Conduction

RBBB

  • RSR’ in V1, slurred S in I, aVL, V6
  • Normal TWI and small amount of STD in VI-V3
  • STEMI in RBBB:
    • Can show up as just lack of normal STD in V1-3
    • Find clear end of QRS in one lead then draw lines to locate end of QRS in other leads and measure out STE and STD – can reveal STEMI that is hidden in the QRS morphology
    • STEM w/ RBBB + LAFB/LPFB is very high morbidity/mortality, often presents in cardiogenic shock, can be difficult to convince consultants this is STEMI and needs to go to the cath lab b/c it can be fast, wide, hard to see the STE – get ECG’s over time to show evolution, keep trying to convince

 

LBBB

  • Hides the Q-waves of MI d/t the R->left depolarization: in the days of ECG-only dx of MI, this lead to the saying of “you can’t dx MI in setting of LBBB” and this addage has been misappropriated to the present era – you absolutely can dx coronary occlusion in the setting of LBBB
  • Nml LBBB morphology includes discordant STE in V1-V3, probably V4 as well
  • Smith-modified Sgarbossa criteria:
    • concordant STE of ≥1mm in 1 or more leads
    • concordant STD of ≥1mm in V1-3 (posterior MI – normally there is discordant STE in these leads
    • Disproportionate discordant STE – STE/Q >0.2 is sensitive for occlusion, >0.25 is specific (normal is ~0.11)

 

Paced rhythm

  • Normally paced from the RV and has LBBB like morphology
  • Can likely apply the same rules for detection of ischemia as for LBBB
  • Atrial paced rhythms can be read just like any other ECG for ischemia

 

LAFB

  • LAF is superior relative to LPF
  • Depolarization proceeds inferior->superior
  • rS in II, III, aVF and qR in I, aVL
  • and left axis

LPFB

  • LPF is inferior relative to LAF
  • Depolarization proceeds superior->inferior
  • qR in II, III, aVF and rS in I, aVL
  • and right axis

 

WPW

  • Accessory pathway leads to abnormal depolarization and thus abnormal repolarization (ST and TW abnormalities that can mimick ischemia)
  • The axis can be weird, often looks sort of like an LAFB or LPFB to me
  • But there is the delta wave
  • 3 kinds of dysrhythmias are possible:
    • Orthodromic AVRT – narrow, fast – vagal maneuvers, adenosine
    • Antidromic AVRT – wide, fast, regular – vagal maneuvers, adenosine
    • Afib in WPW – wide, fast, irregular, variable QRS morphology – no nodal blocking agents (e.g. no adenosine, CCB, amio) – procainamide is an option but cardioversion is safest