Physiology 11.30.12 ECG Flashcards
what are Gap Junctions made from
6 connexon subunits, that surround a central pore and allow ions to easily pass through
What happens with connexon when H+ and Ca2+ added
Both acidosis and increase in Ca (myocardial ischemia or hypoxia) can reduce the open state fo teh chanel, and increase reistance between two cells –> leading to abnormal conduction
what is a dipole
an electrical source consisting of an asymmetrically distributed electrical charge
heart- one position of myocardiumis depolarized while remaining regions are still in resting state at any isntand during spread of a wave of depolarization
P wave
atrial depolarization (AP beings in atria)
simultaneus contraction in both atria
QRS wave
Ventricular depolarization (large mass means greaters size)
\
beginning of ventricular conttaction
T wave
ventricular repolarization (K chanels)
end of T wave is end of ventricular systole
why is T wave an upward reflection?
B/c Epicardium repolarizez before Endocardium so negative charge is going towards negative electrode –> upward deflection
AP duration is shorter in epicardial than in endocardial tissue
U wave
believed to be due to repolarization of papillary muscle
last ventricualr muscle to depolarize- typeically don’t see it; hypertrophied
P-R interval
time taken from first atrial depolarzation to first ventricaul depolarization
Q wave
definition the first downward deflection of QRS, and my or may not be present
what is isoeletric pause between P wave and QRS complex
caused by slow depolarization of AV node –> allows time for blood in atria to fill ventricles
slow conduction through AV node carried by Ca2+
ST segment
“Plateau” of ventricular repolarization ; nothign happening; cells starts to repolarize
if elevated or depressed –> usually sign of serious pathology
Sequence of depolarization in the heart
SA node –> AV node (slow) –> His Bundle (fast) –> R/L Bundle Branches (Purkinje fibers = HIs and R/L branches )
What is Vm at rest?
-85 mV
what doees the voltmeter read when all the cells are depolarized
0! isoeletric line
WHat type of deflection if Depolarization goign towards _ve electrode
upward deflection
depolarization moving towards -ve electrode
downward deflection
Repolarization moving towards positive electrode
downward deflection
repolarization moving towards -ve electrode
upward deflection
What is an “ischemic curren”
Em of ischemic tissue is ~0 mV (suppose to be -85mV)b/c ion channel are not workign properly
therefore during phase 4, there is a net flow of current towards teh -ve electrode , producing a signal below the zero level
During phase 2
Em is ~0, in both helathy and ischemic tissue (as tehya re all depoalrized)
no net current directed to either electrode
What does it mean when you see elevated “ST” segment
indicative of myocardial ishemia
Wolff-Parkinson-White Syndrome
If there’s an extra conduction pathway between atria and ventricle, electrical signal may arrive at ventricles too soon (b/c it bypasses teh AV nosde)
“pre-excitiation syndomes”`
Depoalrization conduction pathway
pacemaker cells –> atria stimulate –> AV node –> left
How fast is conduction in SA node
<0.01 m/s (very slow)
How fast is conduction in atria
1 m/s fast
How fast is conduction in AV node
0.02-0.05 m/s (slow)
How fast is Bundle Branches
2-4 m/s (fast)
How fast is Purkinje Network
(2-4 m/s) fast
How fast is Ventricular muscle
0.5 m/s
What is S wave
downward
Ventricular depolarization is going toward (-) electrode –> goes downward
What is T?
ventricular repolarization
Repol from Epi –> Endo –>
negative repolarization towards negative electrode –> upward reflection
Is action potential shorter in epicardial or endocardial region?
Repolarization begins in eicardial region of ventricle!
Therefore T wave is upward in Lead II
Why is AP shorter in epicardium than endocardium
b/c transient outward current is gerater in epicardium than in endocardium
Bigger drop during Phase I in Epicrardium
What happens if you block ITo (transient) in epicardium?
can make it like endocardium !
What does it mean if P-R interval in longer than normal?
result in A-V block (indicates taht conduction through AV node is slow)
What is normal time of PR interval
0.12-.20 s
What does it mean if QRS interval is longer than normal?
conductino in ventrcile is not normal!
what does QT interval indicate?
AP duration
what does it mean if QT interval is long (what is condsidered “long”
> 430 ms,
“long QT syndrome”
NOrmal QRS complex timing
0.06- 0.10s
What is the mean QRS vector?
It represents mean electrical vector
What is normal degree for QRS
-30 - +105 degrees
What type of pathologies would happen if there is a RAS (righ axis shfit)
- right ventricular hypertrophy (towards hypertrophy)
2. Left ventricular infarction
What pathologies would occur with LAS (left axis shift)
left hypertrophy
right ventricular infarction
What happns iwf ther eis pulmonary hypertsinon
enlarged right ventricular muscle
What would happen if Aortic Stenosis happen
Left ventricuular hypertrophy and shift axis to left
Which leads are “left lateral leads”
Lead I
Lead aVL
What leads are “inferior leads”
Lead II
Lead aVF
Lead III
How many degrees apart are 6 standard limb leads
30 degrees
Placement of V1
4th intercostal space- right of sternum
Placement of V2
4th intercostal space to left of sternum
V3
halfway between V2 and V4
V4
left midclavicular line in teh 5h intercostal space (MI)
V5
left anterior axillary line in the 5th intercostal space
V6
left midaxilalry line in 5h intercostal space
What chest leads show the highest peaks? WHy?
V4 and V5
b/c depolarization wave moves directly toward these electrodes
Which has greater amplitude? Standard leads or chest leads
Chest leads
closer to heart
V5
left anterior axillary line in the 5th intercostal space
V6
left midaxilalry line in 5h intercostal space
What chest leads show the highest peaks? WHy?
V4 and V5
b/c depolarization wavemoves directly toward these electodes
Which has greater amplitude? Standard leads or chest leads
Chest leads
closer to heart
During systole when all parts of the heart is depolarized (including ishcmiec or infarcted area) , what is the reading for ST segment?
It is at 0 level b/c all is depolarizaed!
What does ST segent look like if Subepicardial MI
ST segment elevation!
inuured segment is partially depolarized (therefore baseline is lower b/c difference is
Baseline is shfiten downward
What does ST segment look like if Sub Endocardial MI (non-transmural MI)
ST segment Depression
baseline is shifted upward
