This document provides an overview of normal electrocardiography including: - The history and components of the ECG - Details on electrical conduction pathways and dipoles - Explanation of filtering techniques used to process ECG signals - Description of the 12 standard ECG leads - Identification and measurements of key complexes, intervals, and waves including P, PR, QRS, ST, T, and QT - Normal variations in ECG patterns - Approach to interpreting ECGs by analyzing rate, rhythm, axes, intervals, and overall tracings

1. NORMAL ECG
AIIMS,BHUBANESWAR,CARDIOLOGY

2. 12 LEAD ECG

3. HISTORY OF ELECTROCARDIOGRAGHY

4. • Anterior internodal :Bachman-James
• Middle internodal :Wenchbach
• Posterior internodal:Thaoral

5. DEPOLARISATION
SEQUENCE

6. ELECTRICAL DIPOLE
• A dipole is created when one
part of the muscle strip becomes
electrically negative relative to
the rest of the muscle strip.
Movement of the dipole from
negative to positive (arrow)
creates an electrical field.

7. FILTERING
• An electrocardiogram (ECG) is obtained analog
and, in current machines, is converted into a digital
signal, where it is filtered to block out some of the
“noise” while keeping relevant parts of the “signal.”
Low frequency signals such as respiration are
eliminated using a high pass filter. High frequency
signals such as noncardiac muscle potentials are
attenuated using a low pass filter. Specific “notch”
filters that eliminate electromagnetic interference
at 50 to 60 Hz may also be used.

8. A TOTAL OF 12 LEADS
THREE ARM BIPOLAR LEADS

9. THREE UNIPOLAR LIMB LEADS

10. BIPOLAR LIMB LEADS FRONTAL
PLANE IN 60 DEGREE GAP
• Lead II is 60º
• Lead III is 120º
• Lead aVF is 90º
• Lead aVL is -30º
• Lead aVR is -150º

11. UNIPOLAR IN 30
DEGREE GAP
BIPOLAR IN 60
DEGREE GAP

12. WILSON’S PRECORDIAL LEADS

13. • V1 – Fourth intercostal space to the right of the sternum
• V2 – Fourth intercostal space to the left of the sternum
• V3 – Midway between V2 and V4
• V4 – Fifth intercostal space at the midclavicular line
• V5 – Anterior axillary line at the level of V4, or halfway between V4 and V6 if the
anterior axillary line is unclear.
• V6 – Midaxillary line at the level of V4

14. COMPLEXES
AND
INTERVALS

15. P WAVE
• The P wave represents atrial depolarization
• From the right to left atrium
• Positive in most leads
• The duration is generally <0.12 sec (three small boxes)
• Amplitude <0.25 mv (2.5 small boxes)
• Right atrial depolarization precedes that of the left atrium
• the P wave is often notched in the limb leads and usually biphasic in lead V1

17. PR INTERVAL
• The PR interval =P wave+ PR segment
• From the beginning of the P wave to the first part of the QRS complex
• Time for atrial depolarization (the P wave) and conduction through the AV node and
the His-Purkinje system (which constitute the PR segment)
• PR interval : 0.12 to 0.20 sec (three to five small boxes)
• Shorter at faster heart rates due to sympathetically mediated enhancement of
atrioventricular (AV) nodal conduction
• Longer when the rate is slowed as a consequence of slower AV nodal conduction
resulting from withdrawal of sympathetic tone or an increase in vagal inputs.

18. QRS COMPLEX
• If the initial deflection is negative, it is termed a Q wave
• Small Q waves are often seen in leads I, aVL, and V4-V6 as a result of initial septal
depolarization and are considered normal.
• The first positive deflection of the QRS complex is called the R wave=
depolarization of the LV myocardium
• RV depolarization is obscured because the LV myocardial mass is much greater
than that of the right ventricle
• The small R wave in lead V1 represents initial septal depolarization.

19. QRS COMPLEX
• The negative deflection following the R wave is the S wave, which represents
terminal depolarization of the high lateral wall
• If there is a second positive deflection, it is known as an R'.
• Lower case letters (q, r, or s) are used for relatively small amplitude waves of less
than 0.5 mV (less than 5 mm with standard calibration)
• An entirely negative QRS complex is called a QS wave

20. • QRS duration = 0.06 to 0.10 seconds (1½ to 2½ small boxes) and is not
influenced by heart rate.
• The R wave should progress in size across the precordial leads V1-V6
• Normally there is a small R wave in lead V1 with a deep S wave
• R wave amplitude should increase in size until V4-V6 while the S wave becomes
less deep. This is termed R wave progression across the precordium

22. ST SEGMENT
• The ST segment occurs after ventricular depolarization has ended and before
repolarization has begun
• The time of electrocardiographic silence
• The intersection of the end of the QRS complex and the initial part of the ST
segment is termed the J point
• The ST segment is usually isoelectric

23. T WAVE
• T wave =Period of ventricular repolarization
• the rate of repolarization is slower than depolarization, the T wave is broad, has a slow upstroke,
and rapidly returns to the isoelectric line following its peak (ie, slow upstroke, rapid downstroke)
• T wave is asymmetric and the amplitude is variable
• T wave is usually smooth up and down
• depolarization begins at the endocardial surface and spreads to the epicardium, while
repolarization begins at the epicardial surface and spreads to the endocardium, the direction of
ventricular depolarization is opposite to that of ventricular repolarization
• T wave vector on the ECG normally is in the same direction as the major deflection of the QRS
• he QRS and T wave axes are concordant

24. QT INTERVAL —
• QT interval = QRS complex+ ST segment+ T wave
• QT interval is primarily a measure of ventricular repolarization
• JT interval= ventricular repolarization since it does not include ventricular
depolarization, but in most clinical situations, the QT interval is used
• QRS complex duration is increased, this will lead to an increase in QT interval but
does not reflect a change in ventricular repolarization. A widened QRS, therefore,
must be considered if a prolonged QT interval is being evaluated.

25. QT INTERVAL
• QT (or JT) interval is dependent upon the heart rate
• it is shorter at faster heart rates and longer when the rate is slower
• QT interval that is corrected for heart rate (QTc) is often calculated as follows
(based on Bazett's formula):
• QTc = QT interval ÷ square root of the RR interval (in sec)

26. QT INTERVAL
• QTc in men is ≤0.44 sec
• QTc in women is ≤0.45 to 0.46 sec
• . QTc values, however, are on a bell curve
•

27. U WAVE
• Seen in V2 to V4
• May be from late repolarization of the mid-myocardial M cells
• The amplitude of the U wave is typically less than 0.2 Mv
• Clearly separate from the T wave
• Hypokalemia and bradycardia
• U merge with T wave when the QT interval is prolonged (a QT-U wave)
• Very obvious when the QT or JT interval is shortened [ digoxin or hypercalcemia]

28. APPROACH TO ECG INTERPRETATION
• Step-1:Standardisation
• Step 2: Rate
• Step 3:rhythm
• Step 4:AXIS
• STEP 5:INTERVAL
• STEP 6:P WAVE
• STEP 7:QRS COMPEX
• STEP 8: ST segment-T wave
• STEP 9:Overall interpretation

30. GRID LINES AND STANDARDIZATION OF THE ECG

31. HEART RATE
• The division of 300 by the number of large boxes = heart rate
• The division of 1500 by the number of small boxes = heart rate
• If the rhythm is irregular,
• Number of complexes on the ECG x6
• Normal= 60 to 100
• < 60 is bradycardia
• > 100 is tachycardia

32. BRADYCARDIA

33. TACHYCARDIA

34. BRADYCARDIA

35. RHYTHM

36. RHYTHM ANALYSIS

37. FRONTAL PLANE QRS AXIS

38. QRS AXIS

39. NORMAL VARIANT :JUVENILE T INVERSION

40. EARLY REPOLARISATION

41. ACUTE ST ELEVATION MI

42. FLAVOR WON'T LAST
IT'S THE QUALITY
WORK
MUST WORK IN DAY
ALSO, IN THE DARK