Conduction abn

Question 1

What is a fascicular block

Answer 1

• LBB: divide into anterior and posterior fascicles → pass at the base of corresponding papillary muscle
  o LV depol shift toward blocked fascicle
  o Hemiblock: involves 1 of the division of LBB

Question 2

What type of conduction disturbance HCM cats

Answer 2

L anterior fascicular block

Question 3

L anterior fascicular block is common in

Answer 3

in cats with HCM → turbulent flow in LVOT, myocardial fibrosis

Question 4

Why is anterior LBB fascicle in more vulnerable

Answer 4

o Different blood supply
o Longer/thinner
o Located in turbulent LVOT

Question 5

What vector is affected in ventricular depol by L anterior fascicular block

Answer 5

• Affect 3rd vector of ventricular depol: 3a
  o Initial: block remove initial sup and L activation
   1st vector downward and R
• Q wave appear in lead I and aVL
• R wave in lead II, III, aVF
   Alter initial portion of QRS toward +80-90
  o Late: activation spread to LVFW in sup/L direction
   Depol of anterosuperior portion of LV → slight prolongation, but small effect does not alter QRS duration
   Prominent R wave in lead I, aVL (qR)
   ↑R wave peak time: impulse reach LV later
   Prominent S wave in lead II, II, aVF (rS)

Question 6

ECG characteristics of LAFB

Answer 6

o Normal QRS duration
o Marked L axis deviation: MEA -30 to -60
 aVR usually isoelectric
o qR pattern: small Q wave + tall R wave in lead I and aVL
 From early activation of LV posterior wall
o Deep S wave in lead II, III, aVF

Question 7

ECG characteristics for RBBB + LAFB

Answer 7

o ↑ QRS duration
o Marked L axis deviation
o Small Q wave + tall R wave in lead I and aVL
o Deep S wave in lead I, II, III, aVF

Question 8

L posterior fascicular block

Answer 8

Less common: anatomic organization makes L posterior fascicle ↓ risk to be damaged

Question 9

Which vector is affected by LPFB

Answer 9

• Affect 3rd vector of ventricular depol: 3b
  o Slight delay + antero-posterior direction
  o Early activation of anterior wall → axis deviation of initial portion of QRS to -60

Question 10

ECG characteristics LPFB

Answer 10

not possible to diagnose on surface ECG
o Normal QRS duration
o R waves in lead I, aVL
o Q waves in lead II, III, aVF

Question 11

What are the 3 types of bifascicular blocks

Answer 11

Complete LBBB
RBBB w/ LAFB
RBBB w/ LPFB

Question 12

What does LBBB usually indicates and consequences

Answer 12

severe myocardial damage

o Deteriorated LV systolic fct → worsens intra/interventricular dyssynchrony

Question 13

ECG characteristics complete LBBB

Answer 13

 Normal MEA
 ↑QRS duration from wide R wave
 Q wave can remain present → early electrical activation from lateral RV wall

Question 14

ECG characteristics RBBB + LAFB

Answer 14

o Posterior to superior direction of septal activation apparent
o ECG characteristics
 ↑QRS duration
 MEA: inferior to sup axis btw -60 and -90
 Largest negative deflection in lead I, II, III, aVF

Question 15

ECG characteristics RBBB + LPFB

Answer 15

o Deviate axis to the R and superiorly
 1st vector: upward, to the L → early activation of anterolateral wall of LV
 2nd vector: upward, to the R → late activation of RVFW
o ECG characteristics
 Complete RBBB characteristics
 Q wave in leads II, III, aVF, no Q wave in leads I, aVL

Question 16

Trifascicular block

Answer 16

• Interruption of impulse propagation alternate btw 3 subdivisions
• From extensive damage of conduction system → can progress to 3AVB
• Different patterns:
  o LBBB alternating with RBBB
  o RBBB with LAFB alternating w complete LBBB
  o Bifascicular block + Mobitz type II 2AVB

Question 17

Causes of SA block

Answer 17

impaired automaticity, conduction or both

Question 18

1st degree SA block

Answer 18

• Cannot be recognized on surface ECG
• Prolongation of interval btw sinus impulse and P wave

Question 19

2nd degree SA block

Answer 19

• Type I (Wenckebach periodicity): progressively shorter PP followed by a longer PP interval including blocked P
  o Analogous to progressive ↓RR in 2AVB
  o SA interval is analogous to PR interval
• Type II: dropped P waves during sinus rhythm
  o Pauses are multiple of basic PP interval

Question 20

3rd degree SA block

Answer 20

• Escape rhythm

Question 21

Demonstrate why the distal chamber (i.e., the atria) accelerates in “classic” Wenckebach periodicity. SA block

Answer 21

o Analogous to progressive ↓RR in 2AVB
 ↓PP before the block = acceleration of atrial depol
 Related to increment at which S-A interval progressively increase is smaller → translate into progressive ↓ P-P duration before block

Question 22

2AVB mobitz 1

Answer 22

• Progressive slowing of conduction velocity
  o ↑delay in sinus impulse propagation across AV node until impulse blocked
  o Progressive prolongation of relative refractory period in AV node
   α to prematurity of impulse traveling through it → rate of conduction depend on time the impulse arrives to AV node
• Earlier impulse = longer to conduct
   Impulses are arriving earlier and earlier in relative refractory period → prolongation of conduction delay → until one impulse arrive during absolute refractory period
• RP-PR reciprocity or RP-dependent PR interval
• Period of rest for AV node by blocked impulse → normal conduction on subsequent beat
   Absolute refractory period is normal

Question 23

Max change in PR w/ 2AVB

Answer 23

2nd beat after blocked P

Question 24

Characteristic of RR interval w/ 2AVB mobitzI

Answer 24

o ↓RR before block (↑HR)
* Progressive ↑PR associated to progressive ↓RR

• Increment by which it ↑ is progressively smaller → PR continues to prolong but ↓R-R interval

Question 25

Atypical Wenckebach 2AVB

Answer 25

* Frequent with ratio of AV conduction >7:6 * Variable PR, maximum prolongation is NOT 2nd beat after block * No ↓RR before block

Question 26

Advanced 2AVB

Answer 26

* AV conduction ratio > 2:1 * Hisian or infra-Hisian * ECG characteristics o 2 or > consecutive blocked P waves o Normal or ↑PR o QRS is normal or prolonged if block is infra Hisian

Question 27

Define “ventriculophasic sinus arrhythmia”

Answer 27

* Longer RR with a blocked P wave * Variation of PP intervals induced by ventricular systole * PP interval with QRS is shorter than PP interval w/o QRS o 2:1 2 AVB or 3AVB o Ventricularly paced rhythms

Question 28

ALTERNATING WENCKEBACH

Answer 28

* 2:1 2nd degree AVB with progressive prolongation of PR for conducted waves o Until block worsens to more advanced block (3:1, 4:1) * Mechanism: 2 points block o Proximal in AV node o Distal at His bundle → higher grade of block * Manifestation of functional block in SVT: Afib, Aflutter

Question 29

Define AV dissociation

Answer 29

Atria and ventricles are independent → asynchronous activation

Question 30

Causes of AV dossication

Answer 30

o Slowing of dominant PM → allow independent ventricular PM (junctional or ventricular escape rhythm) o Acceleration of latent PM (↑ automaticity) o Complete heart block

Question 31

DDX

Answer 31

o HypoK+ o Vtach o 3AVB o Focal junctional tachycardia o AIVR

Question 32

Focal junctional tachycardia

Answer 32

* ↑ automaticity or triggered activity in junctional area o Proximal to apex of Koch’s triangle o Posterior to distal AV bundle

Question 33

FJT most common in

Answer 33

Young labs

Question 34

ECG FJT

Answer 34

o Regular ventricular rate 100-160bpm o Isorhythmic AV dissociation o Periods or retrograde ventriculo atrial activation 1:1 ratio  P’ waves in ST segment as pseudo S waves o Gradual onset

Question 35

IAVD

Answer 35

* 2 rhythms: one sinus, one junctional or ventricular o Sinus P waves in close relation but not associated with QRS o When atrial and ventricular rhythm are the same rate

Question 36

What is accrochage

Answer 36

same rate for short or long periods

Question 37

IAVD: types of synchronization

Answer 37

o Type I: continuous fluctuation of P-QRS interval  P wave marching toward and in the QRS  Suspected from BP variations: P waves moves closer to QRS until overlap → ↓ contribution of atrial contraction → small ↓ BP → stimulation baroR → ↑∑ tone → ↑ sinus d/c → ↓P-P o Type II: fixed relationship of P-QRS  Mechanical stimulus from SA node artery pulsation → synchronizing effect on SA node, AV node and conduction system

Question 38

IAVD: effect of retrograde activation

Answer 38

d/c of junctional PM > SA node → suppress SA node PM

Question 39

Mechanism of ventriculo phasic arrhythmia

Answer 39

o BaroR reflex  ↑ arterial BP with ventricular contraction (QRS) → nucleus tractus solitarius → ↑ vagal stimulation → ↓ SA node d/c  Effect begins 600ms after QRS and last 1s * P wave just after QRS: occurs prior to p∑ effect o Sinus arrhythmia  Potential common physiological pathway  Inspiration → ↑ ∑ stim → ↑ SA node d/c  Arrhythmia is abolished by atropine = support this mechanism o Ventricular synchrony  Intrinsic complex (vs paced) → better ventricular synchrony  ↑ ventricular contraction efficiency → ↑ SV → ↑ arterial BP o Blood supply to SA node  Ventricular contraction may ↑ SA node blood supply → earlier SA node d/c after QRS o Mechanical stimulation of SA node  Ventricular contraction → traction on atria → mechanical stimulation of atria → ↑ SA node d/c

Question 40

Paradoxical ventriculo-phasic sinus arrhythmia

Answer 40

* PP interval including QRS are longer than PP w/o QRS

Question 41

Mechanism of paradoxical ventriculo-phasic sinus arrhythmia

Answer 41

* 2 phase chronotropic effect o Positive chronotropic effect (acceleration) → early appearance of P after QRS → ↓PP interval with QRS  Atrial stretch by mechanical effects: may impact d/c of normal SA node impulse  Ventricular contraction may ↑ SA node blood supply → earlier SA node d/c after QRS o Negative chronotropic effect (deceleration) → longer PP w/o QRS  BaroR changes in vagal tone → ↑BP → vagal reflex → ↓ SA node d/c → ↑PP w/o QRS