The ECG records the depolarization and repolarization potentials generated by the atrial and ventricular myocardium over time. It shows: - Atrial depolarization as the P wave - Ventricular depolarization as the QRS complex - Ventricular repolarization as the ST segment, T wave, and U wave.

1. ECG
1
RECORDS THE
DEPOLARIZATION
(STIMULATION) AND
REPOLARIZATION (RECOVERY)
POTENTIALS GENERATED BY
THE ATRIAL AND VENTRICULAR
MYOCARDIUM.
www.medicinemcq.com

2. www.medicinemcq.com
2

3. www.medicinemcq.com
3

4. ECG graph paper
4
 Horizontal axis
 Records the time (interval) between cardiac electrical
events
 Vertical axis
 Records their amplitude (voltage)
www.medicinemcq.com

5. www.medicinemcq.com
5

6. Horizontal divisions
6
 Smallest (1 mm)
0.04
s (40 ms).
 Heavier lines
0.20
www.medicinemcq.com
s (200 ms).

7. Amplitude
7
1 mV = 10 mm with standard
calibration.
www.medicinemcq.com

8. Q wave
8
 The first negative QRS deflection
www.medicinemcq.com

9. R wave
9
 First positive deflection
www.medicinemcq.com

10. S wave
10
 Negative deflection after an R
wave.
www.medicinemcq.com

11. QS wave
11
 Entirely negative QRS complex
 Lowercase letters (qrs)
For
waves of relatively small
amplitude.
www.medicinemcq.com

12. QRS complex
12
 Ventricular depolarization.
www.medicinemcq.com

13. Phase 0 or depolarization
13
 Rapid upstroke of the action
potential
Corresponds to the onset of QRS.
www.medicinemcq.com

14. www.medicinemcq.com
14

15. Phase
2
15
Plateau phase
Corresponds
to the
isoelectric ST segment.
www.medicinemcq.com

16. Phase 3
16
Active repolarization
Corresponds
wave.
www.medicinemcq.com
to the T

17. Ventricular repolarization
17
ST segment, T wave,
and U wave.
www.medicinemcq.com

18. Atrial repolarization
18
 Usually too low in amplitude to be detected.
 Obscured by QRS (i.e., ventricular depolarization).
 May be apparent in
 Acute pericarditis
 Atrial infarction.
 Atrial depolarization causes P wave.
www.medicinemcq.com

19. Summary
19
 Atrial depolarization
 P wave.
 Ventricular depolarization
 QRS complex
 Ventricular repolarization
 ST segment, T wave, and U wave.
www.medicinemcq.com

20. ECG waves
20
P
 Atrial
depolarization.
R
 Ventricular depolarization and atrial
repolarization.
 QRS complex
 Ventricular depolarization
 ST - T - U complex
 Ventricular repolarization
www.medicinemcq.com

21. Unipolar recording
21
 Use only 1 active
electrode.
www.medicinemcq.com

22. Bipolar recording
22
Use 2 active
electrodes.
www.medicinemcq.com

23. Bipolar lead
23
 Measures the difference in
potential between electrodes at two
extremities
Lead
I = left arm-right arm voltages
Lead II = left leg-right arm
Lead III = left leg-left arm.
www.medicinemcq.com

24. www.medicinemcq.com
24

25. Standard limb leads
25
I, II, and III are bipolar leads
Record the differences in
potential between 2 limbs.
www.medicinemcq.com

26. Lead I
26
Between left arm and
right arm with left
arm +.
www.medicinemcq.com

27. Lead II
27
Between left leg and
right arm with leg +.
www.medicinemcq.com

28. Lead III
28
Between left leg and
left arm with leg +.
www.medicinemcq.com

29. V 1 to V 6
29
6 unipolar chest
leads or precordial
leads.
www.medicinemcq.com

30. 3 augmented unipolar limb leads
30
avL, avR, and avF.
Recordings between one limb
and the other 2 limbs.
Increases the size of the
potentials by 50 %.
www.medicinemcq.com

31. Positive deflection
31
Upright deflection

For rest of the slides visit www.medicinemcq.com > Cardiology
www.medicinemcq.com