cardiac conduction system Flashcards
(26 cards)
SAN function
generates normal sinus rhythm
SAN rhythm
60-100 bpm
atrial cells rhythm
<60 bpm
AVN function (2)
builds in delay, acts as back-up pacemaker if SAN fails
AVN rhythm
40-60 bpm
His-Purkinje system components (3)
common bundle, left and right bundle branches, Purkinje fibres
Purkinje fibres rhythm
20-40 bpm
SAN dysfunction complications
bradycardia, tachycardia, tachycardia-bradycardia, sinus arrest, sinus node exit block
sinus node exit block
electrical activity fails to leave SAN so p-wave is hidden
escape rhythm
rhythm generated by other part of heart if SAN fails
junctional rhythm
escape rhythm generated by AVN
automatic re-entry
impulses repeatedly loop through fixed anatomical circuits e.g. scar tissue from previous MI or pathways in WPW syndrome
functional re-entry
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
atrial fibrillation
uncoordinated atrial contractions due to re-entry circuits
atrial flutter
increased coordinated atrial contractions
why are rapid atrial rates harmful? (4)
increased calcium load toxicity, AP shape changes, atrial fibrosis, atrial remodelling
macro-re-entrant tachycardia
leaking of current from tricuspid valve annulus
AVN first degree block (3)
least severe, slowed or delayed conduction, does not require treatment
AVN second degree block
intermittent conduction
AVN second degree block Mobitz T1 (2)
slowing between beats, elongation and eventually QRS depression
AVN second degree block Mobitz T2
no slowing between beats, sometimes signals reach ventricles
AVN third degree block
complete failure, wide QRS complexes
AVN heart blocks causes
pathway fibrosis, CAD, decreased perfusion, inflammation, autoimmunity, hyperkalemia
bundle branch blocks
ventricles contract asynchronously due to infarct or inflammation, often requires pacing
