Discussion Flashcards
____________ refers to the spontaneous time-dependent depolarization of the cell membrane that leads to an action potential in an otherwise quiescent cell.
Pacemaker activity
SA node intrinsic firing rate:
70-80
Primary pacemaker
SA node
Beta adrenergic effect (e.g epinephrine) to SA Node:
Increase conduction velocity
Increase pacemaker rate
1st Sequence of depolarization in cardiac muscle:
Depolarize atria
2nd Sequence of depolarization in cardiac muscle
Depolarize septum from left to right
Third Sequence of depolarization in cardiac muscle
Depolarize anteroseptal region of myocardium toward the apex
Fourth Sequence of depolarization in cardiac muscle:
Depolarize bulk of ventricular myocardium from endocardium to epicardium
1st electrical events of cardiac cycle:
Atrial depolarization initatiated by the SA node, causes the P wave
Second electrical events of cardiac cycle:
With atrial depolarization complete, the impulse is delayed at the AV node.
Limb leads:
I, II, III, aVL, aVR, aVF
Chest leads
V1, V2, V3, V4, V5, V6
4th intercostal space at the right sternal border
V1 or C1 (Red)
4th intercostal space at the left sternal border
V2 (C2) Yellow
On the left on the 5th rib between C2 and C4
V3 C3 Green
5th intercostal space on the left midclavicular line
V4 C4 Brown
PR interval
0.12 - 0.22 secs
The usual paper speed is
25 mm/sec
1 mm (small square)
0.04 sec
5 mm (big square)
0.2 sec
P-waves should precede every QRS complex and the P-wave should be positive in Lead II
Rhythm
The most efficient way to estimate axis is to look at ______ and _______.
Lead I and Lead AVF
Generated by activation of the atria
P wave
Represents the duration of atrioventricular (AV) conduction
PR segment
Produced by activation of both ventricles
QRS complex
Reflects ventricular recovery
ST-T wave
Lead I is formed using the _______ as the negative electrode and the _________ electrode as the positive.
Right arm
Left arm
Lead II is formed using the ________ as the negative electrode and the __________ electrode as the positive.
Right arm
Left LEG
Lead III is formed using the _______ as the negative electrode and the ________ electrode as the positive.
Left arm
Left leg
aVL, aVF and aVR are _________ computed using the information from the other leads.
Composite leads
Limb leads look at the heart in the __________/
Coronal plane
Phase 2 of transmembrane potential
ST-segment
Isoelectric in normal subjects
ST-segment
reflects the duration of depolarization and repolarization
QT interval
Surface reflection of negative after potential
U wave
Repolarization of purkinje fibers and ventricular relaxation
U wave
