cardiac conduction system

Question 1

SAN function

Answer 1

generates normal sinus rhythm

Question 2

SAN rhythm

Answer 2

60-100 bpm

Question 3

atrial cells rhythm

Answer 3

<60 bpm

Question 4

AVN function (2)

Answer 4

builds in delay, acts as back-up pacemaker if SAN fails

Question 5

AVN rhythm

Answer 5

40-60 bpm

Question 6

His-Purkinje system components (3)

Answer 6

common bundle, left and right bundle branches, Purkinje fibres

Question 7

Purkinje fibres rhythm

Answer 7

20-40 bpm

Question 8

SAN dysfunction complications

Answer 8

bradycardia, tachycardia, tachycardia-bradycardia, sinus arrest, sinus node exit block

Question 9

sinus node exit block

Answer 9

electrical activity fails to leave SAN so p-wave is hidden

Question 10

escape rhythm

Answer 10

rhythm generated by other part of heart if SAN fails

Question 11

junctional rhythm

Answer 11

escape rhythm generated by AVN

Question 12

automatic re-entry

Answer 12

impulses repeatedly loop through fixed anatomical circuits e.g. scar tissue from previous MI or pathways in WPW syndrome

Question 13

functional re-entry

Answer 13

multiple small re-entry circuits changing in size and location due to dynamic and transient electrical instability in myocardium with differing conduction velocities and refractory periods

Question 14

atrial fibrillation

Answer 14

uncoordinated atrial contractions due to re-entry circuits

Question 15

atrial flutter

Answer 15

increased coordinated atrial contractions

Question 16

why are rapid atrial rates harmful? (4)

Answer 16

increased calcium load toxicity, AP shape changes, atrial fibrosis, atrial remodelling

Question 17

macro-re-entrant tachycardia

Answer 17

leaking of current from tricuspid valve annulus

Question 18

AVN first degree block (3)

Answer 18

least severe, slowed or delayed conduction, does not require treatment

Question 19

AVN second degree block

Answer 19

intermittent conduction

Question 20

AVN second degree block Mobitz T1 (2)

Answer 20

slowing between beats, elongation and eventually QRS depression

Question 21

AVN second degree block Mobitz T2

Answer 21

no slowing between beats, sometimes signals reach ventricles

Question 22

AVN third degree block

Answer 22

complete failure, wide QRS complexes

Question 23

AVN heart blocks causes

Answer 23

pathway fibrosis, CAD, decreased perfusion, inflammation, autoimmunity, hyperkalemia

Question 24

bundle branch blocks

Answer 24

ventricles contract asynchronously due to infarct or inflammation, often requires pacing

Question 25

left bundle branch block

Answer 25

right ventricle contracts before left ventricle, common in HF patients

Question 26

right bundle branch block

Answer 26

left ventricle contracts before right ventricle