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What is considered the main route of inter-atrial conduction?
Bachmann’s bundle
&0-80% of ventricular filling is passive, meaning …
no atrial contraction is needed
what are the 3 internal pathways making a connection between SA node and A node
superior anterior tract or fast tract
middle tract
inferior posterior tract or slow tract
In majority of the population, what is truly the only tract that attaches to the AV node?
fast tract (other two terminate somewhere in RA
What are the 3 zones of the AV node?
transition, compact, and trigger zones
In a normal heart, where is the only place where an impulse should be able to travel from the aria to the ventricles?
bundle of His
What is responsible for the depolarization of the interventricular septum?
intraventricular septal fascile
describe the left bundle branch
small piece of tissue that separates from His bundle, enters left vent and splits into 3 fascicles - left posterior fascicle (extents across posterior aspect), intraventricular septal fascicle (depolarizes inter ventricular septum), and left anterior fascicle (terminates into purkinje network
describe the right bundle branch
much longer piece of tissue than left bundle, separates from his bundle and enders right event, terminates into purkinje network
What is hearts 3rd pacemaker w/ intrinsic rate of 20-40 BPM?
purkinje network
phase 4
resting state / diastole; cardiac cells ready & can respond to impulse
more K inside cell, Na and Ca outside cell membrane
voltage = -90 mV
phase 0
upstroke (depolarization)
fast Na channels open & rapid influx of Na inside cell
causes positive voltage inside cell
K pours out of cell through open k channels at the same time
phase 1
early repolarization
na channels close and k channels re open; k slowly returns inside causing slight negative charge inside cell membrane
“notch”
phase 2
plateau
ca channels open and ca enters cell membrane causing contraction
influx of ca is matched by continuous influx of K
balance in voltage inside and outside cell
phase 3
rapid repolarization
Ca channels close
K channels remain open and allow influx of K inside cell membrane
inside cell returns to 90mV
absolute refractory period
short period of time after cardiac cell goes through AP, during which cell won’t respond to another stimuli
lasts 180ms
relative refractory
period of time during depolarization where a cardiac cell will respond to second stimuli, however cells are fragile
heart’s vector
true pathway of conduction thru heart is left and down towards the front of the body
which lead has a perfect view of hearts vector and is used for rhythm interpretation universally?
lead II
What is EKG paper printed at?
25 mm per second
what is size of small box
1mm tall and 0.04 s in duration
what is large box size
5mm tall and 0.2 s in duration (5 small boxes)
What are you measuring from left to right on EKG paper?
time
what are you measuring from up to down on EKG paper?
voltage
What is standard EKG machine calibration?
1 large box, or 0.2 s, in duration and 2 large boxes, or 10 mm tall
how many large boxes equals 3 seconds?
15
how many large boxes equals 6 seconds?
30
count down method
r wave on every large box = 300
r wave on every other large box = 150
as you continue to skip additional large boxes, HR becomes 100, 75, 60, 50
**not reliable for HR under 50
300 method
count number of large boxes between 2 consecutive R waves, divide 300 by that number to calculate HR
300 / # large boxes
1500 method
count number of small boxes between two consecutive R waves
1500 / # small boxes = HR
most accurate way to calculate HR
Normal sinus rhythm
rate: 60-100
regularity: regular
P waves: normal, present, married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow
sinus bradycardia
rate: less than 60
regularity: regular
P waves: normal, present, married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
sinus tachycardia
rate: over 100
regularity: regular
P waves: normal, present, married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
sinus arrhythmia
rate: 60-100
regularity: irregular
P waves: normal, present, married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
what happens in sinus arrhythmia
variations in the intervals of heart beats, MC in children
overall result is inc in inspiration and dec during exhalation
what happens in sinus exit block
sinus node fires normal, but impulses are being blocked
results in absence of cardiac cycles
P-P intervals march out across rhythm once electrical activity continues
Sinus exit block
rate: variable but typically less than 1
regularity: irregular
P waves: when present, normal and married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
what happens during sinus pause
SA node stops firing and starts back up again
cardiac cycle reset after pause and P-P intervals will not march out across rhythm strip
sinus pause
rate: variable but typically less than 150
regularity: irregular
P waves: when present, normal and married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
what happens in sinus arrest
SA node stops firing and starts back up again, at least 3 cardiac cycles have been missed
sinus node reset, P-P intervals will not march out across rhythm
sinus arrest
rate: variable but typically less than 150
regularity: irregular
P waves: when present, normal and married to QRS
PR interval: normal in duration 0.12 - 0.2 seconds
QRS complex: narrow or wide
PAC
ectopic impulse originates outside of SA node from; arrive early in cardiac cycle and will have P waves w/ diff morphologies
bigeminy / bigeminal complexes
premature beat occurs every other beat
trigeminal or trigeminy
every 3rd bead is a premature complex
WAP
rate: less than 100
regularity: irregular
P waves: at least 3 different morphologies, still married to QRS
PR interval: variable
QRS complex: narrow or wide
what happens in wap
at least 3 different areas w/in atria competing to be pacemaker
P waves w/ at least 3 diff morphologies
what happens in multifocal atrial tachycardia MAT
exact same as WAP except HR over 100
(at least 3 waves w/ diff morphologies)
MAT
rate: over 100
regularity: irregular
P waves: at least 3 different morphologies, still married to QRS
PR interval: variable
QRS complex: narrow or wide
what is atrial flutter
rapid atrial rate caused by reentry circuit caused by chamber enlargement, scarred, or ischemic tissue unique sawtooth pattern
;
atrial flutter
rate: atrial: 200-350; vent: variable
regularity: regular or irregular
P waves: none, flutter waves present
PR interval: none
QRS complex: narrow or wide
what is atrial fibrillation
most treated; irregular activity of multiple sites w/in atria which suppress SA node; loss of atrial kick; 3 types
paroxysmal: in and out of afib, converts w/o intervention
persistent: responds to intervention
permanent: chronic doesnt respond to interventions
atrial fibrillation
rate: atrial: indeterminate, vent: variable
regularity: irregularly irregular
P waves: none, F waves present
PR interval: none
QRS complex: narrow or wide
what is AV nodal reentrant tachycardia AVNRT / SVT
regular, narrow, complex tachy that’s a consequence of reentrant circuit b/t internodal pathways of SA and AV node
triggered by ectopic focus such as PAC near fast or slow track
AVNRT
rate: 150-300
regularity: regular
P waves: not visible or retrograde
PR interval: none or RP interval
QRS complex: narrow
typical avnrt
circuit travels counter-clockwise down the slow tract and up the fast tract; either no P waves or P waves are retrograde and buried at end of QRS complex
pseudo S wave
p wave that’s retrograde and buried at end of QRS complex
atypical AVNRT
circuit travels down fast tract and up slow tract; retrograde p waves are clearly visible are clearly visible, might be RP interval and not PR interval
junctional escape beat (JEB)
rate: 40-60
regularity: regular
P waves: absent, or inverted, either before or after QRS
PR interval: if present, less than 0.12
QRS complex: narrow or wide
what happens during JEB
occur where next expected R wave should have been
SA node fails to fire or is firing too slowly
av node takes over as main pacemaker and suppresses SA node
ventricular rhythms
wide, abnormal looking, t waves typically contralateral (opposite of R waves), duration typically over 0.12 s, no p wave
PVC
early, before next expected R wave, originates in vents, no p wave, wide ERs, ectopic, contralateral t wave
group of 6 known as run of V tach and requires intervention
idioventricular rhythm (IVR) or agonal rhythm
rate: 20-40
regularity: regular
P waves: none
PR interval: none
QRS complex: wide, longer than 0.12 s
occurs when purkinje takes over; regular, wide w/ no detectable P
v-tach
rate: 100-300
regularity: regular
P waves: none. if present, dissociated and not married to QRS
PR interval: typically non
QRS complex: wide
v fib
rate: 300-500
regularity: irregular
P waves: none
PR interval: none
QRS complex: not measurable
atrial paced rhythm
pacer spike is followed by normal PQRST cycle
vent pacemaker
p wave followed by pacer spike, wide QRS, contralateral T wave
first degree HB
rate: slow or normal
regularity: regular
P waves: present
PR interval: longer than 0.2 s
QRS complex: narrow or wide
benign PR interval delay as result of slowed conduction thru AV, hallmark is sinus rhythm and PR interval beyond 0.2 s
second degree type I wenckebach
rate: slow or normal
regularity: irregular
P waves: normal, present, married to QRS except for dropped beat
PR interval: increasing intervals
QRS complex: narrow or wide
dropped QRS complexes, prolongation of PR interval until a P wave is not conducted
second degree type II / mobitz
rate: slow or normal
regularity: irregular
P waves: normal, present, married to QRS except for dropped QRS
PR interval: normal or wide, but always constant across strip
QRS complex: wide or narrow
consistent PR w/ dropped QRS
3rd degree Hb
rate: atrial: normal vent: slower than atrial
regularity: regular
P waves: present, normal, not married to QRS
PR interval: none
QRS complex: narrow or wide depending on origin
no p waves thru AV junction, regular P-P intervals that are unrelated to regular R-R intervals, P waves appearing to “march through” QRS-T; atrial rate faster than vent;; two independent pacemakers- SA node and AV junction or purkinje / bundle branch fibers
what is p wave
depol of atria, regardless of morphology
duration 0.1 s
PR interval
time from onset of P wave to beginning of QRS complex
duration 0.12 to 0.2 s (3-5 small boxes)
QRS complex
represents vent depol
should be less than 0.12 s
Q wave
first negative deflection following PR interval
represents depol of interventricular septum
must be less than 0.04s (1 small box) w/ low amplitude
R wave
first positive deflection following PR interval or Q wave
represents depol of anterior LV
S wave
first negative deflection following R wave
represents depol of lateral wall of LV
must extend below baseline
J point
where QRS complex ends and ST segment begins
should be baseline, can 1mm variance
ST segment
represents time in between vent depol and vent repol
should be baseline
begins at beginning of J points and terminates at onset of T wave
T wave
represents vent repol
normally should be asymmetric w/ slow, positive upstroke and sharp, terminal down stroke
peak of this wave is dividing line b/t absolute refractory and relative refractory
QT interval
represents all of vent activity during one cardiac cycle
begins at start of QRS and ends at end of T wave
350-450 ms in males; 360-460 ms in females
U wave
deflection immediately after T wave and in same direction as T wave
prominent U waves seen in hypokalemia and hyperthyroidism
TP segment
represents resting state of cardiac cells
end of T wave to beginning of next P wave
best place for assessment of isoelectric line (true baseline)
R-R and P-P intervals
used for assessment of rhythm rate & regularity and heart blocks