Cardiac Conduction System and ECG Flashcards
Initial rapid upward deflection of R wave corresponds to ____ of the action potential
Phase 0 = fast inward INa current
____ corresponds to Phase 0 = fast inward INa current of the action potential
Initial rapid upward deflection of R wave
Which part of ECG is isolectric?
ST segmeent is isolectric
What does ST segment correspond to on action potentiaL?
phase 2 plateau (when Ca2+ influx and K+ efflux balanced)
What does phase 2 plateau correspond to on ECG
ST segment
What does T wave on ECG correspond to on action potential
phase 3 of AP (rapid decrease in voltage as K+ efflux continues)
What does isoelectric segment after T wave correspond to?
phase 4 of the action potential
There must be Concordance between ____ and ___ on ECG
QRS and T wave in every ekg lead
Why is there concordance between QRS and T? is there difference with an individual myocyte?
ventricular myocytes depolarize earliest must repolarize latest
discordance with individual myocyte
what if there is no concordance between QRS and T
ischemia
ventricular hypertrophy
Why is T wave longer than QRS segment?
repolarization requires more time than depolarization
How does depolarization spread from cell to cell?
via gap junctions (formed by connexins that allow ions to pass from cell to cell)
Path of electrical transmission in the heart…
1) SA node (where SVC enters the heart) = spontaneously depolarizes (automaticity)
2) travel from RA and then LA generating P wave
3) when reach AV node –> delay
4) pass to Bundle of His (extension of AV node)
5) Splits into left and right bundle for LV and RV
6) pass to purkinje fibers –> ventricles
Valves on either side of AV _____ conduct electrical signal
DO NOT
Why does signal delay when it reaches AV node?
allows atria time to contract before ventricles contract
mean what?
P wave
QRS
T wave
atrial depol
ventricular depol
ventricular repol
PR interval means
index of conduction
time across AV node
QT interval means
total duration of depol & repol
1st degree AV block
conduction delay but all P waves conduct to ventricles
PR prolonged
2nd degree AV block
some P waves conduct but others don’t
3rd degree AV block
complete block
no P waves conduct & ventricular pacemaker takes over
Three mechanisms by which cardiac conduction cause tachyarrhythmias
abnormal reentry pathways
ectopic foci
triggered activity –> abnormal afterpolarizations
abnormal reentry pathways present where
atria
ventricles
junctional tissue
when does abnormal reentry pathway occur
unidrectional block and slowed conduction through reentry pathway
after slow reentry, previously depol tissue recovered
MOST COMMON MECHANISM OF SERIOUS TACHY
ectopic foci
area of myocardium outside conduction system acquires automaticity
if rate of depol > SA node –> abnormal rhythm occurs
triggered activity
abnormal afterpolarizations by preceding AP
early afterpolarization before AP fully repol –> tachyarrhythmia
delayed afterpol appear after AP is complete –> arrhythmia
