An electrocardiogram (ECG) records the electrical activity of the heart on paper. It is recorded at a rate of 25mm/s, with each large square measuring 0.2 seconds and containing 5 small squares of 0.04 seconds each. The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization. Various intervals between the P, QRS, and T waves provide information about electrical conduction through the heart. Abnormalities in the ECG patterns can provide clues about conditions affecting different areas of the heart muscle.

1. ELECTROCARDIOGRAM(ECG)

2. • It is recorded on to a standard paper travelling at the
rate of 25mm/s
• large sq, each measuring 5mm = 0.2secs
• Each large sq has 5 small sq
• each small sq is 1mm = 0.04 secs
• Vertically: I small sq is 1mm = 0.1mv

7. P wave the sequential activation (depolarization) of the right
and left atria
QRS
complex
ventricular depolarization
T wave ventricular repolarization
PR interval • time from the onset of the P wave to the beginning
of the QRS complex.
• onset of atrial depolarization and the onset of
ventricular depolarization.
ST segment • following the QRS and ending at the beginning of the
T wave.
• time at which both ventricles are completely
depolarized
QT interval time for both ventricular depolarization and
repolarization to occur

8. Precordial Leads
Adapted from: www.numed.co.uk/electrodepl.html

9. Precordial Leads

10. Summary of Leads
Limb Leads Precordial Leads
Bipolar I, II, III
(standard limb leads)
-
Unipolar aVR, aVL, aVF
(augmented limb leads)
V1-V6

13. Anatomic Groups
(Septum)

14. RATE
Rate (rhythm regular) =
• 300 / no. of big boxes between two peaks
• 1500 / no. of small boxes between two peaks

16. RHYTHM
1. Check lead II
2. Regular - ‘r waves’ are at equal interval's (equal no of small/ large
boxes between 2 r waves)
3. Irregular - ‘r waves’ are not at equal interval's

17. EXAMPLE 1

19. The QRS Axis
The QRS axis represents the net overall direction of the
heart’s electrical activity.
Abnormalities of axis can hint at:
Ventricular enlargement
Conduction blocks (i.e. hemiblocks)

21. The Quadrant Approach
1. Examine the QRS complex in leads I and aVF to determine if they
are predominantly positive or predominantly negative. The
combination should place the axis into one of the 4 quadrants
below.

26. ABNORMALITIES
• Depending on the changes in lead, we can find which area of heart is
affected.
I
LATERAL
AVR V1
SEPTAL
V4
ANTERIOR
II
INFIRIOR
AVL
LATERAL
V2
SEPTAL
V5
LATERAL
III
INFIRIOR
AVF
INFIRIOR
V3
ANTERIOR
V6
LATERAL

27. ABNORMALITIES

28. SEQUENCE OF EVENTS IN MYOCARDIAL INFARCTION ON ECG
Elevation of ST segment
Appearance of Q waves
T wave inversion
ST segment returns to baseline within 24-48 hrs
T wave inversion permanent
Called as ST segment Elevation Myocardial Infarctions(STEMIs)
Infarction not full thickness  T wave inversion present  Q waves absent  non-ST
segment Elevation Myocardial Infarctions(NSTEMIs)

29. ABNORMALITIES
• ST elevation - ACUTE MI
• T wave inversion - Chronic MI
• ST depression - Ischaemia

30. ABNORMALITIES- EX 1

31. RIGHT AND LEFT ATRIAL HYPERTROPHY

32. • Thank You