Shock — Cardiogenic and Obstructive

Cardiogenic — ischemic (most common)

• Acute MI with large LV infarct: the leading cause; anterior STEMI with loss of >40% of LV mass is the prototype. Shock is usually not present on arrival but develops within the first 24–48 hours.
• Mechanical complications of MI: papillary muscle rupture (posteromedial papillary muscle, single blood supply from the PDA), ventricular septal rupture, and free wall rupture — typically days 3–7 post-infarct in the reperfusion era.
• RV infarction complicating inferior/posterior MI: preload-dependent failure rather than pump failure per se.

Cardiogenic — non-ischemic

• Myopathic: fulminant myocarditis (viral, giant cell, checkpoint-inhibitor), takotsubo (stress) cardiomyopathy, peripartum cardiomyopathy, end-stage dilated cardiomyopathy in acute decompensation.
• Arrhythmic: sustained VT, rapid AF with loss of atrial kick, or high-grade AV block — the rhythm, not the muscle, is the culprit.
• Valvular/structural: acute severe MR or AR (endocarditis, chordal rupture, dissection), critical AS with a precipitant, prosthetic valve thrombosis.
• Toxic/metabolic: beta blocker or calcium channel blocker overdose, severe acidosis, thyroid storm/myxedema.

Obstructive

• Intrathoracic pressure: tension pneumothorax, dynamic hyperinflation (auto-PEEP) in ventilated asthma/COPD.
• Pericardial: tamponade from malignancy, uremia, trauma, or type A dissection rupturing into the pericardium.
• Vascular: massive PE, air or amniotic fluid embolism, severe pulmonary hypertension.

Cardiogenic Shock Mechanisms

• Decreased contractility: Loss of functional myocardium (>40% of LV in acute MI) reduces stroke volume; impaired calcium handling and energy depletion in heart failure limit force generation
• Afterload mismatch: High systemic vascular resistance (compensatory vasoconstriction) increases LV workload, worsening efficiency and deepening shock paradoxically
• Diastolic dysfunction: Impaired ventricular relaxation (acute MI, hypertension, restrictive cardiomyopathy) prevents adequate filling despite elevated pressures, reducing preload-dependent stroke volume
• Arrhythmias and mechanical complications: Ventricular rupture, acute MR, VSD, or loss of atrial kick (AF, heart block) acutely reduce forward flow
• Neuroendocrine maladaptation: Initial catecholamine surge increases heart rate and contractility but increases myocardial oxygen demand; prolonged activation causes systemic inflammation, myocardial depressant factors, and metabolic acidosis that worsen contractile function
• End-organ hypoperfusion cascade: Renal hypoperfusion triggers renin-angiotensin activation; splanchnic ischemia causes bacterial translocation and release of TNF-α; cerebral hypoperfusion impairs consciousness

Obstructive Shock Mechanisms

• Direct mechanical obstruction: PE blocks pulmonary vasculature, increasing RV afterload acutely; tension pneumothorax collapses lung and compresses mediastinal structures; cardiac tamponade restricts ventricular filling via increased intrapericardial pressure
• RV acute decompensation: Sudden increase in RV afterload (massive PE) causes RV dilation; the interventricular septum shifts left, further compromising LV filling and cardiac output
• Loss of venous return: Pericardial fluid, air, or blood physically prevents atrial filling; mediastinal compression from tension physiology impedes superior vena cava flow
• Increased intrathoracic pressure: Tension pneumothorax creates positive pressure that compresses the heart and great vessels, impairing preload to both ventricles

Classic Signs of Cardiogenic Shock

• Hypotension (SBP <90 mmHg sustained) with altered mental status, cool extremities, and weak pulses reflecting severe hypoperfusion and tissue dysoxia
• Pulmonary edema signs: Orthopnea, paroxysmal nocturnal dyspnea, crackles on lung exam, elevated JVP, S3 gallop (indicates elevated ventricular filling pressures that precede shock)
• Tachycardia and tachypnea: Compensatory responses; in acute MI, bradycardia with shock suggests extensive RV infarction with loss of sympathetic compensation
• Oliguria (urine output <0.5 mL/kg/hr) reflecting renal hypoperfusion and activation of antidiuretic hormone; may progress to acute kidney injury
• Chest pain or dyspnea: Depends on underlying etiology (acute MI, acute decompensated heart failure, fulminant myocarditis)

Classic Signs of Obstructive Shock

• Tension pneumothorax: Acute onset dyspnea, hypotension, unilateral absent breath sounds, tracheal deviation (late finding), JVD, hypoxia—this is a clinical diagnosis requiring immediate decompression before imaging
• Massive PE: Acute dyspnea, pleuritic chest pain, syncope or presyncope, tachycardia disproportionate to hypoxia, elevated JVP, signs of DVT; shock suggests >60% pulmonary vascular obstruction
• Cardiac tamponade: Beck's triad (hypotension, muffled heart sounds, JVD) with pulsus paradoxus (>10 mmHg drop in SBP during inspiration), muffled S1/S2, chest pain relieved by sitting forward (if pericarditis), acute dyspnea
• Acute severe valve disease: Acute MR (acute MI with papillary muscle rupture) presents with sudden loud holosystolic murmur and pulmonary edema; acute aortic regurgitation presents with early diastolic murmur, bounding pulses, and widened pulse pressure despite shock

Important Presentation Variants

• Cardiogenic shock may develop insidiously in decompensated heart failure or acutely after MI; elderly and diabetic patients may have silent MIs with delayed shock recognition
• RV infarction complicating inferior MI presents with shock + elevated JVP but clear lung fields (preserved RV function depends on preload); fluid challenge is therapeutic
• Obstructive physiology may coexist (PE triggering RV failure, tamponade superimposed on cardiomyopathy)

Hemodynamic Definition

• Cardiogenic shock: Cardiac index <2.2 L/min/m² with systolic BP <90 mmHg (or MAP <65 mmHg) for >30 minutes, despite adequate volume status, with pulmonary congestion (elevated PCWP >18 mmHg)
• Obstructive shock: Hypotension with mechanical obstruction identified (imaging, clinical findings); elevated CVP/JVP is expected, PCWP may be normal or low

Diagnostic Tests

• Electrocardiogram (ECG): Essential first test; acute MI (STEMI or NSTEMI) shows ST changes, T-wave inversions, or new LBBB; RV infarction shows ST elevation in V4R; arrhythmias, heart block, or low voltage suggest mechanical complication or tamponade
• Chest X-ray: Cardiogenic shock shows pulmonary edema (bilateral infiltrates, Kerley B lines), cardiomegaly, pleural effusions; tension pneumothorax shows collapsed lung, mediastinal shift, absence of lung markings; massive PE may show Hampton's hump (wedge infarct) or Westermark sign (oligemia)
• Troponin and BNP/NT-proBNP: Elevated troponin confirms myocardial injury (MI, myocarditis); elevated natriuretic peptides confirm cardiogenic etiology and correlate with filling pressures
• Echocardiography (transthoracic or TEE): Gold standard for cardiogenic shock diagnosis; assesses global/regional wall motion abnormalities, ejection fraction, diastolic function, mechanical complications (VSD, papillary muscle rupture, free wall rupture); identifies pericardial effusion/tamponade and RV dilation (PE, RV infarction); measures TAPSE and S' velocity for RV function
• Pulmonary artery catheter (Swan-Ganz): Hemodynamic assessment shows low cardiac output (CI <2.2), elevated PCWP (>18 mmHg) in cardiogenic shock; normal PCWP suggests RV infarction or mechanical complications; useful for ongoing monitoring and titrating inotropes/vasopressors in ICU
• CT pulmonary angiography: Gold standard for PE diagnosis; high sensitivity/specificity; assess for right heart strain (RV/LV ratio >0.9 indicates worse prognosis)
• Bedside ultrasound: Rapid assessment of pericardial effusion (echo-free space around heart), RV dilation (RV/LV ratio >0.9), IVC plethora (dilated IVC without collapse indicating elevated RAP), lung sliding (rules out pneumothorax)
• Lactate: Elevated lactate (>2

Immediate stabilization

• Airway, access, monitoring: oxygen, two large-bore IVs, arterial line, urine output. Intubate only when necessary — positive pressure drops preload and can precipitate arrest in tamponade or RV failure.
• Reverse the obstruction first if obstructive: tension pneumothorax → immediate needle decompression followed by tube thoracostomy, before any imaging (ATLS teaches decompression at the 4th–5th intercostal space in the anterior-to-mid axillary line in adults). Tamponade → urgent pericardiocentesis or surgical drainage.
• Fluids are conditional: cautious boluses in RV infarction, PE, and tamponade (preload-dependent states); avoid volume loading the congested LV with pulmonary edema.

First-line pharmacotherapy

• Vasopressor — norepinephrine is the preferred initial agent for cardiogenic shock; the AHA/ACC and critical care literature favor it over dopamine, which caused more arrhythmias in SOAP II.
• Inotrope — dobutamine (beta-1 agonist) or milrinone (PDE-3 inhibitor) added for low cardiac index; DOREMI found no mortality difference between them. Milrinone accumulates in renal failure and vasodilates more.

Definitive management

• Emergency revascularization for MI-related shock — the SHOCK trial underpins the ACC/AHA/SCAI recommendation for early PCI or CABG regardless of time from symptom onset. Per CULPRIT-SHOCK, perform culprit-lesion-only PCI, not routine multivessel PCI.
• Massive (high-risk) PE: systemic thrombolysis with a fibrinolytic (alteplase) for hemodynamic instability, per AHA and CHEST guidance; catheter-directed therapy or surgical embolectomy if thrombolysis fails or is contraindicated. Anticoagulate with unfractionated heparin.
• Mechanical complications (VSD, papillary muscle rupture) require surgical repair; temporary mechanical circulatory support (IABP, Impella, VA-ECMO) bridges to surgery, transplant, or recovery.

Contraindicated / avoid

• Beta blockers, non-dihydropyridine CCBs, and ACE inhibitors acutely in shock — negative inotropy and afterload collapse.
• Nitrates and diuretics in RV infarction — preload-dependent physiology.
• Routine IABP in MI shock: IABP-SHOCK II showed no mortality benefit.

Complications of the shock state

• Multiorgan failure — the final common pathway. Sustained hypoperfusion produces acute kidney injury (rising creatinine, oliguria), shock liver (transaminases in the thousands with rapid fall after perfusion is restored), and ischemic bowel (pain out of proportion, rising lactate). Emergency.
• Refractory lactic acidosis: anaerobic metabolism; a lactate that fails to clear despite therapy is the strongest signal of ongoing hypoperfusion and predicts death.
• Malignant arrhythmia: ischemia plus catecholamines plus acidosis. Degeneration into ventricular fibrillation / pulseless VT is the shockable pair — defibrillate immediately.
• Cardiac arrest and PEA: in tamponade or tension pneumothorax, PEA with a mechanically empty ventricle; treat the obstruction, not just the rhythm. Emergency.
• Cardiorenal syndrome and diuretic resistance: venous congestion plus low forward flow reduces glomerular filtration; weight gain with worsening creatinine.

Complications of treatment

• Vasopressor-induced digital and mesenteric ischemia: alpha-1 vasoconstriction; mottled fingertips, dusky toes, abdominal pain. Extravasation causes local necrosis — phentolamine is the antidote.
• Inotrope-driven tachyarrhythmia and myocardial ischemia: dobutamine and milrinone raise myocardial oxygen demand; new chest pain or rapid AF signals it.
• IABP: limb ischemia (absent distal pulse), thrombocytopenia, balloon rupture (blood in the helium line), and aortic dissection.
• Impella: hemolysis — plasma-free hemoglobin, cola-colored urine, falling haptoglobin — plus device migration and limb ischemia.
• VA-ECMO: increased LV afterload with LV distension and pulmonary edema (may need venting), and Harlequin (north–south) syndrome — differential hypoxemia with a well-oxygenated lower body and cyanotic upper body; check right radial arterial gas.
• Thrombolysis for PE: intracranial hemorrhage — any new neurologic deficit demands immediate non-contrast head CT. Emergency.
• Pericardiocentesis: RV puncture, hemopericardium, and pericardial decompression syndrome (paradoxical post-drainage pulmonary edema).

• Inferior MI + hypotension + clear lungs + JVD = RV infarction. Get a right-sided ECG looking for ST elevation in V4R. Best next step is an IV fluid bolus; nitroglycerin is the classic distractor and can cause profound hypotension.
• Tension pneumothorax is a clinical diagnosis. Hypotension with unilateral absent breath sounds and JVD → needle decompression before the chest x-ray. Ordering imaging first is the trap.
• Tamponade triad plus electrical alternans plus low-voltage QRS. Pulsus paradoxus >10 mmHg is the bedside clue; pericardiocentesis is definitive. Avoid intubation and positive pressure ventilation before drainage — it can cause arrest by abolishing preload.
• Early revascularization saves lives in MI shock (SHOCK trial, reflected in the ACC/AHA/SCAI revascularization guideline). Per CULPRIT-SHOCK, do culprit-vessel PCI only — routine multivessel PCI in the same sitting is the wrong answer.
• Routine IABP does not reduce mortality in MI-associated cardiogenic shock (IABP-SHOCK II). Choosing "place an IABP" over "take to the cath lab" loses points.
• New harsh holosystolic murmur days after MI: an oxygen step-up from right atrium to right ventricle means ventricular septal rupture; flash pulmonary edema with a soft or absent murmur and a large v wave on the PCWP tracing means papillary muscle rupture (posteromedial, single blood supply). Both need surgery.
• Norepinephrine, not dopamine, is the initial vasopressor of choice in cardiogenic shock — dopamine caused more arrhythmias and worse outcomes in the shock subgroup of SOAP II.
• Hypotensive PE gets systemic thrombolysis (AHA/CHEST); a normotensive PE with RV strain does not automatically. Look for RV dilation with RV/LV ratio >0.9 and McConnell sign (free wall hypokinesis with preserved apex) on echo.