ECG Flashcards
P wave
• The first event in the cardiac cycle is the depolarisation of the sino atrial node
Dp from right to left atria
Generates P wave
Reflect SA node activity
PR Interval
Dp spreads thru AV node to ventricle
Conduction thru AV node is slowed to allow ventricles to be filled
Slowed conduction = PR Interval
duration of PR Interval
more than 0.12 s but less than 0.2 s
>0.12. and <0.2
QRS Complex
Conduction from AV node to Bundle of His through Purkinje fibres and epicardium
QRS complex does not need to have all 3 componenets
Q wave
a negative wave preceding the R wave
depolarisation of ventricular septum
in I II AvL V5 V6
R wave
upward deflection
S wave
deflection below the isoelectric line
T wave
depolarisation frome endocardium to epicardium
repolarisation in opposite direction - epicardium to endocardium
when it moves in opposite direction the T wave is in same deflection as QRS complex
U waves
small deflections in same direction as T wave
T wave does not measure depolarisation of atria but depolarisation of endocardium and epicardium why
ventricular repolarisation
look back at it
limb leads
I, II, III
Augmented leads
AvR, AvL, AvF
limb leads and augmented leads view heart in what plane
vertical plane
chest leads view the heart in what plane
horizontal plane
T wave is always in the ___ direction as the QRS Complex
same direction
Lead I
from right arm to left arm
Lead II
From right arm to left leg
Lead III
From left arm to left leg
Lead AvF
lead I to left leg
Lead AvL
lead II to left arm
Lead AvR
lead III to right arm
anterior surface seen in leads
V1
V2
V3
V4
Lateral surface in seen in leads
I
AvL
V5
V6
Inferior surface in seen in leads
II
III
AvF
Right side of the heart seen in leads
AvR
V1
chest leads
V1 - V6
How is rhythm important in reporting the ECG
Rate should be ~60-100 bpm in the R-R Interval
Regular pattern
Every P wave should produce a QRS Complex
Conduction Intervals
Conduction thru AV Node is slowed and produces PR interval of 0.12-0.2s
Depolarisation of ventricles is rapid and spreads equally to left and right = QRS should be narrow w/ a single peak
AvL detects nothing because…
perpendicular to the flow of depolarisation
Cardiac Axis
cardiac axis represents the general direction of depolarisation w/ the heart
starts in top right (SA node) and spreads to bottom left and apex of heart
what does cardiac axis determine
determines whether a particular lead is large
or small, positive or negative.
aVL meaning and the location of the positive electrode
Lead aVL Augmented Vector Left, positive electrode left shoulder.
aVR meaning and the location of the positive electrode
Lead aVR Augmented Vector Right, positive electrode right shoulder.
aVF
Lead aVF Augmented Vector Foot, positive electrode on Foot.
where is V1 positioned
Fourth intercostals space, right sterna border
where is V2 positioned
Fourth intercostals space, left sterna border
where is V3 positioned
One-half way between V2 and V4 in straight line with them
where is V4 positioned
Fifth intercostals space, left midclavicular line
where is V5 positioned
Fifth intercostals space, left anterior auxiliary line
where is V6 positioned
Fifth intercostals space, left midauxiliary line.
what leads detects the inferior wall of the left ventricle
II, III aVF
what leads detect lateral wall of the left ventricle
I, aVL, V5, V6
what leads detect lateral wall of the intraventricular septum
V1, V2
what leads detect anterior wall of the left ventricle
V3, V4
what leads detect anterior wall of the left ventricle
V3R, V4R
what leads detect posterior left ventricle
V7, V8, V9
