atrial depolarization
- depolarization slows
- allowing time for blood in atria to enter the ventricles
- slow conduction through AV node is carried by calcium (ca++) ions
ventricular conduction system
- originates at His bundle which penetrates AV valves the immedicatley bifurcates (in the interventricular septum) int he the right and left bundle branches
- the His “bundle” and both “bundle” branches are “bundles” or rapidly conduction purkinje fibers.
- like the myocardium, purkinje fibers use fast-moving na+ ions for conduction of depolarization
depolaizaion
- conducts slowly through the AV node (using ca++ ions)
- then conducts rapidly (using na+ ions) through the His bundle to the right and left bundle branches into the terminal filaments of the purkinje fibers
- which depolarizes the ventricular myocytes
ventricular conduction system
- consists of rapidly conducting purkinje fibers
- terminal filaments of purkinje fibers depolarize the ventricular myocardium
- initiating ventricular contraction while inscribing a QRS complex on EKG
entire qrs
represents ventricular depolarization
st elevation or depression
usually a sign of serious pathology that may indicate imminent problems
st segment
- represents the “plateua” (inital) phase of ventricular repolarization.
- ventricular repolarization is rather minimal during the ST segment
t wave
rapid phase of ventricular repolarization
repolarization
-accomplished by K+ ions leaving the myocytes
qt interval
-represent the duration of ventricular systole and is measured from the beginning of the QRS until the end of the T wave
Ca++ ions
produce myocardial contractions
K+ ions
outflow causes repolarization
Voltage
height or depth of waves measures from baseline in millimeters
Time of small boc
.04 seconds
Time of large box
.20 sec
=5 small boxes @ .04 sec
Remember
A wave of depolarization is a progressive wave of positive charges passing through myocardial cells. So, when a depolarization wave moves toward a positive electrode, a positive (upward) deflection s produced on the ekg (or monitor) for that particular lead.
Ekg
Recording cardiac electrical activity from 6 different angles. Gives much greater and more accurate perspective.
