This document discusses the basics of electrocardiograms (ECGs) and common artifacts in ECG recordings. It covers the following key points: 1. An ECG records and measures the electrical activity of the heart to diagnose cardiac conditions and abnormalities. It analyzes waves, segments, and intervals that occur during different phases of the heartbeat. 2. Common uses of ECGs include diagnosing ischemia, arrhythmias, and chamber hypertrophy. It is also used to monitor patients in intensive care. 3. Common artifacts that can affect ECG readings include incorrectly connected or placed leads, underdampening, muscle twitches, and baseline noise or vibration. Proper lead placement and connection are

1. Basics of Electrocardiogram
&
Common artifacts in ECG
recording
Rajan Joseph Manjuran
MD, DM, PGDHRM, FCSI, FICC, FIAE, FISE, FACC
Prof & HOD of Cardiology

2. Electrocardiogram (ECG)
 ECG is the record of the electrical activity of the
heart.
 Electrical activity precedes the mechanical
activity of the heart.
 Atria and ventricles have separate electrical
activity.
 Electrical activity has two phases: phase of
depolarisation and phase of repolarisation

3. Uses of ECG
(1) To diagnose Ischaemia
(2) To diagnose chamber hypertrophy
(3) To recognize arrhythmias
(4) To diagnose miscellaneous conditions like
a) Electrolyte imbalance
b) WPW Syndrome
c) Various channelopathies
d) Certain heart diseases have classical ECG
pattern

4. Uses of ECG (Contd..)
(5)Electrocardiogram is used as “Gold standard” to
time various events in cardiac cycle.
(6)Electrocardiogram is used for patient
monitoring in intensive care units and during
major surgical procedures.

5. ECG: Descriptive terms
Electrocardiogram has:
Waves
Segments
&
Intervals

6. ECG – Waves
 Waves are tracings which are deflections above or
below the baseline.
 Wave indicate a specific electrical activity
P - Atrial depolarisation
QRS- Ventricular depolarisation
T - Ventricular repolarisation
Ta - Atrial depolarisation
U - After potential/papillary muscle
repolarisation/ Purkingie system
repolarisation

7. ECG – Waves (Contd..)
Q - In QRS complex if the first deflection
is negative – that is named ‘q’ wave
R - First positive deflection in QRS
complex
S - Negative wave following ‘R’ wave

8. ECG segments
Segments are Isoelectric. There are 3 segments in
an ECG.
 PR segment - End of P wave to
beginning of QRS complex
 ST segment - End of QRS complex to
beginning of T wave
 TP segment - End of T to beginning of P
wave

9. ECG Intervals
 Include waves and segments
 Indicate specific time period in cardiac cycle
PR interval – Beginning of P to beginning of QRS
 Indicate AV conduction time
 Include P wave and PR segment
QT interval - Beginning of QRS complex
to end of T wave
 Indicate Electrical systole

11. Recording of Electrocardiogram
Leads:-
Limb leads:
Bipolar limb lead - LI/LII/LIII
Unipolar limb leads- aVR/aVL/aVF
Chest leads:
Unipolar chest leads - V1 – V6

12. ECG – Leads
Lead I - LA - RA
Lead II- LL - RA
Lead III- LL - LA
aVR - RA
aVL - LA
aVF - LL

13. ECG – Leads
V1 - Rt 4th ICS close to sternum
V2 - Lt 4th ICS close to sternum
V3 - Between V2 & V4
V4 - At 5th ICS on MCL
V5 - At the same level as V4 on AAL
V6 - At the same level as V5 on MAL

14. Recording of Electrocardiogram
 Standardisation - 1mv = 10 divisions vertically
1 small division vertically - 0.1 mv
Depending on the size of of QRS complex the
standardization can be changed to twice or half.
 Speed of recording – 25mm/sec
1 small division horizontally - 0.04 sec
 Sometimes 50 mm/sec recording is useful to separate
out waves especially in tachycardia (Rarely used)

17. Interpretation of Electrocardiogram
Stepwise analysis -
 Standardization - Is it correct?
 Heart rate - 1500
r-r interval
 P waves - Is it sinus ‘P’ wave
Size & shape – normal or not
 PR interval - Is it normal?
 QRS complex - Duration
 Abnormal Q wave
 Height of R wave
 Depth of S wave

18.  ST segment - Duration
- Deviation
 T wave - Upright, flat,
inverted
 U wave - Prominent or not

19. Interpretation of ECG (Contd.)
 QRS Complex -
Duration - Normal 0.06 – 0.1 sec
Broad QRS - ≥ 0.12 sec
Abnormal Q wave- ≥ 0.04 sec
Height of R wave- ≥ 25mm in V5/V6
Depth of S wave - ≥ 25mm in V1/V2
 ST segment - Isoelectric
- Deviation
- Elevated
- Depressed
- Duration 0.05 – 0.15 sec

20. Interpretation of ECG (Contd.)
 T waves - Normally upright with
rounded top (except aVR, VI &
occasionally in L III)
Abnormal T waves - Inverted
- Tall and peaked
 U waves - Most prominent in V2 or V3
- 5 – 15% the height of T wave
- Same direction as T wave
Abnormal - If inverted
- Tall – as big as 50% height of T
wave

22. ECG - Recording artifacts
 Wrong lead connection
 Under dampening
 Muscle twitch artifacts
 Wrong chest lead placement or connection

23. Common artifacts in ECG
recording
 Limb leads wrongly connected.
 Commonest is LA – RA interchange
 Less common in LA/RA to LL interchange
• Monitoring lead disconnection
• Muscle tremor or twitching
• Noisy or vibrating baseline
 Improper lead contact
 Muscle tremor
 Hiccups