responses

• Sympathetic activation → ↑ SVR → ↑ afterload → worsens LV failure
• RAAS activation → Na⁺/water retention → ↑ preload → pulmonary congestion
• Coronary hypoperfusion → ongoing ischemia → vicious cycle

Microcirculatory Dysfunction

• Elevated lactate despite “normal” macro-parameters
• Mitochondrial dysfunction → cytopathic hypoxia

Hemodynamic Profile (Classic)

Clinical Features

Symptoms

• Severe dyspnea
• Chest pain (ischemic cause)
• Altered sensorium
• Fatigue, collapse

Signs

• Hypotension
• Narrow pulse pressure
• Cold extremities
• Elevated JVP
• Pulmonary crackles (LV failure)
• New murmurs (acute MR, VSD)

Classification

SCAI Cardiogenic Shock Stages (IMPORTANT FOR EXAMS)

👉 Stage C or beyond = true cardiogenic shock

Diagnostic Evaluation

Bedside

• ECG (MI, arrhythmias)
• ABG with lactate
• Urine output
• Focused echo (POCUS)

Laboratory

• Troponin
• BNP/NT-proBNP
• Lactate
• Renal & liver function
• Mixed venous saturation (SvO₂)

Echocardiography (KEY TEST)

• LV/RV systolic function
• Regional wall motion abnormalities
• Valvular pathology
• Mechanical complications
• Tamponade

Invasive Hemodynamics (PAC)

Useful when diagnosis unclear or refractory shock:

• Confirms elevated PAOP with low CI
• Differentiates mixed shock states

Management – Stepwise ICU Approach

1. Immediate Stabilization

• Airway & oxygenation (early NIV/intubation if pulmonary edema)
• Continuous ECG & invasive BP monitoring
• Two large bore IV lines / central access

2. Optimize Preload

• Avoid aggressive fluids
• Small fluid challenge (250 mL) only if hypovolemia suspected
• Use echo-guided assessment

3. Vasopressors (FIRST-LINE)

Norepinephrine – Drug of Choice

• Improves MAP with minimal tachycardia
• Better outcomes than dopamine

❌ Dopamine → ↑ arrhythmias, ↑ mortality

4. Inotropes

⚠️ Risk: hypotension, arrhythmias

5. Treat the Cause (MOST IMPORTANT)

AMI-Related CS

• Immediate revascularization (PCI/CABG)
• Guideline-mandated irrespective of delay

Mechanical Complications

• Emergency surgery
• Bridge with IABP / Impella / ECMO

Arrhythmias

• DC cardioversion
• Temporary pacing for CHB

6. Mechanical Circulatory Support (MCS)

📌 Early MCS before multiorgan failure improves outcomes

7. Adjunctive ICU Care

• Renal replacement therapy if AKI
• Glycemic control
• DVT prophylaxis
• Nutrition (early enteral)
• Avoid beta-blockers acutely

Special Situations

Right Ventricular Shock

• Maintain preload
• Avoid high PEEP
• Inotropes (dobutamine)
• Pulmonary vasodilators (iNO)

Mixed Shock

• Cardiogenic + septic
• Requires combined vasopressor + inotrope strategy

Prognostic Factors

• Age
• Lactate level
• Duration of shock
• SCAI stage
• Presence of multiorgan failure
• Failure to achieve early revascularization

Key Exam Pearls (NEET-SS / INI-SS)

• Most common cause: Acute MI
• Norepinephrine = first-line vasopressor
• Avoid dopamine
• Early revascularization saves lives
• Echo is mandatory
• High PAOP + low CI = cardiogenic shock
• SCAI classification is current standard