Aberrancy

Question 1

Aberrant conduction

Answer 1

• Intraventricular conduction delay of supraventricular impulse
  o Functional bundle branch block → impulse reach conduction system before fully recovered from previous depol
   = transient bundle branch blocks
   Depend on HR and RP of BB

Question 2

ECG characteristics of aberrant conduction

Answer 2

o Wide QRS w LBBB or RBBB characteristics (RBBB more common)
o Previous long or short RR
o Non compensatory pause following aberrant complex

Question 3

Tachycardia dependent block

Answer 3

Phase 3 aberrancy

• Differences in refractory period duration in conduction system
  o RBB have > refractory period in healthy tissue
  o Refractory period duration is related to preceding cycle length
• Phase 3: impulse arrive during incomplete repol → ↓Na+ channels

Question 4

Ashman’s phenomenon

Answer 4

o Associated w abrupt change in cardiac cycle length
 Long RR will prolong refractory period
 Subsequent premature beat can display aberrant morphology

Question 5

Ashman vs VPC

Answer 5

o Ashman: variable coupling interval, short-long-short cycle sequence

o VPC:
 Fixed coupling interval
 Long/identical RR after aberrant beats, no cycle sequence
 Variable QRS morphologies

Question 6

Bradycardia dependent block

Answer 6

Phase 4 aberrancy

• Blocked conduction after end of repolarization
• Slow/progressive depol of membrane potential during long diastolic intervals
  o Prolonged cycle allows gradual depolarization of membrane
  o Progressive ↑ membrane potential (less negative values) → ↓Na+ channel availability
   Significant conduction disturbances manifested at membrane potentials > -70mV
   Cyclical reduction in resting membrane potential typical of latent PM 
  o ↓rate of rise of phase 0 → interfere with impulse propagation

Question 7

Pattern of phase 4 aberrancy

Answer 7

• Almost always LBBB pattern
  o LV conduction system more susceptible to ischemic damage
  o ↑ rate of spontaneous phase 4 depol

Question 8

Causes of phase 4 aberrancy

Answer 8

o Abnormal slow diastolic depolarization
o Shift in threshold potential toward 0
o ↓ membrane responsiveness → conduction impairment develops at -75mV instead of -65mV
o Hypopolarization

Question 9

Linking or sustained aberrant conduction

Answer 9

• Form of function intraventricular block
  o Tachycardia or bradycardia dependent
• Macro re-entrant circuit → 2 branches
  o Preferential conduction pathway → dominant branch
  o Dependent branch: long refractory period = impairs ability to conduct impulse

Question 10

ECG linking aberrancy

Answer 10

o Several consecutive beats with wide QRS and LBBB or RBBB morphology
o Abrupt ↓or ↑ RR before 1st aberrant beat

Question 11

Critical rate

Answer 11

• Critical rate: rate at which BBB develop

Question 12

Fusion beat

Answer 12

• Activation of ventricles by 2 wavefronts
  o Ventricular PM → ventricular ectopy
  o Supraventricular PM → SA node
• Impulse collide at level of AV jct → fusion beat
  o Intermediate morphology btw sinus beat and VPC

Question 13

What does fusion beat confirm

Answer 13

AV dissociation