This document provides an overview of electrocardiography (ECG) including its history, basics, components, and interpretation. It discusses that ECG was invented in 1895 and measures the heart's electrical activity through electrodes placed on the skin. The ECG waveform includes the P wave, QRS complex, and T wave which represent atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively. It also describes the normal ranges for components, abnormalities, cardiac axis determination, and standard 12-lead ECG. The document is a comprehensive review of electrocardiography fundamentals.

1. Electrocardiography:
Basics
- Dr Manoj Kumar
Kurmana
General Medicine

2. ▪ In 1895, William Einthoven has been credited for invention of EKG
who later diagnosed heart problem using string electrometer ECG
▪ In 1924, Noble prize for medicine as been awarded for the same
▪ In 1942, Goldberger, increased Wilson’s unipolar lead voltage by
50% and made augmented leads
History of ECG

3. First ECG vs Present Day ECG machine

4. What is an ECG?
▪ ECG is a graphic recording of electric potential is generated by the
heart and the signals are detected. By means of metal electrode is
attached to the extremities and chest wall and then our amplified
and recorded by an electrocardiograph.
▪ Actually ECG leads display instantaneous potential differences
between the electrodes.
▪ Being a non-invasive, inexpensive and highly versatile test &
immediate availability it is used to detect Arrhythmias , Conduction
disturbances and myocardial ischaemia in clinical utility. ECG may
also reveal findings related to life-threatening metabolic
disturbances or sudden cardiac death syndromes.

5. Electrophysiology
▪ Depolarisation is sudden change in membrane potential, which is
usually from negative to positive charge relatively.
▪ This depolarisation causes Muscle contraction
▪ This Sequential Depolarisation of cardiac muscle tissue causes
activation-excitation front, which results in electrical current or
electromagnetic force or vector as it’s has both
magnitude & direction.

9. Electrocardiocardiological significance of
cardiac anatomy
▪ Although it’s obvious to see the heart is Four chambered,
where as in electrophysiological sense the heart consists of
only two chambers: one formed by the atria and the other
formed by the ventricles The two atria/ventricle function as a
single electrophysiological unit which referred to as the
biatrial/biventricular chamber.
▪ The two electrophysiological chambers are separated by inert
conduction barrier formed by fibrous atrioventricular (AV)
ring.
▪ Communication across this occurs by specialized conducting
system formed by the AV node, the bundle of His, the bundle
branches and its ramifications

10. Cardiac Pacemakers
▪ SA node – dominant pacemaker with an intrinsic rate of 60-100 bpm
▪ AV node : Backup Pacemaker with an intrinsic rate of 40–60bpm
▪ Ventricular Cells : Backup Pace maker with an intrinsic rate of 20-45bpm

11. The ‘‘PQRST ’’ Waveforms
P Wave : atrial depolarisation
QRS complex: ventricular depolarisation
T wave: Ventricular repolarisation

12. Electrocardiographic Paper
▪ Small Square = 1mm
▪ Large Square = 5mm(5xSmallSq)
▪ ECG is conventionally recorded it
paper speed of 25mm/sec
▪ 5 large squares = 1 sec
▪ 1 Large Square = 0.2sec(200ms)
▪ 1 Small Square = 0.04sec(40ms)

13. Conventional ECG leads
12 Conventional leads divided into two
groups depending on orientation to the heart :
1) the frontal plane leads : oriented in
coronal plane of the body and consists of
I,II,III(standard), aVR, aVL, aVF(unipolar)
2) the horizontal plane leads: oriented in
horizontal plane of the body consisting of
Leads V 1 to V6

14. Standard LEAD I
Lead I is derived from placement of the negative electrode on the right arm
and the positive electrode on the left arm

15. Standard LEAD II
LEAD II is derived from the placement of negative electrode on
the right arm and the positive electrode on the left leg

16. Standard LEAD III
LEAD III derived from placement of the negative electrode on
the left arm and the positive electrode on the left leg

17. Unipolar Limb Leads
▪ According to Einthoven, some of the potentials of three leads(I,II,III) is
at any instant equal to ZERO.
▪ So if these three leads are connected to a central terminal the potential
of this terminal will be ZERO.(Indifferent or Neutral Electrode)

18. Derivation of Unipolar Leads

19. DERIVATION OF Unipolar Leads
▪ The central terminal(neutral or indifferent electrode) is connected
to one pole of the galvanometer that Lead will always have
potential value of ZERO.
▪ & The Electrode connected to other pole of the galvanometer will
record the true potential at any given point and this electrode is
termed as exploring electrode.

20. Extremity Leads (LEAD V)
1. Lead aVR : obtained by
connecting the exploring
electrode to the right arm
2. Lead aVL : obtained by
connecting exploring
electrode to the left arm
3. Lead aVF : obtained by
connecting the exploring
electrode to the left leg

21. Horizontal Plane Leads

22. Arrangement of Leads

23. P Wave
• The P wave is those composite
deflection of right and left
atrial activation
• Always positive in lead I & II
• Always negative in Lead aVR
• < 3 small squares in duration
• <2.5 small squares in amplitude
• Commonly biphasic in lead I
• Best seen in lead II

24. Normal P wave Genesis
▪ the maximum duration of normal
Atrial activation is 110 ms
▪ SA node being situated in right
atrium,RA activation begins first
which is reflected by proximal limb
of P wave in most commonly lead
II(fig 3.1 b)ranging 20-40ms
▪ Left atrial activation begins 30ms
after right little activation
constitutes the distal half of the p
wave and ranges from 50 to 60 ms

25. QRS Complex
▪ The normal QRS complex is narrow and
sharply pointed
▪ Duration= 0.08-0.12 secs
▪ Amplitude normally varies from less than
5 mm to more than 15 mm
▪ Non-pathological Q waves may present
in I, Ill, aVL,V5, and V6
▪ R wave in lead V6 is smaller than V5
▪ Depth of the S wave, should not exceed
30 mm
▪ Pathological Q wave > 2mm deep and >
1mm wide or
▪ > 25% amplitude of the subsequent R
wave

26. QRS COMPLEX
▪ Depolarization/Activation of
ventricles is reflected by QRS
complex
▪ QRS complex reflects ventricular
activation as follows
An initial downward deflection
after P wave is termed as Q wave.
an initial upward deflection after. Is
termed as R wave
The S Wave usually represents the
terminal part of ventricular
activation
A second positivity of QRS complex
is termed as r-r' prime deflection

27. T Wave
▪ Normal T wave is asymmetrical &
proximal shallow limb with relatively
blunt apex or nadir
▪ Should be at least 1/8 but less than
2/3 of the amplitude of the R
▪ T wave amplitude rarely exceeds 10
mm
▪ Abnormal T waves are symmetrical, tall,
peaked, biphasic or inverted.
▪ T wave follows the direction of the QRS
deflection.

28. QT Interval
▪ Total duration of Ventricular
Depolarization and
Repolarization
▪ QT interval decreases when
heart rate increases
▪ For HR = 70 bpm, QT <0.40 sec
▪ QT interval should be 0.35- 0.45
sec. Should not be more than
half of the R-R interval.

29. QT Interval Significance
▪ QT interval shortens with Tachycardia and lengthens with
bradycardia(inverse)
▪ QT interval is also inversely related to R-R' interval
▪ QT interval cannot be viewed in absolute terms but must be
corrected for the effect of associated heart rate.

30. Correction of QT interval (QTc)
▪ QT interval is corrected for what it
would theoretically be at a rate of
60 bpm.
▪ Bazett's Formula is the most
frequently used.

31. Abnormal QT Interval
Prolonged QTc
▪ Acute Myocarditis
▪ Acute Myocardial infarction
▪ Drugs(Procainamide, Quinidine, TCAs)
▪ Hypothermia
▪ Hypocalcemia
▪ Hypertrophic Cardiomyopathy
▪ Torsades de pointes
▪ Congenital Long QT syndrome
Shortened QTc
▪ Digitalis Effect
▪ HyperCalcemia
▪ Hyperthermia
▪ Vagal Stimulation
▪ Congenital Short QT syndrome

32. ECG AXIS

33. ECG AXIS
▪ Spatial orientation and polarity of the
six frontal plane leaves is represented
on the Hexaxial diagram (ECG axis)
▪ The direction of this total frontal QRS
vector, defined by the angle it makes
with lead I, is the cardiac axis
▪ In normal circumstances, the direction
of the frontal QRS vector is dominated
by the depolarization forces generated
in the large left ventricular muscle
mass.
▪ The pattern of depolarization of the left
ventricle is in turn dictated by the
precise anatomy of the intraventricular
conducting system.

34. Construction of Frontal Hexaxial System
Frontal plane hexaxial reference system constructed by the
combination of the two triaxial reference systems.

36. Normal AXIS ECG

37. Quadrant Method

38. IsoElectric Method

39. Normal ECG

40. Right Axis Deviation

41. Right Axis Deviation

43. Reference
▪ Leo Schamroth’s : An Introduction to
Electrocardiography
▪ Harrisons Principles of Internal Medicine
▪ Internet (litfl.com)

44. Thank you