Description

• Persistent hypotension and tissue hypoperfusion due to cardiac dysfunction in the presence of adequate intravascular volume and left ventricular (LV) filling pressure
• Most common cause of death in hospitalized patients with acute MI (AMI)
• Underlying mechanisms in AMI:
  • Pump failure:
    • ≥40% LV infarct
    • Infarct with pre-existing LV dysfunction
    • Reinfarction
  • Mechanical complications:
    • Acute mitral regurgitation
    • Ventricular septal defect
    • LV rupture
    • Pericardial tamponade
  • Right ventricular (RV) infarction
• 5–8% of patients with STEMI develop cardiogenic shock

Etiology

• AMI
• Sepsis
• Myocarditis
• Myocardial contusion
• Valvular disease
• Cardiomyopathy
• Left atrial myxoma
• Drug toxicity:
  • β-Blocker
  • Calcium channel blocker
  • Adriamycin

Signs and Symptoms

• ABCs and vital signs:
  • Patent airway (early)
  • Labored breathing and tachypnea (early); respiratory failure (late)
  • Diffuse crackles or wheezing
  • Hypoxia
  • Hypotension:
    • Systolic BP <90 mm Hg for at least 30 min or decline by at least 30 mm Hg below baseline level
  • Tachycardia
  • Weak pulses
• General:
  • Cyanosis
  • Pallor
  • Diaphoresis
  • Dulled sensorium
  • Decrease in body temperature
  • Urine flow of <20 mL/hr
• Neck:
  • Jugular venous distention
• Cardiac:
  • Ischemic chest pain
  • Systolic apical blowing murmur
  • Gallop rhythm:
    • S3 reflects severe myocardial dysfunction
    • S4 is present in 80% patients in sinus rhythm with AMI
  • Systolic click:
    • Suggests rupture of the chordae tendineae
• Abdominal:
  • Epigastric pain
  • Nausea and vomiting
• Neurologic:
  • Obtundation

• Obtain history from patient, family, or EMS for clues to possible etiology
• Medication history

• Perform rapid survey and stabilize ABCs
• Distended neck veins and cool extremities distinguish cardiogenic shock from distributive and hypovolemic shock
• Careful heart and lung exam

Essential Workup

Ancillary studies further define the type and degree of cardiac injury and determine the indications for emergent catheterization or surgical intervention

Diagnostic Tests and Interpretation

• Normal ECG does not rule out AMI
• Classically, findings of AMI (ST-elevations in 2 or more contiguous leads)
• Can also occur in non–ST-elevation acute coronary syndrome
• Dysrhythmias
• LV hypertrophy

• B-type natriuretic peptide (BNP):
  • Diagnostic and prognostic value
• Creatine kinase (CK), CK-MB, troponin
• Electrolytes and renal function:
  • Acute renal failure is a strong predictor of mortality
• CBC:
  • Identify anemia or elevated WBC
• Lactate:
  • Lack of clearance is associated with a higher risk of mortality
• Drug levels (e.g., digoxin)

• CXR:
  • Pulmonary congestion
  • Pleural effusion
  • Cardiomegaly
  • Pneumonia
  • Pneumothorax
  • Pericardial effusion
• Emergent echocardiography:
  • Transthoracic echocardiography (TTE) with color Doppler
  • LV contractility looking for hypokinesis, akinesis, or dyskinesis
  • Acute mitral regurgitation or septal defects
  • RV dilatation, tricuspid insufficiency, high pulmonary artery, and RV pressures suggest pulmonary embolism
  • RV hypokinesis or akinesis, RV dilatation, normal pulmonary pressures suggest RV infarction
  • Pericardial effusion, right atrium, or RV diastolic collapse suggest cardiac tamponade

Differential Diagnosis

• Obstructive shock:
  • Tension pneumothorax
  • Cardiac tamponade
  • Pulmonary embolism
  • Spontaneous esophageal rupture
  • Air embolus
• Distributive shock:
  • Sepsis
  • Anaphylaxis
  • Addisonian crisis
  • Neurogenic shock
• Hypovolemic shock:
  • Hemorrhage
  • GI losses
  • Dehydration
  • Burns

Pre Hospital

• ABCs, IV access, O₂, monitor
• Consider fluid bolus if no crackles
• Aspirin
• Nitroglycerin or morphine sulfate for chest pain in absence of hypotension. Should be avoided if suspicion of RV infarction
• Transport AMI patients to facility with 24-hr cardiac revascularization capability

Initial Stabilization/Therapy

• ABCs
• 2 large-bore peripheral IV lines
• Cardiac monitor
• Endotracheal intubation for airway compromise:
  • Consider etomidate for induction (minimal effect on BP)
• Fluid challenge (100–250 mL normal saline) in absence of pulmonary congestion
• Foley catheter to monitor urine output

Ed Treatment/Procedures

• AMI:
  • Aspirin
  • Heparin or bivalirudin
  • Thrombolysis if percutaneous coronary intervention or bypass surgery not available
  • GP IIb/IIIa inhibitors prior to percutaneous coronary intervention
  • Clopidogrel – Often held until after revascularization attempt as may be contraindicated in patients requiring emergent bypass
• Hypotension:
  • Norepinephrine is first-line vasopressor
  • Consider dopamine in absence of NE
• Normotensive patient:
  • Dobutamine may be used with NE or dopamine; combine with nitroprusside in acute mitral regurgitation
  • Milrinone may be considered in conjunction with dobutamine or dopamine
• Pulmonary edema:
  • Nitroglycerin drip or furosemide in the normotensive patient
• Prompt cardiology consultation is crucial for the initiation of the following therapies:
  • IABP independently improves survival in experienced centers
  • Evaluation for the role of VADs and ECMO in refractory cases of cardiogenic shock
  • Early revascularization is the single most important life-saving measure

Medication

• Bivalirudin 0.75 mg/kg bolus then 1.75 mg/kg/hr IV
• Clopidogrel 600 mg PO
• Dobutamine: 3–5 mcg/kg/min, titrate to 20–50 mcg/kg/min as needed IV
• Dopamine: 3–5 mcg/kg/min, titrate to 20–50 mcg/kg/min as needed IV
• Furosemide: 40–80 mg/d (peds: 1 mg/kg IV or IM, not to exceed 6 mg/kg) IV or IM
• Milrinone: 50 mcg/kg loading dose, 0.375–0.75 mcg/kg/min continuous infusion IV
• Nitroglycerin: 10–20 mcg/min (peds: 0.1–1 mcg/kg/min) IV, USE NON-PVC tubing
• Nitroprusside: 0.3 mcg/kg/min, titrate to a max of 10 mcg/kg/min IV
• Norepinephrine: 2 mcg/min, titrate up as needed IV

Disposition

Admission Criteria
All patients in cardiogenic shock require admission to a critical care unit

See Also

Shock; MI