8) OX Conduction disorders. Flashcards
what are the types of conduction disorders ?
sinoatrial exit block
wandering atrial pacemaker
Av block
Bundle branch block
Fascicular block
WHAT IS THE ETIOLOGY OF CONDUCTION DISTRUBNACES ?
electrolyte disblanace - hyprkalemia
digitalis intoxication , beta blockers , calcium channel blockers
Lyme disease
IHD
chagas disease
Myocarditis
Pericarditis
what is the classification of atrioventricular block ?
Incomplete
1st degree AV block
2 degree av block
mobitz type 1 / wenckeback
mobitz type 2
adavnced AV block
Complete
3 degree av block
what are the causes for AV block and the location the block ?
- there is an increase in vagal tone = usually athletes
- idiopathic fibrosis of conduction system
- ischemic heart disease
- cardiomyopathy - amyloidosis or sarcoidosis
- infection - lyme disease , bacterial endocarditis
- hyperkalemia
- iatrogenic - bb , cab , digitalis , surgery *
location - proximal / distal to bundle of HIS in the atrium or AV node
what is the diagnosis for 1st degree av block ?
delay of impulse conduction from atria to ventricle is
prolonged so that the PR interval - more than 0.2 seconds or more than 5 small boxes in ECG
but no RR change
Every P wave is conducted
what is the treatment for first degree AV block ?
assessment for underlying disease
no specific treatment necessary but follow up
Pacemaker indications
if the patient exhibits wide qrs complexes - identify level of AV block (within or below bundle of His) using INTRACARDIAC ELECTROGRAM = if conduction time from bundle of his to ventricles more than 100ms = pacemaker placement
usually this is asymptomatic - symptomatic patients
what is the diagnosis of second degree av block type 1
conduction from atria to ventricle gradually slows
progressive prolongation of PR-interval (each of which is followed by a QRS-complex)
until one impulse from atria to ventricles completely blocked - one P-wave is not followed by a QRS complex!
the rr interval containing the blocked p wave is shorter than the sum of two PP intervals
treatment of second degree type 1 av block ?
asymptomatic usually - no treatment needed , just followup egg
symptomatic - dizziness , syncope , bradycardia
- hemodynaically stable - monitoring with
have at bedside atropine and transcutaneous pacer
symptoms not reversible - permanent pacemaker
hemodynamically unstable
atropine -0.5-1mg iv
isoprenaline 0.5-2mg iv
if felling better- monitor with continuous cardiac telemetry and always have temporary transcutenoues cardiac pacer
after atropine not improved - IV epinephrine or Iv dopamine or start transcutaneous pacing
prepare for transvenous pacemaker or permanent pacemaker
what is the diagnosis of second degree av block type 2
PR-interval remains CONSTANT (but an be long or normal)
intermittent (regular ) blocked p waves - and it always shows a REGULAR PATTERN
P-wave is followed by
a QRS- complex and then suddenly one (or more) P- wave is not followed by a QRS
AV block is in ratio 2(how many atrial depolarisation) :1 (how many of that reach the ventricles)
impossible to determine if AV block type 1 or two
a long rhythm strip helps
usually where is the conduction block in second degree av block type 2
distal to the AV node (in the bundle of His or even more distally in the Purkinje system)
what are the symptoms of second degree AV block ?
bradycardia fatigue dyspnea chest pain syncope
what s the treatment of second degree AV block type2?
hemodynaically stable - monitoring with transcutaneous pacer
symptoms not reversible - permanent pacemaker
hemodynamically unstable
atropine “
isoprenaline “
if felling better- monitor with continuous cardiac telemetry and always have temporary transcutenoues cardiac pacer
after atropine not improved - IV epinephrine or Iv dopamine or start transcutaneous pacing
prepare for transvenous pacemaker
what is a complication of second degree AV block mobitz type 2 ?
it may progress to third degree AV block and this is an unstable condition
what is a high grade or advanced AV block ?
when AV conduction ration is 3:1 or higher
what is 3rd degree atrioventricular block
when there is complete failure of conduction between the atria and ventricles
no relationship between the P-waves and the QRS complexes = AV dissociation
p waves and qrs complexes have their own regular rhythm and bear no relationship with each other , the atrial and ventricular activities are independent of each other
Ventricles contract in response to an escape rhythm (by latent pacemaker distal to SA node)
what are the ECG finding on 3rd degree atrioventricular branch block
Atria faster than ventricles!
P wave morphologically abnormal
atrial escape rhythm is less than 60 bpm
Some P-waves are in front of QRS, some P- waves inside QRS, some P- waves behind QRS,
sometimes there are 2 P-waves after one another without QRS in between
ventricles can have junctional escape rhythm or ventricular rhythm (
the more distant the impulse generation the slower the ventricle escape mechanism
and the more wider and deformed the qrs complexes
proximal to bundle of his - junctional escape rhythm = 40-60bpm
narrow qrs complex
ventricular rhythm distal to bundle of His
less than 40 bpm
wide and bizarre qrs complexes
what are the symptoms of third degree AV block ?
sudden onset of AV block results in asystole lasts until the ventricles escape mechanism takes over - leading to stokes adams attack
or cardiac arrest
loss of consciousness. Prior to an attack, a patient may be pale with hypoperfusion. Abnormal movements may be present, typically consisting of twitching after 15–20 seconds of unconsciousness
less than 40 bpm bradycardia = cerebral hypo perfusion , fatigue , dizziness syncope
what is the treatment of third degree AV block ?
hemodynamically stable
monitor with transcutaneous padding
permanent pacemaker
hemodynamically unstable
atropine
isoprenaline
temp transcutaneous or transvenous cardiac pacing
low bp - dopamine
heart failure = dobutamine
what does the bundle branch look like in ECG
the 2 ventricles do not depolarize simultaneously, but their depolarization overlaps and thus we do not get two separated QRS
but we get one very looong QRS complex
normal QRS: less or equal 0.10 sec
incomplete BBB QRS: 0.10-0.12 sec
• complete BBB QRS: greater than 0.12 sec
what are the different types of bundle branch block ?
Left
complete LBBB
INCOMPLETE LBBB
right
“”
where in the left ventricle wall is bundle branch block most likely to occur ?
in the septum
anterior wall
or at the apex of the heart
or left anterior fascicle or posterioir fascicle
what is the aetiology of left bundle branch block ?
hypertrophy , dilation , fibrosis of the left ventricular myocardium
ischemic heart disease
cardiomyopathy
advanced valvular heart disease - such as aortic stenosis
hyperkalemia
lenegre disease - degenerative disease of the conducting system
digitalis
diagnosis of incomplete left bundle branch block ?
QRS duration is between 0.10-0.12 s and all the typical LBBB morphology
diagnosis of complete lbbb
the criteria
1) the heart rhythm must be supraventricular in origin
2) QRS is more than or equal to 120ms
3) , q wave should be absent in LEAD 1 , V5 , V6 (lateral leads)
but in the lead aVL, a narrow q wave may be present in the absence of myocardial pathology.
4) deep and broad s wave in V1 -v2 (s wave represents the completion of the ventricular depolarisation in the base of the intraventricular septum)
5) lead 1 ,v5 , v6 and AVL shows slurred R wave / notched / or broad monophasic
6) R peak time ( from the beginning of QRS complex to the peak R wave is more than 60ms in V5 and V6
but normal in V1 , V2 ,V3
lead v1 - may just have a normal rS complex (small r deep s wave)
left axis deviation may be present (lead 1 has most positive deflection , with lead 2and 3 and AVF are negative)
ALWAYS NOTE THAT with LBBB ST and T wave segments are usually opposite in direction the the QRS complex
positive t waves with positive QRS complex (positive concordance) normal
HOWEVER
negative t waves with NEGATIVE qrs complex typically abnormal and may represent myocardial injury / ischemia / infraction
what is the treatment of left bundle branch block
in young if there are no underlying problems that is associated with left bundle branch block then no treatment is necessary
in older people with coronary heart disease - greater risk of death
an AGGRESIVE evaluation is necessary if they have new onset bundle branch block
if symptomatic and having conduction problem
- may need permanent pacemaker
heart failure with left bundle branch lock :
cardiac resynchronisation therapy - helps the ventricles contract at the same time
what are the causes for RBBB?
repair of ventricle septal defect
right ventriculotomy
right ventricle hypertrophy
increase risk in those that live in high altitude
EBSTEIN anamoly
brugada syndrome
what is the diagnostic criteria for complete right bundle branch block ?
criteria
1) heart rhythm must be supraventricular
2) qrs duration more than 120ms (wide) *
3) secondary R wave in V1 or V3
detonated by rsR or rsr or rSR *
4) wide and slurred s waves in the lateral leads 1 , avl v5- V6
5) normal r wave peak time in V5 and V6
but V1-v2 is more than 50ms
the one with asterisk are needed to make diagnosis
what is the criteria for incomplete bundle branch block ?
same as complete except the qrs duration is less than 120ms
in bradycardia what is the clinical manifestations ?
if 3-5 sec = paleness and dizziness
10-15 - loss of consciousness
20-30sec - seizures
30-60 sec - apnea
more than 3 min - brain death
what causes SAN node dysfunction ?
extrinsic
carotid sinus hyperactivity
vasovagal stimulation
bb , cab , digoxin , anti arrhythmic class 1 and 3
intrinsic
chronic and acute MI
SICK sinus syndrome
inflammatory pericarditis or myocarditis
how many types of sino atrial exist blocks are there ?
first degree SA block
second degree SA block - type 1 - mobitz (wenckebach block)
type 2 - mobitz 2
third degree sa block
what is first degree san block ?
lag between SAN node fires and actual depolarisation of atria
how can we diagnose an first degree SAN node block ?
cannot be detectable by ECG
only detected by an electrophysiology stay
is differentiating between the two types of SAN node block necessary ?
differentiation between electrocardiographically but not clinical important
how do we diagnose second degree SAN block type 1 ?
ONLY second degree of SAN nose block that can be recognised on surface ECG
wenkebach - rhythm is irregular
RR or PP interval gets smaller while PR INTERVAL REMAINS CONSTANT
until a qrs segment is blocked or missing
the blocked duration is less than the two preceding pp / rr interval
.The pause duration is less than the two preceding PP intervals.
the pp interval following the pause is greater than the interval just before the pause
how do we diagnose SAN node block type 2 ?
regular rhythm which is normal or slow , pp intervals are fairly constant
follow by a pause - no p or QRS
pause is a MULTIPLE OF THE PP INTERVAL (2-4) usually twice the pp interval
how do we diagnose a third degree SAN node block ?
no SAN node conduction
ECG no p waves
junctional rhythm ensues
If no junctional escape rhythm is present, a long pause resulting in asystole
what is the emergency treatment of sinoatrial block ?
atropine sulfate
or transcutaneous pacing
permanent pacemaker
how do we diagnose a wandering atrial pacemaker ?
Wandering atrial pacemaker occurs when multiple areas (ectopic foci) within the atrium generate consecutive action potentials that are all conducted to the ventricles
three morphologically different p waves especially on lead 2
rate lower than 100 bpm (normal)
different P-r intervals / different pp intervals
EXCLUSION OF FREQUENT ATRIAl PREMATURE BEATS
what are types of fascicular blocks
left anterior fascicular bock
left posterior fascicular block
bifascicular block
trifascicular block
what does left anterior fascicular block look in egg
action potential is only conducted through the left posterior fascicle
major polar depolarisation is left wards and upwards
1) left axis deviation of -45 to -90
lead 1 most positive , with lead 2 and 3 negative
AND Avf
2) large positive voltages in lead 1 and AVL the left sided leads
3) we also see large negative voltage inferiority - in lead 2 , lead 3 , avF negative
qrs normal or slightly prolongerd
4) q(small q wave) R complex in lead 1 and AVL
5) rS complexes in leads 2,3 (especially) ,aVF
the inferior leads
6) delayed r wave peak (endometrial to epicardium) time in aVL
more than 45s
LAFB cannot be diagnosed prior to what condition
LAFB cannot be diagnosed when a prior inferior wall myocardial infarction (IMI) is evident on the ECG.
IMI can also cause extreme left-axis deviation, but will manifest with Q-waves in the inferior leads II, III, and aVF. By contrast, QRS complexes in the inferior leads should begin with r-waves in LAFB.
causes of left anterior fascicular block?
AMI
hypertensive heart disease
degenerative disease of conducting system
myocardial fibrosis
what is the diagnosis of left posterior fascicular block ?
1) right axis deviation - lead 1 positive
lead 2 positive
lead 3 the most positive deflection
AVF positive
2) qrs norma or slightly widened
3) rS complexes in lead 1 and AVL
4) qR complexes in lead 2 , lead 3 and aVF inferior leads
2) no ST segment or t wave changes
must have absence of other c causes of right axis deviation - lateral myocardial infraction , dextrocardia , right ventricular hypertrophy
what is the cause of left posterioir fascicular block ?
left bundle conduction system made of left anterior and posterioir fascicle
left posterioir is shorter and thicker than left anterior fasciale left posterioir also gets dual blood supply both from the left and right coronary artery
- MULTIVESSEL CORONARY ARTERY DISEASE MOST COMMON
what is bifascicular bundle branch block ?
RBBB with either left anterior or left posterioir fascicular block
what is the diagnostic criteria for bifascicular bundle branch block ?
prolongation of the QRS duration 0.12 s or longer
rSR in V1 - the R being broad and slurred
wide and slurred s wave in lead 1 ,V5 and V6
with left or right axis dilation
what are the causes for bifascicular block ?
CAD
degenerative disease of the conducting system
aortic stenosis
hypertensive heart disease
what is trifascicular block ?
the combination of RBBB and LAFB and long PR interval
implies the conduction is delayed in the third fascicle
what are the indications for permanent pacemaking ?
third degree av block
asysotle for more than or equal to 30seconda or any escape rate of less than 40pbm WHILST AWAY
AFTER CATHETER ABLTAION OF THE av junction / node
second degree AV lock with symptomatic bradycardia
