AV blocks Flashcards
what are AV blocks?
delays (prolongation) or interruptions in electrical conduction from the atria to the ventricles
what are the causes of AV blocks/
ischemia, MI, inc vagal tone (MI), lesions that occur w inc age (fibrosis and calcium) and dig tox
blocks within the bundle branches are reversible and not progressive? T or F
F they are progressive and irreversible
whats the diff between blocks in the bundle branches and AV node or HIS bundle in re: how they look o ECG?
QRS wide in bundle branches and normal in AV node and HIS bundle
are blocks in the AV node or HIS bundle reversible and not progressive?
yes they are reversible
AV node is the usual site for what kind of block?
first-degree AV block and type 1 second degree block
Bundle branches are the usual site for what ind of block?
type 2 second degree block
complete AV block occurs where?
at any level but is most common in the bundle of HIS and bundle branches
what is a first degree AV block?
occurs when there is prolongation of conduction in the AV node.
clues on ECG for first degree AV block?
reg p waves
PR interval >.20 and is usually constant but may vary
QRS is usually normal width
reg QRS
is each sinus beat conducted to the ventricles? (first degree AV block)
yes although delayed, it is still 1:1 conduction
possibly causes for first degree AV block?
ischemia, MI (inferior), inc vagal tone, AV node lesion, digoxin
what are some hemodynamic effects of first degree AV block?
usually asymptomatic but if brady can be symp (dec SV, CO, BP),
can deteriorate to higher degree block
treatment for first degree AV block?
usually none treat underlying cause
atropine if symp
what is second degree AV block? - type 1 (wenckebach)
occurs almost always at the AV node level and is usually transient. progressive prolongation of conduction (P-R interval gradually lengthens eg. .24-.30 -.32) delays in conduction progress until an impulse is completed blocked (no QRS following a P wave)
usaually one QRS is blocked and the pattern repeats itself, resulting in “group” beating
clues for 2nd degree Av block? type 1
reg p wabes
PR interval gets longer until a QRS is dropped
normal QRS but irregular
variable conduction bc not all p waves are conducted
group beating “pattern”
possible causes for 2nd degree AV block? type 1
ischemia, MI, inc vagal tone, AV node lesion, dig, calcium channel blockers, beta blockers
hemodynamic effects of 2nd degree AV block? type 1
usually asymptomatic but if brady can be symp (dec SV, CO, BP),
can deteriorate to higher degree block
treatments for 2nd degree AV block? type 1
usually none, continue to monitor
treat cause
atropine if symp
what is 2nd degree AV block - type II?
block occurs within the bundle of HIS (uncommon) or the bundle branches (common) often there is a complete block in one bundle (right bundle, resulting in wide QRS) and intermittent block in the other causing dropped QRS complexes. i
if the block is at the level of the HIS bundle for 2nd degree VA block type 2 is the QRS normal or wide? bundle branches?
hisbundle- normal
bundle branches- wide
PR interval for 2nd degree type 2 AV block?
may be normal or prolonged but it is will be constant or fixed.
what is the hallmark of he 2nd degree av block type 2?
constant PR interval
clues for 2nd degree type 2 AV block?
p waves are normal and will be followed by QRS except when blcoekd
blocked ps can vary 2:1 3:1 4:1
printerval remains constant or fixed
QRS may be normal (block in HIS bundle)
QRS may be wide (block in bundle branches)
possibly cause for 2nd degree type 2 AV block?
ischemia
acute MI
inferior (narrow QRS), anterior (wide QRS) most common
cardiomyopathy
chronic fibrotic disease in elderly
hemodynamic effects of 2nd degree type 2 AV block?
may be asymptotic if rate adequate
even if QRS normal or rate adequate, still may rapidly deteriorate to 3rd degree
usually symptomatic as block more commonly occurs in bundle branches resulting in ventricular escape rate 20-40
dec SV/CO, dec BP, syncope
treatments for 2nd degree type 2 AV block?
atropine may be tried (especially if QRS narrow) but freq does not work
pacemaker
dopamine or rip infusions to inc HR, BP
what is third degree AV block (complete heart block)?
no conduction or association between the atria and the ventricles. they beat indeed of each other.
where is third degree AV block (complete heart block) occurring?
block may occur at the level of the AV node, bundle of HIS, or bundle branches
what is the rate and reliability of the rhythm related toin third degree AV block (complete heart block)?
location of block and the escape pacemaker
if the third degree AV block (complete heart block) block is in the AV node or top of HIS b bundle which pacemaker takes over?
QRS ?
junctional pacemaker at 40-60 and QRS will be normal
what is the pacemaker if its at the bundle level?
ventricles at 20-40 and QRS is wide. often results in asysyole
clues for third degree AV block (complete heart block)?
p waves normal but indeed of QRS ‘no relationship’ and are regular
PR interval vaires
QRS may be normal (block in AV node, HIS bundle) or wide if bundle branches
QRS rate 30-60 (junctional escape) and 20-40 if ventricular escape so bundle branch block
cause of third degree AV block (complete heart block)?
ischemia, acute MI (inferior narrow QRS and anterior wide QRS), acute myocarditis, chronic fibrotic disease (elderly), dig tox
hemodynamic effects of third degree AV block (complete heart block)?
may be asymptomatic if QRS narrow and junctional rate adequate
more often wide QRS and symp with rate of 20-40 so dec CO/SV, dec BP and syncope
treatments for third degree AV block (complete heart block)?
atropine if QRS normal and narrow but freq ineffective
paemaker
dopamine or epi may be used to inc rate and support BP
