Understanding basics of EKG
By Alula A.(R III)
www.le.ac.uk
Topic for discussion
• Understanding of cellular electrophysiology
• Basics – Rate
– Rhythm
– Axis
– Intervals
– P wave
– QRS
– ST/T wave
Abnormal EKGs
Understanding electrophysiology
• The EKG is nothing more than a recording
of the heart's electrical activity
Cardiac cells
•Resting state(mme pump)
•Depolarization
/Repolarization
The Cells of the Heart and action potential
EKG basics
Electrode placement
Right precordial leads V1: right 4th intercostal space
V2: left 4th intercostal space
V3: halfway between V2 and V4
Left Precordial leads
V4: left 5th intercostal space, MCL
V5: horizontal to V4, anterior axillary
V6: horizontal to V5, mid-axillary line
Limb leads
EKG grid • The wave on EKG primarily reflect the electrical
activity of myocardial cell
• Three chief characteristics of the waves.
– Duration
– Amplitude
– Configuration
EKG strip
Einthoven's Triangle
The Six Precordial Leads
• Record forces moving
anteriorly and posteriorly
12
Order of depolarization
Follow the way
Interpretation steps
RRAI- P-QRS-T • Rate
• Rhythm
• Axis
• Intervals
• P wave
• QRS
• T
Rate • Atrial/ Ventricular rate 60 - 90 bpm
•Regular RR; 1500/small box or 300/large box
•Irregular RR –# of QRS waves in 6 sec X 10
–# of QRS on the whole EKG(10 Sec) X6
Rhythm •Normal sinus Rhythm( originated from SA)
The P waves in leads I and II –upright
Same morphology before each QRS
Read on the rhythm strip at lead II if not V1
Axis
• Two technique; I. Identification of isoelectric lead or
II. Look for lead I and aVF
• If needed look for lead II
• QRS axis Frontal Plane QRS Axis: +90 o to -30 o (in the adult)
Normal Axis
Left axis
- LA fascicular block
- Inferior MI
- Pacemaker
lead I +ve and
aVF -ve
Look lead II
+ve = normal axis
-ve = left axis deviation
Right axis
- RVH
- Left posterior fascicular block
- PE
lead I - ve and
aVF +ve
Intervals
• PR interval
– Normal 0.12 - 0.20 sec
• QT interval QTc < 0.40 sec
– Bazett's Formula: QTc = (QT)/SqRoot RR (in
seconds)
P wave • Bi atrial activation
Right to left
Lead II or V1
- duration < 0.12 sec
- 3 blocks wide - amplitude < 2.5 mm
2.5 blocks high
P wave Normal
• Up in lead II
• Down in aVR
• Biphasic, up or down in V1, III
• Same morphology and PR before each QRS
Abnormal
• too wide, too tall, different, unclear, funny (i.e. LAE, RAE, wandering pacemaker/MAT, a fib respectfully)
Wandering Pacemaker
at least 3 different P wave morphologies in a Ventricular response is irregularly irregular , COPD
QRS – Duration < 0.10 sec
– QRS amplitude - variable from lead to lead and
from person to person
– Comment: pathologic Q waves, abnormal voltage
QRS • Q wave
– Narrow (<0.04s duration) and
– Small (<25% the amplitude of the R wave)≈ 0.1mv
– Often seen in
leads I and aVL when the QRS axis is to the left of +60o, and
leads II, III, aVF when the QRS axis is to the right of +60o.
• R-waves begin in V1 or V2 and progress in size to V5. R-V6 < R-V5.
• In reverse, the S-waves begin in V6 or V5 and progress in size to V2. S-V1 is usually smaller than S-V2
• The usual transition from S>R in the right precordial leads to R>S in the left precordial leads is V3 or V4
ST wave
• Normal V1-V3 concave upwards
ST / ST- T wave
• Abnormal ST elevation and/or Depression
• ST elevation
– **compare J point to the TP level not PR**
Early repolarization- concave upwards
ST elevation
Convex or straight upward ST
ST segment depression
abnormal but non specific
T wave
•The normal T wave is usually in the same
direction as the QRS except in the right
precordial leads( V1-V3)
•T wave amplitude is 1/3-2/3 of R wave
• Always upright in leads I, II, V3-6, and
• Always inverted in lead aVR
U wave
• Afterdepolarizations which interrupt or follow repolarization
• U wave amplitude is usually < 1/3 T wave amplitude in same lead
• U wave direction is the same as T wave direction in that lead
• more prominent at slow heart rates and usually best seen in the right precordial leads
Conclusion ECG interpretations
i. Measurements
ii. Rhythm analysis
iii. Conduction analysis
iv. Waveform description
v. ECG interpretation
(normal, abnormal, bordeline)
i. Comparison with previous ECG (if any)
• Remember “RRAI P-QRS-T”
Provided by The Leicester Gondar Link
Collaborative Teaching Project
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.