Unstable Bradycardia with a side of Sgarbossa

Dr. Soumya Murag presented an exciting case of unstable bradycardia in a hyperkalemic patient who also met Sgarbossa’s criteria and turned out to have a concomitant inferior STEMI from 99% ostial stenosis of the RCA.

Here are some high-yield clinical pearls we discussed today:

  • First line treatment for unstable sinus bradycardia is atropine
    • Atropine will not work in Mobitz II 2nd degree heart block or complete heart block (atropine acts on increasing the frequency of firing at the SA node, but these P waves will not be conducted in these situations)
    • The vagus nerve is not always connected in transplanted hearts so atropine may be ineffective in heart transplant patients
  • U waves can be seen in sinus bradycardia without underlying electrolyte abnormalities
  • Acute myocardial ischemia should always be on your differential diagnosis in unstable bradycardia
  • A new LBBB in a patient with chest pain or any presentation concerning for acute coronary syndrome is not a STEMI equivalent, but should prompt you to apply the Sgarbossa Criteria
    • Sgarbossa criteria: 1mm or more ST elevation in any lead with an upward QRS complex (concordant ST elevations) gives 5 points, 1mm or more ST depression in leads V1-V3 gives 3 points, and ST elevations 5mm or more in any lead with a downward QRS complex (discordant ST elevations) gives 2 points
    • A score of 3 or more should prompt urgent cardiac cath
  • Hyperkalemia causes a specific pattern of EKG abnormalities as potassium levels increase, which goes as follows: peaked T waves –> wide, low amplitude P waves with prolonged PR interval –> widening of the QRS –> sine wave
  • Nitrates should be avoided in inferior STEMI patients because they are preload dependent and nitrates can precipitate hypotension
    • Morphine can act in a similar manner so should be used only with extreme caution in inferior STEMI patients


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