Heart block

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  • First-degree heart block - PR interval > 0.2s; no dropped QRS complex
  • Second-degree heart block
    • Type 1 (aka Mobitz I, Wenkebach) - PR interval increases with each beat until exentually you get a dropped QRS complex
    • Type 2 (aka Mobitz II) - intermittent failure of P waves to conduct, not preceded by P wave elongation
    • 2:1/3:1 type - regularly dropped QRS complexes with a 2:1 or 3:1 ratio (P:QRS), not preceded by elongated PR interval
  • Third-degree heart block (aka complete heart block) - P waves never conduct and thus unrelated on ECG but P to P interval is regular as is R to R interval. (HR = 40bpm usually). Causes: usually CAD, particularly inferior or anterior wall MI.


You can use atropine on the first two, and even on third degree while waiting to put in the pacer.

Drugs to avoid

If a patient has heart block, they need to avoid: