Rosen & Barkin's 5-Minute Emergency Medicine Consult (610 page)

Acute Coronary Syndrome: Myocardial Infarction

CODES

410.90 Acute myocardial infarction, unspecified site, episode of care unspecified

BASICS

• An ischemic cerebrovascular accident (CVA), or stroke, is an acute, sudden or gradual, interruption of regional cerebral blood supply
  
• Cerebral reperfusion therapy involves:
  
  • Administration of an IV thrombolytic agent to rapidly dissolve a thromboembolic occlusion
    
  • Site-specific endovascular intra-arterial thrombolysis
    
  • Mechanical clot removal
    

• Thrombotic CVA is from an in situ thrombosis:
  
  • At an ulcerated atherosclerotic plaque or other prothrombotic endothelial abnormality
    
  • From hypercoagulable states:
    
    • Antithrombin III, protein C or S deficiency
      
  • From sludging:
    
    • Sickle cell disease
      
    • Polycythemia vera
      
• Embolic CVA is caused by acute obstruction by an embolus from:
  
  • Cardiac mural thrombus formed in:
    
    • Atrial fibrillation
      
    • Hypokinetic ventricle (MI, cardiomyopathy)
      
    • Ventricular aneurysm
      
  • An abnormal or prosthetic cardiac valve
    
  • Aortic, carotid, or cerebrovascular atherosclerotic plaques
    
• Other occlusive events include:
  
  • Vascular dissection in aorta, cerebral, vertebral, carotid, or innominate arteries
    
  • Cerebral vasospasm induced by:
    
    • Subarachnoid hemorrhage (SAH)
      
    • Vasoconstrictive agents (e.g., cocaine)
      

DIAGNOSIS

• Acute focal neurologic symptoms presenting within 4–5 hr of onset
  
• Time of symptom onset is critical:
  
  • If time of onset cannot be firmly established, the time the patient was last known normal should be used as a surrogate
    
• Historical elements that may suggest an etiology other than routine thromboembolic stroke:
  
  • Neck injury in carotid or vertebral dissection
    
  • Tearing back pain in aortic dissection
    
  • Drug abuse in vasospastic occlusions
    

• Consider reperfusion therapy for symptoms and signs consistent with a distinct vascular supply territory
  
• Middle cerebral artery:
  
  • Contralateral hemiplegia and hemisensory deficits (upper > lower)
    
  • Contralateral homonymous hemianopsia
    
  • Expressive or receptive aphasia (if in dominant hemisphere)
    
  • Contralateral neglect
    
• Posterior cerebral artery:
  
  • Cortical blindness in half the visual field
    
  • Visual agnosia (inability to recognize and identify persons and objects)
    
  • Thalamic syndromes:
    
    • Abnormal movements (chorea or hemiballismus)
      
    • Hemisensory deficit
      
• Vertebrobasilar system:
  
  • Impaired vision, visual field defects
    
  • Nystagmus, vertigo, dizziness
    
  • Facial paresthesia, dysarthria
    
  • Cranial nerve palsies
    
  • Contralateral sensory deficits (pain and temperature)
    
  • Limb ataxia, abnormal gait
    
• Anterior cerebral artery:
  
  • Contralateral hemiplegia and hemisensory deficits (lower > upper)
    
  • Apraxia
    
  • Confusion, impaired judgment
    
• Lacunar (deep subcortical):
  
  • Pure motor hemiplegia (most common), or pure sensory hemiplegia
    
  • Dysarthria with hand ataxia (clumsy hand), or dysarthria with facial weakness
    
  • Ataxic hemiparesis
    
• The National Institutes of Health Stroke Scale (NIHSS) can be used to delineate severity of a CVA as follows (total of subcategory scores):
  
  • 1a. Level of consciousness (LOC): Alert = 0; drowsy = 1; stuporous = 2; coma = 3
    
  • 1b. LOC questions: Answers both correctly = 0; 1 correctly = 1; none correct = 2
    
  • 1c. LOC commands: Obeys both correctly = 0; 1 correctly = 1; none correctly = 2
    
  • 2. Best gaze: Normal = 0; partial gaze palsy = 1; forced deviation = 2
    
  • 3. Visual: No visual loss = 0; partial hemianopia = 1; complete hemianopia = 2; bilateral hemianopia = 3
    
  • 4. Facial palsy: Normal, symmetric = 0; minor paralysis = 1; partial paralysis = 2; complete paralysis = 3
    
  • 5 to 8. Best motor (computed for each arm and leg): No drift = 0; drift = 1; some effort against gravity = 2; no effort against gravity = 3; no movement = 4
    
  • 9. Limb ataxia: Absent = 0; present in 1 limb = 1; present in 2 or more limbs = 2
    
  • 10. Sensory (pinprick): Normal = 0; partial loss = 1; dense loss = 2
    
  • 11. Best language: No aphasia = 0; mild to moderate aphasia = 1; severe aphasia = 2; mute = 3
    
  • 12. Dysarthria: Normal articulation = 0; mild to moderate dysarthria = 1; unintelligible = 2
    
  • 13. Neglect/inattention: No neglect = 0; partial neglect = 1; complete neglect = 2
    

• Stat bedside blood glucose testing
  
• CBC, prothrombin time (PT)/partial thromboplastin time (PTT)
  
  • To assess thrombolytic therapy risk in patients at risk of coagulopathy
    

• Immediate noncontrast head CT scan:
  
  • Can be part of a multimodal imaging protocol
    
  • Can reveal other etiologies of symptoms (such as hemorrhage, tumor)
    
  • Very likely normal in the hours after symptom onset:
    
    • Early signs of ischemia (e.g., edema) should prompt a re-evaluation of time of onset
      

EKG to assess for dysrhythmia, pericarditis, MI

• Serum electrolytes, BUN, creatinine
  
• Urine pregnancy test
  
• Urine toxicology screen
  
• Liver function tests in patients prone to liver dysfunction
  

• Multimodal MRI (with perfusion- and diffusion-weighted protocols):
  
  • Can detect ischemic CVA almost immediately after onset
    
• Perfusion brain CT can reveal a perfusion deficit immediately after onset
  
• MR angiography or CT angiography can provide anatomical information
  
• Carotid US
  
• CXR
  

• Intracranial hemorrhage (ICH) or SAH
  
• Seizure
  
• Complex migraine
  
• Bell palsy or other focal neuropathies
  
• Hypoglycemia and other metabolic abnormalities
  
• Cerebral venous sinus thrombosis
  
• Intracranial neoplasm
  
• Intracranial trauma
  
• Meningitis, encephalitis, or brain abscess
  
• Vasculitis
  
• Air embolism or decompression illness
  
• Spinal cord lesion
  
• Psychogenic
  

TREATMENT

• Assess for deficits:
  
  • Dysarthria, facial weakness
    
  • Arm or leg weakness
    
• Notify and mobilize ED and hospital resources
  
• Test blood glucose:
  
  • Hypoglycemia can mimic a CVA
    
  • Treat hypoglycemia with dextrose
    

• Supplemental oxygen to correct hypoxia (pulse ox <94%)
  
• RSI for airway protection or ventilatory insufficiency if needed
  
• IV access and NS bolus to correct hypotension
  
• Cardiac monitoring and pulse oximetry
  

• Exclude other diagnoses in the differential
  
• Thrombolytic therapy should be reserved for thromboembolic ischemic strokes
  
• Inclusion criteria for IV thrombolytic therapy:
  
  • Age ≥18 yr of age
    
  • Defined onset of symptoms within 4.5 hr
    
  • No hemorrhage on noncontrast head CT
    
• Absolute contraindications to IV thrombolytic therapy:
  
  • CVA, serious brain injury, or intracranial surgery within previous 3 mo
    
  • Prior ICH
    
  • Clinical presentation consistent with SAH
    
  • Arterial puncture at noncompressible site in previous 7 days
    
  • Active bleeding on exam
    
  • Uncontrollable HTN >185/110 mm Hg
    
  • Known bleeding diathesis such as:
    
    • Platelet count <100,000/mm
      ³
      (if no history of thrombocytopenia, tissue plasminogen activator [tPA] can be initiated before platelet count, but should be discontinued if it is low)
      
    • Heparin within 48 hr, with elevated aPTT
      
    • Current anticoagulant use with an INR >1.7, or PT >15 sec
      
  • Blood glucose <50 mg/dL
    
  • Hypodensity in >1/3 cerebral hemisphere on CT
    
• Relative contraindications to IV thrombolytics (weigh risk against benefit):
  
  • Major surgery or trauma within previous 14 days
    
  • Mild or resolving neurologic symptoms
    
  • GI or GU bleeding within 21 days
    
  • Seizure at the time stroke was observed
    
  • Acute MI within previous 3 mo
    
• Treat BP >185/110 mm Hg with 1–2 doses of labetalol, nicardipine, or other appropriate agent:
  
  • Do not aggressively normalize BP
    
  • Stroke patient may be dependent on an elevated mean arterial pressure for cerebral perfusion
    
  • Avoid thrombolytic therapy if BP cannot be reduced to ≤180/110 mm Hg with minimal intervention
    
• Administer IV tPA; alteplase
  
• Avoid antiplatelet agents and anticoagulants for 24 hr
  
• Monitor arterial BP during the 1st 24 hr after treatment with tPA and aggressively treat an SBP >180 mm Hg or a DBP >105 mm Hg:
  
  • Check BP every 15 min for 2 hr, then every 30 min for 6 hr, then every hour for 24 hr
    
  • Keep BP <180/105 mm Hg using medication such as labetalol or nicardipine
    
  • Consider nitroprusside for HTN unresponsive to labetalol or nicardipine, or for a DBP >140 mm Hg
    
• Monitor for signs of ICH:
  
  • Decreased LOC
    
  • Increased weakness
    
  • Headache
    
  • Acute HTN or tachycardia
    
  • Nausea or vomiting
    
• If ICH suspected, obtain an emergent head CT to confirm diagnosis:
  
  • If present, treat as follows:
    
    • Discontinue tPA
      
    • Obtain blood samples for PT, PTT, platelet count, fibrinogen level
      
    • Prepare cryoprecipitate, fibrinogen, and platelets, and infuse as needed
      
    • Obtain neurosurgical consultation
      
• Intra-arterial or mechanical recanalization may be considered for selected patients
  
  • Though not as well studied as IV tPA, they may be administered out to 6 hr from onset