Shock — Cardiogenic

Primary Contractile Dysfunction

• Loss of myocardial contractility occurs when >40% of left ventricular (LV) mass is infarcted acutely, or when extensive fibrosis/remodeling develops in chronic cardiomyopathy
• Reduced ejection fraction (<30%) results in decreased stroke volume (SV) despite compensatory increases in heart rate (HR)
• Cardiac output (CO) = HR × SV; inadequacy of both components creates a "double hit" to systemic perfusion
• Mitochondrial dysfunction and impaired ATP production in ischemic myocardium prevents normal excitation-contraction coupling

Neurohumoral Hyperactivation & Vasoconstriction

• Baroreceptor reflex activation increases sympathetic nervous system (SNS) output, elevating catecholamine levels and peripheral vascular resistance (SVR)
• Elevation of renin-angiotensin-aldosterone system (RAAS) causes sodium/water retention, increasing preload but worsening pulmonary congestion
• Enhanced vasopressin (ADH) release promotes further vasoconstriction and hyponatremia
• Paradoxically, increased SVR augments afterload, which further depresses LV function (negative effect on the Starling curve) and increases myocardial oxygen demand in already ischemic tissue

Peripheral Tissue Hypoperfusion & Metabolic Acidosis

• Inadequate regional blood flow triggers anaerobic metabolism in tissues, producing lactate and causing lactic acidosis
• Reduced renal perfusion pressure activates RAAS and promotes acute kidney injury (AKI) via prerenal mechanism
• Pulmonary edema develops from elevated LV filling pressures, impairing gas exchange and reducing oxygen delivery
• Inflammatory cascade activation (cytokine release, complement, leukocyte infiltration) causes endothelial dysfunction and increases capillary permeability

Right Ventricular Dysfunction (in RV Infarction)

• Acute loss of RV contractility impairs preload delivery to the LV
• RV dilatation causes septal shift that further compromises LV filling
• Elevated intrapericardial pressures from RV distension restrict LV diastolic filling (interdependence)

Acute Coronary Syndromes (Most Common)

• Acute myocardial infarction with extensive LV infarction (anterior, anterolateral territory) or cardiogenic shock develops in 5–10% of MI patients
• Mechanical complications of MI: acute mitral regurgitation (papillary muscle rupture), ventricular septal defect (VSD), free wall rupture with tamponade, or severe LV dysfunction
• Reinfarction or extension of infarction in the acute phase

Acute Decompensated Heart Failure

• Fulminant myocarditis (viral, giant cell, eosinophilic, autoimmune) with rapid progression to cardiogenic shock
• Acute valvular pathology: endocarditis with perforated leaflet, acute severe aortic regurgitation, acute mitral stenosis
• Peripartum cardiomyopathy in pregnant/postpartum women

Chronic Heart Failure Decompensation

• Arrhythmia-induced cardiomyopathy: uncontrolled atrial fibrillation, sustained ventricular tachycardia, or high-output rhythm disorders
• Acute exacerbation of ischemic, dilated, or restrictive cardiomyopathy triggered by infection, anemia, hyperthyroidism, or medication non-compliance
• Stress-induced (Takotsubo) cardiomyopathy with stunning of LV apex

Mechanical & Obstructive Causes

• Pulmonary embolism with acute RV failure
• Tension pneumothorax or pericardial tamponade
• Acute severe hypertension with hypertensive emergency and acute LV dysfunction
• Sepsis with myocardial depression (septic shock evolving to cardiogenic component)

Risk Factors for Development

• Age >65 years, prior MI, diabetes mellitus, anterior MI location, female sex
• Elevated Killip class (≥III) at presentation; elevated APACHE II or SOFA scores
• Delayed revascularization or failed primary PCI

Cardinal Symptoms

• Dyspnea at rest or with minimal exertion; orthopnea and paroxysmal nocturnal dyspnea (PND)
• Chest pain or pressure (in acute MI setting); may be atypical in elderly or diabetic patients
• Altered mental status from cerebral hypoperfusion (confusion, lethargy, coma)
• Oliguria (urine output <0.5 mL/kg/hr) reflecting renal hypoperfusion
• Palpitations or syncope if arrhythmia coexists

Physical Examination Findings

• Hypotension: systolic BP <90 mmHg or MAP reduction ≥30 mmHg from baseline
• Tachycardia (HR >100 bpm), often with narrow pulse pressure
• Tachypnea (RR >20/min); use of accessory muscles; audible crackles throughout lung fields bilaterally
• Elevated jugular venous pressure (JVP) indicating elevated right atrial pressure; prominent S3 gallop (ventricular filling sound)
• Cool, clammy extremities with peripheral cyanosis and delayed capillary refill; mottled skin
• Decreased urine output with poor skin turgor
• Signs of pulmonary edema: frothy sputum, orthopnea, rales; may progress to acute respiratory distress syndrome (ARDS)
• Right ventricular heave or parasternal lift if RV involvement

Severity Spectrum (Forrester Classification)

• Class I: Normal perfusion, no pulmonary edema
• Class II: Pulmonary edema without shock (dry shock not present)
• Class III: Peripheral hypoperfusion without pulmonary edema
• Class IV: Both pulmonary edema AND peripheral hypoperfusion (true cardiogenic shock)

Clinical Criteria for Cardiogenic Shock (Consensus Definition)

• Systolic blood pressure <90 mmHg for >30 minutes OR requirement for vasopressors/inotropes to maintain SBP ≥90 mmHg
• Cardiac index (CI) <2.2 L/min/m² (by thermodilution or estimated from hemodynamics)
• Pulmonary capillary wedge pressure (PCWP) ≥15 mmHg OR elevated LV end-diastolic pressure on echo-Doppler
• Evidence of tissue hypoperfusion (altered mental status, oliguria, elevated lactate, cool extremities)
• Exclusion of hypovolemic, distributive (septic), or obstructive shock as primary mechanism

Hemodynamic Monitoring

• Pulmonary artery catheter (PAC/Swan-Ganz) remains gold standard:
• Cardiac output <2.0–2.2 L/min
• Cardiac index (CI) <2.2 L/min/m²
• PCWP ≥18 mmHg (elevated, indicating elevated LV filling pressures)
• Systemic vascular resistance (SVR) typically elevated (>1200 dyne·s·cm⁻⁵) due to compensatory vasoconstriction
• Right atrial pressure (RAP) often elevated if RV dysfunction coexists
• Non-invasive hemodynamic assessment: echocardiography with tissue Doppler imaging, TAPSE (tricuspid annular plane systolic excursion), strain imaging

Laboratory Studies

• Cardiac biomarkers: elevated troponin (I or T) confirms myocardial necrosis; serial elevation supports ongoing ischemia
• B-type natriuretic peptide (BNP) or NT-proBNP markedly elevated (>400 pg/mL) in acute decompensated heart failure
• Lactate elevated (>2 mmol/L) indicating anaerobic metabolism and tissue hypoperfusion; serial lactate clearance predicts prognosis
• Complete metabolic panel: elevated creatinine and blood urea nitrogen (BUN) reflecting prerenal azotemia; hyponatremia from RAAS/ADH activation
• Complete blood count: anemia exacerbates shock; leukocytosis may indicate infection or MI
• Coagulation studies: elevated PT/INR if liver congestion; monitor for disseminated intravascular coagulation (DIC) in severe shock
• Blood gas analysis: metabolic acidosis with elevated lactate; respiratory alkalosis may coexist from tachypnea

Electrocardiography (ECG)

• ST-elevation myocardial infarction (STEMI) pattern: ST elevation ≥1 mm in contiguous leads (anterior, inferior, posterior, or lateral distribution)
• Non-ST-elevation MI (NSTEMI) with dynamic ST changes or T-wave inversions
• Pathological Q waves indicating prior or acute transmural infarction
• Arrhythmias: sinus tachycardia, atrial fibrillation, or ventricular ectopy
• Right-sided leads (V3R, V4R) show ST elevation in inferior RV infarction

Chest Radiography

• Pulmonary edema: bilateral infiltrates in perihilar distribution (butterfly pattern) or diffuse alveolar consolidation
• Kerley B lines from interstitial edema
• Cardiomegaly: increased cardiothoracic ratio (>50%)
• Pleural effusions (usually bilateral); may indicate elevated PCWP
• Assess for alternative diagnoses: pneumonia, pneumothorax, aortic dissection

Echocardiography (Transthoracic or TEE)

• 2D imaging: assess LV ejection fraction (LVEF), wall motion abnormalities, chamber dilatation, RV size and function
• Doppler assessment: mitral regurgitation severity, diastolic dysfunction patterns (restrictive pattern in cardiogenic shock)
• Mechanical complications of MI: VSD (color flow across septum), acute mitral regurgitation (posteriorly directed jet), LV free wall rupture (echo-free pericardial space with tamponade physiology), papillary muscle rupture
• Pericardial effusion: assess for tamponade physiology (RA/RV collapse, respiratory variation >25%)
• Tissue Doppler imaging (TDI) and strain imaging: detect subtle systolic dysfunction; assess diastolic dysfunction

Cardiac Catheterization

• Indicated in acute MI with cardiogenic shock for coronary angiography and revascularization (Class I recommendation)
• Identifies culprit lesion and assesses collateral flow; determines revascularization strategy (PCI vs. CABG)
• Hemodynamic assessment via PAC during catheterization
• Assess for mechanical complications via ventriculography or angiography

Advanced Imaging

• Cardiac MRI: assess myocardial viability, fibrosis pattern, and etiology in non-MI cardiomyopathy
• CT angiography: evaluate for pulmonary embolism, aortic dissection, or other acute pathology if diagnosis unclear

Immediate Stabilization & Monitoring

• Supplemental oxygen to maintain SaO₂ >90%; intubation with mechanical ventilation if respiratory failure (RR >30, inability to protect airway, altered sensorium)
• Continuous cardiac monitoring, pulse oximetry, blood pressure monitoring; consider invasive hemodynamic monitoring via PAC or arterial line in refractory cases
• Establish IV access (at least two large-bore lines); consider central venous catheter for repeated access and CVP monitoring
• Rapid diagnostic evaluation: ECG within 10 minutes, troponin, lactate, CBC, CMP, coagulation studies, chest X-ray

Revascularization (Primary Intervention)

• Primary percutaneous coronary intervention (PCI) is the gold standard reperfusion strategy in acute MI with cardiogenic shock:
• Target door-to-balloon time <90 minutes for STEMI (or <120 minutes if transfer required)
• Perform coronary angiography urgently to identify culprit lesion
• Revascularize culprit vessel with stent placement (bare-metal stent preferred in cardiogenic shock for potential need of surgery)
• Consider multivessel PCI in selected cases if hemodynamically tolerable
• Delayed reperfusion carries worse prognosis; should not delay PCI for echocardiography or other testing
• Fibrinolytic therapy (if PCI unavailable): door-to-needle <30 minutes with alteplase, tenecteplase, or reteplase; less effective than PCI but may bridge to transfer
• Coronary artery bypass grafting (CABG) reserved for:
• Left main coronary artery occlusion unsuitable for PCI
• Complex multivessel disease not amenable to PCI
• Mechanical complications (VSD, papillary muscle rupture) requiring surgical repair
• Failed PCI with residual ischemia

Pharmacological Agents

Inotropic Support (Increase Contractility & HR)

• Dobutamine (3–20 μg/kg/min IV infusion):
• Mechanism: β₁-adrenergic agonist with some β₂ (vasodilation) and α effects
• Increases contractility and CO; may cause reflex tachycardia and reduce SVR
• Risk of tachyarrhythmia and increased myocardial oxygen demand; avoid in cardiogenic shock from acute MI if possible (worsens outcomes in some trials)
• Used as bridge to mechanical support

• Milrinone (0.25–0.75 μg/kg/min IV infusion):
• Mechanism: phosphodiesterase-3 inhibitor (increases cAMP)
• Positive inotrope AND vasodilator ("inodilator"); reduces PCWP and SVR while increasing CO
• No β-adrenergic effects; less risk of tachycardia and arrhythmia
• Preferred over dobutamine in some centers; useful if concurrent hypertension
• May cause systemic hypotension; requires arterial line monitoring

Vasopressors (Increase Systemic Vascular Resistance)

• Norepinephrine (0.01–3 μg/kg/min IV):
• Mechanism: potent α-adrenergic (vasoconstriction) with β₁ effects (mild inotrope)
• Preferred first-line vasopressor in cardiogenic shock (per ACC/AHA guidelines) due to balanced effects
• Increases SVR and perfusion pressure while maintaining some cardiac output
• Titrate to target MAP ≥65 mmHg; monitor for peripheral ischemia

• Dopamine (5–20 μg/kg/min):
• Mechanism: dose-dependent; low dose (2–5) activates dopaminergic receptors; intermediate (5–10) β₁; high (>10) α effects
• Less favored than norepinephrine in cardi

Mechanical complications of the underlying MI (all surgical emergencies)

• Papillary muscle rupture: the posteromedial papillary muscle has a single blood supply from the posterior descending artery, so inferior MI is the classic culprit; signals itself as new holosystolic murmur with abrupt flash pulmonary edema and a giant v wave on the PCWP tracing. Emergent echo and surgical repair.
• Ventricular septal rupture: harsh holosystolic murmur with palpable thrill and an oxygen saturation step-up from right atrium to right ventricle on PA catheter sampling; left-to-right shunt worsens shock rapidly.
• Free wall rupture with tamponade: presents as sudden pulseless electrical activity or electromechanical dissociation — immediate pericardiocentesis and surgery.

Complications of the shock state itself

• Ventricular fibrillation / pulseless VT: ischemia plus catecholamine load lowers the fibrillation threshold; immediate defibrillation (these are the shockable rhythms).
• Multiorgan failure: prolonged low flow produces AKI (rising creatinine, oliguria), shock liver with markedly elevated transaminases, mesenteric ischemia, and DIC. Failure of lactate to clear despite support signals progression along the SCAI SHOCK stages toward stage E.
• LV mural thrombus and systemic embolism after large anterior infarction with akinesis.

Complications of therapy

• Vasopressors/inotropes: digital and mesenteric ischemia, extravasation necrosis, and tachyarrhythmia with increased myocardial oxygen demand. Dopamine caused more arrhythmic events than norepinephrine in SOAP II, supporting the ACC/AHA preference for norepinephrine.
• Intra-aortic balloon pump: limb ischemia, thrombocytopenia, hemolysis, aortic injury; contraindicated in significant aortic regurgitation or dissection.
• Percutaneous LV assist device (Impella): hemolysis (dark urine, rising LDH, falling haptoglobin), device migration, access-site bleeding.
• VA-ECMO: raises LV afterload and can worsen pulmonary edema unless the LV is vented; differential hypoxemia ("harlequin"/north–south syndrome) when native ejection sends deoxygenated blood to the upper body.
• Post-catheterization: contrast-associated AKI and bleeding on antithrombotics.

• The hemodynamic triad is the whole question: low cardiac index, high PCWP, high SVR. Septic shock has low SVR and high CI; hypovolemic shock has low PCWP and high SVR; obstructive shock (tamponade, PE) has high filling pressures with a non-dilated, hyperdynamic LV. Cardiogenic patients are cold and wet.
• Single best next step in MI-related shock is emergent coronary angiography with revascularization, not more medical titration — the strategy supported by the SHOCK trial and given a Class I recommendation in the 2021 ACC/AHA/SCAI revascularization guideline. Do not delay PCI for echocardiography.
• Culprit-lesion-only PCI is favored in shock; the CULPRIT-SHOCK trial found immediate multivessel intervention worsened the composite of death and renal replacement therapy.
• RV infarction is the classic look-alike: inferior STEMI with hypotension, elevated JVP, and clear lungs. Confirm with ST elevation in V4R. Treat with volume loading and avoid nitrates, morphine, and diuretics — these drop preload and precipitate arrest.
• New murmur after MI means an echo now. Holosystolic murmur with an oxygen step-up RA→RV = septal rupture; flash pulmonary edema with a giant v wave = papillary muscle rupture; sudden PEA = free wall rupture.
• Norepinephrine is the first-line vasopressor, not dopamine — the cardiogenic subgroup of SOAP II showed higher mortality with dopamine.
• Common distractor — the IABP. IABP-SHOCK II showed no mortality benefit, so the balloon pump is no longer a routine or guideline-mandated answer; it is a bridge, not a survival therapy.
• Other distractors to avoid: large fluid boluses in the congested "wet" patient, and starting beta blockers or ACE inhibitors/ARNI during active shock. Guideline-directed HFrEF therapy (ARNI or ACEI/ARB, beta blocker, MRA, SGLT2 inhibitor) begins only after hemodynamic stabilization and weaning of inotropes.