ECG or electrocardiography is the graphical representation of electrical impulses produced by the heart.
The electrical impulses form due to movement of ions in the myocardial cells representing depolarization and repolarization, denotes the conduction pathway of heart, which coincides with cardiac cycle. Apart from normal electrocardiography common arrhythmias are also discussed during this session.
2. ECG is a graphical representation of the
electrical impulses produced in the heart.
The waveform of ECG represent electrical
activity produced by the movement of ions
across the membrane of myocardial cells,
representing depolarisation and
repolarisation.
3. Automaticity-ability to generate an electrical
impulse spontaneously & repetitively
Excitability-ability to be electrically stimulated
or respond to an electrical stimulus
Conductivity-ability to receive an electrical
stimulus and transmit to other cardiac cells
Contractility-ability to response mechanically to
an impulse
4.
5. 3 major cations
K-performs a major function in cardiac
depolarization and repolarization
Sodium plays a vital part in myocardial
depolarization
Calcium is important in myocardial depolarization
and contraction.
Magnesium-acts as transporter for Na & K across
cellular membranes. Also plays an important
function in muscular contraction
6. Resting cardiac cells (Polarization) –inside the
cell is negatively charged. K is greater in the
cell; Na greater outside the cell (positively
charged)-Resting membrane potential
Depolarization (action Potential)-sodium-
potassium exchanged pump resulting in positive
polarity inside the cell membrane. Myocardial
contraction occurs.
Repolarization-recovery or resting phase;
positive charges are again on the outside and
negative charges in the inside
7.
8. ECG Graph Paper
• Runs at a paper speed of 25 mm/sec
• Each small block of ECG paper is 1 mm2
• At a paper speed of 25 mm/s, one small block
equals 0.04 s
• Five small blocks make up 1 large block which
translates into 0.20 s (200 msec)
• Hence, there are 5 large blocks per second
• Voltage: 1 mm = 0.1 mV between each
individual block vertically
10. • Limb leads are I, II, II.
• Each of the leads are bipolar; i.e., it
requires two sensors on the skin to make a
lead.
• If one connects a line between two
sensors, one has a vector.
• There will be a positive end at one
electrode and negative at the other.
• The positioning for leads I, II, and III were
first given by Einthoven. Form the basis of
Einthoven’s triangle.
11. Bipolar leads record voltage between electrodes
placed on wrists & legs (right leg is ground)
Lead I records between right arm & left arm
Lead II: right arm & left leg
Lead III: left arm & left leg
12.
13.
14.
15.
16. P wave caused by atrial depolarization
Duration – 0.06-0.12 (1-3 small box)
17. •Q wave greater than 1/3
the height of the R wave,
greater than 0.04 sec are
abnormal and may
represent MI
18. QRS complex caused by ventricular
depolarization
duration -0.12-0.20 (3-5 small box)
19. T wave results from ventricular
repolarization
Duration-0.16sec (4 small box)
20. • . PR interval: from onset of P wave to
onset of QRS
• Normal duration = 0.12-0.2sec
(120-200 ms) (3-5 horizontal boxes)
• Represents atria to ventricular
conduction time (through His
bundle)
• Prolonged PR interval may indicate
a 1st degree heart block
21. ST segment:
• Connects the QRS complex and T wave
• Duration of 0.08-0.12 sec (2-3 small
box)
QT Interval
• Measured from beginning of QRS to the
end of the T wave
• Normal QT is usually about 0.40 sec(10
small box)
• QT interval varies based on heart rate
22. Rate - 60 -100 b/min
Rhythm- regular
P wave- normal
PR interval- normal
QRS complex- normal
23. heart rate= 1500
small box in RR interval
heart rate= 300
large box in RR interval
6 second method = no. of QRS complexes
in a 6 sec strip x 10 (30 largeboxes in 6 sec
strip)
29. P wave- followed by QRS complex
PR interval-prolonged (>0.20Sec)
Length of prolonged PR interval constant
KEY TO REMEMBER- wife is waiting at home ,
husband comes home late every night , but he
always comes home and it’s the same time every
night
30. Progressing lengthening of PR interval untill a
QRS complex is dropped
PP interval is constant
QRS complex is narrow
KEY TO REMEMBER- wife is waiting at home ,
husband comes home later and later every night
, untill one night he does not come home at all
31. If drug toxicity is the cause,
withhold drug
Artificial pacemaker may be
used as an electrical back up
If rate related sympoms apear,
rate can be accerated by
administering Atropine
cautiously
32. PR interval is constant
PP interval regular
RR interval irregular as of the intermittent and sudden
appearance of drop beat. P waves comes on time but no
QRS complex follows
QRS complex is wider
KEY TO REMEMBER- wife is waiting at home ,
sometime husband comes home sometime he
does not. When he comes home it always same
time.
34. RR interval is constant
PP interval usually constant
atrial rate is usually faster than ventricular rate
No relation between P wave and QRS complex
KEY TO REMEMBER- wife is no longer is waiting at
home , she and her husband now both separate
schedule, no relationship. Each spouse has a
regular individual schedule
42. Rate -150-220 b/min
Rhythm-regular
P wave-abnormal,may be hidden in the
preceeding T wave
PR interval-normal or shortened
QRS complex- normal (usually)
Paroxysmal-starts & ends abruptly
43. Rate and rhythm- atrial -200-350 b/min
and regular
ventricular- > or < 100 bpm
and regular /irregular
P wave-saw toothed pattern
PR interval-not measurable
QRS complex- normal (usually)
51. Rate – not countable
Rhythm-irregular
P wave-absent, fibrillatory wave
PR interval-not measurable
QRS complex-absent
52. Rate - zero
Rhythm- none
P wave- none
QRS complex- none
53. Cardiac standstill
Absence of all ventricular
activity-no waveforms
Check on 2 leads-? Very fine Vfib
Clinical death-absence of pulse
and respirations