His ECG

Question 2

how to perform His bundle ECG

Answer 2

• KT passed in CaVC → RA → RV and withdrawn slowly until typical spike btw P and QRS is seen
  o Usually across TV, near septum
  o Bipolar recording: rapid biphasic spike of 15-25ms

Question 3

His ECG useful for

Answer 3

differentiate proximal from distal blocks in AV node
o Distal: ↑ risk of developing high grade/3AVB

Question 4

Causes of AV conduction abn

Answer 4

o Congenital
o Ischemic heart disease
o Degeneration of conducting pathways (Lenegre’s dz)
o Fibrous replacement lof cardiac skeleton (Lev’s dz)
o Infiltration of cardiac skeleton by other dz (Chaga’s, scleroderma)

Question 5

Deflections on His ECG

Answer 5

o A wave: 1st deflection → lower RA activation
 Latter part of P wave on surface ECG

o H deflection: follows A wave → His bundle electrical activity
 In PR interval
 Recorded by KT lying at base of TV, close to His bundle

o V deflection: last deflection → ventricular activation
 Concurrent with QRS on surface ECG
 Start after onset of QRS since represent RV activation in region of TV

Question 6

Intervals and normal values

Answer 6

o PA interval: intra-atrial conduction time from area around SA node → lower RA
 From onset of P wave → A wave
 Normal = 30-50ms
o AH interval: AV nodal conduction time
 From A wave → H wave
 Normal = 60-125ms
o HV interval: His Purkinje system conduction time
 Normal = 35-55ms

Question 7

Localization of AV node conduction defects

Answer 7

above or below His bundle

Question 8

His ECG nodal escape rhythm

Answer 8

• His bundle potential precede atrial or ventricular activity → followed by atrial → ventricular

Question 9

Effect of glycoside

Answer 9

inhibit Na+/K+-ATPase pump → ↑cell[Na+] → ↓Na+/Ca2+-exch → ↑ cell [Ca2+] → ↑ contractility and vagal tone
o Negative chronotropic effect on AV nodal rhythm
o No effect on His bundle rhythms

Question 10

His ECG 1AVB

Answer 10

• 1st degree AVB: bock above bundle of His
  o Block in AV node, atrio-nodal jct or node-His jct
  o Depending on location of the block → AH, HV or both will be prolonged

Question 11

His ECG: 2AVB mobitz 1

Answer 11

o Progressive ↑AH time
o Usually AV nodal block

Question 12

His ECG: 2AVB mobitz II

Answer 12

o Almost always infranodal block → usually bilateral BBB
Longer AH time

Question 13

His ECG: 3AVB

Answer 13

• 3rd degree AVB
  o Atrial conduction with A wave
  o Separate H and V deflections
  o H can also be associated with the A waves

Question 14

His ECG RBBB

Answer 14

• Normal A-H interval
• Prolonged H-V interval

Question 15

EP studies indications

Answer 15

• Limited to dogs of adequate size → decapolar KT
• Necessitate general anesthesia

diagnosis and treatment
o FAT
o Accessory pathways
o Aflutter
o Afib with high ventricular response rate refractory to mx
o Selected re-entrant tachycardias

Question 16

Radiofrequency ablation

Answer 16

target current converted into heat → coagulation necrosis → fibrous tissue
* AV re-entrant tachycardias in young dogs
* Lone Afib in giant breeds → ablation of PV region
* Afib with high ventricular response rate → AV node ablation + PM implantation