3. Conduction over the heart
• activity starts at the SA
node
• depolarisation spreads over
the atria
• to the AV node
• where there is a delay of c.
120 ms
1
4. Conduction over the heart
• after the delay, activity spreads down the septum
• and then out over the ventricular myocardium
• from the inside (endocardial) surface to the outside
(epicardial) surface
• until all the ventricular cells are depolarised
5. Sequence of activation
• Activation of the ventricles begins ~ 0.15 sec after the
atria. This delay between atrial and ventricular
activation assures maximal ventricular filling.
• The sequence of activation within the ventricle insures
efficient contraction and ejection by:
i) stabilizing the septum and valve leaflets early in the
contraction.
ii) activating from apex-to-base . The latter results in
pushing the blood towards the aortic valve.
6. Electrical activity that may be recorded
from the heart:
• Atrial depolarization
• Atrial repolarization
• Ventricular
repolarization
• Ventricular
repolarization
7. The Electrocardiogram
• The myocardium is a large mass of muscle undergoing
electrical changes all more or less at the same time
which generates a large changing electrical activity which
can be detected by electrodes on the body surface this is
the electrocardiogram
10. So that
• P wave - atrial depolarisation
• QRS wave- ventricular depolarization
• T wave - ventricular repolarisation
11. •Willem Einthoven was a Dutch physician and physiologist.
-He invented the first practical electrocardiogram (ECG or EKG)
in 1895.
- Received the Nobel Prize in Physiology or Medicine in 1924
for it
22. The basic pattern of the ECG is logical
• Electrical activity towards a lead causes an
upward deflection
• Electrical activity away from a lead causes a
downward deflection
23. The amplitude of the signal depends on:
• How much muscle is depolarising.
• How directly towards the electrode the
excitation is moving
24. Why some leads are predominantly positive
deflection,while the others are not?
28. ECG Description& Interpretation
•ECG should be read in tow steps: description & then
interpretation.
•The description of ECG should be performed in an
orderly fashion as fellow :
1-Technical quality 2-Rhythem 3-Rate
4-Cardiac axis 5-Pwave 6-PR segment
7-PR interval 8-QRScomplex 9-St-segment
10-Twave 11-Qt-interval
12-additional waves
29. Technical quality
• Look at speed which should be 25mm/s.
• look then to the voltage amplitude which is normally 10mm/s
both these data are provided in the ECG paper.
• Then look to aVR lead ,normally the deflection is downward
and
P-is usually upward in leads I and II.
If these are not present think of:
1-reversed limb lead placement
2-dextrocardia
3-right ventricular hypertrophy /strain or RBBB
30. Rhythm
The rhythm could be either regular or not
depending on R-R interval.
Causes of irregular rhythm:
• Sinus arrhythmia, frequent ectopic beats ,
• Atrial fibrillation ,
• Atrial flutter, 2nd degree heart blook with
variable response
38. Main Axis of the heart:
• The axis of ECG: is the major direction of
overall electrical activity of the heart.
• The average deflection of depolarization wave
in the ventricle spread from 11 o'clock to 5
o'clock.
• Its therefore moving a way from aVR and
toward other limb lead mainly lead II.
45. • First-degree AV block
occurs when impulses
from the atria are
consistently delayed
during conduction
through the AV node.
• Conduction eventually
occurs; it just takes
longer than normal
46.
47. • Normal PR interval=0.12-0.2 sec.(3-5 small squares)
• More than 0.2(>5 squares) consider abnormal.
• Rhythm is regular
• Rate is usually normal
48. • Also called Mobitz type I
block,(Wenckebach)
• type I second-degree AV
block occurs when each
successive impulse from the
SA node is delayed slightly
longer than the previous
impulse.
• That pattern continues
until an impulse fails to be
conducted to the ventricles,
and the cycle then repeats
49.
50. • Type II second-degree AV
block, also known as Mobitz
type II block,
• It occurs when occasional
impulses from the SA node fail
to conduct to the ventricles.
• is less common than type I but
more
• serious
51.
52. • Also complete heart block,
third- degree AV block
• Occurs when impulses from the
atria are completely blocked at the
AV node and can’t be conducted to
the ventricles.
• The ventricular rhythm can originate
from the AV node and maintain a
rate of 40 to 60 beats/minute.
• Most typically, it originates from the
Purkinje system in the ventricles and
maintains a rate of 20 to 40
beats/minute
53.
54.
55.
56. QRS complex
QRS wave:
• Q-wave: first negative
deflection.
• R-wave: first positive
deflection.
• S-wave: second negative
deflection
57. QRS complex
• Normal QRS ≤ 0.10 sec
(≤2.5 small boxes)
• Normal if QRS is primarily
upright in leads I and II
• Downward in lead aVR
Inspect for:
-Bundle branch block
- ventricular hypertrophy
- pathologic Q-wave
63. Atrial fibrilation:
• Atrial fibrillation, sometimes called A-fib, is defined
as chaotic, asynchronous, electrical activity in atrial
tissue.
• It is the most common sustained tachyarrhythmia.
• The ectopic atrial impulses may fire at a rate of 400
to 600 times/minute.
• The AV node protects the ventricles from the rapid
erratic atrial impulses that occur each minute by
acting as a filter and blocking some of the impulses
• Ventricular response is irregular, less than 150
68. Features:
A- Comes early.
B-abnormal morphology(wide QRS)
C-followed by a pause.
• May occur after one normal cardiac
beat)bigeminy, or trigeminy (every two normal
beats).
77. Pathological Q-wave:
• Pathologic- Q- waves are more prominent ,
typically having a width greater than or equal
to 1 small box in duration or
• a depth greater than 25% o the total height o
the QRS.
