Rosen & Barkin's 5-Minute Emergency Medicine Consult (467 page)

• 358.00 Myasthenia gravis without (acute) exacerbation
  
• 358.01 Myasthenia gravis with (acute) exacerbation
  
• 775.2 Neonatal myasthenia gravis
  

BASICS

• Also known as blunt cardiac injury
  
• Pathologically characterized by discrete and well-demarcated area of hemorrhage
  
• Usually subendocardial
  
• May extend in pyramidal transmural fashion
  
• Most commonly involves anterior wall of right ventricle or atrium due to anatomic location
  

• Blunt trauma to chest:
  
  • High-speed deceleration accidents
    
  • May occur in accidents with speeds as low as 20–35 mph
    
• Auto–pedestrian injuries
  
• Falls
  
• Prolonged closed-chest cardiac massage
  
• Heart may be compressed between sternum and vertebrae.
  
• Heart strikes sternum during deceleration.
  
• Heart is damaged by abdominal viscera upwardly displaced by force on abdomen.
  
• Concussive forces (e.g., explosion)
  
• Associated conditions:
  
  • Life-threatening dysrhythmias
    
  • Cardiogenic shock/CHF
    
  • Hemopericardium with tamponade
    
  • Valvular/myocardial rupture
    
  • Intraventricular thrombi
    
  • Thromboembolic phenomena
    
  • Coronary artery occlusion from intimal tearing or adjacent hemorrhage and edema may rarely occur.
    

DIAGNOSIS

• Clinical picture is varied and nonspecific:
  
  • Chest pain
    
  • Cardiogenic shock
    
  • Subtle EKG changes without clinical symptoms
    
• Most common sign is tachycardia out of proportion to degree of trauma or blood loss.
  
• Friction rub may occur rarely.
  
• Retrosternal chest pain unrelieved by nitroglycerin:
  
  • Often delayed up to 24 hr
    
  • May respond to oxygen
    
• Evidence of significant thoracic trauma:
  
  • Contusions, abrasions
    
  • Palpable crepitus
    
  • Sternal fracture alone with normal EKG and negative serial troponin I does not predict BCI
    
  • Visible flail segments
    
• Other injuries may mask signs and symptoms of myocardial contusion.
  

• Mechanism of injury (e.g., MVA, fall, explosion, missile to chest wall)
  
• Any syncope or loss of consciousness suggests possible dysrhythmia.
  
• Crush injury
  

Obtain and consider pre-existing cardiac disease and concurrent medications in elderly patients following blunt cardiac injury.

Due to increased compliance of pediatric chest wall, significant cardiac compression and contusion may be present with minimal or no external signs of trauma.

Complete physical exam as in any trauma patient:

• Evaluate for jugular venous distention (JVD)
  
• Decreased or muffled heart sounds
  
• Extra heart sounds
  
• Crepitus
  
• Pulsus paradoxus
  
• Evidence of chest wall trauma
  

• No single diagnostic study (other than autopsy findings!) confirms presence of myocardial contusion.
  
• EKG:
  
  • Best initial screening tool
    
  • Most common rhythm is sinus tachycardia (70%).
    
  • Normal EKG does not rule out myocardial damage.
    
  • EKG changes may be subtle or include nonspecific findings such as ST changes, right bundle branch block, and premature atrial and ventricular contractions.
    
  • At least 1 repeat EKG is recommended because changes may occur over time.
    
  • Serious dysrhythmias may result in hemodynamic instability:
    
    • Atrial fibrillation/atrial flutter
      
    • Ventricular tachycardia/ventricular fibrillation (commotio cordis)
      
• Troponin I is now the recommended screening lab test over CK-MB to be interpreted with EKG.
  
• Echocardiography should be performed on all patients with any EKG changes, elevated troponin I or troponin T.
  
• Transesophageal ECG (TEE) more sensitive than transthoracic ECG (TTE) but technically more difficult and time-consuming.
  
• Multidetector CT angiography or MRI may be of benefit.
  

• Troponin I is the preferred lab test.
  
• Troponin T less sensitive than troponin I.
  
  • Levels should be sent on all patients where BCI suspected.
    
  • Should be repeated at 6–8 hr after injury.
    
  • Any elevation requires admission.
    
• Cardiac troponins are more specific than CK-MB for cardiac injury.
  
• CK-MB no longer routinely recommended.
  

• Radiographs, CT, MRI detect associated injuries:
  
  • Pulmonary contusion
    
  • Rib or sternal fractures
    
  • Acute pulmonary edema
    
  • No specific findings in cardiac contusion
    
• Focused assessment with sonography for trauma (FAST) should be performed on all patients to assess pericardium and possible concurrent intra-abdominal injuries.
  
• ECG:
  
  • Generally regarded as best imaging study for detecting cardiac contusion
    
  • Detects wall-motion abnormalities and effusions
    
  • Allows direct visualization of cardiac chambers and valves
    
  • May not visualize small (possibly clinically insignificant) contusions
    
  • TEE preferable to TTE if patient stable enough for procedure.
    
  • TTE may be performed although may also visualize great vessels.
    
• Radionuclide ventriculography:
  
  • Has been largely abandoned owing to wide availability of ECG
    
• Thallium
  ²⁰¹
  scintigraphy (single photon emission CT [SPECT]):
  
  • Sensitive and specific to left ventricular injury
    
  • Unable to evaluate right ventricle, which is most commonly injured
    

• Pericardiocentesis:
  
  • For treatment of cardiac tamponade, preferably under US guidance
    
• Thoracotomy:
  
  • Consider in patient with acute cardiac arrest or decompensation in ED or after unsuccessful pericardiocentesis
    

• Cardiac rupture
  
• Tamponade
  
• Valvular damage
  
• Other traumatic chest wall injury
  
• Angina or MI
  

TREATMENT

Pre-hospital personnel should convey accurate information to emergency department personnel:

• Mechanism of injury
  
• Motor vehicle status
  
• Steering wheel and dashboard damage
  
• Use of restraint devices
  
• Vehicle speed
  
• Patient position
  
• Time to extrication
  
• Any loss of consciousness
  

Manage airway and resuscitate as indicated:

• Oxygen:
  
  • IV access
    
  • Cardiac monitoring
    

• Dysrhythmias may be treated with same pharmacologic agents used for nontraumatic dysrhythmias:
  
  • Supraventricular tachycardia:
    
    • Adenosine or calcium channel blocker if patient not hypovolemic
      
  • Bradycardia:
    
    • Atropine
      
    • Pacing
      
  • Ventricular dysrhythmias:
    
    • Electrical conversion
      
    • Amiodarone
      
    • Lidocaine
      
    • Procainamide
      
  • Cardiac arrest:
    
    • Epinephrine
      
    • Atropine
      
    • Other interventions as appropriate
      
  • Rapid atrial fibrillation or flutter:
    
    • Diltiazem, or digoxin if patient not hypotensive
      
• Prophylactic treatment of dysrhythmias is not indicated.
  
• Cardiogenic shock caused by myocardial contusion:
  
  • Judicious fluid administration
    
  • Inotropic support (dopamine or dobutamine)
    
  • Intra-aortic balloon counterpulsation may be necessary.
    

• Medications used in cardiac contusion are supportive for dysrhythmias or hemodynamic compromise secondary to injury.
  
• There is no primary therapy for cardiac contusion.
  
• Adenosine: 6 mg rapid IVP (peds: 0.05–0.1 mg/kg rapid IVP), may repeat 12 mg q1–2min twice if no response
  
• Amiodarone: Load 150 mg IV over 10 min (peds: 5 mg/kg), then 1 mg/min for 6 hr, then 0.5 mg/min (peds: 5 μg/kg/min)
  
• Atropine: 0.5–1 mg (peds: 0.02 mg/kg/ dose, min. 0.1 mg) IV or endotracheal tube (ET)
  
• Digoxin: Load 0.5 mg (peds: 0.02 mg/kg) IV, then 0.25 mg (peds: 0.01 mg/kg) IV q6h for 2 more doses
  
• Diltiazem: 0.25 mg/kg IV for both adults and peds over 2 min, may rebolus 0.35 mg/kg (adult and peds) 15 min later
  
• Dobutamine: 2–15 μg/kg/min (adults and peds)
  
• Dopamine: 2–20 μg/kg/min (adults and peds)
  
• Epinephrine: 1 mg (peds: 0.01 mg/kg) IV or ET for cardiac arrest (1:10,000 solution)
  
• Lidocaine: Load 1 mg/kg IV, then 0.5 mg/kg q8–10min to max. 3 mg/kg (adults and peds); infusion 1–4 mg/min (peds: 20–50 μg/kg/min) IV
  
• Procainamide: start at 3 to 6 mg/kg/dose over 5 minutes not to exceed 100 mg to a titrated maximum of 15 mg/kg/loading dose
  
• Verapamil: 0.1–0.3 mg/kg up to 5–10 mg IV over 2 min (not approved in children)