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
