cardiac conduction 2 Flashcards
P wave =
atrial depolarization
QRS =
ventricular repolarization
T wave =
T wave =ventricular repolarization
PR interval =
index of conduction time across the AV node
QT interval =
total duration of depolarization and repolarization
The Q is an
initial negative deflection,
the R is the
upward deflection
the S is a
terminal negative deflection.
The sinus node depolarization initiates the
beat but is too small to see
on the ECG.
how many separate leads in a ECG?
12
the shape of the QRS depends on?
where the positive electrode is placed
On EKG, The first signal seen is the
P wave generated by depolarization of first the right and then the left atrium.
why is QRS voltage greater than P?
The QRS voltage is much greater than the P voltage because ventricular mass exceeds atrial mass.
Why is the T wave wider than QRS?
The T wave is wider than the QRS because ventricular repolarization takes considerably longer than depolarization.
why is atrial depolarization not seen?
because normally it s buried in the QRS which is a much larger signal.
If the activation wave is \_\_\_\_\_, a positive (upward) deflection will be recorded
toward a sensing electrode
the ____ the muscle mass, the ___ the voltage recorded
greater
greater
the pattern of deflection varies with the____
position of the recording electrodes
The SA node is high in the ____ and the depolarization wave sweeps _____.
right atrium
downward and leftward.
a lead with a positive electrode near the right arm normally has a predominantly ____ QRS
negative
a lead with a positive electrode near the left leg has a ____ QRS.
positive
normal sequence of activation of the ventricles
- The upper portion of the septum is depolarized from left to right.
- There is then depolarization downward in the septum to the apex.
- Depolarization is from endocardium to epicardium
- Depolarization moves upward from apex in the free walls of both ventricles.
- depolarization of the base of the ventricles.
SA (sinoatrial node) abnormalities:
cause “sick sinus syndrome” resulting in slow sinus rates or takeover by other pacemakers which may be either fast or slow.
3 types of AV block
1st, 2nd, 3rd degree
First degree AV block:
conduction delayed but all P waves conduct to the ventricles.
2nd degree block:
some P waves conduct but others do not
3rd degree block:
none of the P waves conduct & a ventricular pacemaker takes over
When the right bundle is blocked,
QRS widening with delayed conduction to the right ventricle
When the left bundle is blocked
QRS widening with delayed conduction to the left ventricle
When left bundle fascicles are blocked
there are shifts in direction of depolarization but no QRS widening.
