Cardiogenic shock is what happens when the heart fails as a pump so badly that tissues can’t get enough perfusion—despite adequate intravascular volume. On Step 1, it’s a classic “cold and wet” shock state tied most commonly to an acute MI, and it’s loaded with testable hemodynamics, murmur clues, and “what pressor/inotrope next?” management decisions.
Where cardiogenic shock fits in shock physiology
Definition (board-style): Shock due to primary cardiac pump failure → ↓ cardiac output → systemic hypoperfusion, typically with ↑ filling pressures.
Key hemodynamic signature
- ↓ Cardiac output (CO)
- ↑ Systemic vascular resistance (SVR) (compensatory vasoconstriction)
- ↑ PCWP (pulmonary capillary wedge pressure) = left-sided filling pressure (pulmonary congestion)
- ↑ CVP/JVP if right-sided involvement (e.g., RV infarct)
Quick comparison table (high-yield)
| Shock type | CO | SVR | PCWP | Skin | Classic clue |
|---|---|---|---|---|---|
| Cardiogenic | ↓ | ↑ | ↑ | Cold, clammy | MI, pulmonary edema |
| Hypovolemic | ↓ | ↑ | ↓ | Cold, clammy | Hemorrhage, dehydration |
| Obstructive (PE, tamponade) | ↓ | ↑ | variable | Cold, clammy | JVP up, clear lungs in PE/tamponade patterns |
| Distributive (septic) | ↑ early / ↓ late | ↓ | ↓ | Warm early | Fever, bounding pulses early |
First Aid cross-reference: Shock hemodynamics table; MI complications; HF pharmacology (inotropes/vasopressors).
Pathophysiology: why the spiral happens
Cardiogenic shock is often a vicious cycle:
- Pump failure (most commonly acute MI) → ↓ stroke volume → ↓ CO
- ↓ MAP triggers sympathetic response:
- ↑ HR
- ↑ contractility (limited reserve)
- ↑ SVR (afterload goes up)
- Afterload increases → the failing LV struggles more → even lower CO
- ↑ LV end-diastolic pressure → ↑ left atrial pressure → pulmonary edema (↑ PCWP)
- Myocardial ischemia worsens (low coronary perfusion, higher wall stress) → further pump failure
- End-organ hypoperfusion → lactic acidosis, AKI, altered mental status
Core concept to remember
Cardiogenic shock = low forward flow + high backward pressure.
- Forward failure: hypotension, cool extremities, organ hypoperfusion
- Backward failure: pulmonary congestion/edema (left), JVP elevation (right)
Etiologies (what Step 1 loves)
#1 cause
- Acute MI (especially large anterior MI from LAD occlusion)
Other high-yield causes
- Mechanical complications post-MI (timing matters; see below)
- Arrhythmias
- Sustained VT/VF
- Complete heart block (inferior MI pattern)
- Acute decompensated heart failure
- Severe valvular disease
- Acute mitral regurgitation (papillary muscle rupture)
- Critical aortic stenosis (older patients)
- Myocarditis (viral, giant cell, etc.)
- Stress (Takotsubo) cardiomyopathy (often mimics MI)
Clinical presentation: “cold and wet” clues
Symptoms
- Dyspnea, orthopnea (pulmonary edema)
- Chest pain (if MI)
- Fatigue, confusion, syncope (low perfusion)
- Oliguria
Signs
- Hypotension (often SBP < 90 or MAP low)
- Cool, clammy extremities (high SVR)
- Tachycardia (compensatory; unless bradyarrhythmia)
- Crackles/rales, frothy sputum (pulmonary edema)
- S3 gallop (volume overload + systolic dysfunction)
- JVP elevation (esp. RV failure or biventricular)
- Narrow pulse pressure (low stroke volume)
Labs and imaging “supporting cast”
- ↑ Lactate (tissue hypoperfusion)
- Metabolic acidosis
- Elevated troponin if ischemic cause
- CXR: pulmonary edema, cardiomegaly
- EKG: STEMI/NSTEMI patterns, conduction blocks, arrhythmias
- Echo: low EF, wall-motion abnormalities, mechanical complications
Diagnosis: what seals it on exams and in real life
Clinical diagnosis: shock + evidence of cardiac dysfunction (and not primarily hypovolemia or distributive).
Hemodynamic criteria (Step-style)
- Low CO/CI (cardiac index often < 2.2 L/min/m²)
- High PCWP (often > 15–18 mmHg)
- High SVR
The must-not-miss: post-MI mechanical complications
These can present with sudden hypotension and new murmurs—high yield.
| Complication | Timing after MI | Key finding | Murmur | Mechanism/artery |
|---|---|---|---|---|
| Papillary muscle rupture | 2–7 days | Acute pulmonary edema, shock | Holosystolic at apex → radiates to axilla (MR) | Posteromedial papillary muscle, RCA/PDA (single blood supply) |
| Ventricular septal rupture | 3–5 days | Shock + pulmonary edema | Harsh holosystolic at LLSB | LAD (anterior septum) |
| Free wall rupture → tamponade | 5–14 days | PEA arrest, JVD, hypotension | Often none; muffled heart sounds | LAD; risk ↑ with transmural MI |
| LV aneurysm | Weeks–months | HF, arrhythmias, thrombus | — | Persistent ST elevation, mural thrombus |
First Aid cross-reference: MI complications + murmurs; tamponade physiology.
Treatment: stabilize first, then fix the cause
Think in two tracks:
- Immediate stabilization (ABCs + perfusion)
- Definitive therapy (revascularize or fix structural problem)
Step 1 algorithm mindset
Cardiogenic shock due to MI → urgent revascularization is the definitive move.
Immediate management (high-yield)
- Oxygen as needed; consider intubation if severe pulmonary edema/respiratory failure
- IV access, continuous monitoring, urine output
- Careful fluids
- Many are “wet,” so fluid boluses can worsen pulmonary edema
- Exception: RV infarct—often preload dependent; gentle fluids can help
Medications: what the exam expects you to choose
1) Norepinephrine (first-line pressor in many cardiogenic shock protocols)
- α1 vasoconstriction ↑ SVR → ↑ MAP
- β1 some inotropy
- Used to maintain perfusion pressure when hypotensive
2) Inotropes (dobutamine, milrinone)
- Dobutamine (β1 > β2): ↑ contractility, can ↓ SVR slightly
- Great for low-output states if BP can tolerate it
- Milrinone (PDE-3 inhibitor): ↑ inotropy + vasodilation
- Can cause hypotension; useful in certain HF patients, including with pulmonary HTN/RV failure contexts
3) Diuretics (e.g., furosemide)
- For pulmonary congestion once perfusion is stabilized
4) Avoid/hold negative inotropes in acute shock
- β-blockers can worsen acute cardiogenic shock (they’re chronic mortality meds, not acute shock meds)
- Many vasodilators (e.g., nitrates) can drop BP in shock
First Aid cross-reference: Autonomics drugs; HF meds (dobutamine, milrinone); shock pressors.
Definitive therapy (what saves the myocardium)
- Acute MI: PCI (or thrombolysis if PCI unavailable and indicated)
- Mechanical complication: emergent surgery (e.g., VSD repair, papillary rupture repair)
- Arrhythmia-driven shock: cardioversion/defibrillation or pacing
Mechanical circulatory support (Step 1/2 concepts)
- Intra-aortic balloon pump (IABP) (classic board concept):
- Inflates in diastole → ↑ coronary perfusion
- Deflates in systole → ↓ afterload
- Other devices exist (Impella, VA-ECMO), but IABP remains the “teachable” one.
Special scenario: Right ventricular infarct (testable twist)
Clues
- Inferior MI (II, III, aVF) + JVP up, clear lungs, hypotension
- Often RCA infarct affecting RV
Management difference
- RV is preload dependent → give IV fluids cautiously to optimize preload
- Avoid nitrates/diuretics initially if they tank preload and worsen hypotension
High-yield associations & “exam traps”
1) Hemodynamics are not optional
If you see shock + pulmonary edema, think:
- PCWP high (backward congestion)
- SVR high (compensation)
- CO low (primary problem)
2) New murmur after MI = mechanical complication until proven otherwise
- MR murmur (apex holosystolic) → papillary muscle rupture
- VSD murmur (LLSB harsh holosystolic) → septal rupture
Both can produce rapid cardiogenic shock.
3) “Cold and clammy” is a catecholamine clue
Cardiogenic shock looks like hypovolemic shock on the skin exam (both high SVR), but cardiogenic has congestion (high PCWP, pulmonary edema).
4) Don’t reflexively give big fluid boluses
Unless RV infarct or clear evidence of hypovolemia, aggressive fluids worsen pulmonary edema.
Rapid review (what to memorize)
Cardiogenic shock
- Cause: pump failure (most often MI)
- Findings: hypotension, cool/clammy, pulmonary edema, ↑ JVP (sometimes), S3
- Hemodynamics: ↓ CO, ↑ SVR, ↑ PCWP
- Dx tools: EKG, troponin, echo, CXR, lactate
- Tx: stabilize (pressors/inotropes, oxygen/ventilation), urgent revascularization for MI, fix mechanical complications, consider IABP